add SE PA to PP amp

[allsavy]

I've got a fender princeton reverb 2 that has been converted from 2 6v6 to 2 6l6 output tubes (fixed bias) and the preamp is tweaked to perfection. The phase inverter is a 12au7 long tail pair. The amp sounds fantastic but is too loud for apt. recording.
What I'd like to do is build a little single ended output section (one el84 and one small se OT) that can be switched into the circuit as a lower watt alternative to the normal PP output stage.
How might this be configured for switching?

[6267]

You could try putting the 6L6s into triode mode instead, by connecting the plate to the screen. This will kill 6V6s at that voltage though. The volume should be much lower with a clearer, warmer sound. You may also be able to use a 4-ohm on the 8-ohm tap in this case.

You can also try using shared cathode bias, with only one tube receiving drive, aka "Self-Split Push pull" which is quieter than full P-P and has good sonics for guitar.

Be aware that if you go the small SE amp side chain way, that EL84 really doesn't require much to go to full output. You will likely want to lower the signal with a voltage divider.

[Alf]

The phase inverter is a 12au7 long tail pair.

What values did you use in the PI or did you just swap the 12ax7 for a 12au7 ?

I would like to know if you tweaked the plate resistor values and the the other resistors in the PI .

Alf

[allsavy]

I could not find any good reference for appropiate values to use a 12au7 as a phase inverter but since mt LTP had been changed from the typical fender 82k/100k at the plates, with 820R/22k tail by replacing the 22k with a choke to approximate the effect of a constant current source and made the plate resistors equal @ 100k ea. The 12aus seems happy in there and sounds great as well. I think that normally a 1.2k cathode resistor and 100k plate would be appropiate for one stage of a 12au7 so the 820R for common cathode seems right. There is no bypass cap in this circuit.
This is from memory... hope it makes sense.

[Alf]

It definitely makes sense !
I was wondering if the tube had enough gain to drive the output tubes.

I usually use a 12at7 for PI .

Thanks for the info

Alf

[d95err]

The amp sounds fantastic but is too loud for apt. recording.

If you want to be able to crank the amp or at least get some poweramp compression/distortion, an SE EL84 PA would still be way too loud for appartment use. Even 0.5W is probably too loud.

I would look at using a small dual triode as PA, e.g. a 12AU7 or 12AT7. You could keep it push-pull and retain the character of your PI. AX84 has some low power dual triode PA designs on their site.

But even with a small triode PA, you may have to use some kind of attenuator, powerscaling or an iso-box.

[ThermionicScott]

I've got a 2x6AU6 homebrew that puts out no more than 1.2W clean, and it's still pretty loud when cranked. Nice pentodey crunch though!

In case you want another data point...

[allsavy]

ThermionicScott, with the 6au6 what kind of pentode sound- like a 6v6 (round/muddy) or like a el84 (more articulate) ?