[Elecraft] [K2] KPA100 above 20m - not enough drive on USB; LSB fine

[dl0tuh]

An owner of a K2/100 (S/N < 2000) showed me the follwing problem: it looks as
if the mic drive were not enough for driving 100 watts USB on 17m band. A
whistle test could only reach abt 20 watts.

However, on LSB the same whistle test produces full power output. Playing
with CAL FIL, I moved BFO frequency to the wrong side of bandbass,
effectively making LSB instead of USB. It is definitely useless on the air,
but full power output was reached in this test.

How do you think, where can this kind of difference between "right" (USB)
and "wrong" (LSB) sideband reside? Up to now, I can only think about L34 on
RF board, but isn't the Q there too low to make such a difference between
sidebands? Builder Alert #22a is the closest thing I found on the web, but,
again, that would influence both sidebands.
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