[Hallicrafters] S-20R cabinet parts

[Richard Knoppow]

----- Original Message ----- 
From: "Richard Knoppow" <1oldlens1 at ix.netcom.com>
To: <Hallicrafters at mailman.qth.net>
Sent: Saturday, January 22, 2011 6:23 PM
Subject: [Hallicrafters] S-20R cabinet parts


>     I just got an S-20R for $20 at a local swap meet. Its
> in fair shape but the fluted chrome trim strips from the
> cabinet sides are gone. I wonder if there is a chance in 
> the
> world that someone has a pair or even a junk cabinet.
>
    Thanks to the list I was able to find the trim parts. I 
have a few other projects going but will get to the S-20R 
soon. I have another mostly done by someone else. While it 
worked I had to restore some of the circuitry (he had 
disabled the noise limiter and other stuff) and it doesn't 
have the original speaker. Its a nice little receiver. The 
one I just got appears to be complete other than the side 
trim and I prefer working on stuff that is pretty much 
original.
    BTW, if anyone has an original field coil speaker for an 
S-20R I would be glad to hear from them. I think the same 
speaker was used in the early S-40 and perhaps some other 
receivers, the one in my Sky Buddy appears to be the same.
    Another note: The S-20R has a detector which can 
sometimes produce fairly high distortion. Its easy to modify 
it to a grid leak biased type that has quite low distortion 
but I suspect the bias is the culprit. Where the detector 
and first amp are in the same envelope and share the same 
cathode the detector cathode must necessarily run at a bias 
value that can cause clipping on high modulation. This was 
cured or at least aleviated in old receivers by a 
"clarifier" bias. In the S-20R and early S-40 the entire IF 
secondary circuit is biased through a string from the B+. I 
think if that value is not right the detector will clip. 
When the set was changed from a field coil to a plain 
resistor I think it may have shifted the voltage at the 
detector. I never tried to adjust the final dropping 
resistor to see what effect it has but will investigate that 
when rebuilding this receiver. While the grid leak biased 
detector works very well its not original and I would like 
to have this set original if possible.


--
Richard Knoppow
Los Angeles
WB6KBL
dickburk at ix.netcom.com