[Boatanchors] Backwards Microphonics?

[Barry Hauser]

Hi Gang

I've come across microphonic tubes in my time -- like one in an HQ180
where it was picking up my drumming fingers on the table and even my
voice if I yelled at the front panel. That was a 6GH8, as I recall.

But the microphonic in this E.H. Scott SLR-F goes the other way. It's
more of a "speakerphonic". I was checking it out using headphones.  Took
them off and I could still hear something.  Unplugged the phones and it
was still there.  (Yes, with no speaker connected and, yup -- the sound
stops when I switch it off, just in case there are any jokers in the
woodwork -- besides me, that is. ;-).

Can a tube do that?  I would suspect the output transformer, but the
sound is coming from the opposite side of the chassis.  Besides, the
audio tranny is an oil-filled Thorardson so I doubt if the windings could
be loose from the core or something.

Aside from the rectifier, all the tubes are metal types.

This is one of those pre-war/WWII receivers which was over-built with
extra shielding for use by the Navy to minimize RF radiation and,
thereby, detection by the enemy.  I don't know about AF radiation -- just
a sec ... Hey you!!!  Loose lips sink ships!!!.  Nah, I don't think
that'll work.

Are these like the AR88's audio setup?  The word is on AR88's that the
output transformer can get wrecked if operated for more than a short time
on headphones alone, without some load on the speaker terminals.

Any clues will be appreciated.

BTW -- Merry Xmas to All

Barry

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