[Boatanchors] Hum sources?

[Ian Wilson]

The culprit turned out to be the 1st audio stage, half a 12AT7. (I had
measured
the B+ hum, very clean).

It took me longer to replace the 12AT7 than I expected: two tubes had their
own problems, and one that I thought was a NIB RCA turned out to be a
totally
different type(!).

There was apparently a lack of audio gain from the original defective tube
also.
Now I get audible audio with the AF gain control on its lowest setting, and
VERY LOUD audio from my favorite AM BC stations with the AF gain on
higher settings.

73, ian K3IMW


On Mon, Sep 19, 2011 at 3:09 PM, J. Forster <jfor at quikus.com> wrote:

> 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
>
> =================
>
>