Balanced vs Unbalanced?

Ralph, I agree with all of that. I wasn't very clear when I said

for everything to work as designed you have to have a circuit capable of producing 2 signals that are exactly the same except for their polarity.

I never meant to make any correlation between signal and CMRR. I should have said

to maximize CMRR the circuit must amplify any common mode signal to produce 2 noise signals that are exactly the same except for their polarity.

If one side amplifies the common mode signal i.e. noise more than the other then they don't completely cancel. That can't be corrected in the next stage. Sorry for the confusion.

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Herman, Yes, that's true. I've found in practice though that it does not seem to come up. Also, again the CCS circuit plays a huge role in this- even if there is a mismatch in the tubes, you don't seem to get any extra noise.

BTW, any tube amp with a single-ended input can be modified to have a true balanced input, often without any change to the way it operates with a single-ended input, and without using an input transformer. IOW its possible to have a balanced front end and an SET as well, with all the benefits.

...any tube amp with a single-ended input can be modified to have a true balanced input, often without any change to the way it operates with a single-ended input, and without using an input transformer.
Atmasphere (Threads | Answers)

How is that accomplished exactly?

Ralph, you are such a tease.