[BC] Te st Your Wits on This

[David Senft]

In this business, it doesn't take long to learn to ask the question, "What
was the last thing you did?" It was our suspicion that the spur problem had
something to do with the installation of the replacement filament contact
ring but what? During tests, the spur was solid. As the station in question
is some hours drive away and I'm tending to my wife who was released from
hospital not many hours before this incident, I wasn't sure of some of the
details of the diagnostics but I later found that neither the plate nor grid
tuning controls affected it. After exhausting all ideas, a variation of
Richard Rudman's comment about rotating the tube 90 degrees was attempted.
By rotating the filament contact ring 60 degrees, (six mounting holes on the
flange) the mystery was solved.  There appears to be no explanation other
than the finger-stock on the ring has a gap one finger-space wide that is
probably inevitable in manufacturing (unless you are very careful). The
finger stock is cut from a flat strip and welded to a circular flange. In
this case, the characteristic of the contact ring appears to have affected
the PA's reaction to the combiner module but not with the broadband nature
of the dummy load. It appears to be good practice to mark the orientation of
the contact ring when replacing it. My sincere thanks to all who offered
suggestions and I want to extend special thanks to Cowboy who responded
off-line to me personally. Although I don't recall meeting any of you at
conventions, by reading the Digest I feel I know you all. Best wishes to all
and especially Barry. Keep the fun coming!
Dave.