plenty of resourses out there.. Sometimes class B sounds better for guitar than class A amplifiers. A 's fidelity is too high for coloration at power tube break up....
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As I said before "some confusion over terms"!
There is a tendency for people to mix up push-pull operation (where the two OP valves are effectively in series) and the amount of standing current in the stage which defines their "class". "Cathode bias" is also thrown in to further add confusing **** to the mix!
Basically, the CLASS of a valve stage decides whether or not the device conducts for the duration of a whole cycle. Now, ALL audio p-p valve amplifiers are class AB to some extent. That means that BOTH valves pass anode current for small amplitude signals (and are thus effectively class A) but as the drive voltage rises one valve is cut off at the highest negative peak. This does not matter as the other valve IS conducting. When the waveform goes through zero, the valves swap duty. Obviously you can't do this with ONE valve!
The only time an audio amplifier would be biased to 'pure' class B, i.e. BOTH valves just cut off, is when you need to save power. Running on car batteries and rotary converters i.e. fairgrounds. Military RF modulators.
Re class A, even the venerable Vox AC30 which is always called "class A" departs from absolute purity when you really drive the beans off it. The old Mullard 5-20 and 5-10 designs are "hi fi" but still AB. (the 3-3 is of course SE A)
Solid state designs are of little import here? Too many variables, two OP transistors? 4, 6, 8? Bipolar, MOSFET? The combinations are legion. If you want to know look up Duggy Self's book on sstate PAs.
Dave.
