[R-390] Calibration issue

Tim Shoppa shoppa_r390a at trailing-edge.com
Sun Mar 19 18:17:37 EST 2006


Oh, a couple more comments about frequency stability/calibration/etc.:

1. 50 years ago a frequency counter was unobtanium. (Well, they sort
of existed but filled up an entire rack). But today they're cheap and
everywhere. Do not neglect this as a tool to narrow down the problem!

I know, the purists will insist that using any tool not mentioned in
the official Army/Navy docs is a violation of the sacred rules. But
it's easy and really does work.

A simple coil put around the oscillator tubes will be enough to get
amplitude sufficient to run most any counter. Sometimes the waveforms
you will see at V401 will be a bit funky. The 100kc calibration
is really a 200kc oscillator and a 5814A multivibrator (divide by
two) and of course it has lots of harmonics. The 17kc osc on the
RF deck only runs below 8Mc.

And it's easy enough to pull the coax cable running from the PTO
to check what it's putting out.

2. Check the 0A2. Purple glow is good. But even if you've got a
purple glow check out the +150V test point. I have been thoroughly
unimpressed with the quality of lots of "consumer" 0A2's over the
years.

Tim.


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