# Ceriatone 2550 Build - PT Question



## _Knighthawk_

Hi guys,

I have been trying to source a PT for this build (and avoid ordering one from Ceriatone in Malaysia). I had hoped to order one from Hammond but the voltages/amps don't match the Ceriatone spec for this amp which are:

Primary 120V (per USA or Canada)
Secondary = 350-0-350 200-250mA (700VCT) -> ie Plexi 50 or JTM45 spec?
Heaters = 6.3VCT (6-9A)

So, Hammond does have a JTM 45 PT but its 345 V (200 mA) with the heaters at 6.3 VCT (5 A).

I suppose what I am trying to avoid is under-powering the amp with this PT. Is it worth finding a better match to the Ceriatone specs? Or am I dancing on a pinhead for no reason?

Choke and the OT will be ordered from MM.


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## jb welder

2x EL34 & 3x 12AX7 is 4A heater requirement. The Hammond is fine. Ceriatone voltage chart calls out 340 to 350V secondary, so the 345 of the Hammond is again ok.
One thing that bugs me about Ceriatone is their poor documentation and lack of schematics. Calling for 6-9A heaters is just wrong.


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## _Knighthawk_

jb welder said:


> One thing that bugs me about Ceriatone is their poor documentation and lack of schematics. Calling for 6-9A heaters is just wrong.


Couldn't agree more! Nik is very responsive to email but it is a pain not having a schematic. For example, there is a herd of diodes in the build (at least 2 different kinds) but I have no idea what they are. I cant recall any other kit supplier not providing a schematic - just ceriatone. It's very curious.


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## epis

He's not inventing anything new, original schematics are enough.
1n4007 are all you need.


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## _Knighthawk_

epis said:


> He's not inventing anything new, original schematics are enough.
> 1n4007 are all you need.


Thanks. I do have the original schematics.


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## _Knighthawk_

The lockdown in Malaysia lasted about a month so this package was 'delayed'. Anyway, it is here and looks like a lot of fun!

(Not sure about the no-name, bright orange filter caps. May need to order some F&Ts. Alpha pots and Mallory mustard knock-off may also be replaced.)


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## epis

Nothing wrong with yellow signal caps and alpha pots.
Even orange electrolytics, if you googled 600 volts electrolytic caps, you'll find there is no need to replace existing ones.


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## jb welder

epis said:


> Nothing wrong with yellow signal caps and alpha pots.
> Even orange electrolytics, if you googled 600 volts electrolytic caps, you'll find there is no need to replace existing ones.


Agree about the Mallories, 150's are the cap of choice for many builders. I googled but couldn't find anything about the orange electros, what are they?


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## _Knighthawk_

I did some digging on the orange caps. They're something called 'holy grail'...which is obviously a great marketing tag but I dunno about the quality. I haven't started building the circuit yet - still mulling over whether to use these components.


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## _Knighthawk_

Oh, and I dont think these are Mallorys. I think they are some kind of knock-off (I use mallorys in most of my builds).


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## epis

jb welder said:


> Agree about the Mallories, 150's are the cap of choice for many builders. I googled but couldn't find anything about the orange electros, what are they?


I apologize for not being clear enough, I assume they are ETR made in China, brand what Justradio is selling as well.
Ft do not offer 600 volts axial caps.
If you go to mouser or digikey, they sell Vishays for more then ridiculous price, for example, 20uF/600V for $50.
Ceriatone layout requires 600 volts axials, for certain positions.


P.S.

I have found more info on caps, but I still think they are ETRs.

The Guitar Column: A Visit To Ceriatone Amplifiers Part II


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## _Knighthawk_

Assembly begins!

I have installed most of the hardware (except for the cliff jacks) and have been generally impressed by the quality of the chassis, the organization of the components and the layout of the design (love how roomy it is).

The only thing that is a bit odd is that I actually needed to dust off a flat head screw driver. What's with that!?!?!?



Will be starting on the main board soon!


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## _Knighthawk_

An of course the Hammond PT doesn't quite fit. 

There always has to be something.


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## _Knighthawk_

So, I finally got back to this build...7 months later (it's been a long strange trip, those 7 months). Anyway, I have this pretty much nailed down but I am not familiar with this component (see picture). There is a PCD and an OMRON G5V-2-H1 (DPDT 5V relay). I think I am okay with how this is oriented and wired up but the pictured component is a bit of a mystery. 

I did note that it fits the OMRON pins - just not sure what I am supposed to do with it.

Any big brains out there that might know?


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## greco

Hopefully @jb welder and @epis will see this. 
I await with curiosity and the opportunity to learn.


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## epis

greco said:


> Hopefully @jb welder and @epis will see this.
> I await with curiosity and the opportunity to learn.


It's just an IC socket, but it's not gonna fit that relay and pcb, check distance between the pins. Thera are some relays made to fit these sockets.


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## _Knighthawk_

epis said:


> It's just an IC socket, but it's not gonna fit that relay and pcb, check distance between the pins. Thera are some relays made to fit these sockets.


I thought maybe on the other side of the PCB? This would essentially sandwich the PCB between the relay and the socket.

The relay does fit the socket (although some of the holes are obvioualy empty since the relay has only 8 pins).


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## _Knighthawk_

Right...well, I will have to figure that out.

OT should arrive any day from California and I can I begin to wire things up in the chasis. Pictured is progress on the boards (as you can see, I have decided to go with the 'holy grail' caps).


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## epis

_Knighthawk_ said:


> I thought maybe on the other side of the PCB? This would essentially sandwich the PCB between the relay and the socket.
> 
> The relay does fit the socket (although some of the holes are obvioualy empty since the relay has only 8 pins).


If it fits socket, that's cool, if relay needs to be replaced.


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## _Knighthawk_

epis said:


> If it fits socket, that's cool, if relay needs to be replaced.


Thanks, yes. What I don't really understand is why I need the socket at all. Would I not solder the relay to the PCB? And then trim the pins?

The socket seems superfluous so I think I must be imagining this incorrectly.


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## _Knighthawk_

epis said:


> If it fits socket, that's cool, if relay needs to be replaced.


I'll use the socket. I can trim the socket pins to fit the board. Thanks again.


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## Jimmy_D

_Knighthawk_ said:


> Thanks, yes. What I don't really understand is why I need the socket at all. Would I not solder the relay to the PCB? And then trim the pins?
> 
> The socket seems superfluous so I think I must be imagining this incorrectly.


Socket is so you don't melt the relay when soldering, the socket also makes whatever's in it interchangeable which can be a good thing.


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## _Knighthawk_

Jimmy_D said:


> Socket is so you don't melt the relay when soldering, the socket also makes whatever's in it interchangeable which can be a good thing.


Thanks Jimmy D. Makes sense!


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## _Knighthawk_

So, I always try to buy local. In this case, I bought a Hammond PT and Hammond Choke for my Ceriatone build. And, of course, the wiring for the PT in the Ceriatone wiring layout is specific to whatever PT Ceriatone usually ships for this build and not for the Hammond. So, I am little concerned about how to wire up the primary.

My question: Do I wire up the 120V (Black) to the power switch and the Brown 0V to star ground and the White 0V to neutral, trim/ tape the rest?

The link to the PT documentation is here:


https://static6.arrow.com/aropdfconversion/2028d01fd160eb1c95afe06956a643db1e05a838/290lex.pdf



Here is the Ceriatone drawing for the 2550.









Any better informed opinion than mine is welcomed and appreciated!


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## Paul Running

Dual primaries on this TFM. For 120VAC operation, you should parallel the primaries...120V from one primary is shunted with the other. Brn with Wht and Blk with Blu.
With the 5VAC, 3A secondary, you have the option to add a tube rectifier...a nice feature to select between semi-con and VTT rectifiers.


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## Alan Small

_Knighthawk_ said:


> Hi guys,
> 
> I have been trying to source a PT for this build (and avoid ordering one from Ceriatone in Malaysia). I had hoped to order one from Hammond but the voltages/amps don't match the Ceriatone spec for this amp which are:
> 
> Primary 120V (per USA or Canada)
> Secondary = 350-0-350 200-250mA (700VCT) -> ie Plexi 50 or JTM45 spec?
> Heaters = 6.3VCT (6-9A)
> 
> So, Hammond does have a JTM 45 PT but its 345 V (200 mA) with the heaters at 6.3 VCT (5 A).
> 
> I suppose what I am trying to avoid is under-powering the amp with this PT. Is it worth finding a better match to the Ceriatone specs? Or am I dancing on a pinhead for no reason?
> 
> Choke and the OT will be ordered from MM.


that hammond is just fine. dont sweat the small differences..there is always wiggle room


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## _Knighthawk_

Paul Running said:


> Dual primaries on this TFM. For 120VAC operation, you should parallel the primaries...120V from one primary is shunted with the other. Brn with Wht and Blk with Blu.
> With the 5VAC, 3A secondary, you have the option to add a tube rectifier...a nice feature to select between semi-con and VTT rectifiers.


Can I assume that I don't need to twist the two primaries (shunting them together to switch)? That is, I assume they are in phase so there really is no need?
Or am I way off base here?


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## Paul Running

Correct they are in phase, blk with blu (hot), wht with brn (neutral). You could twist all 4 together if the length is a fair stretch.


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## _Knighthawk_

Paul Running said:


> Correct they are in phase, blk with blu (hot), wht with brn (neutral). You could twist all 4 together if the length is a fair stretch.


Thanks. Should I be grounding any of the leads from the primary to the chassis?


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## Paul Running

No, none of the primaries should see Gnd., however, the Grn/Yel is a chassis gnd. wire.


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## _Knighthawk_

Paul Running said:


> No, none of the primaries should see Gnd., however, the Grn/Yel is a chassis gnd. wire.


Thanks Paul. I have that one sorted. Cheers.


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## _Knighthawk_

So, the build is complete and testing has begun. I have a significant power issue - or rather an underpowered issue - and I am not sure if it is me who messed up (likely) or perhaps a bad PT (less likely).

The voltages are very low across the pin chart (V1 to V5). For example, on Pin 1, V1 through V3 are half of what I would expect (56, 51, and 67VDC respectively). Where you would expect serious voltage, Pin 3/4 on V4 and V5 and Pin 6, V1 through V5, the numbers are terribly low (all under 100 VDC).

