Question on changing power tubes in my Pro Reverb

[Alan0354]

I experimented to adapt 6V6 into Pro Reverb that uses 6L6. I use series 12V zener diode to lower the main voltage switchable from 440V to 375V and also grid from -45V to -40V at the same time. I also adjust the bias to -33V when I switch to 6V6.

This first video is for cranked sound, I have volume on 6, bass and treble on 5, bright switch is off.

1) 6V6, +B=375, bias = -33.

2) 6L6, +B=375, bias =39.

3) 6L6 +B=440, bias =-45.


6V6 6L6 high - YouTube

The lower voltage using 6L6 and 6V6 does not sound as good......particular the 6V6. What can I do to improve the sound?

For the fun of it, I switch to 440V on the 6V6 and adjust the bias a little. It seems to open up the sound. It's almost like the tubes like higher voltage!!!




This is comparison in clean sound at lower volume. Volume at 3, bass and treble at 5, bright switch is off.

1) Normal SF stock except two 2000pF caps removed from the grid of the power tube. +B=440V, grid bias = -45V.

2) Reduce +B=375V, grid bias = 39V.

3) 6V6 +B=375V, grid bias =33V.

All settings are vol=3.5, treble=bass=5, bright switch off.

YouTube

It seems the normal 440V 6L6 -45V still sounds the best.

What can I do to improve the sound?