# A little help - Traynor YCV50 power section



## allthumbs56

Gents,

My bandmates YCV50 went on the fritz last night and I told him to leave it with me for a bit of a look-see (I am semi-smart but by no means an amp tech). Symptoms were a lack of power and some break-up/distortion apparent on the clean channel. Up on the bench I powered it up and noticed that the "inside" EL34 (closest to the speaker) did not glow/heat up whilst the outer did. I tried my Strat and sure enough there was some output but it was strained, far quieter than it should be and was clipped/broken up - especially if I increased pick attack.

"Piece of cake", I though and pulled out a spare pair of EL34s. Powered her back up to the same exact symptoms........ including a severely furled brow.

Any thoughts from those of you in the know? Any help is more than welcome.

As a follow-up, I was looking at the block diagram and it lists 3 12ax7s - 2 as preamps and 1 identified as a "splitter" prior to the power tubes. I don't know what this "splitter" does but a guessing man might think it could be a suspect?????????


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## keto

Yeah, phase splitter, splits the power to the 2 power tubes (this may not be exactly right, but some of the words are  ). Yes, you should grab a 12AX7 and replace each preamp tube 1 at a time see if you identify a culprit. If still not, I'd open the chassis and look for burnt resistors or signs of bad capacitors.


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## nonreverb

Was the replaced EL34 glowing or not?


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## LydianGuitars

nonreverb said:


> Was the replaced EL34 glowing or not?


Good point. Another thing to try to plug into the effects return (if it has one). If the sound is ok, that means the problem is before that point (the phase inverter). If not, the problem is definitely in the power amp. 

Basics to check for on the output tubes are plate voltage, bias voltage, heater voltage and screen voltage but you must be careful - Voltages in those amps can be lethal. If you are not familiar with safety procedures, ask a tech to help out.


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## WCGill

To me "no glow" means no heater voltage is getting to the tube or the filament is open in the tube.


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## allthumbs56

nonreverb said:


> Was the replaced EL34 glowing or not?


Not glowing or warm at all.


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## dtsaudio

That would be the most likely culprit. Pin 2 and 7 are the filaments (AC voltage). You've probably got a bad socket, broken board trace, bad solder joint, etc.
The last 12AX7 and the 2 EL34's are wired in parallel on the same filament tap of the transformer.


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## allthumbs56

dtsaudio said:


> That would be the most likely culprit. Pin 2 and 7 are the filaments (AC voltage). You've probably got a bad socket, broken board trace, bad solder joint, etc.
> The last 12AX7 and the 2 EL34's are wired in parallel on the same filament tap of the transformer.


Which is considered to be the "Last" 12AX7? Looking in at the board in the amp there are 3 on the one board - 2 more or less together and one further away. Looking at the board diagram it looks to me like the "splitter" is leftmost - close by the send/return jacks but furthest from the EL34s (which are on a 2nd board).

I have tried another 12ax7 in this position as well as another pair of EL34s to no avail so far.


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## dcole

I agree with the symptoms pointing to heater issues and check the screen resistor if possible as well. Do you have experience working in tube amps? If not the safest thing is to take it into someone who does.

The phase splitter takes 1 signal in, usually after the master volume and generates 2 signals out that are 180 degrees out of phase. As the first signal is raising in voltage the second one is falling in voltage which is required for a drive signal for a push-pull power amp. Hence the name push pull. As one side of the phase splitter is *pushing* the first tube up, the other side of the phase splitter is *pulling* the other tube down. In simplistic terms anyways. From the sounds of it, replacing the 12AX7's will accomplish nothing.

David Cole


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## allthumbs56

Great advice so far gents. I'm not an "amp" guy but can go as far as ruling out the easy stuff. I'll visit my electronics friend on the weekend and we'll open it up and see what we see. Makes sense as you've indicated that if the tube is not glowing then it's a power supply issue rather than a signal issue. I'll report back.


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## allthumbs56

Phew! So prior to taking the amp to my chum's to open her up I thought I'd reverse the two EL34s to confirm what what appeared to be happening. Sunofagun if it didn't turn out that one of my "good" spares turned out to be a dud - and that I happened to pt that one in the same spot as the first bad one.

So at the moment I have one good original and one good spare in the amp and it's working like a charm.