The numbers at the diodes (left and right coming off the standby switch)

VAC: 395 and 419
VDC:-243.5 and -2.6

I have reviewed the wiring against the diagram a dozen times - looks good. I have checked the diodes (although I suspect this problem is happening before the diodes see any voltage).

Anyway, if anyone with some experience might have some ideas as to what is going on with this this, I would be most grateful for the input. Here are some images of my mess:


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## Paul Running

Are all these voltages referenced to 0V ground?
What is the B+ voltage with no load...open-circuit voltage? What is the AC voltage at the rectifier?
Verify no load voltage vs. a light load voltage.


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## _Knighthawk_

Geez, I wrote the post in very 


Paul Running said:


> Are all these voltages referenced to 0V ground?
> What is the B+ voltage with no load...open-circuit voltage? What is the AC voltage at the rectifier?
> Verify no load voltage vs. a light load voltage.


Checking now. It is a solid state rectifier.


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## _Knighthawk_

Popped out the tubes to measure B+ with no load. Reading is: -12.8 VDC

Not sure what mean exactly you mean by reference to 0V ground. I have the black (COM) multimeter in the chassis when I do these readings.


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## Paul Running

The B+ will be a High + voltage, in your case about 475 to 565VDC for most EL34 Marshalls...only the bias supply should be - in a typical tube-powered amp.
I wonder why Ceritone is so tight about their schematics?
I'm conditioned to trouble shoot by a schematic...I build by the schematic too. Please excuse my lapses...I was never much for layout drawings, always learnt by trial and error in the end...sometimes theory is way off the mark....you cannot replace the experiments. Look at how many inventions have been discovered, by co-incidence. It's not quite accidental, if you believe in destiny.


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## Paul Running

_Knighthawk_ said:


> I have the black (COM) multimeter in the chassis when I do these readings.


Yeah, that's an acceptable termination for ground...everything, eventually has to transfer back through that green wire.


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## _Knighthawk_

Paul Running said:


> The B+ will be a High + voltage, in your case about 475 to 565VDC for most EL34 Marshalls...only the bias supply should be - in a typical tube-powered amp.
> I wonder why Ceritone is so tight about their schematics?
> I'm conditioned to trouble shoot by a schematic...I build by the schematic too. Please excuse my lapses...I was never much for layout drawings, always learnt by trial and error in the end...sometimes theory is way off the mark....you cannot replace the experiments. Look at how many inventions have been discovered, by co-incidence. It's not quite accidental, if you believe in destiny.



B+ is labelled on their wiring diagram but it is a bit unorthodox for a measurement (it runs from under the board to the 50k bias pot). With no load, I was seeing 470 VDC ish on the pins of V4 and V5.


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## _Knighthawk_

B+ is 510V. 

Voltage chart:









I also found some low DC voltage on the 'Presence' pot - which I thought a bit odd but apparently this is common (similar to a plexi in that sense).

Still no sound at all through the speaker (guitar signal is completely absent) but I think I have a problem somewhere in one of the 12AX7s (tube or wiring - not sure yet).

I am going to bias it to see if I can bring the voltages down a bit...and then do some troubleshooting in the preamp area.


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## _Knighthawk_

Fixed the tube issue (replaced the tube (V1)).

Biased amp - voltages are still too high (got the B+ down to 480, no room left on the 50k bias pot) - and still no sound coming from amp. Checked all diodes and resistors. Found a bad resistor. Next: check all capacitors.

Therapy later today. May take up drinking full-time. More soon.


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## Paul Running

_Knighthawk_ said:


> Therapy later today. May take up drinking full-time. More soon


Take a couple deep breaths and try to relax your mind. 480VDC B+ is ideal for push-pull EL34s. What is the DC voltage on pins 5 of the EL34s? It should be near -36VDC.








Okay, the output tubes are near cut-off...-51VDC on the control grid is virtual cut-off, 13 and 17mA cathode current, both tubes are near cut-off, therefore no output.
The bias pot should have a range of -45 to -30VDC for EL34s at that plate voltages.
V1A plate voltage is very high...410VDC...it is turned on however, not enough Double-check the plate circuit wiring. Check the plate-load resistor value.
Those 500+ readings are high because there is a low current draw...they should drop a bit under the proper loading.


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## nonreverb

The picture doesn't clearly show what's going on @ V1. Can you take another pic? It looks like there may be a problem with the wiring in the first half but I can't be sure.


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## _Knighthawk_

Sure. I went over it with a fine tooth comb and in the end - changed the tube so I am no longer seeing 400+ volts on pin 1. Here are the pics:


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## _Knighthawk_

Paul Running said:


> Take a couple deep breaths and try to relax your mind. 480VDC B+ is ideal for push-pull EL34s. What is the DC voltage on pins 5 of the EL34s? It should be near -36VDC.
> View attachment 355471
> 
> Okay, the output tubes are near cut-off...-51VDC on the control grid is virtual cut-off, 13 and 17mA cathode current, both tubes are near cut-off, therefore no output.
> The bias pot should have a range of -45 to -30VDC for EL34s at that plate voltages.
> V1A plate voltage is very high...410VDC...it is turned on however, not enough Double-check the plate circuit wiring. Check the plate-load resistor value.
> Those 500+ readings are high because there is a low current draw...they should drop a bit under the proper loading.


Thanks. I actually thought the drinking full time wasn't a bad idea...but I guess a deep breath will work too (I do hope you realize I was only kidding - I am actually extremely patient with these things)

After biasing (which basically imposed the full 50k on the circuit), the pin 5 voltage is down to just over - .38. This voltage chart needs to be rewritten (post bias). I am at work now so I can't do much. Will reply further a bit later on this evening.

V1 has been replaced and the voltage is no longer 410V.


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## Paul Running

_Knighthawk_ said:


> Thanks. I actually thought the drinking full time wasn't a bad idea...but I guess a deep breath will work too (I do hope you realize I was only kidding - I am actually extremely patient with these things)


If an altered state helps, try cannabis however, I don't advise when you are in close proximity to lethal potentials.
What exactly are we looking at here:









I am going by this schematic:










the bias network:










is this correct? Not really if you mention a 50K pot.


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## _Knighthawk_

Connections to pin 1 and 5 respectively (left to right). Just behind terminal strip (not reslly visible) is the connection from board to pin 3.


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## Paul Running

_Knighthawk_ said:


> Connections to pin 1 and 5 respectively (left to right). Just behind terminal strip (not reslly visible) is the connection from board to pin 3.


Okay, so pin 1 is the plate of V1A and pin 5 should short to pin 4 which is the high side of the filament (6.3VAC system).
Pin 3 is the cathode of V1A.

The area of concern as per layout drawing:


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## Paul Running

_Knighthawk_ said:


> After biasing (which basically imposed the full 50k on the circuit), the pin 5 voltage is down to just over - .38.


If you mean -0.38VDC...that is too hot, keep the bias below -25VDC which is still a bit hot at those plate voltages. I believe that a safe operating range would be between -32 to -38VDC, with -38VDC getting a little cold but it depends on your tastes...less tube stress on the cold side.
Early model EL34s were primarily designed for true class B operation. The quick reference guides do not mention class A operation:








The key is to operate in class B...it requires special attention to avoid cross-over and tight regulation of the screen-grids.


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## dtsaudio

This thread seems to be getting ahead of itself. We're looking at two different issues at the same time.
I think the OP needs to re-do the voltage chart now that V1 is sorted out. But is it correct?
And it would be good to know what the voltage is on pin 8 of the output tubes assuming there is a resistor there to measure across.
One other thing. Are pin 1 and 8 on the EL34's connected together? That's a mistake I've seen a few times from kit builders.


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## Paul Running

dtsaudio said:


> One other thing. Are pin 1 and 8 on the EL34's connected together? That's a mistake I've seen a few times from kit builders.


That's why it is important to go by the schematic.
The schematic is primary...layout secondary.


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## _Knighthawk_

dtsaudio said:


> This thread seems to be getting ahead of itself. We're looking at two different issues at the same time.
> I think the OP needs to re-do the voltage chart now that V1 is sorted out. But is it correct?
> And it would be good to know what the voltage is on pin 8 of the output tubes assuming there is a resistor there to measure across.
> One other thing. Are pin 1 and 8 on the EL34's connected together? That's a mistake I've seen a few times from kit builders.


Thanks Dan. I agree that the voltage issue should be sorted first. I will speak to that in my next outage. I will also repost an updated voltage chart. My primary concern right now is secondary - I am getting 386v off the secondary to the standby switch (should be 345v). Not sure why but it might explain the voltage issues I am seeing.

With respect to Pin1 and Pin8, as per the wiring diagram, they are connected together. Your suggesting that the drawing is incorrect? It is a consistent build characteristic in each of the Ceriatone 2550s I have seen pictures of (a feature rather than a bug).


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## dtsaudio

_Knighthawk_ said:


> Thanks Dan. I agree that the voltage issue should be sorted first. I will speak to that in my next outage. I will also repost an updated voltage chart. My primary concern right now is secondary - I am getting 386v off the secondary to the standby switch (should be 345v). Not sure why but it might explain the voltage issues I am seeing.
> 
> With respect to Pin1 and Pin8, as per the wiring diagram, they are connected together. Your suggesting that the drawing is incorrect? It is a consistent build characteristic in each of the Ceriatone 2550s I have seen pictures of (a feature rather than a bug).


The 40 volt difference may be a non issue depending what the amp is doing. Your output tubes could be running cold, the other tubes too.
All this may sort itself out. It's also possible the Hammond you are using has better regulation than the one Ceriatone supplies, so voltages may be higher.
Pin 1 and 8 should be connected. Break that connection and see what happens😁. Something I've seen more than a few times, is guys going from 6L6 tubes to EL34's. The 6L6 has that connection internally the EL34 does not. Some amps don't have that external connection, and then the owner wonders why his amp don't work.


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## _Knighthawk_

Updated voltage chart. I am seriously considering putting a terminal strip in and doing the math on a couple resistors to bring down the voltage from the secondary before it hits the Standby switch. It's a bit a ridiculous how high it is right now (380 v/760VCT).  It should be 345V/690VCT.


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## _Knighthawk_

Paul Running said:


> If an altered state helps, try cannabis however, I don't advise when you are in close proximity to lethal potentials.
> What exactly are we looking at here:
> 
> 
> I am going by this schematic:
> 
> View attachment 355511
> 
> 
> the bias network:
> 
> View attachment 355512
> 
> 
> is this correct? Not really if you mention a 50K pot.


