heater current used for bias

[Andy Le Blanc]

so the bias resistance is not only provided by heaters of the first pre tube
but also by a secondary of the opt that also is a source for feedback.
and the bias voltage is also utilized for hum balance. The neat, how does it sound?

[Andy Le Blanc]

played the amp out, and everything is fine. no issues. even with the power
comeing and going in a blizzard up there at the Solon Hotel.

I did find a schematic with the heaters of two 12ax7 used in series to bias 4 6v6.
The intresting thing is that the same scheme are are presented for many brand
names, valco, supro, dano, wards, silver tone, etc.....
so...... who was the maker? it seems that it might be one manufactures choice
to try it. It reduces the heater dressing to one wire through the pre.
Time and wire are halved. Its a penny pincher, where it can be applied.

[ic-racer]

so the bias resistance is not only provided by heaters of the first pre tube
but also by a secondary of the opt that also is a source for feedback.
and the bias voltage is also utilized for hum balance. The neat, how does it sound?

That circuit is actually a cathode coupled ultralinear. It's a nice sounding HiFi amp; worth fixing up.