Traynor YBA-3 - not very loud, bias testing

[beedoola]

Thanks, would 10uf 450 be alright? - only thing my local electronics store has. I may get a geared trim pot too if they have them, to make an adjustable bias.

[loudthud]

Yes, 10uF at 450V would be OK.

[beedoola]

Here are my findings:

The bias current to each tube socket is the same. I used the strongest tube and tested it in each socket, all gave the same bias. That tube, which I call "1" gave"

.062

The other better tube - "2," gave .052

Tube "3" gave .020

And tube "4" would do .009

I replaced the caps - minded the polarity. I didn't get a trimmer pot as my local store didn't have adequate trimmers.

Would be wise to replace all the power tubes and order a match quad? I actually had the amp listed to sell but was concerned about the power and now finding the pairs are mismatched and one tube isn't good, I don't feel right selling it that way so I guess I have to get new tubes.

is EH the only 6AC7 makers out there? I'm not sure if these were a bad batch - they have Tube Depot stickers on them...

[g1]

I think you are better off looking at EL34's. There is probably better selection. The Traynor's often came with EL34's or tubes marked as EL34/6CA7. They supplied EL34's exclusively as replacement tubes after 6CA7's became less common in Canada. For the purposes of this amp, you can consider them to be the same tube.

[beedoola]

Remove all the tubes. Choose one only and try it in each socket. The readings should be very similar for all sockets. If not, there is an amp problem.
Now choose one socket and try each tube in that socket. This will tell you how well matched the tubes are. It sounds like you may have a bad tube, or 2 pairs that are quite different from each other and will likely give poor results.
The phase inverter balance pot matches the 2 halves of the waveform (for the push and pull of the power amp) so they are the same amplitude. You need to understand what the phase splitter does before the alance pot will make any sense.

I got the JJ 6AC7s. I used a 47k resistor in series with a 25K pot - a 22k resistor only yielded around 47k with the trimmer maxed. So I set the combo I make to around 51k and I'm getting 30/31MA

Can someone explain how the phase splitter so I can adjust the balance pot accordingly? I'm getting some "peak" sounded when picking hard.

Can I getting a reading on it with my DMM to get the correct setting?

[Jazz P Bass]

As there is not any documentation on this 'adjustable' PI, I would say that it attempts to set the amplitude of each PI signal to the same height.
Fender uses an 88K & a 100K plate resistor for the same 'attempt'.

You will need a signal source running through the amp.
With your meter set to read Volts/ ac you should see a change of the amplitude of the signal at the plates.

What would really be ideal is if you could draw the PI circuit & the adjustment circuit.