Traynor Custom Reverb - Setting bias - but bias goes thru tremelo control

[1ampman]

Have a Traynor Custom Reverb from the 60s. Replacing the output tubes and trying to set the bias. Bias voltage goes thru the trem intensity control and changes the bias on the output tubes. The intensity pot causes a wide variation in bias voltage. What would be the correct bias on this amp (6ca7s)?

[Helmholtz]

Have a Traynor Custom Reverb from the 60s. Replacing the output tubes and trying to set the bias. Bias voltage goes thru the trem intensity control and changes the bias on the output tubes. The intensity pot causes a wide variation in bias voltage. What would be the correct bias on this amp (6ca7s)?

Do you have a schematic?
What do mean with "Bias voltage goes thru the trem intensity control"?

Bias voltage should be between -40V and -50V. It should be adjusted for suitable idle currents (e.g. 30mA to 35mA depending on dissipation).

Intensity pot must not change the bias value. You might have a leaky (coupling) cap.

[1ampman]

Helmholtz, I guess you never worked on one of these. Or looked at the schematic. The bias to the outputs comes out of the intensity control wiper and that's how the amp is wired. The trem varies the bias for effect.

[Helmholtz]

Helmholtz, I guess you never worked on one of these. Or looked at the schematic. The bias to the outputs comes out of the intensity control wiper and that's how the amp is wired. The trem varies the bias for effect.

Guess why I asked for the schematic.

Always good practice to provide it from the start.
Post it and I might be able to tell what is normal and what not.

[The Dude]

Helmholtz, I guess you never worked on one of these. Or looked at the schematic.....

That's because you haven't provided one.

[Enzo]

Please include schematics. I managed to find one - I hope is same model - in the Schematic Hell section above
traynor_customreverb_ysr1.pdf (schematichell.com)


The trem control should not vary the bias One end of the trem pot connects to the bias supply, the wiper to the power tube grids, and the other end of th pot connects to a cap, which will block DC if healthy. Assuming the cap is OK, turning the pot should not vary the bias. Lift that cap and see if that is the case.

I don't see any bias adjustment.

When the trem is on, the large LFO signal comes through the cap, and that adds to or subtracts from the bias, the wiper determines the amount. In my shop we called those "bias wigglers". But the steady state DC bias doesn't change.

[1ampman]

Maybe someone with know how and experience will chime in...

[The Dude]

Some have! You still haven't clarified if the schematic Enzo linked is the correct one. You still haven't uploaded one. Enzo has explained how the circuit in his diagram works. There's a bias calculator here:
https://www.tedweber.com/bias-calc/
and plenty of others online. It's really no different than checking bias on any other amp. The tremolo circuit is the same as any other bias wiggle trem used in plenty of other amps. I'm not sure what more you want?

[Enzo]

I have worked on a few amps, maybe someone more experienced...?

[The Dude]

Yeah, if you're looking for better/more experienced technical minds than Enzo and Helmholtz, good luck on that quest.

[Helmholtz]

Nothing to add to Enzo's explanation.

Check C31/15/16/ (at least that's what the numbers look to me) for leakage - provided it's the correct schematic.

[g1]

Schematic attached.
The trem modulates the bias, it does not 'adjust' it. It's a common circuit used by some Fender models and many other manufacturers.
The other end of the pot connects to a cap, so there is no DC path. The 250K series resistance that the pot offers does not have any significant effect on the idle current, due to the high resistance of the power tube grids.
Adjusting the value of R48 in the bias circuit would be the usual way of adjusting bias/idle current.
What is wrong with the stock bias setting?

edit: forgot to refresh and missed all the new posts, sorry.

[nosaj]

Maybe he will see the error of his way and apologize . By far more than 75years of experience dominating this thread. Plenty of people in this thread that can do some serious schooling.
nosaj

[1ampman]

Mr. Helmholtz, I apologize for my rude reply....and I Thankyou for being a part of this great forum...I was out of line... Also I thank all the members reminding me how to act. This amp was fustrating me. Not an excuseThough....

[g1]

Here is a page with some info about the different types of trem, this type is covered under 'bias shifting tremolos'. He also gets into some of the issues with the circuit, particularly the bias/idle current setting. That is why I was asking about changing the stock arrangement, it can cause problems in these types of amps, which are typically biased quite cold to deal with those issues.

http://carlscustomamps.com/types-of-...s-in-tube-amps