Hiwatt DR504OL circuit question

[Leevi]

What is the purpose of the V4b triode before the PI?


https://hiwatt.org/Schematics/DR504OL.gif


/Leevi

[sluckey]

V4B cathode follower provides a fixed bias voltage to the grids of the LTP PI. We usually see the grids "bootstrap" biased with a resistor to the cathode circuit.

[Leevi]

Yes of course
Thanks Sluckey


/Leevi

[CascoSieg]

I'm considering some version of the DR504 for my next build. Some of the Hiwatt circuits I've seen push the signal through a DC coupled CF and some use the V4b triode just to provide fixed bias voltage. Simulations show seemingly minor differences in the same signal run through each circuit option as it appears on the PI grids. There will certainly be differences when clipping is involved, but I'd love be able to breadboard both and compare for real.