[Hallicrafters] SX42 restoration notes

[Barry Hauser]

Hi Joe --

Verrrrry interesting!  There's a tendency to focus on the paper tubulars
and electrolytics.  Meanwhile, seems to be a growing trend toward bad
micas.  Maybe the 50 year warranty ran out.  

Your post should be put up on one or more of the web sites along with the
other restoration stuff.  Do you think a cap checker would have caught
these -- tested at rated voltage?  I seem to recall a post somewhere that
said a 20 meg scale wasn't high enough -- a megger is needed on a higher
range and the needle still shouldn't budge.  Not sure though.  If they're
difficult to test, then they probably should be added to the routine
replacement list along with the waxworks wonders.

Are CM05's silver micas?  Where'd you get 'em?

Many thanks!

Barry



On Sun,  5 Jan 2003 19:18:00 -0500 "Joe " <jhanulec at mail.portjeff.net>
writes:
> After changing all the wax coated paper capacitors and all the out of 
> tolerance resistors the radio still lacked gain even though all the 
> IF and RF coils peaked.  All the tube voltages measured nominal so I 
> tried replacing the mica capacitors in IF can T3 which seemed to be 
> most deficient.  The improvement was a surprising 10 dB at 455 kHz 
> and 6 dB at 10.7 MHz.  After changing capacitors in the other two IF 
> cans, the receiver become "alive" and a real performer, even though 
> I didn't pick up as much gain with T2 and T1.  The mica caps that 
> were removed didn't measure any leakage on a 20 Meg scale so I can 
> only assume that the ESR was the problem.  Apparently the ESR was't 
> bad enough to show up as inability to peak the tuned circuits.  The 
> 455 kHz coils are very delicate and made up of very fine litz wire, 
> don't break any of the leads as I did.  I used CM05 mica capacitors 
> for the replacement. 
> 
> Now I'm close to the specification of 60 uv for S9 at 14MHz.  I say 
> close because the S meter which is speced at 5 ma FS actually is 
> almost 7 ma FS.  Does it need a magnetic jolt? 
> 
> The receiver is a delight to use on both AM and FM especially with 
> the sweet audio from the P-P 6V6's and R42 speaker.   
> 
> Now I need to do the same on my SX62 which has low FM gain. 
> 
> Joe Hanulec 
>    

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