Hoffman Amplifiers Tube Amplifier Forum

Amp Stuff => Tube Amp Building - Tweaks - Repairs => Topic started by: Leevi on July 12, 2021, 06:26:02 am

Title: Hiwatt DR504OL circuit question
Post by: Leevi on July 12, 2021, 06:26:02 am

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


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


/Leevi

Title: Re: Hiwatt DR504OL circuit question
Post by: sluckey on July 12, 2021, 06:46:50 am

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.

Title: Re: Hiwatt DR504OL circuit question
Post by: Leevi on July 12, 2021, 06:53:38 am

Yes of course
Thanks Sluckey


/Leevi

Title: Re: Hiwatt DR504OL circuit question
Post by: CascoSieg on July 12, 2021, 10:10:24 am

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.