[R-390] Mechanical filter failures ?
Robert Nickels
w9ran at oneradio.net
Tue Dec 18 00:15:41 EST 2007
Hi Jon,
Well it would be the greatest coincidence, but just today I found one
of the FA type filters in a Collins 354A-1 mechanical filter adapter
in a 51J-3 had developed a hard short from on of the input coil
terminals to ground (case). I measured it at 4 ohms and it was enough
to pull the plate voltage down to nothing. Figuring I had little to
lose, I put 10 volts from a current-limited power supply on it and
next I knew, the short was gone. I was measuring around 22 ohms
through each coil, along with the unwanted short to the case.
I understand the typical failure mode is when the foam rubber
protective material inside the filter degrades and messes up the
mechanical characteristics, but it's worth checking for shorts to the
case.
73 and good luck,
Bob W9RAN
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