Saturday, February 23, 2013


     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!


  1. 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.

    At 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.


  2. Great work on the schematic - Lots of things to ponder.

  3. Eck, 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.

  4. Congrats on the receiver! It certainly pays to be at the right place at the right time with some cash in your pocket, huh?

    73 de Mick - WB4LSS

  5. AHA!!!!!
    At 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!!!