David Franklin dfranklyn at MINDSPRING.COM
Tue Jun 15 21:22:56 EDT 1999

I thought I would share my experiences with an NC-173 that became
mine at the Charlotte Hamfest this year. When I saw it sitting
there on the table with it's matching speaker, I couldn't go home
without it.  The radio was in good condition and received on all bands
but had hum in the audio that increased with the AF gain.

The hum became worse when paralleling 10 mfd electrolytics with the
8 mfd power supply filters.  Removing the original and replacing
with the 10 mfd did not change the level of the hum. The filter
choke measured OK.

About this time I was able to get a capacitor checker and as expected
the original capacitor checked good.  Put it all back together. The
hum was coming in strong.

Next step was to replace all of the waxed paper bypass caps.  I had
intended to do this any way.  I used Orange Drops in the audio and
ceramic disks in the RF and IF sections. All of the paper caps measured
some leakage on the capacitor checker. The leakage averaged from 2 to
about 20 meg ohms at 100V test voltage. Two of them pegged the meter.
Some pain, no gain as far as the hum was concerned.

All of you "old salts" are going to get a chuckle out of this, I next
decided to substitute the tubes.  The 6AC5 AVC Amp was the culprit!
Replacing it made the hum totally inaudible.  The tube tests good with
no shorts in my tube tester.

I then realigned her and she is performing like a champ and am listening
as I "hunt and peck".

Thanks for your ear,
Dave Franklin

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