Idea for a 2 tube 6080 PP amp.

[jazbo8]

Thanks for sharing the test results.

 

[jhstewart9]

New measurement results for the PP self inverting output stage, this time with cathode current increased to force Class A operation. The results are much better.
But still looks like a proper phase inverter is a better choice.
The IMD tests are based on equal signals at 1.5 & 2 KHz.

 

[Lingwendil]

Still not too good, but at least it's not as bad...

Not that I'm considering a build utilizing self split, but do you think a stiffer CCS like an NPN or depletion Mosfet cascode would improve things?

Also, my gut feeling is that this may work best with higher gm tubes...

 

[jhstewart9]

In the earlier work (reported three posts up from here) I found that an NFET vers (IRF840) did not work as well as the LM317 or Hammond 5H choke, even when returned to -22.4V. It didn't seem to make sense to try again.
Those I did try were significantly better.
At some future time I'll try a real phase inverter on this for comparison.

 

[Lingwendil]

Do you have EL84 to try? I suspect higher mu and gm may improve things. Then it's a trivial thing to DC couple a fet to the driver tube to try a concertina phase inverter with minimal changes at the drive voltages required.

I would probably want to try a ring-of-two bipolar cascode, or a cascoded DN2540 depletion set as a CCS, should be an order of magnitude better than a single fet or the 317.

 

[jhstewart9]

Do you have EL84 to try? I suspect higher mu and gm may improve things.

Why will that improve the subject amp? And by how much?