Ed Lambert" "K1ZOK
ma.locksmith at JUNO.COM
Sat Jan 13 17:36:02 EST 2001
Actually, it's pretty easy to find a microphonic tube.
Advance the volume control to a point just before it begins to howl.
Then tap all the tubes with the eraser end of a pencil. The one that
makes the noise is bad.
On Sat, 13 Jan 2001 15:12:54 -0600 Ron Evans <cosmos41 at IX.NETCOM.COM>
> I recently bought a Hallicrafters S-38D (I know...very minimal
> receiver!) which was my first receiver back in 1957.
> This one has a few problems, some of which I can repair but I need
> help on a pretty simple (for you guys!) problem. Although I've been
> ham since I was 16 years old, the technical side of it just never
> was my
> forte. But now, I'm enjoying working on old radios and really just
> the beginning stages.
> Question: When I advance the Volume control to a certain point,
> is a loud "howl" for want of a better word. It sounds like it
> continue getting louder and louder (like feedback) if I didn't
> the volume setting. Is this possibly a microphonic tube? If so,
> it be more likely to be the Detector & Audio Amp 12SQ7 whose grid
> connected to the volume control, or could it be the Audio Output
> I don't have a tube tester, so I'm kinda shooting in the dark. I
> have a
> lot to learn; I know that! I guess the first thing I've learned is
> I need a tube tester! I could substitute known good tubes if I had
> but hate to buy a full set on speculation.
> Anyone have a buoy they could throw a drowning senior?!
> As always, my gratitude.
> Ron - K5MVR
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