[Hallicrafters] EXT :Re: SX-100 (and SX-96) microphonics

[Carl Nord]

I had a SX-28 that during alignment showed horrible micorphonics. Everything
was tried, every reflector queried and frustration ran rampant for several
months. It was so bad that you could actually speak into the receiver (cover
off ) and hear the modulated voice.

Long story short on a lark we hooked it to an antenna and it worked/sounded
fine. I used it for a number of years with no problem.

The theory we (it was a friend and I, not the ham radio "we') developed was
that with a silent unmodulated signal generator carrier
Any small vibration wiggled the tuning cap plates, or something else, and
modulated the carrier a bit. However when regular band signals, noise etc
was fed into the receiver the microphones got (pardon the pun) "lost in the
noise"

I'm sure if we found a strong dead carrier on the band we would have
duplicated that, but maybe not.

Carl
WA1KPD
Visit My Boatanchor Collection at
http://home.comcast.net/~chnord/wa1kpd.html


-----Original Message-----
From: hallicrafters-bounces at mailman.qth.net
[mailto:hallicrafters-bounces at mailman.qth.net] On Behalf Of Jim Wilhite
Sent: Monday, November 21, 2011 2:32 PM
To: Hallicrafters List
Subject: Re: [Hallicrafters] EXT :Re: SX-100 (and SX-96) microphonics

After my experience with an SX 100 and many hours of chasing the microphonic
problems including everything mentioned but put it on foam, I decided you
can't put lipstick on a pig and sold it.  Poorest designed receiver I ever
had for such an expensive one.

Jim/W5JO




----- Original Message ----- 

> Clean the crud (dirt and grit) out of the bearing races on the main 
> and BS caps, use alcohol or acetone then repack using moly grease..
>

>
> I own a late SX-100 MK2A and have rebuilt dozens but havent 
> experienced any microphonics outside of a bad tube or bad ground 
> connection under the chassis.
>
> They all have a somewhat flimsy chassis which results in poor 
> mechanical stability. Soldering the spring brass variable cap wipers 
> to the chassis helps...as it does in many sets of all brands...but its 
> not a complete cure.
>

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