No. I have a copy of the schematic and there are departures from the wiring diagram. Ceriatone's diagram calls for a 50k pot. As you know, they do not provide schematics.


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## Paul Running

_Knighthawk_ said:


> Updated voltage chart. I am seriously considering putting a terminal strip in and doing the math on a couple resistors to bring down the voltage from the secondary before it hits the Standby switch. It's a bit a ridiculous how high it is right now (380 v/760VCT).  It should be 345V/690VCT.
> 
> View attachment 355579


If your cathode resistors are 1Ω...the bias it's too hot.
Check this chart, with your plate voltages...2 X 30mA...2 X 30mV in your case:


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## Paul Running

_Knighthawk_ said:


> It's a bit a ridiculous how high it is right now (380 v/760VCT).  It should be 345V/690VCT.


You can easily operate EL34s at 600VDC on the plates...they are spec'd for 800V and will do so with very good sockets and proper HV wiring practices. You should be able to source 60WRMS at the voltages you are running.


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## Paul Running

dtsaudio said:


> The 6L6 has that connection internally the EL34 does not.


The EL34 is a true pentode (5 elements or terminations), it has a suppressor grid...the 6L6 is a beam-tetrode (4 elements or terminations), it does not have a suppressor grid...don't be fooled...to avoid being tricked, slow down.


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## dtsaudio

Paul Running said:


> The EL34 is a true pentode (5 elements or terminations), it has a suppressor grid...the 6L6 is a beam-tetrode (4 elements or terminations), it does not have a suppressor grid...don't be fooled...to avoid being tricked, slow down.


Actually close.
The EL34 is a true pentode. The original design of the 6L6 was indeed a tetrode, as were variations of the 6CA7 depending on who made them. That was back when these things were new.
Today almost all of these tubes are built closer to pentodes than beam tetrodes. JJ actually calls their 6L6GC a beam pentode.
The tetrode and pentode react the same way. The beam focusing plates and the suppressor grid perform the same function, and if were separated in the bottle would be wired the same way externally, ie connected to the cathode. It's more a matter of nomenclature than anything else due to back in the day when Philips held the patent on the suppressor grid.
Bottom line, they perform the same function.
And don't ever patronize me again.

Enough of the hijack. Back to the amp.


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## dtsaudio

Paul is right, the current through the EL34's is way too high. You need to get that down. The rest while high are fine and within the specs of the tubes. Going to make the amp cleaner as it will be harder to overload.
Just make sure the caps can handle the voltage.
Still no sound?


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## _Knighthawk_

Paul Running said:


> If your cathode resistors are 1Ω...the bias it's too hot.
> Check this chart, with your plate voltages...2 X 30mA...2 X 30mV in your case:


I am absolutely positive that I was to derive meaning from this post but I have no idea what you are trying to tell me. Thanks though.


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## _Knighthawk_

dtsaudio said:


> Paul is right, the current through the EL34's is way too high. You need to get that down. The rest while high are fine and within the specs of the tubes. Going to make the amp cleaner as it will be harder to overload.
> Just make sure the caps can handle the voltage.
> Still no sound?


Yeah, the 450V caps are either being pushed or are already shot. What do you think about a voltage reduction circuit for the secondary. My aim would be to bring the voltage down from 760VCT down to 690VCT before the voltage hits the Standby switch. Grasping at straws a bit here.

I have the 50k bias pot dialed right up and it is still not enough to tame the voltage. 

I am obviously open to suggestions to get the voltages down.


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## gtrguy

What’s your wall voltage?


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## dtsaudio

_Knighthawk_ said:


> I am absolutely positive that I was to derive meaning from this post but I have no idea what you are trying to tell me. Thanks though.


You're measuring across a 1 ohm resistor. So the current through the tubes is the same in amps as the volts. That is according to ohms law
I=V/R or I = volts/1. So you're running 69ma of current through that one tube and 62 through the other. Multiply that by the 473V on the plate, and your tubes are trying to dissipate 32 watts, when they're rated for 25 max. So you either have to get the current down, or the voltage.
Getting more negative voltage is necessary. 

Getting the high voltage down is not easy. Using a resistor in the power supply will work, but now you are dealing with heat, and fluctuating voltage as more or less curreng is drawn.
You could look at a buck transformer (google that), or getting the right transformer.


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## _Knighthawk_

gtrguy said:


> What’s your wall voltage?


122V (throughout the house). It ain't perfect (I use power conditioning PDUs for my amps once they leave the bench - and for all of my computers).


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## _Knighthawk_

dtsaudio said:


> You're measuring across a 1 ohm resistor. So the current through the tubes is the same in amps as the volts. That is according to ohms law
> I=V/R or I = volts/1. So you're running 69ma of current through that one tube and 62 through the other. Multiply that by the 473V on the plate, and your tubes are trying to dissipate 32 watts, when they're rated for 25 max. So you either have to get the current down, or the voltage.
> Getting more negative voltage is necessary.
> 
> Getting the high voltage down is not easy. Using a resistor in the power supply will work, but now you are dealing with heat, and fluctuating voltage as more or less curreng is drawn.
> You could look at a buck transformer (google that), or getting the right transformer.


Thanks Dan. I hear ya on the heat and the fluctuating voltage.

I thought I did get the right transformer but it is grossly out of spec and I couldn't return or swap it since I bought it a year ago (first time I have had an issue with a Hammond PT). I guess could get the Hammond 290GZ (same tranny - only with single primaries). I think I might have to bite the bullet and replace the f'ing thing. Bummer.


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## dtsaudio

Just a thought. You haven't hooked up any of the other primaries have you?


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## jb welder

_Knighthawk_ said:


> I am absolutely positive that I was to derive meaning from this post but I have no idea what you are trying to tell me.


Your target for bias is the 35mV at pin1 or 8 of each power tube. That should be the max. that you do not want to exceed. Adjust the bias so you get that figure. Please do not use the bias to try and drop the high voltage DC, it will only cause trouble and possible damage.
How high is the DC on the 450V caps with all tubes installed?

You are expecting things from the PT specs that are not possible and getting a bit fixated about it. 
The 690VAC is when loaded at 200mA with 120VAC on the primary. Your line voltage is higher than 120V so the secondary voltage will be higher. You are loaded at less than 200mA, so this will also increase the secondary voltage. When it's running at full tilt you would probably get the spec. number if you had 120V line voltage.
Your only real worry is sustained voltage in excess of 450V on those 450V caps.


----------



## Paul Running

dtsaudio said:


> And don't ever patronize me again.


The intent was not to betray your superiority...the intent was to tell the OP the importance of the schematic and data sheets and the term beam pentode is a misnomer...pentode means 5.


----------



## Paul Running

dtsaudio said:


> Getting the high voltage down is not easy. Using a resistor in the power supply will work, but now you are dealing with heat, and fluctuating voltage as more or less curreng is drawn.


The use of active components is a more efficient method to decrease the voltage...power MOSFETs are one solution.
Try to keep your screen voltages below 400VDC. As I mentioned before, you can operate EL34s at 600VDC plate voltages.


----------



## Paul Running

_Knighthawk_ said:


> Yeah, the 450V caps are either being pushed or are already shot.


Connect 2, identical caps in series to double the working voltage...remember that the overall capacitance will be one half...follow the rules for caps in series.


----------



## Paul Running

_Knighthawk_ said:


> I guess could get the Hammond 290GZ (same tranny - only with single primaries). I think I might have to bite the bullet and replace the f'ing thing. Bummer.


Don't give up now man...this setup will work and you will be amazed at it's performance.


----------



## Paul Running

_Knighthawk_ said:


> I thought I did get the right transformer but it is grossly out of spec


That's the ideal TFM for high-powered, EL34 operation. I can fix it for you but you won't learn anything...teach a man how to fish...I will fix it if you wish however, the cost of shipping is ridiculous.
Pro bono on the labour and ship without tubes.


----------



## _Knighthawk_

dtsaudio said:


> Just a thought. You haven't hooked up any of the other primaries have you?


Initially, I had run both primaries in parallel (blue/black and white/brown). Yesterday, I went back to using just blue/brown. Yellow/green goes to ground.


----------



## Paul Running

_Knighthawk_ said:


> Initially, I had run both primaries in parallel (blue/black and white/brown). Yesterday, I went back to using just blue/brown.


The parallel connected windings will operate more efficiently during high-power operation...think of a tandem truck with one set of it's rear wheels lifted...it's about load distribution.


----------



## _Knighthawk_

jb welder said:


> Your target for bias is the 35mV at pin1 or 8 of each power tube. That should be the max. that you do not want to exceed. Adjust the bias so you get that figure. Please do not use the bias to try and drop the high voltage DC, it will only cause trouble and possible damage.
> How high is the DC on the 450V caps with all tubes installed?
> 
> You are expecting things from the PT specs that are not possible and getting a bit fixated about it.
> The 690VAC is when loaded at 200mA with 120VAC on the primary. Your line voltage is higher than 120V so the secondary voltage will be higher. You are loaded at less than 200mA, so this will also increase the secondary voltage. When it's running at full tilt you would probably get the spec. number if you had 120V line voltage.
> Your only real worry is sustained voltage in excess of 450V on those 450V caps.


Hi jb and thanks. I will take a measurement on the 450V caps later today. I have already ordered 4 more of these as I am pretty sure I have likely already fried them.

Can I ask what you mean by "You are loaded at less than 200mA"? What is this number and how did you derive it?


----------



## _Knighthawk_

Paul Running said:


> The parallel connected windings will operate more efficiently during high-power operation.


Thanks. Easy to switch it back. I was just trying to rule things out.


----------



## _Knighthawk_

Paul Running said:


> The intent was not to betray your superiority...the intent was to tell the OP the importance of the schematic and data sheets and the term beam pentode is a misnomer...pentode means 5.


The OP is aware of the importance of these things but is under-trained, inexperienced and a bit thick.


----------



## _Knighthawk_

Paul Running said:


> Connect 2, identical caps in series to double the working voltage...remember that the overall capacitance will be one half...follow the rules for caps in series.


I do not believe I am presently qualified to perform this High G manuevre.


----------



## _Knighthawk_

Paul Running said:


> Don't give up now man...this setup will work and you will be amazed at it's performance.


I won't give up - I will simply adjust my approach until I succeed. Worse case scenario...

I don't fly without a parachute. His name is Chris Church - he knows stuff.


