• WARNING: Tube/Valve amplifiers use potentially LETHAL HIGH VOLTAGES.
    Building, troubleshooting and testing of these amplifiers should only be
    performed by someone who is thoroughly familiar with
    the safety precautions around high voltages.

6550, 6L6, or 6V6??

Hi,

For a push-pull, Class AB1 amplifier, pentode connected, running cathode feedback, some GNB (circlotron, twin-coupled, or something else), what should I expect in terms of sound quality from each of these tubes?

If the system were to be bi- or even tri-amped, would your answer change?

OPT is undecided yet, but would be "high quality". Bias would be optimized for each tube. Speaker efficiency is such that Class A or triode isn't going to fly.

I'm just trying to gauge expected sonic quality under best circumstances for each tube.
 
Speaker efficiency is such that Class A or triode isn't going to fly.

A pair of 6V6's in pentode AB1 can do 15 to 25 watts depending on how hard you push them. NFB is required to tame the output impedance.

I can get 15 watts from a pair of 6550's in triode class A without any feedback. 30 watts is available in UL mode, again in class A, with little or no feedback.

As stated you need to consider your budget and how much power you really need (or want) and any preferences for amp type (triode, UL, pentode, and class A, or AB).