[Boatanchors] Backwards Microphonics?

Wed, 25 Dec 2002 15:52:18 -0700

Hmmm...... Demons!

the unit either needs a visit
from a priest or be shredded!

be sure that no one added a speaker or headphone element inside the case
somewhere..  we have one at the museum that has a speaker inside the case!
the previous owner did this to reduce clutter on the desk... It did indeed
scare me when I turened it on for the first time and  booming sound came out
of it without the normal exterior speaker hooked up!

Please check our web site at
 http://www.smecc.org
to see other engineering fields, communications and computation stuff we
buy, and by all means  when in Arizona drop in and see us.

address:

 coury house / smecc
5802 w palmaire ave
glendale az 85301

thanks Ed Sharpe archivist for SMECC

----- Original Message -----
From: "Barry Hauser" <[email protected]>
To: <[email protected]>
Sent: Wednesday, December 25, 2002 3:09 PM
Subject: [Boatanchors] Backwards Microphonics?

> 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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