[Boatanchors] halli S-20R

[Geoff]

With only cosmetics and minor circuit changes the S-9, S-15, S-20R, S-40 
series, S-85, and a few later models, they are all the same circuit starting 
in 1936.
Nothing special in performance and with Hallis usual drift and out of the 
catalog components..

A Kiwa filter in the IF will improve selectivity a lot for AM use.

Carl
KM1H



----- Original Message ----- 
From: "Richard Knoppow" <1oldlens1 at ix.netcom.com>
To: "Phil" <dgnova at verizon.net>; <Boatanchors at mailman.qth.net>
Sent: Monday, February 27, 2012 1:20 PM
Subject: Re: [Boatanchors] halli S-20R


>
> ----- 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
>
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