[Collins] 32S-3 Manual

[Dr. Gerald N. Johnson, electrical engineer]

Identifying the radio's vintage is more difficult. Serial numbers were
issued in random order. You need to look at date codes on tubes (if
original) and crystals, to get an idea of manufacturing date. Somewhere
between 63 and 69, I believe the front panel emblem changed from winged
to "meatball." That should give a hint of age also. There is no known
registry of serial number to know age by serial number.

One tube getting hot can mean that tube alone is oscillating, or that
tube has lost grid bias. A problem with the feed back capacitor in the
neutralization should make both tubes oscillate. After you replaced the
.001 feedthrough, you need to do a complete neutralization of the PA,
driver and RF feedback circuits.

Loosing grid bias would not be frequency sensitive, so I suspect the
tube position has a parasitic oscillation. That can most likely happen
if the resistor in the plate parasitic suppressor has gone way up in
value (or burned open). You can't check that resistor with an ohmmeter
because its shorted by the coil of the parasitic suppressor. That single
tube oscillation could also come from a failure in screen bypass (going
open) but that oscillation should involve both tubes equally. Look for
that parasitic suppressor resistor cooked.

73, Jerry, K0CQ, Technical Advisor to the CRA
-- 
Entire content copyright Dr. Gerald N. Johnson, electrical engineer.
Reproduction by permission only.