Traynor YVC80 Tube Amp (Project)

[52 Bill]

Before I reassemble everything, I am curious to learn about the biasing methods for this amp and grounding.

This amp has an auto bias circuit based around transistors Q13 and Q14. There are 1 ohm resistors in line with the output tube cathodes. Q13 and Q14 monitor the voltage at the power tube cathodes across these 1 ohm resistors and control how much bias voltage is applied to the control grids of the output tubes.

[g1]

I'm wondering if that auto-bias circuit has anything to do with the low power output under test conditions (steady tone input). Not sure if Guy said anything about the "why", but 55W clean out of four 6L6's seems pretty weak to me.