[R-390] re: tube test extenders tip

[W. Li]

Here is a handy hint re tube extenders. Some of them
are faulty, in that an internal wire has opened. This
is easy to spot, if you confirm continuity between
each pin, its test point, and its socket for EACH and
EVERY pin prior to putting them into service.

We all know that they can be a convenient aid in
checking operating tube pin voltages; but what none of
us need is a unrecognized faulty test tube extender.

I ran into this problem, as I found out by rendering
an operative R-390A inoperative by inserting a tube
extender. Took me a while to tumble to the fact, that
it was the extender and not me that was at fault. Dumb
me!

One thing: it pays to deOxit all the pins when you get
them. They are often crudded up.

One principle that I have learned through the years,
is to continuously go thru and double-check my test
equipment. It is a bit like preflight checks: 99%
boredom, and 1% panic at discovering a fault. As an
example: I use a T-BNC connector on my URM-25F, and
monitor its frequency with a modern counter.

This advice may seem elementary, but sadly, it is the
simple obvious stuff that often gets us!!

W. Li


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