Closed loop bias control. The circuit is lifted from an RCA amplifier design-I have never really gotten into it other than to build it on the breadboard and see that it worked well from 300 to 400V B+, the only change between the two voltages was to swap the triode plate and cathode resistors from 15K to 22K, to keep the dissipation down.
Probably should though-It was originally for a 7199. There is more detail here:
Using the Pentode/Triode Tube as the Amplifier/Phase Splitter.
Max, K4ODS is who modified the circuit. There's a whole page of its usage, although less on the how'sitworks.
I've just used it a few times and had excellent results-less than 0.5% distortion is very easily gotten.
Probably should though-It was originally for a 7199. There is more detail here:
Using the Pentode/Triode Tube as the Amplifier/Phase Splitter.
Max, K4ODS is who modified the circuit. There's a whole page of its usage, although less on the how'sitworks.
I've just used it a few times and had excellent results-less than 0.5% distortion is very easily gotten.
