output power selector

[jrwalsh33]

Hello Friends,

I have my heart set on producing a tube amp that will replicate the '59 Bassman and a 2 el34 plexi AND ALSO have a selector to cut output power (percieved loudness). I know Cornell and others have some nifty approaches. I would reallly appreciate opinions on the best solution, why, and especially how.

Thanks,

Joe

[CarlZ]

There's a lot of ways to skin that cat and most will dramatically affect the tone and feel of the amplifier. Some fairly common options would include;

Pentode/triode mode switching. This basically involves using a switch to strap the screen grids directly to the HT rail.

Fixed/cathode bias switching. pretty self explanatory on this one.

Cathode ground lift on two out of four output tubes. not completely applicable in your situation though. You'll probably want to change output trannies to some sort of compromise value as two tubes would be taken out of circuit.

Built in speaker attenuation with set value. probably the most effective but also the most complex...particularly if you want to be able to use selectable output impedances.

That's pretty much what I can come up with off the top of my head. I'm sure others will chime in on their relative effect on tone and ease of implementation. But this should get the ball rolling at least.

Carl Z

[daz]

Pentode/triode mode switching. This basically involves using a switch to strap the screen grids directly to the HT rail

Wait....are you saying all you do is bypass the screen resistors and thats triode mode?

[defaced]

The Mesa 50/50 has a HI/LO switch that drops the PI B+ from 436v to 112v.

[CarlZ]

Wait....are you saying all you do is bypass the screen resistors and thats triode mode?

Noooo, you don't bypass the screen resistor, you connect the screen to the plate. In production amps there's frequently a fairly basic circuit protection scheme to keep everything happy, but once you look past the bells and whistles that's basically all there is to it.

Carl Z

[jrwalsh33]

Wow, really quick and helpful...thanks guys.