Altec A256C Amps. Info needed.

[johnny_fever]

A year ago I found an incredible pair of Altec A256C theater amps. My friend is getting them up and running as we speak. Does anyone have any factory info on this model amp? Especially addressing the bias procedure. Cant seem to find much info. I did post pics a year ago ok Audiokarma https://audiokarma.org/forums/index....c-amps.982411/ Any bias help or info would be appreciated. Thanks. Rick AKA Johnny Fever

[RonSSS]

The schematic over on AK shows the bias voltage. Not only at the supply, but also at the grids of the 807’s. So what’s the issue?
Have they been powered up?

I had a similar pair, but they didn’t have an input section. Just an input transformer direct to the 807 grids. They were meant to be driven by a small power amp. The official designation was “booster amp”
They came from a local bicycle race stadium and were used as PA amps.

[johnny_fever]

Thanks for your reply.
V5 & V6 are biasing high. He questions one of the caps associated with bias. Not sure his ESR meter will check voltages that high. I will report back. But still would love any factory info on this A256C model. Thanks. Rick

[RonSSS]

The ones I had were A247A. I never found any info. Very rare.

The bias circuit is very simple. Caps in an amp 65 years old should be replaced anyway.

I have an Altec literature and engineering book from 1959, those weren’t in there.