B+ reduction

[Kevin Kuehn]

Very roughly speaking, Class A just means that with respect to it's power tube's DC bias voltage, one or both of the power tubes are not driven by a previous stage so far negative as to cause one or both tubes to be shut off during any 360 degree portion of the signal and the power tubes are in fact both swinging signal for the entire 360 degrees of any sine wave.
Biasing the tube to a very hot/high current actually means that the bias voltage is closer to zero and the drive signal appearing on the power tube's grids can push negatively far enough to over ride the smaller grid bias voltage so far as to effect the bias state of the tube so it goes into cutoff.
The 5E3 (as an amp circuit) can easily do this with the relatively low voltage seen in the power tube's cathode biasing and the two stages of gain prior to the cathodyne driver.
That means the driver and PA of the 5E3/5E3X2 are merely working in high idle current power tube, Class AB1.

Bruce, I'm confused by your statement. I do realize you said very roughly speaking I was always tought that class of operation had to do with how the tubes are biased relative to their operation on the load line. So, if a tube is biased right in the middle of its load line, it is operating Class A regardless of input drive signal. A very strong drive signal would still drive it equally into saturation and cutoff? A lower bias voltage(closer to zero) would actually cause the grid to conduct sooner on the positive swing. Of course capacitor coupling would cause signal duty cycle shift, so the grid never really draws much current. What am I missing

Kevin