NC-57 deafness problem
 

I've been hitting a wall with this restoration. I recapped and
completed a full alignment, and while it performs beautifully from
broadcast band to 12 mhz (bands C, D and E ), it is quite deaf on
bands A and B (basically 12-mhz up). I didn't realize it during
alignment because I had been feeding a robust RF generator signal and
it was aligning quite nicely on those upper bands. But once I hooked
up an antenna, I noticed that nothing but the strongest stations come
through on bands A and B, 12 mhz and above. I traced the antenna coil
section very carefully and checked all three sections for open coils,
open bandswitch contacts and cold joints. I can inject an antenna
signal at the bandswitch wafer in the mixer section and the
sensitivity comes back. It seems the signal is getting held up at the
antenna coil section only on bands A and B, but for the life of me, I
can't find the issue, which makes me think I'm missing something. Any
suggestions would be greatly appreciated!

NC-57 deafness problem
 

You might also ask the question on the National reflector on qth.com. You
need to go to qth.com to subscribe.

Sounds like a common problem on older RXs. Worked on a more recent NC-125
that was deaf on 15 and 10. A local uses a preselector/pre-amp
on his older gear.

Good luck.

73 Dave K4JRB

NC-57 deafness problem
 

On Jun 7, 6:50*pm, petev wrote:
I've been hitting a wall with this restoration. I recapped and
completed a full alignment, and while it performs beautifully from
broadcast band to 12 mhz (bands C, D and E ), it is quite deaf on
bands A and B (basically 12-mhz up). I didn't realize it during
alignment because I had been feeding a robust RF generator signal and
it was aligning quite nicely on those upper bands.
=======================
The local oscillator operates on the low side of the signal frequency
on bands A and B and on the high side for the other bands. Aligning
with the LO on the wrong side of the signal frequency will kill the
sensitivity. You may want to check this out.

NC-57 deafness problem
 

I've checked that, thanks for the help though. I've put it on the
shelf for a while, its driving me nuts
Will check out the qth reflector!