[Boatanchors] Hum sources?

[J. Forster]

If:

The B+ filter caps are not dried out and have lost uFs
and
There are no signs of modification (like a different transformer)

I'd look for H-K leakage on the audio tubes. Other places to look would be
ground lugs that might not be making good contact por missing shields.

Best,

-John

=================



> I'm working on an AN/TRR-5 (Espey R-366) morale radio.
>
> The otherwise rather nice audio system is outputting more hum
> than I think is normal. The level of hum is independent of the AF
> gain control setting.
>
> The B+ filtering - my first suspect - is very clean, so it appears
> that the electrolytics are in good condition. There is a 3rd stage
> of B+ filtering going to the low-level gain stages in addition.
>
> Looking at the schematic, the only places where I can see hum
> being injected are the first audio amplifier (1/2 12AT7), the second
> audio amplifier/phase splitter (12AU7), or possibly the muting
> switch from the bandchange switch to the o/p tube grid. Possibly
> a screened wire has become detached from ground.
>
> Anywhere else? For some reason the power cable has a 2-pin
> plug on it, but the receiver schematic shows a ground connection
> (and I can see the wiring from power socket to chassis ground).
>
> I can try substituting the double triodes this evening (would this
> mean heater/cathode leakage?) but wondered what the most
> likely source is - and whether I am overlooking something.
>
> 73, ian K3IMW
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