[BC] Te st your wits on this

[David Senft]

As the cliché goes, "the plot thickens". As noted by others, there may be an
issue with the socket (with another "wrinkle" added in). Perhaps the failure
was a symptom rather than a cause, although failure of the inner ring isn't
uncommon. With the smaller contact-area combined with a filament demand that
parallels welding-currents, one would not suspect anything unusual in the
event of a failure. However, the heat generated by the failure may have
caused other problems, -perhaps with the filament bypass capacitor(s)
sandwiched between the socket components. For this reason we ordered a
socket but don't expect it to clear Customs before Monday. The other
"wrinkle" involved a spectrum sweep of the PA amplifier that included a
neutralization check. The amplifier comes up clean into a 50 ohm load but
when attached to the terminated combiner module, a monster spur appears
about 1 mHz below carrier. This would seem to indicate the reactance of the
combiner and the current condition of the amplifier completes the loop.
Perhaps there always was an inclination toward this and all it took was a
small shift in the parameters of the socket to push it over the edge. All it
may take is a few picofarads. 
D.