# YBA-1 (Tube Rectifier) with no B+/High Voltage, what's up?



## bluefactoryflam (Oct 18, 2014)

Hey guys,
I recently recapped an old YBA-1 with tube rectifier. Afterwards it sat on the bench for a few hours cranked into a dummy load with no issues, then after playing it for a few weeks it has stopped working. When I replaced the fuse, it powered up but I don't read any high voltage. Same thing with the power tubes pulled, no high voltage coming out of the rectifier.

I don't read any shorts in the high voltage section either that would be pulling it down to ground.

The standby switch is working properly (grounds the centre tap on the HV winding). With the power tubes pulled (or not pulled) and the amp on, the voltages I read off the rectifier are:

pin 4 = 360 vac
pin 6 = 361 vac
pin 2 = 0 vac / -.216 vdc
pin 8 = 5.5vac / -.216 vdc

The rectifier is a 5ar4 and the filament is nicely lit up, but other than that I have no way to test it (and stupidly, no replacement on-hand to swap out). 

Hope everyone is enjoying the holidays!


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## dtsaudio (Apr 15, 2009)

First thing to try is a new rectifier tube. Just because the filament is lit doesn't mean it's working. Your transformer appears to be working fine though.


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## bluefactoryflam (Oct 18, 2014)

dtsaudio said:


> First thing to try is a new rectifier tube. Just because the filament is lit doesn't mean it's working. Your transformer appears to be working fine though.


I took a 5U4GB out of my deluxe reverb and tried it in the YBA-1 and everything worked properly, looks like the Mesa 5AR4 gave up the ghost. First time I've come across a blown recitifier.


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## dtsaudio (Apr 15, 2009)

Happens all the time, especially with new manufacture rectifiers. They don't seem to be as rugged as the old ones. Yours just died, quite often failure is a little more spectacular.


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## bluefactoryflam (Oct 18, 2014)

Just an update to this post:

I got the new 5AR4 into this amp and noticed as soon as I flipped the standby ON, the *rectifier tube lit up very brightly *for a split second and made a concerning *"Crackling" noise*. After that, the amp worked fine and the B+ voltage was normal. 

I tried to get it to happen again and it would only happen occasionally. A few times when it would happen, it also took the mains fuse out with it.

I then replaced the 5AR4 with a new 5Y3 and the same thing happened, only the flash inside the rectifier was a lot more subtle and there was no noise or blown fuse. 

Then I tried a 5U4GB and I noticed that the filament was intermittent and I could hear a buzzing noise, and wobbling the tube in the base would get the filament to be steady. 

So I then thought the problem was the rectifier's socket, so I tensioned all the pins and cleaned everything. I also removed a lot of goopy solder on the pins from a shoddy repair years ago. After that, I put the new 5AR4 back in and could not get the flash & noise to happen. I'm finding it hard to believe that a bright and noisy arcing inside the rectifier tube at startup could be caused by an intermittent socket connection.. 

Is there something else I should be checking for this problem and has anyone seen this before?

FWIW, this YBA-1 has the standby wired to ground the centre-tap and it differs from the published schematic in that HV is taken from Pin 8 of the rectifier tube, not Pin 2 as shown. It has recently been recapped and all of that work seems to check out and the main filter capacitors are 50uF instead of 40uF as shown on the schematic.


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## nonreverb (Sep 19, 2006)

Yes, your socket connection could indeed do that. Any inconsistencies with the pins making contact can cause all kinds of trouble. Remember, it's high voltage it will make any bad connection very apparent. As for the 5AR4's, you'll have to live with what's available on the market as dtsaudio states. The alternative is finding an old Mullard or Telefunken which are pricey.


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## bluefactoryflam (Oct 18, 2014)

nonreverb said:


> Yes, your socket connection could indeed do that. Any inconsistencies with the pins making contact can cause all kinds of trouble. Remember, it's high voltage it will make any bad connection very apparent. As for the 5AR4's, you'll have to live with what's available on the market as dtsaudio states. The alternative is finding an old Mullard or Telefunken which are pricey.


With a new rectifier and a cleaned and retensioned rectifier socket, I'm finding that the amp is blowing fuses again. 

