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Title: Hallicrafters S-40 - Odd Wiring around V-2 Post by: KW4H on September 17, 2022, 06:02:11 PM I've got an S-40 on the bench -- a restoration project for a friend (KI4BNS). The receiver belonged to his grandfather (who was licensed), then was passed on to him. For the most part, the receiver appears to be all factory, which is always helpful. However, his grandfather had been into the radio, and I've found a circuit alteration on V-2 that I'm uncertain about. This is a 2nd revision model of the S-40, by the way.
The attached schematic shows V-2 and the area around it as originally designed by Hallicrafters. Have a look at pin 5 (grid #1) -- the alteration I'm seeing is off of there. Here are the changes: - R30 (10 ohms) is eliminated - C16 connects directly from pin 5 to S/IF - C26 connects directly from pin 5 to ground So, the modification puts three connections on pin 5 -- R7 to ground, C26 to ground, and C16 to S/IF. Before deciding whether to revert this back to factory, I'm curious as to why this might have been done. I've searched online and can't find this modification anywhere. 73 - Steve, KW4H Title: Re: Hallicrafters S-40 - Odd Wiring around V-2 Post by: KW4H on September 20, 2022, 11:57:52 AM As a follow-up, the decision was made to restore to factory original. Best guess is that the original owner was experimenting to try to improve performance, especially on the upper bands. The high band on the S-40 (as with many other lower-cost radios of that era) was notoriously deaf.
73 - Steve, KW4H Title: Re: Hallicrafters S-40 - Odd Wiring around V-2 Post by: wb1ead on September 20, 2022, 02:37:50 PM Hi Steve..honestly tasked with "what to do ?" I wudda ended up the same way..original might not be what was intended but here's my thought on that..there are a few various types/designs out there for outboard pre-amps..I've used two..both were the Ameco brand as they had a RF sensed delay/relay..I think MFJ has some too and I'm certain a "wire direct" type is out there..FWIW I own the same rig you have..the National NC-125..probably as sensitive or lacking on the top end as ur S-40..those pre-amps DO work..not so much on the lower bands 160/80/40..but for sure especially on 10mtrs..the downside is if there's hash/noise etc it will boost that too..right now I'm working on restoration of the Johnson T/R box which has a slight ability to add gain but not sure yet as it is unfinished....best-o-luk Steve and do let us know if you get it running OK...73 de DAVE WB1EAD AMfone - Dedicated to Amplitude Modulation on the Amateur Radio Bands
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