Boredom got the best of me: AA5 hum and loop antenna

[JohnCT]

So I revisited this old Emerson I recapped a few years ago but never used. It's a 50A-1 standard AA5, and after recap, had a significant hum (vol up or down) and distorted sound.

It had the dual section filter changed before I got it so I just assumed it was wired wrong and I put it away for another time.

Time being now, I took another look at it and confirmed the filter was wired correctly.

To cut to the chase it was a 12AT6 with heater to cathode leakage. I mean, this replicated the sound of a bad filter perfectly.

With too much time on my hands, I tried measuring the leakage with an ohmmeter (something I never tried) and indeed it read 2.5M ohms from the cathode to the heater. I put it on my leakage tester and it was reading about 20ua at 100V. I then put the leakage tester on 600V (what the heck) and after a few minutes, the leakage dropped like a reforming capacitor until it read zero leakage.

Back in the radio, the hum was gone. I let it run a few hours, and still quiet. I tried it again the next day and still no hum.

I pulled it back out, marked it as test only with int hum and put the new one back in.

BUT, I have a question specifically regarding the loop antenna which has *three* wires on the antenna board. The wires were broken off, but I wired the loop section between the osc and first IF tubes as normal, and indeed it works fine. The third wire on the antenna board is not electrically connected to the loop, but is a wire about 4" long that runs along side the loop coupled inductively.

The schematic shows it, but shows it not actually connected to anything - just hovering over a ground symbol.

Here is the schematic: http://www.nostalgiaair.org/PagesByM...1/M0004651.pdf

Any ideas where the wire goes?

John