Screen Supply For PP Amp

[6f6]

If I'm going to build a Push-Pull amp with a quad of 6v6 operated in "pentode" mode with fixed bias, I know that this amp will need a regulated source of screen voltage- most likely an 0D3 and a 0C3.

My question:
Would it be best to use one common screen supply for all tubes, or would it be better to use one gas reg or zener stack for each side of the push-pull arrangement?

[ray_moth]

Theoretically, a single regulated screen supply should do it. It would have to have a pretty low impedance and I don't think you'd succeed with a single VR tube stack. An active regulator would be my choice for a single screen supply. BTW, if you regulate the screens, then you should also regulate the fixed bias supply.

[Audio_idiot]

Hi,
I'm interested in this too.

Why should we regulate both? And is it really neccessary to regulate?

I don't have any intention to argue , I'm really new in this.

Cheers

[Miles Prower]

Originally posted by Audio_idiot
Why should we regulate both?

Plate current varies with both screen and grid voltages. If you nail one down, but let the other vary, the plate current varies along with the wandering voltage.

And is it really neccessary to regulate?

No, and there have been lots of commercial designs that don't include screen regulation. However, it's been known since at least the mid-1930s that pentode amps operate with greater linearity and less distortion if you regulate the screen voltage. My own preference for this is an active screen voltage regulator. I've done two different designs with power pentode finals, and included hollow state, series pass screen regulation.

[Audio_idiot]

Hi Miles,
I had a shunt regulated screen supply for my 832 for a different reason, the grid2 voltage accent over time and the current along with it

What about autobias?

Cheers