----------



## Paul Running

_Knighthawk_ said:


> but is under-trained, inexperienced and a bit thick.


Try to have confidence, don't consider yourself thick...self-respect will get you through this.


----------



## Paul Running

_Knighthawk_ said:


> I do not believe I am presently qualified to perform this High G manuevre.











Series and Parallel Capacitors | Capacitors | Electronics Textbook


Read about Series and Parallel Capacitors (Capacitors) in our free Electronics Textbook




www.allaboutcircuits.com




.


----------



## Paul Running

_Knighthawk_ said:


> I don't fly without a parachute.


That's a smart attitude, use that same attitude with high voltage circuits...safety is number one.


----------



## _Knighthawk_

Paul Running said:


> That's the ideal TFM for high-powered, EL34 operation. I can fix it for you but you won't learn anything...teach a man how to fish...I will fix it if you wish however, the cost of shipping is ridiculous.
> Pro bono on the labour and ship without tubes.


Thanks, that is very kind, but this fish is trying to learn how to ride a bicycle. Success is measured not only in a working amp but in how much I learn and whether I live to re-use what I have learned in my next build (the second item is of primary importance to myself and others).


----------



## _Knighthawk_

Paul Running said:


> Series and Parallel Capacitors | Capacitors | Electronics Textbook
> 
> 
> Read about Series and Parallel Capacitors (Capacitors) in our free Electronics Textbook
> 
> 
> 
> 
> www.allaboutcircuits.com
> 
> 
> 
> 
> .


Thanks. I understand the concept of capacitors in series and in parallel but it is much more than that needs to be understood:

1) I don't like schematics (alone) because I can't visualize what the wiring looks like. I see the concept and understand the math but I need to see a working example to 'get it'.

2) Your saying I need to up the voltage but I have no idea where or even why. It seems counter-intuitive since I thought my problem is too much voltage. I had worked out a two resistor voltage reduction circuit to reduce voltage and now you're suggesting that I increase voltage. My compass is spinning...and I am no closer to north.

3) It is one thing to say 'just go ahead and slap together a couple of caps in series' but given the above and the fact that I have no idea where this might be effective, it is a rather moot exercise. I could put two capacitors in series on the igniter of my barbecue, would that work? Obviously, I'm being hyperbolically facetious but I hope you see my point.


----------



## Paul Running

_Knighthawk_ said:


> Your saying I need to up the voltage but I have no idea where or even why.


Higher plate voltages on the output tubes will increase headroom...if that's what you are looking for.


----------



## Paul Running

_Knighthawk_ said:


> I had worked out a two resistor voltage reduction circuit to reduce voltage and now you're suggesting that I increase voltage.


The only place for those 500+VDC is on the plates of the output tubes. The rest can be derived from voltage reduction. There are several methods to accomplish this. You could use 3 identical caps in series and source the voltages from the tap points or use active circuitry, an example (of course, your TFM is not centre-tapped):










and then came power scaling:










Note the importance of center-tapped TFMs.


----------



## _Knighthawk_

Paul Running said:


> Try to have confidence, don't consider yourself thick...self-respect will get you through this.


Paul: you seem like a nice guy and you are clearly fairly knowledgeable when it comes to this stuff but your annotations specific to my self-esteem/respect are not required.

I am obviously extremely confident in myself or I wouldn't be risking my life playing around with 700 volts of power. Keep in mind that this is a hobby for me and that my talents lay elsewhere. My self-esteem and self-respect are also derived elsewhere. Last, I am extremely aware of my learning style so when I say I am a bit thick, it is a reflection of my ability to learn in the manner that you would teach me. In this circumstance, where teaching style and learning style clash, adjustments must be made. I have made clear to you where my challenges are but your instruction pattern (for which I am very grateful) has not changed. So, the adjustment is mine to make and in this regard (learning in this way), yes, I am a bit thick. Please do not misconstrue this as anything other than what it is.


----------



## Paul Running

_Knighthawk_ said:


> Paul: you seem like a nice guy and you are clearly fairly knowledgeable when it comes to this stuff but your annotations specific to my self-esteem/respect are not required.
> 
> I am obviously extremely confident in myself or I wouldn't be risking my life playing around with 700 volts of power. Keep in mind that this is a hobby for me and that my talents lay elsewhere. My self-esteem and self-respect are also derived elsewhere. Last, I am extremely aware of my learning style so when I say I am a bit thick, it is a reflection of my ability to learn in the manner that you would teach me. In this circumstance, where teaching style and learning style clash, adjustments must be made. I have made clear to you where my challenges are but your instruction pattern (for which I am very grateful) has not changed. So, the adjustment is mine to make and in this regard (learning in this way), yes, I am a bit thick. Please do not misconstrue this as anything other than what it is.


Okay, sorry for my misunderstanding. This is a hobby for me too. I admit that I may become over-enthusiastic with electronics and I may allow myself to appear pig-headed. Again, sorry for adding stress to the situation.


----------



## _Knighthawk_

Paul Running said:


> The only place for those 500+VDC is on the plates of the output tubes. The rest can be derived from voltage reduction. There are several methods to accomplish this. You could use 3 identical caps in series and source the voltages from the tap points or use active circuitry, an example (of course, your TFM is not centre-tapped):
> 
> 
> 
> and then came power scaling:
> 
> 
> 
> Note the importance of center-tapped TFMs.


No.//but I do see resistors, capacitors and a tube.


----------



## _Knighthawk_

Paul Running said:


> Okay, sorry for my misunderstanding. This is a hobby for me too. I admit that I may become over-enthusiastic with electronics and I may allow myself to appear pig-headed. Again, sorry for adding stress to the situation.


I really like the enthusiasm and I don't actually think you're pig-headed. No apology required. I know you mean well and that there is meaning in what you are saying, I am just not at a point where I can make much of it yet. I'll get there eventually but for now, I am still a noob and a good portion of what you are telling me is not computing.


----------



## Paul Running

_Knighthawk_ said:


> No.//but I do see resistors, capacitors and a tube.


Here is a voltage divider network derived from series caps...the resistors in parallel are for load distribution. As you will note, the 333VDC could be used for preamp power and also screen. After the circuit is working, you could increase the screen voltage:








Here's a classic example of this concept here on the Silvertone model 1484...a great sleeper amp for modding but a SOB to work in the chassis...cramped, very cramped:








it uses voltage doubling and cap voltage distribution networks...480VDC from 2, 170VAC discrete windings.


----------



## _Knighthawk_

Paul Running said:


> Here is a voltage divider network derived from series caps...the resistors in parallel are for load distribution. As you will note, the 333VDC could be used for preamp power and also screen. After the circuit is working, you could increase the screen voltage:
> View attachment 355679
> 
> Here's a classic example of this concept here on the Silvertone model 1484...a great sleeper amp for modding but a SOB to work in the chassis...cramped, very cramped:
> View attachment 355684
> 
> it uses voltage doubling and cap voltage distribution networks...480VDC from 2, 170VAC discrete windings.


That's a lot of work for a 1Watt Amp!

Anyway, in the diagram that you drew, what are the resistor values? Do they matter?


----------



## Paul Running

Here's an article that explains the balancing act:
The value of the balancing resistor can be approximated by the following formula:
R= 10/C
where
C= Capacitance in uF.
R= Resistance in mega-ohms.
To calculate the Balancing resistor value more accurately do the following:
1. Determine the leakage current of the capacitor.
2. Calculate the DC resistance value of the capacitor using the formula
3. Balancing resistor value will be 10% of the calculated DC resistance value.
RDC= Rated voltage
Leakage current
4. Balancing resistor wattage rating is calculated by determining the amount of current flowing through the balancing resistor multiplied by the voltage across the resistor.


----------



## Paul Running

_Knighthawk_ said:


> 1Watt Amp


Silvertone advertised it as 60W...but hell it's only a watt, a 60W amp is only twice as loud as a 6W amp...all perception.


----------



## nonreverb

Forgive me for winding this back a bit....can you tell me what the filament voltage reading is? I notice it's not included in the various voltage readings and since everything is high by a noticeable margin, I figure it's worth eliminating the power transformer as the issue once and for all....


----------



## _Knighthawk_

nonreverb said:


> Forgive me for winding this back a bit....can you tell me what the filament voltage reading is? I notice it's not included in the various voltage readings and since everything is high by a noticeable margin, I figure it's worth eliminating the power transformer as the issue once and for all....


Yes, of course. Filaments are 3.3V on each lug. Heaters are the same V1 through V5. Yes, a touch warm but my main is a touch warm as well at 122V - sometimes even 123V.


----------



## jb welder

_Knighthawk_ said:


> Can I ask what you mean by "You are loaded at less than 200mA"? What is this number and how did you derive it?


That is the transformer spec that you have mentioned, but you keep leaving out the 200mA that gives all the context.  It is from the transformer data sheet.
The transformer has a voltage rating at 200mA current on the HV winding. When it is idling (or completely unloaded, the voltages will rise a lot. We want the voltage to hold up when the amp is putting out full power. So the manufacturers spec them that way.



Paul Running said:


> Try to keep your screen voltages below 400VDC.


I'm not sure why you say this. EL34's are rated for 450V on the screens. In real life we see many amps running them higher than that. This amp is a proven design, screens will be around 5V less than plates.

This discussion has gone somewhat sideways I think. There is no need yet to be talking about modifications to a known good circuit. Just normal de-bugging of a new build.
The only possible issue I'm aware of so far is that the first 47uF450V may have too high voltage on it. If that turns out to be the case, I wonder if the 10K resistor feeding it is the right value. Worst case it can be tweaked.


----------



## _Knighthawk_

jb welder said:


> That is the transformer spec that you have mentioned, but you keep leaving out the 200mA that gives all the context.  It is from the transformer data sheet.
> The transformer has a voltage rating at 200mA current on the HV winding. When it is idling (or completely unloaded, the voltages will rise a lot. We want the voltage to hold up when the amp is putting out full power. So the manufacturers spec them that way.
> 
> 
> I'm not sure why you say this. EL34's are rated for 450V on the screens. In real life we see many amps running them higher than that. This amp is a proven design, screens will be around 5V less than plates.
> 
> This discussion has gone somewhat sideways I think. There is no need yet to be talking about modifications to a known good circuit. Just normal de-bugging of a new build.
> The only possible issue I'm aware of so far is that the first 47uF450V may have too high voltage on it. If that turns out to be the case, I wonder if the 10K resistor feeding it is the right value. Worst case it can be tweaked.


