Robyn T-240D humming

[Deleted]

I recapped one for a friend (I am never doing that again LOL). I have a hum during receive. He disappears when someone keys up and talks, and then returns when he unkeys. Pretty sure it was there before and still there after recap. Works fine otherwise. Any ideas?

[Sandbagger]

Feb 22, 2017 22:58:58 GMT -5 @vinnies said:

I recapped one for a friend (I am never doing that again LOL). I have a hum during receive. He disappears when someone keys up and talks, and then returns when he unkeys. Pretty sure it was there before and still there after recap. Works fine otherwise. Any ideas?

I have a similar problem with my Tram Titan (and D201 for that matter). There's always a low level hum in the receiver, even though filter caps have been taken care of. It's frustrating because it's tough to nail down the source. It could be a ground loop somewhere, a loose ground, or a microphonic or internally shorted (or nearly so) tube, or a microphonic disk capacitor (I found one of those by the tap-tap test). It's not going to be easy to find, and the amount of effort you expend should be weighed against your ability to learn to live with the problem.

[Deleted]

It goes away with squelch!

[Sandbagger]

Feb 25, 2017 0:11:42 GMT -5 @vinnies said:

It goes away with squelch!

That's a clue. It means that the hum is being introduced before the audio stages, upstream of the squelch. If you have the means, the first thing I would do is sub out the receiver tubes to see if any of them are gassy or have some sort of heater to cathode leakage. The major hum I initially had on my Tram D201 was caused by a bad receiver front end tube.

[2600]

60-HZ hum is a bad tube. Leakage from the 60-Hz heater voltage into the tube's signal circuit.

120-Hz hum is a bad filter cap.

If they have all been replaced, that seems less likely.

73