[Collins] Peculiar Request - 872A

[Dr. Gerald N. Johnson, electrical engineer]

I think those indicator jewels were stock items for the era. 1" diameter
on sockets for 6S6 120 volt lamps. (pear shaped Christmas tree lamps,
usually clear). Probably standard Chicago Miniature parts. I don't see
them in my handiest modern catalogs though.

There will be about 20 volts forward drop in the 872, and it may take
more than that to make it conduct. The blue glow is from ionized mercury
vapor that will require there to be a significant plate current. The 872
will demand to be upright (base down) and heated with the filament alone
for about a day to be sure there's no mercury on the plate to make it
conduct with reversed polarity.

I've seen similar indicator jewels in Collins built TU-9 FAA
transmitters. Same size, but not faceted.

I think I may have seen them on vintage Motorola base and repeater
stations too.

73, Jerry, K0CQ, Technical Advisor to the CRA
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Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
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