[Boatanchors] halli S-20R

[Richard Knoppow]

----- Original Message ----- 
From: "Phil" <dgnova at verizon.net>
To: <Boatanchors at mailman.qth.net>
Sent: Monday, February 27, 2012 8:56 AM
Subject: [Boatanchors] halli S-20R


>I have been offered a Hallicrafter. Is this a very good 
>receiver ? It is of
> the 1RF stage and 2IF stage type of receiver.
> Phil
>
     I have two S-20R's, one of which is restored and the 
other waiting until I can get to it. The S-20R was a 
relatively low priced receiver, the least expensive one 
Hallicrafters made with an RF stage. It is a reasonably good 
performer for the class. It was also the first of a long 
line of very similar receivers made by Hallicrafters. Its 
post-WW-2 successor was the S-40/A/B and others later. 
Hallicrafters continued to build similar receivers for a 
couple of decades.
     Because of the tubes used and the design of the coils 
of the time the sensitivity above perhaps 15mhz is not very 
good but it does work. Also keep in mind that the 
selectivity of the single RF stage is limited so that the 
image rejection at higher frequencies is poor.
     If you can get the receiver for a reasonable price, and 
if its in decent condition, it makes a nice collector's item 
and a useable listening around receiver. The quality of the 
audio is pretty good.
     The receiver will need a complete recapping. Exact 
duplicate can electrolytics are available from Hayseed 
Hamfest and I suggest using either modern film capacitors or 
ceramics with high quality dielectric (type C0G or NP0, 
which are the same, i.e., Class-1 dielectric). The ceramics 
will have slightly better RF performance and work fine for 
audio.
     Some time ago I posted a high resolution scan of the 
instruction book on BAMA. Included is an ad from QST from 
about when the receiver was announced.
     S-20R's were built from about 1940 until the entry of 
the U.S. into WW-2, they were than discontinued until the 
end of the war and then went back into production until 
supplanted by the S-40, which is a better receiver.
     The S-20R uses an old-fashioned detector which relies 
on being biased correctly to minimize distortion of highly 
modulated signals. The DC value may not be right without 
trimming a resistive devoured that provides the bias. If you 
are not a purist you can modify the detector to a 
self-biased type that has much less distortion.


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