So today I finally finished the alignment on my Motorola 55x15 "Mothers Day" radio. I buttoned it back up in the case and everything was fine. I listened to it for about an hour and all seemed well, so I powered it off and went about some other business. A short while later I turned it back on, and the horrible buzzing is back. I don't believe it's environmental, as the radio is exactly where it was when it was working, and changing location and orientation didn't remedy the problem even slightly. I don't have any spare tubes, so I can't swap them out for testing. Before I buy a whole new set of tubes, does anyone know what the cause might be? I've included two video links. One is with the radio working perfectly in the case. The second is the unit after the buzzing forced me to pull it back out of the case for inspection. As always, any help is GREATLY appreciated.

http://www.youtube.com/watch?v=V5Upb2yAIeE

http://www.youtube.com/watch?v=asf5zVOUzjA

The radio is acting like an open in the loop antenna circuit. Check the connections were it returns to the AVC line.

:So today I finally finished the alignment on my Motorola 55x15 "Mothers Day" radio. I buttoned it back up in the case and everything was fine. I listened to it for about an hour and all seemed well, so I powered it off and went about some other business. A short while later I turned it back on, and the horrible buzzing is back. I don't believe it's environmental, as the radio is exactly where it was when it was working, and changing location and orientation didn't remedy the problem even slightly. I don't have any spare tubes, so I can't swap them out for testing. Before I buy a whole new set of tubes, does anyone know what the cause might be? I've included two video links. One is with the radio working perfectly in the case. The second is the unit after the buzzing forced me to pull it back out of the case for inspection. As always, any help is GREATLY appreciated.
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:http://www.youtube.com/watch?v=V5Upb2yAIeE
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:http://www.youtube.com/watch?v=asf5zVOUzjA
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I don't have the Sams on that one, but you must first determine if the buzzing is internal or external to the radio; first, remove the antenna. If the buzzing is still there (and at the same level), the source is internal. Since the radio was working, look for bad connections; this could be almost anywhere, from the power supply to the RF section. It could be a silver mica cap problem in the IF transformers; they will need to be dismantled and the caps replaced.
Johnnysan-

I wish you would have left it on a station, as the audio didn't actually sound garbled as it often does when an antenna lead is disconnected. Still, that could be your problem. Do any of your other radios make this sound in this location. If not, then most likely you have a disconnected antenna lead.

T.

Now I'm really REALLY confused. Late last night I turned it on and everything was back to normal. I ran it for two hours with no abnormal behavior at all. Then I shut it off and went to bed. Turned it on this morning and it's buzzing again. When I disconnect the antenna all noise disappears except for the familiar low amplifier hum. I've tried moving it to different rooms and pointing the antenna in different locations, nothing seems to change. Is my apartment under EM bombardment at odd hours of the day? There must be a reason it's behaving this way. Oh, also, the loop antenna on the back has continuity between terminals, at about 3.4 ohms of resistance. Thanks for the replies!

:Now I'm really REALLY confused. Late last night I turned it on and everything was back to normal. I ran it for two hours with no abnormal behavior at all. Then I shut it off and went to bed. Turned it on this morning and it's buzzing again. When I disconnect the antenna all noise disappears except for the familiar low amplifier hum. I've tried moving it to different rooms and pointing the antenna in different locations, nothing seems to change. Is my apartment under EM bombardment at odd hours of the day? There must be a reason it's behaving this way. Oh, also, the loop antenna on the back has continuity between terminals, at about 3.4 ohms of resistance. Thanks for the replies!

You can always check your environment for RF interference with an AC/battery operated radio, line interference on the AC and RF interference with the battery.
Lewis
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I can't believe I kept forgetting to try that. I hooked the 55x15 loop antenna to my home theater receiver's AM antenna terminals, and I got zero noise. So I moved the antenna back to the 55x15 and now it's back to being buzz free. I guess I'll just have to wait til the buzzing comes back and then try my home theater again to see if it's environmental or something intermittent in the radio. And I thought the complete rebuild was going to be the hardest part... Thanks for the advice!

Sounds like an intermitent connection to the antenna or a broken wire in it.

:I can't believe I kept forgetting to try that. I hooked the 55x15 loop antenna to my home theater receiver's AM antenna terminals, and I got zero noise. So I moved the antenna back to the 55x15 and now it's back to being buzz free. I guess I'll just have to wait til the buzzing comes back and then try my home theater again to see if it's environmental or something intermittent in the radio. And I thought the complete rebuild was going to be the hardest part... Thanks for the advice!
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:Sounds like an intermitent connection to the antenna or a broken wire in it.
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::I can't believe I kept forgetting to try that. I hooked the 55x15 loop antenna to my home theater receiver's AM antenna terminals, and I got zero noise. So I moved the antenna back to the 55x15 and now it's back to being buzz free. I guess I'll just have to wait til the buzzing comes back and then try my home theater again to see if it's environmental or something intermittent in the radio. And I thought the complete rebuild was going to be the hardest part... Thanks for the advice!
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Try wiggling or tapping the antenna wire when it happens or when it is quiet?