[ARC5] FW: Way OT -- SX-28 - ARC5 selectivity
howard holden
holden7471 at msn.com
Sat Aug 7 21:31:53 EDT 2021
Interesting that the original S-38 had a BFO oscillator but not the succeeding models. In the mid 60s when was stationed at Gitmo and had my own station KG4DF, I used a Halli WR-600 (S-120 with a phony wood grain cabinet) which had a fancier version of the regen IF stage of the S-38. Instead of the gimmick caps it used a pot from the suppressor to ground to control regeneration. Like any scheme of this type it wasn’t the greatest, but I used it even on 15M CW. The WR-600 was the only SW receiver in the PX that was usable on the ham bands so I made it do. One hand on the tuning all the time…..
Howie WB2AWQ
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From: Richard Knoppow<mailto:1oldlens1 at ix.netcom.com>
Sent: Saturday, August 7, 2021 1:25 PM
To: arc5 at mailman.qth.net<mailto:arc5 at mailman.qth.net>
Subject: Re: [ARC5] FW: Way OT -- SX-28 - ARC5 selectivity
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
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