Now, I guess my next question is should I replace these as a matched factory pair - or can I continue with the mixed pair that are working. They obviously aren't "matched - but they are both identical Electroharmonics and the amp is described by Yorkville as "self biasing".

Thoughts?


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## dcole

If it is of the self biasing variety, then it will adjust the bias to each tube individually, thus mismatched tubes will be automatically balanced. I would send an e-mail to Traynor with the model and serial number to confirm. The service manuals online seem to contradict what they actually did on these circuits, but from past experience, Traynor is a very helpful company when contacted. You may also have to adjust the overall bias, the circuit will automatically balance the two tubes though.


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## jb welder

Heater failure in a power tube is extremely rare. It is almost inconceivable that you have 2 separate EL34's with bad heaters.
It seems much more likely to me that you have an intermittent solder connection at the socket, which is making contact again now that it has been wiggled around.
You might want to try both those "bad" tubes in the socket that never had a problem.


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## dtsaudio

I agree with jb on this. I would check the solder on the filament connections (pins 2 and 7) of this amp. The board traces are pretty flimsy and undersized. I would recommend re-soldering them.

Despite what Traynor says, this amp is NOT self biasing. There is an adjustment internally that sets the bias for both tubes. A matched pair would be recommended as the spec is for measuring 350mV across the two cathodes. page 9 of the service manual pdf file clearly states this.


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## dcole

Those service manuals posted on their website don't always show how things are done. If you notice the cathode resistors are shown as 2 ohm resistors. The 350 mV level would give a very high plate current.

If you look here, you'll see the autobias circuitry in the bottom right hand corner.

http://i131.photobucket.com/albums/p315/naazrael/TraynorYCV40.gif


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## dtsaudio

You're absolutely right about the 2R resistors. They should be 10R. Also you are correct about the service manuals not showing everything. That auto biasing circuit is not present on the YCV50 schematic. More correctly though it should be called an auto balancing circuit as it still requires the bias to be in the ballpark to work. 
The amp should still be opened up and checked as I had one of these on the bench a while back (the reason I have the manual) and that bias circuit was not there. In fact that was the owners problem. He had a tube die and the amp sounded really bad. When the owner replaced it with an old tube he had, it still sounded bad. Upon checking the bias we found one tube drawing about 40ma the other down around 10-12 ma. 
Interesting that they show it on the YCV40 schematic and not the 50.


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## drwow

I had this exact problem with a 2004 YCV50 Blue I bought a couple of months ago, I noticed that there was no heater glow on one of the output tubes...first thing I did was to swap the EL34's (probably the original EH tubes) in order to discern whether it was the tube or the socket/circuit — it was the tube.

Putting in a fresh pair of EL34's fixed that problem.

I have since changed a lot of things in the amp and am going to update it to at least June 2005 specs (add a bias trim pot and add the jumper from P10 to S3).


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## dcole

Thats interesting that they would call it self biasing, advertise the amp as such when its just balances the current flow in the tubes but then also not build it into all the amps. I wonder which years / models actually have this circuitry built inside.


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## drwow

dcole said:


> Thats interesting that they would call it self biasing, advertise the amp as such when its just balances the current flow in the tubes but then also not build it into all the amps. I wonder which years / models actually have this circuitry built inside.


Yeah, "self-biasing" is a bit misleading (as well I don't think they call it that). These are fixed bias, with resistors before June '05 and with resistors/trim pots after, I think - revision 11. " _...auto_-matching tube circuit that maintains _bias_ balance... ". So, the tubes aren't biased automatically, there's just balancing circuitry.


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## allthumbs56

drwow said:


> Yeah, "self-biasing" is a bit misleading (as well I don't think they call it that). These are fixed bias, with resistors before June '05 and with resistors/trim pots after, I think - revision 11. " _...auto_-matching tube circuit that maintains _bias_ balance... ". So, the tubes aren't biased automatically, there's just balancing circuitry.


From the Owner's Manual;

_"This amplifier features Yorkville’s auto-balancing / auto-matching tube biasing technology. As a result, when the time comes to replace the tubes in your Yorkville amplifier, there is no need to pay a premium for a matched set – nor does the bias need to be adjusted when you use a different brand. We make no claims as to which brands of tubes might sound best, but with auto-balancing / auto-matching, you are free to experiment without any need for concern that the amplifier or tubes will be distressed. Please note that auto-balancing / auto matching cannot fully compensate for different types of tubes - 6L6/5881s versus 6CA7/EL34s, for example. "

_Marketing Hoakum?


