[R-390] EAC power hum

[Tisha Hayes]

You can keep the radio EAC, just replace the transformer with one off of a
different deck.

The transformers all come from the same place. For all intents and purposes
the deck will still be EAC, just with a transformer off of another deck.

Keep the old transformer in case the new(er) one fails.

You can buy a R-390A power supply deck off of Ebay for around $30-50.

I will not go into the folks who just part-out R-390A's because their value
as parts is greater than their value as a radio but it does happen. Through
this method I have picked up enough spare parts to build a new radio (except
for the chassis).

I assume we are speaking about a mechanical hum that is coming from the
transformer core/windings being loose in the hermetically sealed case. If
the sound is really pronounced then I would expect that there is some sort
of looseness within the transformer where the laminations are coming apart
or the bobbin is loose on the laminations or the entire transformer is loose
in the case. These are supposed to be potted but the potting may have dried
out over the years or just deteriorated from the heat.

This transformer will probably fail (eventually) when a winding breaks or
the eddy currents from the loose laminations cause an increase in heating.
In the long run, all components fail so this is a very subjective thing when
we are talking about radios that are 40-60 years old.

As far as changing out the line filter, I replaced mine with a hospital
grade Corcom line filter with much better isolation characteristics than
anything that can be in the radio. With all of the computers, cheap
fluorescent light fixtures and other electronic-noise-generating devices in
our modern world you can do the radio a favor by eliminating some of that
coming in on the power line.

While you are at it, put a good MOV on the incoming AC, a CL90 to lower the
line voltage a bit and to give the radio a "soft start" and if the radio
does not have it yet, put a B+ fuse in. All of the work is in the same part
of the radio.

I have not added an IEC compliant plug on the back of my radio. I just
really do not want to take a chassis nibbler to the back of the radio.

-- 
Ms. Tisha Hayes

----------------
"I will not recant the truth. I am corn, not chaff; I will not be blown away
with the wind or burst by the flail. I will survive both."
-Walter Milne, 1558