I'm wondering if it does have something to do with the Standby Switch wiring now. The standby switch grounds the HV centre-tap, which according to this page ( http://www.valvewizard.co.uk/standby.html ) *"If you allow the rectifier to warm up first, and then throw the switch, the massive inrush to the reservoir capacitor can lead to flashover in the valve."* 

That accurately describes the exact problem I was having, a large flash inside the rectifier valve itself and getting more intense the longer I wait to switch the Standby On and the most intense flashes also taking the fuse out with it.


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## nonreverb (Sep 19, 2006)

Is the fuse blowing right away or after some time? Pull your power tubes and try again. You might also have a bad B+ cap.


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## WCGill (Mar 27, 2009)

Try not using the standby switch, especially when you first turn the amp on. With a slow-start rectifier like the 5AR4, it's not necessary. It sounds like a bad cap to me as well.


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## jb welder (Sep 14, 2010)

As mentioned above, power tubes, bias failure, or bad filter cap are top suspects.


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## bluefactoryflam (Oct 18, 2014)

jb welder said:


> As mentioned above, power tubes, bias failure, or bad filter cap are top suspects.


Thanks guys, I'll report back on all of those things soon.


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## bluefactoryflam (Oct 18, 2014)

bluefactoryflam said:


> Thanks guys, I'll report back on all of those things soon.


Okay so I tested a few things on the amp and here are the results:

With the choke disconnected, the first 3 filter caps (50/50/.047 uF) joined together measure 100uF on the meter, and 3.6 Mohm to ground.

The choke itself measures 100 ohms, and OPEN to ground at either end.

cap 4 (50 uF) measures 50uf and 24M to ground.
cap 5 (50 uF) measures 49uF and 3M to ground.

When standby is thrown closed, the rectifier tube occasionally "flashes over" but doesn't blow fuse. The amp then idles fine. The power tubes read:

V5 = 456V / 43mA / 65%
V4 = 457V / 42mA / 64%

When turned up and played, rectifier will "flash over" with a loud note and blow fuse. FWIW, I'm using 3A SLO BLOW. The schematic indicates a 3A fuse, and so does the rear panel.

This is now with a new JJ 5AR4/GZ34. I don't have another one to try, but I did try with a few different types. With a 5U4GB, I can crank the amp and it doesn't blow fuse. With a 5Y3 I did notice some flash over when standby was closed, but I was also able to crank up the amp and play it without blowing the fuse.


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## WCGill (Mar 27, 2009)

Is it possible that you've had 2 bad rectifiers in a row? I'm definitely not a fan of having all the power supply caps after the stand-by. Current production 5AR4's are not very robust and throwing the standby after warm-up leads to early mortality.


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## jb welder (Sep 14, 2010)

Max capacitance for a 5AR4 to be connected to is 60uF. You have 100uF there, disconnect one.
The original circuit was 80uF at the rectifier. You could get away with that much with NOS 5AR4's, but not modern ones.
This is what happens when mods/upgrades are installed without considering all the repercussions. :smile-new:

The 5AR4's in current production are notorious for failure. You can use NOS 5AR4 if you go back to 80uF (or preferably less), or just disconnect one of your 50uF's which will leave 50uF, ok for a modern 5AR4 to run into.

WCGill's suggestion of turning it on without using standby might do the trick, but it's still cheating.


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## jb welder (Sep 14, 2010)

One thing I missed was the standby switch arrangement. It must be changed over to match the schematic of the tube rectifier version. That is probably the main reason for your problems, even more so than the capacitor values. The recitifier needs to be connected to the main filter caps while it is warming up. This is only possible if the standby switch is wired up like the schematic shows.
The standby circuit that connects the CT to ground is only for solid state rectifier versions.


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## bluefactoryflam (Oct 18, 2014)

jb welder said:


> Max capacitance for a 5AR4 to be connected to is 60uF. You have 100uF there, disconnect one.
> The original circuit was 80uF at the rectifier. You could get away with that much with NOS 5AR4's, but not modern ones.
> This is what happens when mods/upgrades are installed without considering all the repercussions. :smile-new:
> 
> ...


Thanks JB. I didn't realize that the 5AR4 had a 60uF max capacitance. I reduced it to just a single 50uF cap before the choke, and I also rewired the standby switch to be before the choke as the schematic shows and put another new JJ 5AR4 in there. 

So frustrating: I've fired it up a few times without any rectifier tube flashover and the amp was working great. Turned it off, turned it back on again.. rectifier flashover and fuse blown. Tried a new fuse, amp turned on great.. played it for 10 minutes, cranked it to 10 - fuse blown. 