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## jb welder

dtsaudio said:


> the spec is for measuring 350mV across the two cathodes. page 9 of the service manual pdf file clearly states this.





dcole said:


> notice the cathode resistors are shown as 2 ohm resistors. The 350 mV level would give a very high plate current.





dtsaudio said:


> You're absolutely right about the 2R resistors. They should be 10R


Could you guys point me to where it shows 350mV for bias across 2R resistors?
The current version from the website ( http://traynoramps.com/downloads/servman/smycv50b.pdf ) shows 75mV across the 2R resistors. With approx. 410V at the plates, that works out to about 15W dissipation at idle.
Maybe there was a typo on a different schematic or different cathode resistor values?


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## jb welder

On closer look, I think you guys are looking a 2 separate drawings, the old way was 350mV with 10R cathode resistors, the newer version specs 75mV across 2R cathode resistors.


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## drwow

jb welder said:


> Could you guys point me to where it shows 350mV for bias across 2R resistors?
> The current version from the website ( http://traynoramps.com/downloads/servman/smycv50b.pdf ) shows 75mV across the 2R resistors. With approx. 410V at the plates, that works out to about 15W dissipation at idle.
> Maybe there was a typo on a different schematic or different cathode resistor values?


The previous version ("YCV50 Blue") of the amp, or ( http://traynoramps.com/downloads/servman/smycv50blue.pdf ) on both page 9 and page 13.

It's important to note a few things: 

- it's impossible to get any copy of older versions of service manuals/schematics for any specific YCV amp from Traynor/Yorkville, even if you "know somebody", they only keep the latest revisions (including "discontinued" models).

- It's likely that unless you have a new amp or the last revision of a discontinued model, what you look at on the pdf, will not be exactly the same as the circuit/layout you're working on.

- I suspect there's a few errors


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## nonreverb

I remember getting one of these treasures in with serious bias problems due to the auto bias circuit being totally whacked. I eventually reverted it back to a previous version without the autobias and it worked perfectly...more importantly, the customer was happy...



allthumbs56 said:


> From the Owner's Manual;
> 
> _"This amplifier features Yorkville’s auto-balancing / auto-matching tube biasing technology. As a result, when the time comes to replace the tubes in your Yorkville amplifier, there is no need to pay a premium for a matched set – nor does the bias need to be adjusted when you use a different brand. We make no claims as to which brands of tubes might sound best, but with auto-balancing / auto-matching, you are free to experiment without any need for concern that the amplifier or tubes will be distressed. Please note that auto-balancing / auto matching cannot fully compensate for different types of tubes - 6L6/5881s versus 6CA7/EL34s, for example. "
> 
> _Marketing Hoakum?


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## drwow

nonreverb said:


> I remember getting one of these treasures in with serious bias problems due to the auto bias circuit being totally whacked. I eventually reverted it back to a previous version without the autobias and it worked perfectly...more importantly, the customer was happy...


A few questions, if that's okay.

Do you have copies of older service manuals, schematics, etc?
Which version of the amp first came with the auto-balance feature?
How does the auto-balance feature work?
How do you remove it?

BTW, we know each other, ...long-time no see, brother.

~ R. Ewald


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## jb welder

drwow said:


> Do you have copies of older service manuals, schematics, etc?
> Which version of the amp first came with the auto-balance feature?
> How does the auto-balance feature work?
> How do you remove it?


Back in post #15 dcole posted a link to a drawing showing the auto-match bias circuit. Complete (older) service manual is available here: http://www.toomanyhelicopters.com/schems/Traynor_YCV40_Technical_Manual_w_Schem.pdf It is for the YCV40, version 12.01, Dec.2005.
Here are the transistors that sense the cathode current of each output tube and adjust the bias to each tube independently







Here is how it mates with the output tubes (AS,BS to cahtodes, A-,B- to grid feeds):







AS and BS sense the current through the cathodes, Q4 and Q5 adjust the bias voltage to the grids of the output tubes accordingly. You should be able to remove the auto match circuit by changing it over to the newer version schematic.

