VVR is working, but the Volume is the same

[Baby Thomas]

Hello!
I made a simple one channel clean amp with somewhat strange output section - SE with 6AN5. I also installed a VVR circuit (first time for me) to alter the B+ for the output tube (acting as an additional Volume Control). The circuit is working as expected, changing the voltage for 6AN5's anode and screen between ~122vDC and ~32vDC. However the output volume doesn't change at all, it's pretty much the same. On the scope I can view the clean output power changing from ~0.3W to ~0.03W, but to my ears there isn't any volume drop. The only thing that happens is I loose headroom as soon as the pot is in the lower 25-30% of it's range.
Is this normal? Is it because the power is already too low? Is it the tube type I used? Is it because it's SE?
Any help will be highly appreciated. Thanks!

[Latole]

You can't trust your ears from so low power.
Look everything is working.

[JB]

I have a 1W SE amp (EL91) with VVR.  I scale the EL91 anode and screen only, not the pre-amp.  Works fine however you do need to reduce the drive to the output stage otherwise it will distort early.  You're getting that effect, as you say you're losing headroom.  Hence I think your VVR is working but at such low power and only chaging from 0.3 to 0.03W it's hard to hear it. 

[kagliostro]

Latole & JB gived you the correct answer

Maybe this can help to understand easily



Franco

[PRR]

Gain and power are two different things.

The gain of a tube amplifier changes very little with supply voltage.

The maximum power does change with supply voltage.

[Baby Thomas]

I'm somewhat familiar with power vs. volume relationship, but I thought if the power goes down 10 times (0.3W -> 0.03W) I'll have half the volume.

Yesterday I didn't have the schematic with me, I'm attaching it now.

[d95err]

VVR reduces headroom, not volume. Although maximum volume will of course decrease as you turn down the voltage.

You describe that you get a reduction in headroom, so it looks like it works as expected.

[PRR]

I'm somewhat familiar with power vs. volume relationship....

Gain and power are two different things.