1966 GE AA5 noise

[maxhifi]

Hi,

I've got a cheap plastic GE 5 tube AA5 radio which is giving me some issues. It is one of the ones built on a single circuit board, and slotted into the cabinet. Very light and cheap, not even a single screw used in the radio!

The issue is that when tuned between stations, there is a loud rushing/rumbling sound. The sound goes away totally when you ground pin 7 of the 12BE6 through a capacitor, and mostly when you ground pin 1 of the 12BE6. Other radios do not pick up the same sound, so I cannot blame the ambient environment.

I'm trying to figure out where it is originating from to no avail - the resistors I have checked test fine, and the AVC circuit appears to be working properly.

I am thinking it is probably not the IF transformers, since the noise goes away when the 12BE6 grids are grounded, and I also have tried to substitute both the 12BE6 and 12BA6 without any luck. The 12BE6 does get hotter than I'd expect it to.

Any ideas would be appreciated!

See video here for the issue: https://www.youtube.com/watch?v=51Jm8qgZKdA

-Max

[Electronic M]

Could be an IF or RF circuit is self oscillating. Sometimes strategic detuning of the RF / IF or returning the IF a few KHz up or down will fix it.

[maxhifi]

Originally Posted by Electronic M

Could be an IF or RF circuit is self oscillating. Sometimes strategic detuning of the RF / IF or returning the IF a few KHz up or down will fix it.

One thing I should add, is that the radio has been in service for about 10 years, working properly, and suddenly started doing this last week. It's used for about half an hour every day.

I did already rock the IF tuning in both directions without any luck. Have not tried RF but all there is, is a trimmer to adjust dial calibration, no RF stage.

[maxhifi]

Another thing to add, is once the radio has been on for a long time, it stops doing this and works properly.

[Electronic M]

Originally Posted by maxhifi

Another thing to add, is once the radio has been on for a long time, it stops doing this and works properly.

Cold solder joint or tin whiskers could do that.

[maxhifi]

Originally Posted by Electronic M

Cold solder joint or tin whiskers could do that.

Tin whiskers where?

[maxhifi]

Touching up the solder on the board was no help - I redid all the connections, many looked tarnished but none cold.

[maxhifi]

I redid the alignment and it seemed to help, but the volume level jumped a few times while playing, so I looked closer st the AVC components. The AVC filter capacitor had a hairline crack. I replaced it, and the radio seems to work properly now.