mixing tubes question

[pkb123]

I realise that people are going to think I'm mad in asking this but...

A quad of EL84's needs an OT of approx 4K
A pair of EL34's needs an OT of approx 3.5K

Is it possible to put a single EL34 and a pair of EL84's on each anode of a 7.5K OT (2 x EL34 and 4 x EL84 in total)? Obviously, the EL84's and the EL34's would require separate bias supplies and the anode voltage would have to be carefully picked to ensure the EL84's didn't blow up, but is it possible? I just wondered if it was possible to use a pot to vary the input between two separate PI's feeding either EL84's or EL34's but to have them feeding the same OT.

Thanks in advance for any help.

[julkke]

THD yellow jackets make that possible, check them out.

[demonufo]

Surely yellow jackets compensate for the difference in impedance... That won't work.

Back to OP, you want to mix a pair of EL84's in push-pull, and a single EL34 in what configuration exactly? Reproducing one half of the wave perhaps...
EL34's and 84's are so massively different in both their behaviour and specs (um, plate voltage alone...) that there isn't a single reason I can think of why this would ever be a good idea, I'm afraid.

[demonufo]

I just re-read. A clean EL34 pulling opposing a pair of dirty EL84's pushing or vice versa is an even crazier idea, regardless of whether or not it can be done.

[pkb123]

Perhaps I didn't explain myself clearly.
I'm wondering whether I can have a pair of el84s and an el34 on each side of a push pull configuration... I.e. 4x el84 and 2x el34 in total, with the el84s fed from one preamp and the el34s fed from another.

[demonufo]

Meh. They behave so differently I don't see the benefit. Personally if I were to set it up, I'd use a seperate PI for each to allow to proper tweak the circuit for each tube set, and if going down that road, might as well have two seperate OT's.

EL84's are just far too gainy in comparison to EL34's. And EL34's aren't going to operate nicely at voltages that will suit EL84's.

[pkb123]

I can see why a PI for each type of tube would be the right way to go... that's what I would have done. I would have a common input, two discrete preamps and PI's and then the power tubes connected together into the OT. Bad Cat have created such an amp in the past with a model called "Tone Cat" but schematics seem non-existant so I can't see the finer points of how it was done (and I don't fancy blowing up 50 watts of OT).

Thanks for the opinions anyway

[Ferrari-Dude]

In the past I've run one pair of Yellow Jackets w/Mullard EL-84's and a pair of Mullard EL-34 XF2's in a Marshall Super Bass 100W. Its not exactly what you were asking but somewhat close.

It sounded pretty good. It had the bark & power from the 34's and the gnarly midrange & chime from the 84's. It also cuts down the power output a bit so power tube distortion starts a bit sooner on the volume knob. I liked it.

Try a pair of yellow jackets with the other tubes in a 100w amp to get some sense of your tonal possibilities.

Caveat: Yellow jackets have a maximum plate voltage, so they may not work in all amps.

[Reeltarded]

Back to OP, you want to mix a pair of EL84's in push-pull, and a single EL34 in what configuration exactly?

Ever see Doctor Dolittle? Push-pullme-push-pullyou.