Thanks jb. I knew that had come from somewhere!

This was suggested to me privately:

"You could increase the dropping resistor going to phase inverter. Try using a 22K 2W or 3W instead of the current one?
You want the PI plates to be about 230-250V."

I assume that the resistor being cited here is the 100k that feeds pin 6 in V3? Or am I completely off?


----------



## Paul Running

jb welder said:


> I'm not sure why you say this. EL34's are rated for 450V on the screens. In real life we see many amps running them higher than that. This amp is a proven design, screens will be around 5V less than plates.


I did not say EL34s were rated for 450V...I said: Try to keep your screen-voltages below 400VDC. This is as per the data spec'd at post #55. Players may wonder why they have pre-mature failures with these tubes. Sure they can take the limited value of 425VDC but not at continuous duty for long. People seem to ignore the importance of the screen voltage and it's control of the tube's functionality.


----------



## jb welder

Paul, I understand you are a datasheet guy. I am a practical guy. We are not going to agree on lots of this stuff. 
You can change the design of the 2550 to meet some datasheet or other, but then it is not going to sound like a 'real' 2550 anymore.
The amount of amps I work on with designs that exceed datasheet max values is probably higher than those that obey them.

I'd really like to step back and have a look at the bigger picture here. There are no voltages grossly out of whack (beyond standard +/-20%). Is the amp working yet? Fix first, tweak later. 

@_Knighthawk_ can you adjust bias for 35mV at pins 1 of power tubes, then do another run on the voltage chart? Also include DC volts on both sides of the 10K between the 50 & 47uF caps.


----------



## _Knighthawk_

jb welder said:


> Paul, I understand you are a datasheet guy. I am a practical guy. We are not going to agree on lots of this stuff.
> You can change the design of the 2550 to meet some datasheet or other, but then it is not going to sound like a 'real' 2550 anymore.
> The amount of amps I work on with designs that exceed datasheet max values is probably higher than those that obey them.
> 
> I'd really like to step back and have a look at the bigger picture here. There are no voltages grossly out of whack (beyond standard +/-20%). Is the amp working yet? Fix first, tweak later.
> 
> @_Knighthawk_ can you adjust bias for 35mV at pins 1 of power tubes, then do another run on the voltage chart? Also include DC volts on both sides of the 10K between the 50 & 47uF caps.



Will do jb. Unfortunately, I have to work this afternoon but I will get on this asap.


----------



## nonreverb

Sorry to jump in again in mid stream I seem to have missed some of the discussion during my absence and may have missed the point where the amp came alive....Have we ascertained that the amp is at least making sound now?


----------



## Paul Running

Not that I know of Rich.


----------



## _Knighthawk_

nonreverb said:


> Sorry to jump in again in mid stream I seem to have missed some of the discussion during my absence and may have missed the point where the amp came alive....Have we ascertained that the amp is at least making sound now?


No. It did for a split second once and then with a hiss/pop, that was it.


----------



## nonreverb

I'll assume there is nothing coming out..no background noise/hiss?


----------



## _Knighthawk_

nonreverb said:


> I'll assume there is nothing coming out..no background noise/hiss?


No, not like what you would expect. It does make scratchy sounds when I touch certain pings and a kind of whispering/whooshing noise as I adjust the 'Presence' pot. It makes a low but audible hum when I engage the Standby but not through the speaker.


----------



## nonreverb

Have you tried swapping out V2 and V3 just for the hell of it?


----------



## _Knighthawk_

nonreverb said:


> Have you tried swapping out V2 and V3 just for the hell of it?


I have. I also have a couple dozen vintage 12AU7s kicking around that I could plug in just for shiggles.


----------



## Paul Running

I have the 50k bias pot dialed right up and it is still not enough to tame the voltage. 

I am obviously open to suggestions to get the voltages down.
[/QUOTE]
Try dialing it the other way.


----------



## nonreverb

Did you try a jumper between the send and return of the FX loop?.....just trying to eliminate the obvious.


----------



## Lincoln

has adding a choke been suggested for bringing the system voltage down?


----------



## _Knighthawk_

jb welder said:


> @_Knighthawk_ can you adjust bias for 35mV at pins 1 of power tubes, then do another run on the voltage chart? Also include DC volts on both sides of the 10K between the 50 & 47uF caps.


@jb welder










I re-biased the amp to 35.9 mA using plate voltage of 487V. Please see revised voltage measurements above. As per your request, I also measured the voltage on either side of the 10k resistor that sits between the 47uf and 50 uf cap (left side is looking at the amp upside down from the pot side). Voltages are still high.

Interestingly, after biasing, I could hear some hiss coming from the speaker so I plugged in and lo and behold - guitar! I then changed channels and it went away and didn't come back.


----------



## _Knighthawk_

Lincoln said:


> has adding a choke been suggested for bringing the system voltage down?


Hi Lincoln. Long time, no see. 

No. That has not come up. It does have a choke. I assume you mean another choke?


----------



## _Knighthawk_

nonreverb said:


> Did you try a jumper between the send and return of the FX loop?.....just trying to eliminate the obvious.


Interesting! No, I have not. I will give that a go after chow.


----------



## Lincoln

_Knighthawk_ said:


> Hi Lincoln. Long time, no see.
> 
> No. That has not come up. It does have a choke. I assume you mean another choke?


Oh, I'm watching from the sidelines. 

and sorry. I didn't see a choke in the layout on about page 2 or 3. Good way to drop about 40 volts if an amp doesn't already have one.


----------



## nonreverb

You also might try strumming a few chords with a guitar connected to the return. If by chance it works, you can pretty much eliminate the PI and power tubes as the problem.


----------



## Paul Running

jb welder said:


> Paul, I understand you are a datasheet guy. I am a practical guy. We are not going to agree on lots of this stuff.


I don't believe you will with an attitude like that.


----------



## _Knighthawk_

nonreverb said:


> You also might try strumming a few chords with a guitar connected to the return. If by chance it works, you can pretty much eliminate the PI and power tubes as the problem.


So, HUGE NEWS! 

As per your suggestion, I plugged the guitar into the 'Return' input of the effects loop and VOILA! Sound.
(I also jumped the effects loop but that didn't do anything)

What I noticed was that only the 'Master Output' impacted volume. Nothing else on that end had any effect whatsoever including (which you would expect, I think): 'Lead Master' pot, Channel Select switch, 'Input Gain' and Rhythm Clip switch. I noticed also that there wasn't much volume or gain. That said, the signal was solid and stable.

So, that's at least something to work with. If I am not mistaken, there's a tiny light at the end of this tunnel.


----------



## nonreverb

_Knighthawk_ said:


> So, HUGE NEWS!
> 
> As per your suggestion, I plugged the guitar into the 'Return' input of the effects loop and VOILA! Sound.
> (I also jumped the effects loop but that didn't do anything)
> 
> What I noticed was that only the 'Master Output' impacted volume. Nothing else on that end had any effect whatsoever including (which you would expect, I think): 'Lead Master' pot, Channel Select switch, 'Input Gain' and Rhythm Clip switch. I noticed also that there wasn't much volume or gain. That said, the signal was solid and stable.
> 
> So, that's at least something to work with. If I am not mistaken, there's a tiny light at the end of this tunnel.


Great! That eliminates the power tubes, V3 and half of V2. So now you have to work back from there. As you might expect, the gain would be low as you're inserting the signal past the main preamp gain stages. Now to look at the diagram and see where to concentrate on.


----------



## nonreverb

Here's something else to eliminate. Plug in a patch cord into the main input with the amp off and test the other end between tip and sleeve for a dead short.


----------



## _Knighthawk_

nonreverb said:


> Here's something else to eliminate. Plug in a patch cord into the main input with the amp off and test the other end between tip and sleeve for a dead short.


Continuity test complete. Signal to cliff jack is good.


----------



## nonreverb

So it reads open?


----------



## _Knighthawk_

nonreverb said:


> So it reads open?



It is possible that I have misunderstood what you were wanting to be done. I plugged in the cable and checked for continuity between the tip of the cable and the second lug of the cliff jack. I am thinking this is not what you asked?

How do I test for a dead short between tip and sleeve?


----------



## nonreverb

The intention of the exercise was to see if the activated input was shorted to ground. With the jack inserted, if there's a dead short (0 ohms) between the tip and sleeve, that indicates a short between the input jack and V1's input to ground which would prevent any signal from reaching V1. I hope I'm not wearing you out with all this...I'm just trying to eliminate the obvious stuff first. I think it's safe to say that based on the tube data, it's not a tube and we now know it's not the second half of the circuit. So we're now faced with eliminating areas around V1 and half of V2.
Although a scope would be handy right now, this situation forces us to use other troubleshooting skills to solve the problem....kinda interesting IMHO.


----------



## _Knighthawk_

Ah, I see. Right, we should see 1 megaohm of resistance. Yes? So, I did this:

"With the amp off, insert a guitar cable into the input jack, then measure the other end of the cable from tip to sleeve for resistance."

The result: 0

I then inspected the cliff jack but I do not see how it could be sending signal to ground. I am using a known good cable so it has to be the jack wiring but I don't see an issue. There is a cap in the mix - would the cap's polarity cause an issue if it were reversed? (I don't know if that particular cap is polarized or not)


----------



## nonreverb

_Knighthawk_ said:


> Ah, I see. Right, we should see 1 megaohm of resistance. Yes? So, I did this:
> 
> "With the amp off, insert a guitar cable into the input jack, then measure the other end of the cable from tip to sleeve for resistance."
> 
> The result: 0
> 
> I then inspected the cliff jack but I do not see how it could be sending signal to ground. I am using a known good cable so it has to be the jack wiring but I don't see an issue. There is a cap in the mix - would the cap's polarity cause an issue if it were reversed? (I don't know if that particular cap is polarized or not)


If you're seeing 0 ohms, you may have found your problem. I would check the shielded cable running from the input to the V1 input. All it takes is one missed strand of the copper shielding to be touching the hot and *<poof>* no signal. Also check for solder splashes and the cap as it might be the problem.


----------



## _Knighthawk_

nonreverb said:


> If you're seeing 0 ohms, you may have found your problem. I would check the shielded cable running from the input to the V1 input. All it takes is one missed strand of the copper shielding to be touching the hot and *<poof>* no signal. Also check for solder splashes and the cap as it might be the problem.


