Traynor YBA-1 Master Volume

[Chuck H]

.. - the 2.2Meg "safety" resistors which are the entire rationale of the Lar Mar design is too high a value to prevent thermal/grid current runaway if the wiper loses contact,...

Agree. I typically use a higher pot value and a lower safety resistor value. Say you have 220k bias feed resistors. I would use a dual 500k pot and parallel 470k resistors.

[mtlbasslad]

Hi Lorne. The schematic on pg.7 or 8 of the attached package should be good (the last one on pg.9 already had 3-prong).
Do you mean the 'trainwreck type 3' master from the Robinette site? That is a cross-line type that just cancels out the out-of-phase signals at the power tube grids.

Actually, I think it's page 6 (marked '3' because the font for the tubes matches. See pic in post #11.

Thanks to all for your suggestions - I have gone the simple route with just a ! meg pot on the pin 5's, seems to work fine. The LarMar may well be superior but I would have needed someone holding my hand to trace the circuit. Although I have a nice soldering iron, meter, signal generator & Oscope - I'm a little short on theory... without this forum I'm lost. So I'll make another donation now.

We will see what the owner thinks.

Thanks again,
Lorne

[g1]

Actually, I think it's page 6 (marked '3' because the font for the tubes matches. See pic in post #11.

The pg.6 has a choke instead of a 470R10W resistor, and a 1K10W feeding the power tube screens (instead of another 470R10W).
In yours I did not see a choke, but see two 470R10W, so I ruled out pg.6

[mtlbasslad]

The pg.6 has a choke instead of a 470R10W resistor, and a 1K10W feeding the power tube screens (instead of another 470R10W).
In yours I did not see a choke, but see two 470R10W, so I ruled out pg.6

It gets stranger & stranger with the schematics - I didn't find a choke either ? But mine has a fuse not a circuit breaker... so?

[g1]

It gets stranger & stranger with the schematics - I didn't find a choke either ? But mine has a fuse not a circuit breaker... so?

Then I would say pg.7 of the pdf package is it. Maybe even with the errors uncorrected by the handwritten changes.
The font matches the one in your photo, and the circuit best matches what you have there.

[mtlbasslad]

I finally got the review from the owner - he is thrilled.