Class A Push Pull - output transformer specs

[abbey road d enfer]

What can I say, comparing some clean stuff, the Class A 260v version is 1.2dB louder than the Class AB 325v version.

Class A has more gain than class AB, but less max output power. That's because in class A the output tubes are in the middle of their slope, when in class AB their are at the beginning.
It's easily noticeable on an amp with variable bias. Often, people tune them for maximum output when strumming their guitar, which tends to be at the maximum of the bias range. They often red-plate the tubes.

 

[CJ]

Get a dummy load and hook it to a 1/4" jack,

feed in a sine wave into amp and measure voltage across dummy load.

I have a table of values at work up on the wall,

5 volts = 12 watts,

25 volts = 50 watts

etc

Class A might have different harmonic content than AB, I don't know, I ain't no rocket scientist, I just stick in different components til it sounds good.

Don't forget that fixed bias class a might sound different than cathode bias class a. Maybe some compression on the self bias? Maybe some compression with a 5U4? Maybe some compression due to transformer DCR?

I don't know, what kind of weird amp did Hubert Sumlin use?

 

[CJ]

dummy load, stereo in case i get a weird amp in like a JC 120,

100 w at 8 ohms each, jacks on the outside are for a speaker load, Altec 15" on each side,

i can parallel those resistors if checking a 200 watt pig amp

transformer for isolating the output signal for the scope, sometimes the amp does not like a scope ground connected to the chassis, (oscillation)

V-AC for power and milliamp meter for doing a death bias, (shunting B+ to OPT primary)