Thank you for this. Will check. For the record, I much prefer the switchcraft jacks that I use for my Fender amps. Cliff jacks are a pain in the ass!


----------



## Paul Running




----------



## nonreverb

Paul Running said:


> View attachment 355858


In partnership with one of these plus a felt washer for the front.....to keep those pesky ground loops out of the circuit.


----------



## _Knighthawk_

The switchcraft jacks are so much more durable than the cliff jackets (which are basically just cheap plastic junk IMO).

Do you use the felt washer on the front with cliff jacks or the back?


----------



## Paul Running

I do, mainly for the electrically conductive jacks. It's not worth guessing whether your grounding is proper...isolating high-impedance circuitry from ground loops is a sure thing with them...a superb choice in materials, the soft mass prevents fractures in phenolic and you know how brittle that material can be. Some people are able to do it without the insulated washer system...I don't chance my grounding scheme and practices...go metal and go insulated man.


----------



## Paul Running

_Knighthawk_ said:


> @jb welder
> View attachment 355784
> 
> 
> 
> I re-biased the amp to 35.9 mA using plate voltage of 487V. Please see revised voltage measurements above. As per your request, I also measured the voltage on either side of the 10k resistor that sits between the 47uf and 50 uf cap (left side is looking at the amp upside down from the pot side). Voltages are still high.
> 
> Interestingly, after biasing, I could hear some hiss coming from the speaker so I plugged in and lo and behold - guitar! I then changed channels and it went away and didn't come back.











If this is your latest V chart...I notice that V4 and V5, EL34s are idling at an 18% differential (.039/.033). Both tubes are within spec + or - but as you will note they are at opposite ends of the tolerance bandwidth. You may want to swap those two tubes...put 4 into 5 and vise versa. If the readings are mirror-imaged then that verifies that argument. Do you know if they were matched pairs?


----------



## _Knighthawk_

nonreverb said:


> If you're seeing 0 ohms, you may have found your problem. I would check the shielded cable running from the input to the V1 input. All it takes is one missed strand of the copper shielding to be touching the hot and *<poof>* no signal. Also check for solder splashes and the cap as it might be the problem.


You are on a roll. So I did check my shielded cable - could not see an issue. So, I ran a little experiment: removed cap from the connection and inserted piece of wire. Presto-bango - 1M of resistance on the meter immediately.

Trying to dig out another 0.047 cap and move on to the next issue. 

Many thanks for the thinking.


----------



## nonreverb

_Knighthawk_ said:


> You are on a roll. So I did check my shielded cable - could not see an issue. So, I ran a little experiment: removed cap from the connection and inserted piece of wire. Presto-bango - 1M of resistance on the meter immediately.
> 
> Trying to dig out another 0.047 cap and move on to the next issue.
> 
> Many thanks for the thinking.


Looking forward to hear (pardon the pun) if it's now working.


----------



## _Knighthawk_

nonreverb said:


> Looking forward to hear (pardon the pun) if it's now working.


Cant seem to find an 0.047 cap. 

Will have to order one.


----------



## nonreverb

_Knighthawk_ said:


> Cant seem to find an 0.047 cap.
> 
> Will have to order one.


A question if I may: Doe's the cap test short on the meter?


----------



## _Knighthawk_

Yeah, I get OL. Meter doesn't even blink at it.


----------



## nonreverb

Actually, when I look at the diagram again, it wouldn't matter if it was short as it's not a direct path to ground and the amp would still work...it would just be resistively coupled with the 68K resistor. It might have just been a solder issue.


----------



## nonreverb

OL is good. That means it's infinite resistance....It's not the cap....unless it's lost all it's capacitance. However, the issue was a short so i think you might have inadvertently corrected the issue when you removed the cap.


----------



## _Knighthawk_

Okay. I will put the cap back on and see what happens.


----------



## nonreverb

_Knighthawk_ said:


> Okay. I will put the cap back on and see what happens.


Do another resistance test once it's in to make sure then fire that sh*t up!


----------



## _Knighthawk_

So, I did do the resistance test with the same result - just OL. HOWEVER, I also fired that sh*t up and and I did signal!!!

LOUD. Very LOUD! 

Slight snag though...when I tried to switch channels, she went dead as a door nail. So, one channel is not working - but that is okay.

I turned the amp off - waited a minute and put it back on the working channel. Good, loud signal. Then I used the foot switch to change channels - same result. Other channel kills the sound. And it stays silent when I switch back to the working channel.

So, back to the old drawing board - but hey, more progress. 

(I did order more of the 100V 0.047 caps and I will be switching that one out - regardless. I know it has nothing to do with the current problem (pun intended) but I will liely do it anyway).


----------



## nonreverb

Probably a fault in the switching circuit or relay board.


----------



## _Knighthawk_

nonreverb said:


> Probably a fault in the switching circuit or relay board.


I was afraid you would say that (it's exactly what went through my mind).


----------



## _Knighthawk_

I am reading that if there is a voltage issue with the relay coil, the amp won't switch. I'm going to start there - once I figure out what and where the relay coil is.


----------



## dtsaudio

Relay coil is just that. A coil. When energized creates a magnet and trips the relay. Look at the pin spacing on the relay you have. Two pins are further away than the other 6. Those two are the coil. Measure there with your DC volt meter and switch channels. It should toggle with the switch.


----------



## nonreverb

_Knighthawk_ said:


> I am reading that if there is a voltage issue with the relay coil, the amp won't switch. I'm going to start there - once I figure out what and where the relay coil is.


The relay coil and board. The relay is switching. We know this because you pressed the channel button and it knocked out the sound. I suspect there's a wiring issue on the dead channel side.


----------



## jb welder

Odd that it stays dead when you switch back to the good channel. Could be the relay is iffy. Or it is triggering something further up the circuit that is common to both channels.


----------



## nonreverb

jb welder said:


> Odd that it stays dead when you switch back to the good channel. Could be the relay is iffy. Or it is triggering something further up the circuit that is common to both channels.


I think it had to do with the footswitch being plugged in. Something's amiss with the wiring I suspect.


----------



## jb welder

One simple thing to try would be to get it into fault condition and make sure the FX return jack still works.

Attaching Marshall schematic which shows relay workings.


----------



## nonreverb

jb welder said:


> One simple thing to try would be to get it into fault condition and make sure the FX return jack still works.
> 
> Attaching Marshall schematic which shows relay workings.


I believe it would regardless. If you look at the wiring diagram, the FX return is inserted into the second half of V2 which is past the channel switching part of the circuit..


----------



## _Knighthawk_

dtsaudio said:


> Relay coil is just that. A coil. When energized creates a magnet and trips the relay. Look at the pin spacing on the relay you have. Two pins are further away than the other 6. Those two are the coil. Measure there with your DC volt meter and switch channels. It should toggle with the switch.


Thanks! That nails it right down. I saw the relay. I did not see the coil. I still do not see a coil but I do understand the principle. I will give this a go at some point today.


----------



## Paul Running

__





Understanding Relays & Wiring Diagrams | Swe-Check


A relay is an electrically operated switch. Learn how to wire a 4 or 5 pin relay with our wiring diagrams and understand how relays work.




www.swe-check.com.au


----------



## _Knighthawk_

nonreverb said:


> The relay coil and board. The relay is switching. We know this because you pressed the channel button and it knocked out the sound. I suspect there's a wiring issue on the dead channel side.
> View attachment 355930


I will definitely explore this with a fine tooth multimeter. Just so that my fuzzy mind is less fuzzy, you're suggesting that the switching mechanism (relay coil) is likely fine but that the wiring extending from it may be the issue.


----------



## _Knighthawk_

jb welder said:


> One simple thing to try would be to get it into fault condition and make sure the FX return jack still works.
> 
> Attaching Marshall schematic which shows relay workings.



I can definitely try this experiment. Thanks jb. Will give it a go.


----------



## _Knighthawk_

Thanks gentlemen. You've given me a lot to think about (ie. learn!). I will dig into all of this after work today.


----------



## nonreverb

_Knighthawk_ said:


> I will definitely explore this with a fine tooth multimeter. Just so that my fuzzy mind is less fuzzy, you're suggesting that the switching mechanism (relay coil) is likely fine but that the wiring extending from it may be the issue.


Yes. If the relay coil was not working, one set of contacts are what's called "Normally Closed"....in other words, if you couldn't energize the coil, one set of contacts in the relay is always connected. So if you pressed the channel switch and nothing happened, chances are the relay would be inoperative......That's not what happened in your case. When you pressed the channel button, it DID switch. The circuit that is connected to, the contacts when the relay is energized, is not operating correctly. IMHO


----------



## _Knighthawk_

nonreverb said:


> Yes. If the relay coil was not working, one set of contacts are what's called "Normally Closed"....in other words, if you couldn't energize the coil, one set of contacts in the relay is always connected. So if you pressed the channel switch and nothing happened, chances are the relay would be inoperative......That's not what happened in your case. When you pressed the channel button, it DID switch. The circuit that is connected to the contacts when the relay is energized is not operating correctly. IMHO


I understand (I think). That seems very logical to me. Will dig into this later this afternoon.


----------



## _Knighthawk_

jb welder said:


> One simple thing to try would be to get it into fault condition and make sure the FX return jack still works.
> 
> Attaching Marshall schematic which shows relay workings.


I can now confirm that the guitar can be heard when plugged into FX loop return while the amp is in a fault condition.

(But damn does it sound bloody glorious when it is not!!!)


----------



## nonreverb

_Knighthawk_ said:


> I can now confirm that the guitar can be heard when plugged into FX loop return while the amp is in a fault condition.
> 
> (But damn does it sound bloody glorious when it is not!!!)


You're almost there!


----------



## jb welder

_Knighthawk_ said:


> (But damn does it sound bloody glorious when it is not!!!)


If you get desperate and need a playing fix, or have to wait for parts etc., you can jumper across appropriate relay contacts so one channel or other works.


----------



## _Knighthawk_

So, I spent the evening testing continuity and trying to hunt down what might be causing the issues with the relay coil (a new term that I am still not comfortable using since I still don't think I fully understand the 'coil' part of it). I found something interesting. I made a major gaff that I am embarrassed to report. I missed a wire to star ground from the second cap 47uF cap on the main board (reading right to left). BIG over sight - sometimes I piss myself off.

