BFoelsch wrote:


Don't get creative with the bias. It has nothing to do with the power
output, but everything to do with balancing tube life with low distortion.

When your bias is low, your tubes are cut-off on opposite cycles, and you

get

cross over distortion.


Huh? The tubes in the HW-101 are in parallel, not in push-pull!!

A senior moment, and audio habits, made that phrase come out. Sorry!

A resonating tank circuit makes how you think of Class A, AB, B, and C
operation somewhat different, though.

(A = 360 degree plate conduction;
AB1 = less than 360, but more than 180 degree conduction, no grid current;
AB2 = less than 360, but more than 180 degree conduction, w/some grid current;
B = 180 degree plate conduction;
C = less than 180 degree plate conduction.)

The tank "free-wheels" through the areas of non-conduction in the RF signal,
effectively taking the place of the second tube in a push-pull amplifier,
thus making AB, B, and C modes of operation usable with one tube.

But the tank does nothing to improve amplification linearity.

The correct amount of bias is still chosen for the same reasons as in the
push-pull amplifier: so that the stage remains suitably linear under normal
operation, and tube life is adequate for the mission. In this case, the
correct bias puts the stage in the Class AB1 region.

The OP was running a pair of 6146's, at 20ma bias, and commenting on how
turning the bias up a bit made his too low output power rise a little.
I assumed he meant 20 ma each tube, as the usual bias for a pair of
6146's (ala Collins) is 40ma, 50ma if you are running into a linear.

If he was indeed running 40ma to a pair of 6146's, and his output power
was still too low, the usual reason is he has a used up pair of finals.

And the thread went (some would say downhill) from there...

-Chuck