FWIW, The fuse is a 3A slo-blo as shown on the schematic. I measured the draw of the amp and it draws about 2.6A when cranked and playing hard.

EDIT:

I also replaced the rectifier tube socket just in-case (the old one was mangled anyways) and I'm still having the same problem. Even worse actually, now the rectifier tube flashes over and blows the fuse whenever audio is applied. Does flashing over ruin the rectifier tube or make it more likely to keep flashing over? This is getting a bit ridiculous..


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## WCGill (Mar 27, 2009)

Man, you're having a time of it. Yes, flashing over will hasten your rectifier's demise. As well, rapid turn-on of the amp (power, not stand-by) while the rectifier is still hot will help it to an early grave as well (hot-switching). Normally I wouldn't worry about 80uf after the 5AR4, but if you're playing cranked it may become an issue. Do you have any filter caps before the stand-by switch? That's where that 50uf should be, in my books. How about those output tubes? And while you're at it, check the output transformer. Something is drawing a lot of current in that amp.


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## jb welder (Sep 14, 2010)

WCGill said:


> Do you have any filter caps before the stand-by switch? That's where that 50uf should be


This is important. The 50uf should be wired straight to the rectifier socket, so it is connected to the rectifier no matter whether standby is on or off.

Also, have you been using the same power tubes all along? You need to try other known good power tubes.


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## dtsaudio (Apr 15, 2009)

When you re-capped the amp. What make of caps did you use? I ask because I've run across a problem with one particular brand that is normally quite good, but I've had a couple of stinkers recently.


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## bluefactoryflam (Oct 18, 2014)

dtsaudio said:


> When you re-capped the amp. What make of caps did you use? I ask because I've run across a problem with one particular brand that is normally quite good, but I've had a couple of stinkers recently.


*Caps*
i used F&T 50/50 can capacitors.
It is now wired as per the schematic. The rectifier output goes to a single 50uF section and a .047/600V orange drop are before the standby switch. The standby switch goes to the choke (measures 100ohm) and then the choke goes to a 50uF section -> resistor -> 50uF section -> resistor 10uF F&T. 

When I tested the caps for resistance to ground, they all tested very good (like 10Mohm) and their capacitance measured spot-on. That being said, I never measured the 10uF F&T. 

Can caps fail in ways other than losing capacitance or shorting? and is there anything else I should be doing to test these caps?

*Tubes/Bias*
The rectifier has been flashing over with old sovtek 6L6's and now I've put brand new JJ 6L6's in and rebiased the amp with the same problems. When the amp decides to run, tubes are running at: 
V5 = 456V / 43mA / 65%
V4 = 457V / 42mA / 64% 

*Amp Draw*
The figure I gave of *2.4A* when the amp was cranked and playing hard through it.. that's nearly *300W*. I've never measured another amp to be honest, so I don't know if that does indicate a problem or not. With standby on, it draws about *.5A* or *60W*, at idle I believe the amp was drawing *.8A* or about *100W*

*Output Transformer*
How do I test this? Disconnect it and test the resistances to ground, and the resistances of the windings? I will do that soon and post the results. 

*Me*
I gotta admit, that to get this amp to flash over, I will turn the standby off and on repeatedly while watching the rectifier tube in the dark. I've also turned the power off and turned it back on, as WCGill described it as "hot-switching" to try to get this amp to fail. When it does work, I've been putting all knobs at 10 and playing very hard through it.. with the amp going into a 200W 8ohm dummy load, connected to an oscilloscope. 

*Thanks*
I just wanted to say thanks for everyone's help so far on this. I'm annoyed by the amp yeah, but without you guys and this forum it would be out the window and on the street in a million pieces by now


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## WCGill (Mar 27, 2009)

You need a new rectifier. You have tortured it to death.


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## jb welder (Sep 14, 2010)

bluefactoryflam said:


> Can caps fail in ways other than losing capacitance or shorting? and is there anything else I should be doing to test these caps?


