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if the 120 ohm cathodes resistor is used, will the amp be in class a?

Nah...


Don't get caught in the mojo...

The 18 watt really runs in Cathode Biased, AB mode (although claims are made that it is Classs A it's not really).

AB amplifiers are biased so that the plate current flows for the entire cycle at lower output levels so it is operating in conditions similar to class A. So some claim it is a Class A. If you bias it hotter, I guess you'll be closer but not really there.

A true class A amplifier has no crossover distortion and the tubes are biased on close to max all the time. They are much less efficient.

In an AB amplifier each tube amplifies a bit more than half the signal so the AB has more distortion.

Also, it's interesting to note that the average plate current in a class AB amplifier increases with load causing sag and a tonal change. Different from the true class A.

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Stephen
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And of course the same goes for the TC-15, as well as all cathode-biased Vox, Matchless and Bad Cat amps. In fact almost every currently made guitar amp rated above 10W is Class AB, despite whatever their marketing may say.

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