Hum in tram d201 speaker

[joec]

I have a hum in my D201 handwired tram, also if I touch the D104 screen it will sound like scratching in the radio speaker,can someone tell me how to correct this problem,Joe.

[cbrown]

I'd suggest looking in the microphone connector for a loose or broken ground (shield) wire. If it's not at the connector going into the radio, it'll either be in the cord itself or in the microphone base.

Start there and see if that corrects the problem.

[2600]

I believe the hum you're asking about is in the radio's speaker on receive.

Unplug the mike and see if it goes away.

If not, this suggests either one or more failed tubes, or MOST likely, failed filter capacitors.

The radio has plenty of them. And they are ALL too old to be trusted. Electrolytic capacitors have a limited service life, and all of the factory-original ones are over 35 years old now.

The usual advice for a radio full of old electrolytic caps is to replace them all. Good advice, but not a beginner's project. And not cheap if you hire a tech to do it for you. We call that the "100,000-mile tuneup".

Back in the day, you could find a tech who would track down and identify the "one" bad cap when this happened. But back then, the radio would have been ten years old or less.

Besides, the tool for identifying a bad filter cap is an oscilloscope, along with a good spare for each cap that might go bad. You clipped the new cap in the circuit. If that made the hum go away, that cap was the cause, and it would get replaced.

But the filter caps in that radio should be falling like dominoes, one by one if they are all original. Even if you identify and replace that "just one" cap, another one will fail before long.

73

[joec]

Thanks looks like I will be making a trip to Louisville soon,Joe.