[Milsurplus] Solved: Where'd the Harmonic Come From?

[David Stinson]

Figured it out.
Set the bias wrong in the Master Oscillator.
Can't just tweak it for "maximum smoke."  It was
driving the PA grid too hard and pushing the 6S4 
waaaay deep into Class C, making it act like
a frequency multiplier.  Was pushing nearly twice
the grid current (4 mills) needed ( 2 mills ).
Tweaked the MO grid leak value down and the output
waveform at the 50 Ohm non-reactive load 
cleaned right up.  Making good headway with the
modulators as well.

Looks like in AM, the 6S4 tubes are going to
be good for just over 4W carrier, a little better
than 12W PEP.  If we're biasing just for CW,
you can get about 6.5W carrier.  You can push
the PA grid current and get more, but the output
waveform suffers.

TNX ES 73 DE Dave AB5S