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Hallicrafters S-72 - Printable Version

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RE: Hallicrafters S-72 - BrendaAnnD - 09-27-2013

    Marty,

That's just it. There IS no wire, nor any electrical connection of any kind. Maybe it's supposed to feed back through the B+ line, but I don't think so, or it would get to places it's not supposed to. Not a very good schematic here, but you can see it's a simple Hartley oscillator. It is actually difficult to make these NOT work.

RE: Hallicrafters S-72 - BrendaAnnD - 09-27-2013

Note that the top switch is power (B+) The bottom switch is for a noise blanker that isn't part of this particular version of the radio. This, and its accompanying resistor and capacitor do not exist.

Anyone know if there are any OTHER differences between the S-72 and the S-72r?

RE: Hallicrafters S-72 - Arran - 09-27-2013

This is the one thing I hate about communications sets, too many of the HAMs that owned them seemed to think that their license was equivalent to an engineering degree and made half baked mods. So they take a perfectly functional design and started screwing with things, drilling holes, adding switches, taking stuff out, second guessing the armies of engineers at the Hallicrafters/National/Hammerlund plants and rewiring them.
Regards
Arran

RE: Hallicrafters S-72 - Mondial - 09-27-2013

It is strange that the BFO circuit no longer oscillates. Did you change any parts in the circuit?

I am surprised that they used a 22k grid leak resistor for a low transconductance battery tube like a 1U5, as it loads down the tuned circuit and there is not much gain to spare. You might try a 47k or 100k instead and see if it makes a difference.

RE: Hallicrafters S-72 - marty - 09-28-2013

Hi All;
Brenda Ann, Sorry, I wasn't trying to mislead you, but, I was going by what you typed as a guide.. ""The only coupling is via stray inductance into the 2nd IF"" and that was Why I said that maybe a wire had been moved, maybe I was reading too much into Your Sentance..
THANK YOU Marty

RE: Hallicrafters S-72 - marty - 09-28-2013

Hi All;
First I want to Thank Brenda Ann for posting the Schematic for her Oscillator..
I have been trying to copy down the Schematic for my Philco 024 Signal Generator and even though it is a very simple circuit, I keep on getting lost and making Wrong connections.. Yes, it arrived today, late this afternoon.. I have ordered the papers from Chuck..
Probably too late to be doing this.. And Lo and Behold, but Brenda's schematic is close enough to help me figure it out.. So, THANK YOU Brenda Ann..
THANK YOU Marty

RE: Hallicrafters S-72 - Radioroslyn - 05-14-2018

Don't usually pull on these old threads but was gifted a S-72 recently from one of are esteemed members from LINY. As Brenda mentioned the R version I can't find anything on it either. This is marked w/ both S-72 and S-72R There was a S-72L it has a LW band and less SW coverage. In good shape barring a broken leather handle and the corners are a bit tatty from wear. Was serviced back in '04 and still works. A cursarary testing tells me that it could use a going over, sensitivity is not all that great. More later.

RE: Hallicrafters S-72 - jcassity - 05-15-2018

i am on my 7th resto on halllicrafters,,, i do agree they are very stable units.. the highest model i have resto'd was the S-53 which was free.

the BFO is prob some simple gimik cap where a wire is wrapped around a certain other wire for a minimum of 2 turns,, yet i have played around with that idea and have found that 4 turns wakes up the bfo sensitivity really good.

at the moment i am on the hunt for an SX-42,,, i think this would be the very best radio ever made for all things SW & FM,, but its gonna be a true representation of what we call boat anchors.

RE: Hallicrafters S-72 - Radioroslyn - 05-18-2018

https://www.antiqueradio.org/halli07.htm
Life is short I think I'd run the other away...