The YCS amps have a circuit with a transistor across the bias trimpot. I'm not clear on exactly what it is doing. The base of the transistor seems to be sensing the screen grid voltage. The early versions of the YCS claimed to be able to run either 6L6 or EL34's, with the bias auto adjusting. Perhaps that is what this circuit is doing.
Anyone familiar with this circuit please comment:











drwow said:


> it's impossible to get any copy of older versions of service manuals/schematics for any specific YCV amp from Traynor/Yorkville, even if you "know somebody", they only keep the latest revisions (including "discontinued" models).


This statement is incorrect. If you mean they only keep current versions on-line, then yes that is the case.
But they certainly have older versions of the schematics. After all, they have to work on the stuff themselves in their service dept. And I can say that I have personally received older revision schematics that are not found online. Perhaps you will need to verify that you are actually working on a unit (serial #, board revision number etc.), but they have schematics for older revisions. Within reason of course, there may not be many versions available for extinct models.


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## drwow

jb welder said:


> Back in post #15 dcole posted a link to a drawing showing the auto-match bias circuit. Complete (older) service manual is available here: http://www.toomanyhelicopters.com/schems/Traynor_YCV40_Technical_Manual_w_Schem.pdf It is for the YCV40, version 12.01, Dec.2005.
> Here are the transistors that sense the cathode current of each output tube and adjust the bias to each tube independently
> View attachment 5598
> 
> Here is how it mates with the output tubes (AS,BS to cahtodes, A-,B- to grid feeds):
> View attachment 5599
> 
> AS and BS sense the current through the cathodes, Q4 and Q5 adjust the bias voltage to the grids of the output tubes accordingly. You should be able to remove the auto match circuit by changing it over to the newer version schematic.
> 
> The YCS amps have a circuit with a transistor across the bias trimpot. I'm not clear on exactly what it is doing. The base of the transistor seems to be sensing the screen grid voltage. The early versions of the YCS claimed to be able to run either 6L6 or EL34's, with the bias auto adjusting. Perhaps that is what this circuit is doing.
> Anyone familiar with this circuit please comment:
> View attachment 5600
> 
> 
> 
> 
> This statement is incorrect. If you mean they only keep current versions on-line, then yes that is the case.
> But they certainly have older versions of the schematics. After all, they have to work on the stuff themselves in their service dept. And I can say that I have personally received older revision schematics that are not found online. Perhaps you will need to verify that you are actually working on a unit (serial #, board revision number etc.), but they have schematics for older revisions. Within reason of course, there may not be many versions available for extinct models.


I love being wrong, it's an opportunity to learn something.

After my fourth attempt at getting information out of Yorkville (w/ serial #, etc.) I got a reply from Guy Beresford with the correct schematic for the earliest YCV50 version (V.1).

For those interested:









Here's the bias circuit:








Sorry about those files, they didn't parse full size, I'll fix it later...


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## jb welder

drwow said:


> After my fourth attempt at getting information out of Yorkville (w/ serial #, etc.) I got a reply from Guy Beresford with the correct schematic for the earliest


 Glad to year you got it sorted, Guy IS the man.


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## nonreverb

He is indeed...he just set me up with the Hughes & Kettner Statesman Dual 6L6 schematic...I wouldn't have touched this amp with a 10 foot pole without it.



jb welder said:


> Glad to year you got it sorted, Guy IS the man.


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## Adicted to Tubes

Any headway on the cause?

Never mind,I saw the part about the bad tube in his spares.

Having worked at L&M on lots of Traynors,I conclude the design is just plain dumb,especially the standby circuitry.I told that to Guy at Traynor and he spouts of about how brilliant it is. Really? A mosfet circuit to drop voltage to the power tubes as a standby circuit?An auto bias circuit? Why I ask? 
Too much circuitry inside what should have been an otherwise simple amp makes for tons of revisions as you can see by the schematic changes and updates.
Simple is always best in my book.


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## allthumbs56

Adicted to Tubes said:


> Any headway on the cause?
> 
> Never mind,I saw the part about the bad tube in his spares.
> 
> Having worked at L&M on lots of Traynors,I conclude the design is just plain dumb,especially the standby circuitry.I told that to Guy at Traynor and he spouts of about how brilliant it is. Really? A mosfet circuit to drop voltage to the power tubes as a standby circuit?An auto bias circuit? Why I ask?
> Too much circuitry inside what should have been an otherwise simple amp makes for tons of revisions as you can see by the schematic changes and updates.
> Simple is always best in my book.


