RadioBanter - View Single Post - Problem with National NC-57

Don Bowey · January 28th 08, 08:26 PM posted to rec.radio.amateur.boatanchors

On 1/28/08 9:37 AM, in article
, "N4JOY"
wrote:

Hi -- I recently completed some repair work on a National NC-57. I
did the typical replacement of electrolytics, out of tolerance
resistors, etc. It was functioning reasonably well beforehand but was
in need of some TLC. Following my repair work, I turned the unit on
and am only receiving a hum with no RX. I conducted some resistance
measurements at all tube sockets and every measurement was nominal
(according to my NC-57 manual) except for pin 6 of tube 7 (6V6GT).
The manual indicates a resistance reading of 380K ohms and I'm
receiving around 50K ohms (same as pin 3 and pin 4). To be honest, I
can't see how pin 6 should be 380K ohms. The output transformer
primary shunt resistor is 22K ohms and everything is wired correctly
at the tube socket. I double checked my work and carefully reviewed
the schematics -- everything looks good. I'm really stumped here...

Any help would be greatly appreciated!

Chris, N4JOY

There is either a wiring error or a defective component. Pin 6 of the tube
socket is not used by the tube, so it is obviously used as a tie-point.
Trace in both directions from pin 6 and you should find the problem.

Hmmmmm... Are you certain that each tube is in it's correct socket?