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RE: Class A Operation/Bias Points with PP 6B4G

Eli, while I agree that
"Class "A" operation means the tube is conducting 100% of the time."
is the definition of Class A, that definition disagrees with the the very book you got it from.

If one reads the discussion that follows the definition it is made clear (in most books) that Class A is when the tube is operated only in the most linear part of the plate curve.

In the 1955 Sylvania Technical Manual, under Class A Amplifier is states;

"A Class A, or Class A1, Amplifier is one in which the grid bias and signal voltages are such that plate current in the tube, or in each tube of a push pull stage flows at all times.

(that sounds a lot like the normal definition)

[second paragraph]

This is accomplished by operating at the center point of the plate current vs. grid voltage curve and using signal voltages which do not drive the grid into either the positive region or into the sharp bend near cur-off voltage."

"FWIW, I like to set PP "finals" up in "shallow" Class "A". Under that regime, both tubes are conducting MOST of the time. Only when peak power O/P is demanded, are the tubes alternately cut off. The small amount of crossover/notching distortion is hidden in the loud music."

I do the same thing but this is Class A/B operation. It is more to the "A" side of A/B, but Class A/B none the less.

Please see the link below for a more detailed discussion.

Thanks, Tre'




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