2 different tube pairs into one OT ?

[Dom]

Hi forum members,

Is it possible to use 2 different pairs of power tubes in a 100 Watter with one OT?
Technically you have to put 2 different bias units in the amp and that's it?
For 2 KT66 and 2 EL34 would be the 1202-84 with 4kOhms or the 1202-132 with 1.75kOhms?
I think the issue with the different loads is the only concern ?
Any thought on this?

Cheers

Dom

[demonufo]

Mixing EL34's with 6550's or KT88's doesn't have any other issues apart from bias currents (as long as you lower the bias splitters for 6550's/KT88's), but mixing EL34's with KT66's doesn't seem such a good idea since they will mismatch impedance-wise. Personally if I were going to mix EL34's with KT66's I'd only consider it with two OT's, early JTM45/100 style. But then, that really limits the amp for flexibility.

[Roe]

no problem IF you bias. you probably have to build two bias circuits. both the 1k7 and the 4k load should work with the standard tubes

[demonufo]

no problem IF you bias. you probably have to build two bias circuits. both the 1k7 and the 4k load should work with the standard tubes

Yes it will work, but won't one pair be working harder than the other because of the different loads? Can't quite figure it out.