Choosing the right triode as a Phase Inverter

[rsumperl]

Greetings everyone,
How does one choose the proper triode for a phase inverter? Here are the specs on a triode (6M11) I am considering:

Triode Class A Amplifier
Plate Voltage 125 V
Grid No. 1 from 120 Ω
Amplification Factor 58
Plate Resistance (approx) 10K Ω
Transconductance 8K µ
Plate Current 8 mA
Grid No. 1 Voltage for Ib of 50 µa -4.5 V

[SY]

Well, since there are about a million phase inverter circuits, each one with different requirements, it might help to be a bit more specific. Diff amp? See saw? Cathodyne? Cross-couple? Paraphase?

[DF96]

Which circuit you pick might depend on the context: how much voltage swing do you need, what HT voltage do you have, hi-fi or guitar, how concerned are you about exact balance, what are the output valves and their configuration?

Alternatively, do the best you can with what you have and put up with whatever you get.

[rsumperl]

Well, application is Hi-Fi and feeding P-P AB1. I'll need about 75V P-P. The B+ for the "drivers" is around 200v.

[TheGimp]

Also consider what mode your are in (probably AB1, but some people run AB2), and what the drive current to the output tubes is going to need (easy to drive tubes or difficult to drive?)

[SY]

Well, for a 75 volt swing, 200V B+ seems a bit low. Any chance you could increase this?

[rsumperl]

I could, what would you recommend?

[SY]

The higher, the better. If you can manage 400V or so, a 6SN7 as a constant current diff amp (long tail pair) will easily swing 75V p-p and very low distortion. I don't know what the linearity is for a 6M11.

[rsumperl]

How could I, how do you, determine the linearity?

[SY]

I set up tubes in a test jig and measure distortion using a sound card and an interface box (Pete Millett's is excellent for this purpose). See, for example, Morgan Jones's tests on 6SN7s and 417s in "Valve Amplifiers" 3rd edition.