[Collins] R-388

[Dr. Gerald N. Johnson, electrical engineer]

The R-388 is basically a Collins 51J. Its not modular like the 390(a).
As far as I remember the input is already about 50 ohms, not balanced or
unbalanced like the 390(a).

Electrolytics will object to having voltage applied. Sometimes they blow
up and fill the chassis with shredded foil, conductive crepe paper, and
conductive electrolyte. If they've not had voltage for several years,
more than two or three they may have that violent failure mode. Bringing
up with a variac is pandering to the old electrolytics, nothing else
needs that care. Sometimes bringing up the voltage slowly reforms the
electrolytics. It would be better to bring each electrolytic up with an
external variable voltage DC supply with careful current limiting.
Bringing up the radio with a variac won't have controlled current
limiting.

If there are molded paper capacitors like the infamous Black Beauties
they should be replaced by Orange Drops. The molded paper capacitors are
leaky and will mess up AGC, lower screen voltages, and make audio stages
draw excess plate current (by the leakage driving the grids positive).
Its not worth the effort to check each capacitor for leakage, just
replace all of them and you will reduce later troubleshooting efforts by
at least an order of magnitude. A good leakage test requires completely
removing the capacitor from the radio, so replacement saves doing that
in a way to have enough lead to put the removed capacitor back.

73, Jerry, K0CQ

-- 
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.