VVR

[M Fowler]

Is there any benefit or would it even work to use two VVR3's one to control whole amp and another to control power tubes?

[John_P_WI]

Mark,

Yes, an approach is to scale the Power tubes (plate and screen) and use a second to scale the pre amp and PI. This has an added benefit as the power amp is dialed down and draws less current the pre amp voltages can be adjusted for consistent tone or dialed down as a drive compensation.

[M Fowler]

Thanks John,

I was reading Dana's instructions and brain storming

[John_P_WI]

IIRC Dana had once mentioned for fun he scaled every node. Maybe he will chime in.

Of course if you are scaling the pre with a second unit, a simple VVR like the original is all that is needed as you are not dealing with tracking bias or the power tube screens, you are truly using it only as a voltage regulator.

I have found that there is more tonal change in varying the pre amp voltages than the power tube voltages, darkening with less headroom as the voltages are lowered, similarly to the difference between a tube and SS rectifier.

[Kagliostro]

That is an interesting argument

As I can know preamp aren't so sensible to B+ level change

but if we go really low what will happen there ?

the use of a PPIMV is advised also by KOC and has the obvious consequences, but what about this different approach ?

hope that someone has experimented about and chime in

Kagkliostro

[Masco]

Don't know if there's much benefit if you're scaling the whole amp. I do know that if you are scaling just the plates and screens of the output tubes, your preamp/PI voltages can raise as much as say 70v from unloading, so you're kind of getting counter headroom from the pre/PI side.
You could voltage clamp your pre/PI so it doesn't exceed a certain amount. I've also thought about experimenting w/ adding a separate PS regulator + control for the pre/PI just to hear if there is much difference in tone when dialed.

[roberto]

It depends on what kind of preamp you have.
Hi-Gain preamps sound usually more focused with fixed high voltages from V1 to PI.
Lo-Gain preamps sound warmer-darker at lower voltages, also because they usually have to work together with the power section to obtain the right sound.