"N4JOY" wrote in message
...
I appreciate everyone's suggestions. Per Richard's great
advice, I
verified that the NC-57 I own is indeed a NC-57B. Also,
the slight
hum does change in volume. However, I noticed that my
6SL7 (AF amp-
BFO) was only slightly warm to the touch while the other
tubes were
obviously quite hot after several minutes. Perhaps I have
a filament
going out or the tube has failed. I'll replace the 6SL7
and update
the group. Hopefully this will work!

Chris, N4JOY

Check the voltages at the tube socket. Its possible
there is a cold solder joint at the filament. Note that only
part of the heat of a tube comes from the filament so beng
warm but not hot may not indicate a bad tube but may
indicate the HV is not there. Make sure the "send/receive"
switch has not failed. That would cause a similar problem.
All of the handbooks have charts showing voltages at the
tube sockets. These should be checked with the tubes in
place, either at the bottom of the socket or by using a
socket extender. There may be a clue there.
Also, don't trust the replacement resistors and
capacitors to be working. While they are in general quite
reliable you may have gotten a bad one so they should be
checked. I have a feeling this is something very simple of
the sort making you say Doh! when you find it:-)
BTW, the NC-57 looks like a very good little receiver,
probably better than its competition the Hallicrafters S-40.


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Richard Knoppow
Los Angeles, CA, USA