The Dynaco ST120 amp has a single regulated supply rail, with a big capacitor blocking the DC from the output stage. Is it then a Class A amp?
About as far from class A as you can get. Output stage bias current determines class, and it’s biased at zero or damn near it - and isn’t even temperature stable. The output quiescent DC voltage being about half way up the rail can’t help with that.
Look at those heat sinks, could it possibly be class A at 60W per channel?
But a single supply does not mean single-ended.
But a single supply does not mean single-ended.
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Ok I thought class A meant no switching distortion, and having a single-polarity supply would mean no switching between polarities (push-pull). Not so?
Whether an amplifier uses a single supply or a dual supply, has nothing to do with switching/crossover distortion, or whether it is class A in operation.
Class A circuits have a large idle current (equal to the peak load output current) and do not switch between devices like a push pull circuit does.
More info: https://www.electronics-tutorials.ws/amplifier/amplifier-classes.html
The single supply ST120 still switches between the upper and lower halves. It has crossover distortion. And oh boy does it have crossover distortion.