[Hallicrafters] SX-100 Bandswitch knob and microphonics

[Chris Kepus]

Hi Gents,

I recently acquired a SX-100.  It plays very nicely and is very sensitive on
all bands.  It does have some problems that I hope the list can help me fix.

Does anyone have a bandswitch knob for the SX-100 they are willing to sell?
Mine is toast unless someone has a suggestion for repair.  A previous owner
apparently stripped or split the plastic portion of the knob. An epoxy
repair was attempted that was not adequate and was kinda sloppy. Both set
screws only partially tighten the knob to the shaft.  When the knob is
turned on the shaft, it appears the knob has re-split. The aluminum skirt
and band lettering is in fine shape.  However, it looks like some epoxy was
accidently (?) applied to a spot on the underside of the undamaged skirt.
As a result, the skirt is solidly attached to the badly damaged plastic
knob. I might be able to cut the skirt out of the epoxy with a Dremel.

Even if I were successful in freeing the skirt, the knob, which already
looks to be damaged (subject to the opinions and knowledge of this group),
would likely be terminally damaged by the efforts to free the skirt.  Has
anyone successfully removed the skirts off any of the knobs without damaging
the skirts?  How did you do it?  If the skirts can be removed from the knob
without damage...and I can free my skirt, then I would be able to use any
matching Halli knob to make a new bandswitch knob.

The set has microphonics real bad.  Any touch causes the micrphonics to be
heard.  The softer the touch, the less the microphonics are heard. Where
should I start in tracking down and eliminating the microphonics? 

Thanks,
Chris
W7JPG



-----Original Message-----
From: hallicrafters-bounces at mailman.qth.net
[mailto:hallicrafters-bounces at mailman.qth.net] On Behalf Of Jim Liles
Sent: Thursday, July 06, 2006 5:30 PM
To: hallicrafters at mailman.qth.net
Subject: [Hallicrafters] SR-400A audio

Just finished restoring an SR-400A.  After completely aligning this radio, 
found it to have poor audio.  Sounded fuzzy like it had some 60Hz overtones.
Checked for ripple on the audio and found 4 millivolts of ripple and no 
flattening.  This indicated that it was not an amplitude problem.  
Started injecting pure sine into the audio amp and backward.  Sounded 
great until the second receive mixer where the VFO is injected.  The fuzzy 
reappeared.  Put a scope on the VFO output and found no ripple meaning it
had to be an FM problem.  Put the VFO output on a spectrum analyzer 
and found the waveform to look like a saw blade was superimposed.  This 
was a vcap problem.  The audio was best when the calibrate or RIT pots 
were not centered and it was always better when using RIT.  Note that on 
the SR-400A, the calibrate pot is 50K and the RIT 25K and the SR-2000
both are 25K.  Added a 2ufd cap to ground on the center of both pots 
and the waveform was pristine as well as the audio.  What was the 
difference?  The SMeter on this SR-400A reads S3 on a 1uv and S1 
on a .3 uv signal. Before the change, I could copy a 1 uv or above 
sideband signal and after, one that would barely move the needle 
and the background noise was perceptibly lower.  If you have an 
SR-400A, test by tuning through a cw signal with cal pot centered 
and then with it fully clockwise.  If it sounds fuzzy centered and 
better fully clockwise, put a 2uf cap from the center of the pot to 
ground.  Have a great day --- Kindest regards Jim K9AXN    
 Phone 847-913-8576  
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