GE 516F - static and intermittent reception after playing for 10-15 minutes

Restoring a GE 516f clock radio. Tubes all test good. Fully recapped. It plays great and has good sensitivity for about 10 to 15 minutes. Then, the signal weakens/fades and is sometimes accompanied by loud static (sometimes the static is very soft). The volume controls the loudness of the static. Tapping tubes doesn't affect operation.

The radio has a built in loop antenna. If the reception has faded, often i can get some reception back by putting my hand on the antenna. The sound is somewhat distorted. If I don't touch/disturb the radio, static comes and goes as does reception. Sometimes returning fully to normal from time to time.

Turning the radio off for 15 minutes then turning it on has the same results as noted above except it takes less time to act up. So, obviously heat is a factor.

The schematic is good and gives details on voltages so I'll be checking those today. There is a ceramic resistor, 1000ohms (R16) ......it gets very hot....about 130 degrees F. It tests just at 1046ohms.

It plays better/longer without issue in normal operating position than it does on it's side (where I can get to the underside of the chassis and check parts while it's playing.

So.....in my newbie status and this being only my 4th restoration (2 successes and 2 under construction), I seek your collective wisdom on this GE.

I suspect one of your I F transformers has gotten leaky. Caused by silver mica disease. The pop rivet corodes, causing leakage between primary, and, secondary mica caps in transformer. There are two good ways to repair this.
Either replace the internal built in mica caps with correct value caps., or, replace entire transformer.
Voltage testing will tell which one is the culprit.
If you get any positive voltage on the secondary, that transformer is the culprit.
Good luck.
Bill Cahill

Thanks Bill. I'm checking pin voltages with the B- post on the chassis as the reference. Is that also where I check the IF cans? If so, then T1 is the culprit. I show 1VDC postive on the secondary pins, with 90VDC on the primary side, the 90VDC is right in spec. The ground pin of 12AV6 has -.55VDC, the ground pin of 50C3 has +.5 VDC, the specs show 0 VDC on those pins. Those pins are connected with that interesting 4 part ceramic cap. I stand corrected on my earlier remark....I didn't replace ALL the caps....that one is still original. Earlier, it played for 4 minutes before losing signal and going to static. As I was checking voltages, it came back and played for over 20 minutes with no issues. Thanks.

Is it still playing correctly?
Bill Cahill

No. During that time it played correctly more than not, but it lost signal and went to static 5 or 6 times during a 30 minute period. I saw no change in voltage readings whether it was playing correctly or not.

Try tapping, and, wiggling tubes. If that isn't it, check voltages on I F's again.
If you still have a positive voltage, then, that's your culprit.
The positive voltage on audio out. grid wouldn't cause a reception problem, but, you'd totally lose audio in time, and, dammage the tube, and, other components.
All paper caps need to be replaced, or dammage can be done.
Bill Cahill

Tapped and wiggled. Nothing. I'll check again for positive voltage and I'll replace that 4 part ceramic cap unit with individual pieces. I may be chasing 2 issues....something in that ceramic cap and a bad IF.

If it all went smoothly....I wouldn't learn anything!

Back to the workshop! Thanks for the help.

I wouldn't replace that cuplate just yet.
Bill Cahill
If you are getting reception problems, you are looking in the wrong place.
The cuplate isn't likely to do that.

Best to stock up on those little cute brown 100pf silver mica caps.

Let it play without touching a thing. Played for well over 20 minutes, no issue. So I moved the tuner and lost signals got just a little light static. Turned up the volume and the signal returned clearly. Ultimately through trial and error found that just touching the lead of the silver mica on the converter tube with a non conductive probe could lose the signal or bring it back. After about 45 minutes of operation, lost the signal completely but no static. I'm guessing due to heat. Also after 45 minutes, the voltage on 2 of the pins on the converter tube that should have been 90VDC and was such earlier, had moved up to 112VDC. So....I'm guessing that little silver mica has failed.

If that does not fix it check your tube sockets, had one do same thing to me years ago..Sprman : )

I'll be back on this one today, have a 50c3 and new micas ready to install. Thanks for the help....I'll post results after replacing parts.

Have you checked the tuning condenser itself?
Look and make sure none of the plates are touching, as even a little vibration could cause them to short if there to close to one another.

Another clue is if the insulation on the varible cap has a conductive trace has developed from moisture. Its like a path that develops from high voltage, dust and moisture. Another thing would be some variable caps have a brass finger that touches the tuning shaft to ground it to the cap frame. They need cleaning and be causing intermittent reception.

Replaced a couple of suspect tubes. Also, obtained a signal tracer from my father in law and took some voltage readings.
When the audio goes out and I hear static from the radio speaker, there is still a strong signal out of the 1st IF. The second IF has the sound I hear from the speaker.

When cold, the voltages are 98 into the IF's (90 is the spec). The 1st IF has +.5 volts on both the "out" pins. The 2nd IF has -.3 out of both pins. When the audio drops and the static sound starts, the 1st IF goes to +1 volts out and the 2nd IF goes to +2 volts out. The audio came in and out while I was checking voltage and I noted that when the sound returned, the 2nd IF went back to -.1 volts.

So, to this newbie, looks like the 2nd IF is really the issue, although given that the 1st IF also shows positive voltage, it's got issues too. I may try to tackle the repair, but where can one find suitable 455 IF's for this radio?

Thanks for the help gang!

Are they miniature, or, standard size?
Bill Cahill