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...

Remove the tube. Does the resistance change?
--scott
--
"C'est un Nagra. C'est suisse, et tres, tres precis."

On Jan 28, 3:03*pm, (Scott Dorsey) wrote:
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...

Remove the tube. *Does the resistance change?
--scott
--
"C'est un Nagra. *C'est suisse, et tres, tres precis."

Hi -- the resistance of pin 6 to ground at 6V6 is 67.9K ohms. It
remains unchanged when the tube is removed.

Thanks,

Chris, N4JOY