[bucma]

Very few classic tube guitar amplifiers were Class A, the vast majority being AB. Really the only ones that were class A are single tube amplifiers like the Fender Champ. The Vox AC/30 that everyone thinks is class A is just cathode-biased class AB. The Marshalls that Hendrix played through, the Fenders that Steve Ray Vaughn used, and the Boogies that Santana is known for, all class AB.

Sure, class A does tend to have more even-order harmonics, compared to AB, but even class AB tube amplifiers have more than any solid state one.

[ris]

So... did these tube AB designs have particularly asymmetrical lobes to their gain curves? Otherwise I don't see where these even order harmonics are getting introduced.

[crmd]

Yes a bit due to asymmetry in the phase inverter circuit driving TD push-pull, but mostly because the odd harmonics are naturally cancelled out in the output transformer.