Class of operation for Tube Power Amps

@westcoastaudiophile 

my comment was related to “real” class A design, not hybrid (pseudo ab) A2/A3 with enabling output tubes grid currents! 

Class A is defined simply as the output device does not go into cutoff at any point of the waveform, regardless of output power, right up to clipping. Class A2 and A3 meet that definition; are not 'hybrid' or any such since you can run class A2 or A3 in a single-ended embodiment.

The only class A3 amp we had in the shop was an SET. Running a single 300b, it made 50% greater power with less distortion running zero feedback than a class A1 amp can using the same tube. 

IOW all three variants are "real"; none are AB in any respect. 

A2 and A3 require the driver of the power tube to maintain linearity when grid current is present. AB1, just so you know, does not require this, no grid current. AB2 does. Its my surmise, although I've not talked to the inventor (Jack Elliano) of A3 (for which he holds a patent) about this, but a class AB3 is likely also possible. 

Contact manufacturer??🤔

FWIW, Aric Audio makes some lovely PP tube amps that run exclusively in Class A, like his Transcend Push Pull, which I own and love.

+1 wrm57 - I also own an Aric Audio Transcend "Push Pull" EL34, and it runs exclusively in Class A. It also is the finest tube amplifier I've ever owned, of the 6 I've owned over the years.

Aric Kimball of Aric Audio makes some extraordinarily good preamps and amps, using the highest quality components available. He'll also make custom changes if one is so inclined, and upgrade tubes to NOS tubes if they are available.....and I find his products to be rather affordable compared to much of the competition.