[ARC5] FW: Way OT -- SX-28 - ARC5 selectivity

[Richard Knoppow]

    The S-38A and later had no control other than a switch for 
AM/CW. The AVC was partly shorted by this switch along with 
connecting a feedback circuit. The feedback consisted of a couple 
of "gimmick" wires that coupled the output back to the input of 
the IF amp. I don't remember if there is any procedure for 
adjusting it in the manual. When the switch was thrown the BFO 
came on. I was able to copy CW and even SSB with a lot of 
tweaking. The receiver is not very stable which doesn't help. The 
original S-38 had an additional tube which functioned as a "real" 
BFO and also a noise limiter. That had a pitch control and an 
additional switch for the NL. I have an S-38 but never got around 
to restoring it. My original S-38B is a mess. Been in storage for 
many years. One day I will restore it. It was my first SW receiver.
    I think Hallicrafters might have had a patent on the circuit 
they used but very similar circuits were in a number of other 
receivers so the patent does not seem to have restricted its use.

On 8/7/2021 12:05 PM, Hubert Miller wrote:
>> On Behalf Of Richard Knoppow
>   I think this is the same trick Hallicrafters used in the later S-38 (starting with the S-38A I think) also in the National
> SW-54 and probably many other receivers. Eliminated needing a separate tube for the BFO. If was made regenerative
>> and the AVC was disabled. On my S-38B it sort of worked.
> I think that sums it up, it works "sort of". If I'm not mistaken, the Star Roamer had AVC plus the regeneration.
> I tried that once on a Command Sets receiver and found it unsatisfactory. There's something goofy about a control
> that varies selectivity and gain at the same time. It's harder, I think, than operating a regenerative receiver.
> I recall that past articles recommended this also for the ARC-2.
> And that some Japanese WWII field portable receivers used  regen IF.
> Just not what I would recommend.
> -Hue
>
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-- 
Richard Knoppow
1oldlens1 at ix.netcom.com
WB6KBL