Yup, turned out to be a bad spare. Amp is sounding great now.

Amazing discussion initiated though. I really enjoyed following it...... thanx guys!


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## jb welder

Adicted to Tubes said:


> the design is just plain dumb,especially the standby circuitry... A mosfet circuit to drop voltage to the power tubes as a standby circuit?An auto bias circuit? Why I ask?


The official party line I got was that it was based on the philosophy that hardware (pots, switches, etc.) is expensive, semi-conductors are much cheaper. So at the mfgr. level, a mosfet is pennies, a switch than can handle standby switch current costs maybe a dollar or more.
But it didn't work out so well as far as field failures went. So the new versions still use the cheap low current standby switch, but instead of turning the high voltage off via mosfet, the high voltage is now left on, and standby just mutes the audio signal.
As far as the auto-match transistor circuit, I think it was a way for them to allow owners to use inexpensive and unmatched tubes.
I'm not sure if they phased that out due to field failures, or because of customers wanting to be able to bias manually. I suspect the latter, lack of adjustable bias seems to be almost sacrilegious these days, even though it was the norm during the "golden era" of tube guitar amps.


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## barfoden

When i read the thread about one tube working and the other one not,, i thought immediately of a burnt screen resistors... 

According to the schematic the YCV40 and the YCV50 share the same power supply and has the auto bias circuit, which I guess the YCV50 has slightly lower grid voltage to bias the EL34 pentodes within range compared to the 6L6GC beam tubes in the YCV40.

Power supply is 410V on the plates,, a 390 ohm B+ dropper to the screen, a ~ 20 µf screen capacitor and small 220 ohm 1 watt screen resistors on each power tube.. 
This is probably fine with large 6l6GC beam tubes but EL34 pentodes draw a lot more screen current when driven hard and the screen will light up and eventually burn, or the 1W 220 ohm resistors will burn before as it draws more power than the 1 watt rating allows.. 

Maybe it is the autobiasing that prevents the screen from being driven to hard or the YCV50 are actually are fitted with higher value and more robust screen resistors than the schematic suggest..


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## GoldenBrown

Hey folks, hate to revive an old thread, but my ycv50 is having very similar issues and has a reallly particular quirk! There seemed to be couple knowledgeable people in here, so I'm wondering if based on my symptoms I could get a some ideas on what the diagnosis may be. 

I have the same problems, and had gone out and bought new el34s. When I first installed them, the amp went to full volume (after warming up on standby) for maybe 200-300ms before crapping out again. I lost faith and swapped all the preamp tubes around to no luck. The volume was always gone, not like when I put new power tubes in. Tonight I went back at it and switched the power tubes around, and the same initial loudness followed by the loss of volume less than a second later happened.

I'm wondering if this is indicative of a failure in the autobiasing section maybe? It only seems to get to proper volume (even for a second) when I put new power tubes in. I'm not overly familiar with the schematic but if I thought it was a reasonable repair for me to do myself I'd get acquainted and give it a go.
thanks!


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## jb welder

As you can probably tell from this thread, there is a lot of difference between versions, so you need the schematic for the exact board version you have.
That being said, it sounds like the high voltage regulator or something else in the high voltage supply for the power tubes may be failing.
These are not simple amps to repair, just dis-assembly alone can be a pain. If you do not have at least some amp repair experience I would suggest you take it to an authorized service station, or contact Yorkville directly and ask them to recommend a service center.
If you do have some experience (especially with high voltage safety), get the board number, get the correct schematic and post it here. Then we can suggest some checks for you to make.


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## nonreverb

I agree, I found this particular series particularly difficult to service. Best to contact Guy at Traynor with the specifics so he can get you the proper schematic. If you're doing the repair yourself, put your seatbelt on.....you're going for a ride!



jb welder said:


> As you can probably tell from this thread, there is a lot of difference between versions, so you need the schematic for the exact board version you have.
> That being said, it sounds like the high voltage regulator or something else in the high voltage supply for the power tubes may be failing.
> These are not simple amps to repair, just dis-assembly alone can be a pain. If you do not have at least some amp repair experience I would suggest you take it to an authorized service station, or contact Yorkville directly and ask them to recommend a service center.
> If you do have some experience (especially with high voltage safety), get the board number, get the correct schematic and post it here. Then we can suggest some checks for you to make.


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