[Collins] Collins 32S3

[Dr. Gerald N. Johnson, electrical engineer]

A time delay fuse makes better power supply protection than a fast blow
because the time delay fuse can have a lower current rating and still
handle the turn on surge. If the power supply has been made solid state
the turn on surge will be much larger charging the filter capacitors
rapidly. Tubes prevent that part of the turn on surge. New and larger
filter capacitors make the problem worse.

The line voltage the transformer was designed for was most likely 115
volts, and your line voltage is more likely above 120 volts. That
increases the saturation of the core and some transformer core materials
will have a high retention (stays magnetized at the last peak when
turned off) causing the core magnetization to draw a larger surge on the
first half cycle, if the applied voltage is opposite the polarity of the
last half cycle the core saw. Higher voltage at some times of the week
will make this surge magnitude greater at those times. There may be a
"thung" sound from the transformer core the instant its turned on. A
sign of this phenomena.

I'd go to a MDL 3 fuse, maybe a MDL 3.2. Its decently slow blow to
handle turn on surges, yet more sensitive to continued overloads. I'd
wish for an MDL 3.5 but they aren't made.

According to my 32S1 diagram, the 6.3 for the 312B-4 console lamp comes
from the same circuit that supplies the 32S1 meter lamp, PTO filament,
and the PTO dial lamp. I have no idea where that wire enters the harness
or where the actual connection was made. Only tracing by tugging will
have any chance at all of finding the lost voltage. Though checking that
part of the heater circuit may show up something. 

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