Is it possible to have fully balanced from input to output amplification with only 1 tube?

[mhardy6647]

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There you go. Yes, of course -- this would require two tubes for stereo. This I understand.
Derp. The originally-referenced post said one tube per monoblock. I missed that in the OP.

I was thinking the poster implied one dual triode for a stereo amp. Sorry!

 

[DonH56]

There are schemes that take one output from the plate and the other from the cathode to provide complementary outputs. I have rarely tried that as matching gain and phase for the two paths can be very challenging, plus you (or at least I) usually needed a buffer after the tube due to high load sensitivity. That said, it has been decades since I did any tube design, maybe @SIY has better ideas.

 

[Ken Tajalli]

There are schemes that take one output from the plate and the other from the cathode to provide complementary outputs. I have rarely tried that as matching gain and phase for the two paths can be very challenging, plus you (or at least I) usually needed a buffer after the tube due to high load sensitivity. That said, it has been decades since I did any tube design, maybe @SIY has better ideas.

That would be a phase splitter. I think the OP wanted a balanced input, balanced output tube buffer.

 

[SIY]

I have rarely tried that as matching gain and phase for the two paths can be very challenging

It's actually easy- keep the loads equal and the balance will be automatic and pretty damn close to perfect.

 

[DonH56]

That would be a phase splitter. I think the OP wanted a balanced input, balanced output tube buffer.

Ah, you are right, that will not provide a balanced input itself, though any dual triode/pentode will allow you to utilize both halves. I left that part out, duh, assuming he was thinking of a tube with two sections internally. The last few balanced tube preamps I designed (ages ago) used dual triodes for differential pairs throughout.

 

[DonH56]

It's actually easy- keep the loads equal and the balance will be automatic and pretty damn close to perfect.

After I wrote that post I realized I had the answer already, just match the loads. I was thinking of the output impedance of the plate vs. the cathode and of a cathode follower vs. the output from the plate side. Need to stick with transistors and stuff I know (and/or remember) a little better.

Thanks!