Anyway, fixed that and began testing continuity and tracing the wiring. I didn't find any other wiring anomalies so I started testing components. What I found was that the 22uf cap that ties in to the switching wiring is essentially dead (reading as 0.1 nF on my meter). I tested it about 4 times.

I am not sure if this could be causing the issues I am having but I will replace it.

I also noticed that the channel switch on the chassis does work when the footswitch is plugged in. I expect that this is normal (so a good thing) but I thought I would mention it. Anyway, that is as far as I got with this tonight. I don't think I made much progress.


----------



## _Knighthawk_

jb welder said:


> If you get desperate and need a playing fix, or have to wait for parts etc., you can jumper across appropriate relay contacts so one channel or other works.


 I actually spent an hour and a half playing through the OD channel late this afternoon. Was glorious!!!


----------



## jb welder

Were you checking that cap out of circuit? You'll often get odd readings in circuit due to other components that are connected.


----------



## nonreverb

_Knighthawk_ said:


> So, I spent the evening testing continuity and trying to hunt down what might be causing the issues with the relay coil (a new term that I am still not comfortable using since I still don't think I fully understand the 'coil' part of it). I found something interesting. I made a major gaff that I am embarrassed to report. I missed a wire to star ground from the second cap 47uF cap on the main board (reading right to left). BIG over sight - sometimes I piss myself off.
> 
> Anyway, fixed that and began testing continuity and tracing the wiring. I didn't find any other wiring anomalies so I started testing components. What I found was that the 22uf cap that ties in to the switching wiring is essentially dead (reading as 0.1 nF on my meter). I tested it about 4 times.
> 
> I am not sure if this could be causing the issues I am having but I will replace it.
> 
> I also noticed that the channel switch on the chassis does work when the footswitch is plugged in. I expect that this is normal (so a good thing) but I thought I would mention it. Anyway, that is as far as I got with this tonight. I don't think I made much progress.


If that cap is in fact, dead, that's troubling. Brand new caps shouldn't be dead. FWIW I might take the time to check any others of the same value/brand. Sometimes, although not common, they get a bad batch.


----------



## greco

Very enjoyable thread! 
I feel like a vicarious imposter...LOL


----------



## _Knighthawk_

jb welder said:


> Were you checking that cap out of circuit? You'll often get odd readings in circuit due to other components that are connected.


I did wonder about that. I notice that when I measure resistors in circuit, they are usually spot on (+/- 5%). The caps though are quite a different story.


----------



## _Knighthawk_

greco said:


> Very enjoyable thread!
> I feel like a vicarious imposter...LOL


You're always welcome greco. These threads are very instructive and educational (at least for noobs like me, anyway).


----------



## _Knighthawk_

I have a bunch of F&Ts coming to replace the 47uF 'Holy Grail' caps. This one is 22uf and unique in this build.


----------



## _Knighthawk_

dtsaudio said:


> Relay coil is just that. A coil. When energized creates a magnet and trips the relay. Look at the pin spacing on the relay you have. Two pins are further away than the other 6. Those two are the coil. Measure there with your DC volt meter and switch channels. It should toggle with the switch.


@dtsaudio So, I have done my homework on this and now understand more fully the concept of the relay/coil. Last night I traced back from the coil to the board and double-checked all of the components. All seems in order wiring-wise but I am little concerned about a 22 uf capacitor in that area. Anyway...

I was a little worried about measurement as I don't like sticking both hands into the chassis...but I think I can make this measurement with a com lead in the chassis and only one had in the chassis. So, tonight's the night for this (after I put the board back on). Thanks again for the nod in this direction. I will elt you know what I come up with.


----------



## Paul Running

You may wish to inspect the solder connection to the grid-stopper resistor and others. Solder does not provide a secure mechanical bond...it is a soft alloy. Due to the lack of support at this connection, I would advise making a hook-joint and slide a neoprene sleeve over the connection to provide additional support.








I worked for a number of years in a Repair and Overall department and a great deal of my repairs involved soldering faults. I believe that it is very important to learn how to solder properly, a skill that requires practice. Years ago, most companies taught their assemblers how to solder properly...typically a one week course on just how to solder properly and perform proper connections. There are manuals online describing such practices and I encourage you to review them.


----------



## tomee2

There's a pdf of a 1950s book on the web, somewhere, showing the accepted practice for aviation electronics assembly, which had nice pictures on how to dress leads and place components.. wish I could find it.
Might be on the rob robinette site.

Yes, found it, lots of tips here.




__





Build an Amp


How To Build a Tube Amplifier



robrobinette.com


----------



## _Knighthawk_

tomee2 said:


> There's a pdf of a 1950s book on the web, somewhere, showing the accepted practice for aviation electronics assembly, which had nice pictures on how to dress leads and place components.. wish I could find it.
> Might be on the rob robinette site.
> 
> Yes, found it, lots of tips here.
> 
> 
> 
> 
> __
> 
> 
> 
> 
> 
> Build an Amp
> 
> 
> How To Build a Tube Amplifier
> 
> 
> 
> robrobinette.com


Huge fan of the Robinette site. About two or three years ago, before he put all the advertising on the site, I ripped the whole thing to PDF (was worried he might take it down). It has been a go-to for me in my journey.


----------



## _Knighthawk_

Paul Running said:


> You may wish to inspect the solder connection to the grid-stopper resistor and others. Solder does not provide a secure mechanical bond...it is a soft alloy. Due to the lack of support at this connection, I would advise making a hook-joint and slide a neoprene sleeve over the connection to provide additional support.
> 
> I worked for a number of years in a Repair and Overall department and a great deal of my repairs involved soldering faults. I believe that it is very important to learn how to solder properly, a skill that requires practice. Years ago, most companies taught their assemblers how to solder properly...typically a one week course on just how to solder properly and perform proper connections. There are manuals online describing such practices and I encourage you to review them.


I am not a big fan of flying leads (Stephen Cohrs at Trinity has lots to say on this subject). I normally make a small loop in the resistor if I have to use one (no room for a terminal), run the connection through, and then squeeze the loop before applying solder. It has been a good solution - never let me down.


----------



## _Knighthawk_

Some progress last night/this morning (testing last night, wire replacement to the relay board and then put everything back together this morning). The amp switches now. I found one wire from the relay board that had no continuity (looked fine, was well soldered, but wasn't passing current). I replaced it and bingo - switching! Well, kind of...

It will switch out of the OD channel to the clean channel without dropping off. Just what we want! However, when I hit the switch again, the LED indicator changes but it does not switch back to the OD channel. It stays on the Clean channel.

As an aside, as per @dtsaudio, I did measure the current on the relay coil. It is a bit odd but I am not experienced enough to know if this is expected behaviour or not. On the R- negative side, the current goes from 70mV to 6.4V when I hit the switch. On the R+ side, the current doesn't really change much at all when I hit the switch. It goes from 6.9v to 7.5 V. I suspect (but I don't know, cuz I'm a noob) that the voltage present on the plus side is omni-present to accommodate the switching (ie. no voltage, no switch).

Anyway, that's the mostly good news. I will be working more on this in the morning. I'm all ears if anyone has any thoughts/suggestions.


----------



## nonreverb

Do you have a diode across the relay power terminals?
The reason I ask is because when a relay is de-energized , the energy stored in the coil reverses direction (Counter electromotive force) and unless shunted through a diode, can delay the relay from returning to it's "off" state.


----------



## tomee2

_Knighthawk_ said:


> Huge fan of the Robinette site. About two or three years ago, before he put all the advertising on the site, I ripped the whole thing to PDF (was worried he might take it down). It has been a go-to for me in my journey.


Nice! BTW I'm in awe of you taking on this project. I've recapped many old tube hifi amps and a few guitar amps, but building from scratch, even with a kit, to me is a different ball game. Hats off to you.


----------



## _Knighthawk_

nonreverb said:


> Do you have a diode across the relay power terminals?
> The reason I ask is because when a relay is de-energized , the energy stored in the coil reverses direction (Counter electromotive force) and unless shunted through a diode, can delay the relay from returning to it's "off" state.


Not directly between + and -, no. There is a diode in the circuit in the R- path (as below).


----------



## _Knighthawk_

tomee2 said:


> Nice! BTW I'm in awe of you taking on this project. I've recapped many old tube hifi amps and a few guitar amps, but building from scratch, even with a kit, to me is a different ball game. Hats off to you.


I have built my last couple from scratch (al though I did order the chasses from different vendors). I really wanted this amp so I decided to go with the kit. It is a bit more complicated in some ways than my last build (63 Fender VibroVerb) and some of it is relatively new to me so it has been very challenging. I'm learning though and the names you see in this thread represent the super heroes whose support has helped me to get this far.


----------



## nonreverb

_Knighthawk_ said:


> Not directly between + and -, no. There is a diode in the circuit in the R- path (as below).
> 
> View attachment 356351


...and there isn't one on the relay board either I suspect....interesting. There should be as it allows the relay coil to decouple the energized contacts almost instantaneously.


----------



## nonreverb

You could give this a try for no other reason than my own selfish interest: Take a non-conductive item like a pen and when you switch channels, give the relay a gentle tap to see it that helps it switch.


----------



## Paul Running

nonreverb said:


> Do you have a diode across the relay power terminals?
> The reason I ask is because when a relay is de-energized , the energy stored in the coil reverses direction (Counter electromotive force) and unless shunted through a diode, can delay the relay from returning to it's "off" state.


What Rich mentions here is important. Using a relay in a circuit where the relay will be ON for long periods can lead to unstable contacts because the heat generated by the coil will affect the insulation, causing a film to develop on the contact surfaces. Be sure to use a fail-safe circuit design that provides protection against contact failure or coil burnout...make sure the relay is protected.
The G5V series relays do not have internal protection:


----------



## dtsaudio

_Knighthawk_ said:


> to 6.4V when I hit the switch. On the R+ side, the current doesn't really change much at all when I hit the switch. It goes from 6.9v to 7.5 V


I see you're measuring each side to ground. Normally you measure across the two terminals, but in this case the effect is the same. What concerns me is that you have 6.9V on a 5V relay. You are approaching out of spec here. Get a spare just in case.


