mixed tubes in push pull

[allsavy]

I've tried combining an el84 with a 6v6 in a two tube PP output stage (both cathode bias) and while the result is interesting there is way too much fat. Coupling caps to the outputs are .002. there is no tone stack.
As an experiment I tried running the the 6v6 in triode mode (pins 4&5 connected through a 100k resistor and the result seemed more along the lines of what I wanted. The thing is there seems to be some sort of quiet ratty distortion as the signal dies out. No doubt from interaction of the odd combination of triode and pentode. What else would one need to consider to continue in this direction?

[allsavy]

I was thinking a coulpling cap might be needed?

[Chuck H]

The rub is that either tube responds differently to the input signal. Triode or otherwise. When one tube begins to clip the other hasn't started yet and where each responds to drive level differently you get an imbalance that probably results in crossover distortion or at least an oddly assymetrical waveform. The post subject is "push pull" but have you considered running them parallel in class A?

You might do a little better if you adjusted the drive voltage to each tube from the PI. A scope would help alot to see what each side is doing at different drive levels and also to detect crossover distortion or waveforms that are too bizzare to be useful.

Chuck

[allsavy]

Yeah well that is getting complicated. I don't have a scope and such. It is more like plug this in there and see if the result warrents further development.
I thing I might as well go with 2 + 2 parallel and be done. The issue of having triode and pentode would then be moot.
I'll no doubt need another source of filtered B+ for the extra tubes and heater supply as well.
I'm now thinking 6L6s for bigger soundstage and #4 (early breakup) el84s to add some mojo.
Does any one make an amp as such ? Reviewing some sound clips might be in order before I go ahead with all the work.

[allsavy]

Or is it only the heater supply I would have to worry about and just run the 2 el84s off of the same B+ tap as the 6L6s (with a resistor to knock down the voltage. ???

[defaced]

I'm doing a mixed push-pull output section with four tubes. Currently running KT-88 and E34Ls. What you need is separate bias supplies and separate coupling caps/grid resistors/bias resistors between the PI and the power tubes. So basically add a bias supply and six more parts and you've got it. If you're interested, I'll upload a shem when I get home.

[allsavy]

Thanks but a schem is not required.
My PA is cathode biased so that simplifies things.
I've simply paralleled the 84s off of the existing 2 tubes...apparently this is wrong ???
The noise I've been hearing is most likely crossover distortion... I'm sure.