The acronym stands for "Super Regenerative Receiver" and I think it was their first foray into the old amateur radio 5 meter band, before the sophisticated 1-10 "Ultra High frequency" receiver was much more than a gleam in James Millen's eye.
It's a tiny thing, 7¾" x 7¾" x 7" and 5 meters is where it tops out; with a minor reshuffling of coil connections, it covers the lower ham bands, from 10 meters down to 160 meters.
As a "rushbox" super-regen without an RF amplifier to isolate the detector from the antenna, it's not a good citizen on any of them; in operation, it radiates a broad swath of noise, inherent in the superregeneration process.*
And I own one. There it was, at the Indiana Historical Radio Society's Spring swapmeet, standing out on a seller's table to anyone with an eye for old National equipment, at a remarkably low price. I made an offer and somehow ended up with a nice homebrew absorption wavemeter in the bargain.
Have a look inside the receiver:
The coil and socket are standard 4-pin "tube base" configuration, unusual for a National product; they usually preferred their own designs. But that will make it simpler to wind new coils. The one in the socket probably isn't for this receiver -- not just the "Hammarlund" name on it, it lacks the cathode tap found on all SRR coils. I may have coil-winding data. I'm certainly going to give it a try!
Rough schematic:
It uses a version of National's "S-101" interstage coupler that I had not seen before. The S-101 is a weak point in the design, as the internal audio choke (inductor) has a very high impedance, meaning many turns of small-gauge wire, which tends to perish in the potting compound. Checking that will be the first order of business.
_________________________________
* I believe it was Howard Hughes' 1938 around-the-world flight that found radio communication nearly wiped out by interference from people trying to listen in with simple superregenerative receivers. This is why the later 1-10 had an RF amp, to keep that detector from getting in the way!
Looking like a fine old radio. If the choke is history look around for a BC221 they used a similar choke save for form factor.
ReplyDeleteAt the other end of their line I get to work with a HRO 60 in near mint condition as an instrumentation receiver. Sitting next to an AOR 5000 it's hard to use the AOR.
Eck!
Very cool!
ReplyDeleteGreat work on the schematic - Lots of things to ponder.
ReplyDeleteEck, Hammond sells a high-value choke suitable for this, too -- but that darned tap is an oddity! Most S-101 units didn't have one.
ReplyDeleteCongrats on the receiver! It certainly pays to be at the right place at the right time with some cash in your pocket, huh?
ReplyDelete73 de Mick - WB4LSS
AHA!!!!!
ReplyDeleteAt long last you have solved the mystery of the empty hulk in my radio collection! I got the cabinet knobs and dial,(all still assembled!) without
any internals save for the pots!, at a hamfest years ago. I could NEVER decide if this HAD been a bona fide National product or not! Who Knew!...THANKS!!!
Fantastic to see this information thank you. Yes the Audio transformer has a total of 20,000. turns tapped at 6,000 turns, the tapping is on the innermost windings, all windings use 44 AWG wire, I had to rewind mine, not a job for the faint hearted it's like using a spider web for wire. I'm doing a restoration job on mine, unfortunately somebody has visited mine in the past and the wiring has been changed, just would like to confirm which side of the dial the volume and reaction controls are placed? I think mine have been transposed.
ReplyDeleteFantastic….. Really nice to see some information on this set … Thank you… ! Yes the audio transformer is a problem, if you want to rewind the transformer the total number of turns is 20,000 tapped at 6,000 the tapping is on the innermost windings the gauge of wire is 44AWG, rewinding the transformer is not for the faint hearted using this gauge of wire is like using the strands of a spider web. I’m in the throws of restoring my set, unfortunately somebody has altered mine and I was wondering if somebody could tell me which side of the dial the reaction control is place looking from the front?
ReplyDelete