Paul Running said:


> What Rich mentions here is important. Using a relay in a circuit where the relay will be ON for long periods can lead to unstable contacts because the heat generated by the coil will affect the insulation, causing a film to develop on the contact surfaces. Be sure to use a fail-safe circuit design that provides protection against contact failure or coil burnout...make sure the relay is protected.
> The G5V series relays do not have internal protection:


What Rich is describing is for protecting the coil, and for preventing inductive kick. It won't prevent overheating in any way.
One side benefit of the diode across the coil is that often in relay circuits you get a pop through the speakers when the relay energizes and de-energizes. That's the counter EMF mentioned or called inductive kick. The diode will prevent the pop. Just get the diode in the right direction or the relay won't trip at all.

I wouldn't worry about any of this until you get the amp working.


----------



## Paul Running

I believe that the amp is operational now and what I mentioned about the precaution is in the manufacturers data sheet. Check here for yourself...see Precautions:









This is the exact relay on the PCB images, posted by the owner:









Here’s the complete data sheet:


----------



## dtsaudio

Not saying you were wrong, just the diode mentioned by Rich is not going to protect the coil from overheating.
I've used these particular relays for over 30 years, and contact failure is extremely low. We used to use them in programmable logic controls for machine control. Severe duty, and highly reliable. 
In the case of this amp the best way to prevent contact failure or coil overheating is to reduce that coil voltage. 5V relay with 7V on it is not good. Get it down to 4.5V.
Could put a 5V zener across it, that would solve both concerns.


----------



## nonreverb

dtsaudio said:


> What Rich is describing is for protecting the coil, and for preventing inductive kick. It won't prevent overheating in any way.
> One side benefit of the diode across the coil is that often in relay circuits you get a pop through the speakers when the relay energizes and de-energizes. That's the counter EMF mentioned or called inductive kick. The diode will prevent the pop. Just get the diode in the right direction or the relay won't trip at all.
> 
> I wouldn't worry about any of this until you get the amp working.


Kind of handy for protecting transistor drivers as well from the effects of the coil flyback voltage.


----------



## dtsaudio

nonreverb said:


> Kind of handy for protecting transistor drivers as well from the effects of the coil flyback voltage.


Absolutely. Used to do that on the PLCs I worked on back in the day.


----------



## nonreverb

dtsaudio said:


> Absolutely. Used to do that on the PLCs I worked on back in the day.


You worked in the instrumentation field at one time?


----------



## dtsaudio

Machine automation and control


----------



## _Knighthawk_

dtsaudio said:


> In the case of this amp the best way to prevent contact failure or coil overheating is to reduce that coil voltage. 5V relay with 7V on it is not good. Get it down to 4.5V.
> Could put a 5V zener across it, that would solve both concerns.


I can do that. What would that look like in the circuit? Would a 4.7V be better?


----------



## _Knighthawk_

Something like this?


----------



## Paul Running

The drop-out voltage for that relay is 3VDC. Look at the coil rating...it will operate from 3 to 48VDC:


----------



## jb welder

Paul Running said:


> .it will operate from 3 to 48VDC:


I think that is showing the range of voltage models available for that series. In the data sheet you posted, it says the 5V model can handle up to 120% of it's rated voltage (so 6V max).
edit: that's the H1 version so 180% or 9V max.


----------



## Paul Running

_Knighthawk_, sorry if I may have mislead you on the high-side operational voltage for your relay...the winding on that coil would melt rather quickly with 48VDC on it. I did come across an interesting tech sheet on relays that may be of interest to you and others following this thread:


----------



## _Knighthawk_

nonreverb said:


> You could give this a try for no other reason than my own selfish interest: Take a non-conductive item like a pen and when you switch channels, give the relay a gentle tap to see it that helps it switch.


I did try this - gave it a little whack with a chop stick but it didn't do much. I am a bit uncertain about how to affix the zener. Once I have confirmation of that, I can give that a shot.

I am frankly not sure what else to do at this point.


----------



## nonreverb

_Knighthawk_ said:


> I did try this - gave it a little whack with a chop stick but it didn't do much. I am a bit uncertain about how to affix the zener. Once I have confirmation of that, I can give that a shot.
> 
> I am frankly not sure what else to do at this point.


It gets tricky to assist now as there's quite a bit going on in that circuit.


----------



## jb welder

The zener can go right at the coil pins of the relay. Cathode side of zener goes to most + end of coil (R+ on ceriatone drawing).
I just remembered about the IC socket for the relay mounting, are you using it? Have you tried cleaning the pins? Sockets are handy but one more link in the reliability chain.


----------



## nonreverb

jb welder said:


> The zener can go right at the coil pins of the relay. Cathode side of zener goes to most + end of coil (R+ on ceriatone drawing).
> I just remembered about the IC socket for the relay mounting, are you using it? Have you tried cleaning the pins? Sockets are handy but one more link in the reliability chain.


A bent pin would also cause these symptoms. Those sockets can be tricky when trying to mount chips and worse...relays with thin, pliable mounting contacts.


----------



## _Knighthawk_

jb welder said:


> The zener can go right at the coil pins of the relay. Cathode side of zener goes to most + end of coil (R+ on ceriatone drawing).
> I just remembered about the IC socket for the relay mounting, are you using it? Have you tried cleaning the pins? Sockets are handy but one more link in the reliability chain.


I am using the socket - I have not tried cleaning the pins. I soldered them to the board and trimmed them. I am going to take advice that was given here and order a couple more of these relays - good to have around just in case.


----------



## _Knighthawk_

nonreverb said:


> A bent pin would also cause these symptoms. Those sockets can be tricky when trying to mount chips and worse...relays with thin, pliable mounting contacts.


Socket is soldered to the board. I can definitely check on the relay itself though.


----------



## _Knighthawk_

jb welder said:


> The zener can go right at the coil pins of the relay. Cathode side of zener goes to most + end of coil (R+ on ceriatone drawing).


And the other end to ground, I assume?


----------



## jb welder

No, to the other relay coil pin. (R-)
Funny, it looks like there are a couple holes there on the board with nothing stuffed that are meant either for this, or for the other type diode that was mentioned.


----------



## _Knighthawk_

Yes, I see what you mean. It seems odd - but then I do not see a zener (or any diode) there on the original schem either.


----------



## Paul Running

There is no voltage regulation to power the relay.
D9 (high-lighted green), is the protection diode for your relay coil.
D8 is the half-wave rectifier that converts the heater voltage (6.3VAC), with the filter cap C22, to 8VDC...the power to your relay.


----------



## _Knighthawk_

Just FYI...

I swapped out all of the 'Holy Grail' caps for F&Ts. Also, I don't want to come off as a 'components snob' but I am a little bit leery of buying some parts from Sayal. So, my Digikey order should arrive today and I can move in to the next phases of troubleshooting for this amp. More to come soon...


----------



## _Knighthawk_

So, an update:

I added the zener diode (4.7V) as directed but nothing has really changed (although the relay IC is protected). Next step: order a new new relay IC and see if that makes a difference. It still switches to the clean channel but does not switch back.

I also swapped out the voltage dropping 10K 5W for an 18K 5W to lower the voltage travelling up the board to the two 47uF caps (which I had already replaced with F&Ts). Last, I re-biased the amp (probably didn't need to but I had it on the bench so what the hell).

I have to say that outside of the channel switching issue, the amplifier itself does sound pretty AMAZING! Marrying it to my Gibson LP R8 is absolutely heavenly (WOW!). I am really liking it - exactly what I was hoping to get out of the build and add to the arsenal of sonic goodies in the music room.


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## Paul Running

_Knighthawk_ said:


> It still switches to the clean channel but does not switch back.


You have just described the action of a latching relay but you know that you have the correct part, probably a sticking contact...good to see you learning about the innards of your amp.


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## dtsaudio

Since this thread is getting long, and I'm too lazy to go searching, you're still not getting the channels to switch?
When you first turn on the amp you get output. Then when you change channels you get nothing, or does it change, but not change back when you trip the change channels again?


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## _Knighthawk_

When I first turn on the amp, I get signal through the speaker. When I change channels (to the clean channel), I get clean channel signal through the speaker. When I switch it again (ie. try to go back to dirty channel), it does not switch - it stays in the clean channel (with signal to the speaker) and the only way to get back to the dirty channel is by turning the amp off completely and powering it back on.


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## dtsaudio

Got it.
Check the voltage on the relay. Does it toggle on and off with the channel switching?


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## _Knighthawk_

An update:

As per @dtsaudio's request, I have checked the voltage by measuring VDC at the plus and minus before the zener that I installed.

The voltage is as follows (with the amp in dirty channel):

R - : .484 VDC
R - : (after switch) 6.18 VDC

R + : 4.75 VDC
R + : (after switch) 7.23 VDC

Interestingly, the amp now DOES switch back from the clean channel to the dirty channel - sometimes. And sometimes not. There seems to be a co-relation between how long I wait to switch back to the dirty channel but that might just be in my head (I keep lots of fantastical things in there so I could be imagining this co-relation). The switching from the dirty channel to the clean channel is consistent and there is no time variable in play. 

So, it is a bit of a puzzle to me still.


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## Paul Running

The coil of the relay is an inductor...an inductor stores energy, just like a capacitor stores energy.


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## jb welder

_Knighthawk_ said:


> R - : .484 VDC
> R - : (after switch) 6.18 VDC
> 
> R + : 4.75 VDC
> R + : (after switch) 7.23 VDC


Clip one meter probe to R- and the other probe to R+ so that you don't need to hold the probes. You can solder in some wires to clip on to if that makes it easier. 
Set meter for DC volts.

Switch back and forth between channels. And try both the footswitch and the front panel switch to be sure.
Verify that every time you throw the switch, the voltage changes. Should be approx. 5V in 'dirty' position and approx. 0V in the 'clean' position.
When the fault occurs, is the relay getting it's appropriate voltage, or not?
Dirty channel is when relay is engaged. So when you switch back to dirty, and amp stays in clean (fault mode), there should be 5V showing on the meter. If that is the case, the relay is faulty.
If the 5V is not showing when the fault occurs, the problem is somewhere else, and the command is not getting to the relay.


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## _Knighthawk_

Thanks jb.

 Okay. I guess I have to go and buy clips. I only have probes for my MM at present (which has become too limiting). Also, I did order another relay but I think it is coming by sea turtle from somewhere in Asia. I will DEFINITELY complete this once these items arrive. More to follow on that...

In the meantime, I picked up the head cab on the weekend (made by Derek Bell @ Veteran Guitar Cabinets - Veteran Guitar Cabinets). Here's a shot of the finished product (relay warts and all):


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