Caps can have shorts that only show up at high voltages. Unless you have a high voltage cap tester, you can only find them by substitution.
Your current measurements seem ok, tube amps are very inefficient. 300W draw from the wall when the amp is putting out 100W sounds pretty normal. On standby you still have all the heaters running, so 60W sounds ok.




bluefactoryflam said:


> I gotta admit, that to get this amp to flash over, I will turn the standby off and on repeatedly while watching the rectifier tube in the dark. I've also turned the power off and turned it back on, as WCGill described it as "hot-switching" to try to get this amp to fail.





bluefactoryflam said:


> Even worse actually, now the rectifier tube flashes over and blows the fuse whenever audio is applied. Does flashing over ruin the rectifier tube or make it more likely to keep flashing over? This is getting a bit ridiculous..


I'm not sure about those 2 statements. The first sounds like the problem doesn't occur under normal operating conditions, but you have to keep turning it on and off to make it screw up. That is not good for it or for the rectifier tube.
But the second statement sounds like it screws up just passing signal, which is definitely a problem. Or does that only happen after you have "induced" flash-over?


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## Church-Audio (Sep 27, 2014)

jb welder said:


> Caps can have shorts that only show up at high voltages. Unless you have a high voltage cap tester, you can only find them by substitution.
> Your current measurements seem ok, tube amps are very inefficient. 300W draw from the wall when the amp is putting out 100W sounds pretty normal. On standby you still have all the heaters running, so 60W sounds ok.
> 
> 
> ...


That's very true about caps generally I find if a cap is over value it's just old if it's way under value it will most likely fail or break down under high voltage.


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## bluefactoryflam (Oct 18, 2014)

jb welder said:


> I'm not sure about those 2 statements. The first sounds like the problem doesn't occur under normal operating conditions, but you have to keep turning it on and off to make it screw up. That is not good for it or for the rectifier tube. But the second statement sounds like it screws up just passing signal, which is definitely a problem. Or does that only happen after you have "induced" flash-over?


The first time firing up the amp with new rectifier #2, the amp flashed over and blew a fuse only when I cranked it and played hard through it. The second time it did the same thing, then I started flicking the standby switch off and on to see if it flashes over when the switch is toggled.. after about 10 times of doing that, the rectifier did flash over and blew the fuse. After that, it would flash over and blow a fuse any time the audio was applied.


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## jb welder (Sep 14, 2010)

See post #21.
I would try to find a different version of rectifier tube, preferably NOS.


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## nonreverb (Sep 19, 2006)

+1 All my amps have NOS Mullard GZ34's as I haven't yet found a reliable new GZ34 from any manufacturer.



jb welder said:


> See post #21.
> I would try to find a different version of rectifier tube, preferably NOS.


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## bluefactoryflam (Oct 18, 2014)

jb welder said:


> See post #21.
> I would try to find a different version of rectifier tube, preferably NOS.


Thanks guys, will source one to try and report back. Is it worth trying one of those solid state rectifier replacements? 

I had a chance to test the output transformer. The tube side reads *251 ohms* end to end, and *148 ohms* and *104 ohms* between the CT. The output side measures *1.2 ohms*. My probes measure *.8ohms*. Could the output side of the OT really only measure .4ohms?


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## WCGill (Mar 27, 2009)

Those readings are in the ballpark. The secondary can read 0 ohms. CT to either leg on the primary should be approximately half from leg to leg. Your transformer isn't very balanced. 

When you do get that Mullard GZ34, just in the interests of science, flick the standby back and forth and count how many times before the tube flashes and blows fuses. Just in the interests of science of course. ;-)


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## bluefactoryflam (Oct 18, 2014)

WCGill said:


> When you do get that Mullard GZ34, just in the interests of science, flick the standby back and forth and count how many times before the tube flashes and blows fuses. Just in the interests of science of course. ;-)


Sounds good! You buy the tube, I'll buy the fuses, deal?


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## jb welder (Sep 14, 2010)

bluefactoryflam said:


> Is it worth trying one of those solid state rectifier replacements?


 I'll say yes if it has a sag resistor. Something like the Weber copper cap.
In the long run it should save money and act the same as a tube rectifier would (minus the light show  )
A plain solid state replacement will increase the high voltage and stiffen the supply which will change the response and "feel" of the amp, and may stress the filter caps. So you don't usually want a plain type.
But something like the Weber copper cap has voltage drop and sag built in, so it should act the same as the rectifier tube would.


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## epis (Feb 25, 2012)

wcgill said:


> when you do get that mullard gz34, just in the interests of science, flick the standby back and forth and count how many times before the tube flashes and blows fuses. Just in the interests of science of course. ;-)


 ....... Lol


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