This Heathkit Economy Short Wave Listener's Radio is a three tube four band regenerative set covering 140kHz to 18 mHz. Tubes are 35W4 as rectifer, 50C5 for audio output and a 12AV7 dual triode as the regenerative RF detector and a first stage of audio.
Unlike near identical circuits such as the Allied Knight kit Space Spanner, the Lafayette Explor-Air KT-135, and similar AC-DC sets, the Heathkit incorporates an isolation transformer for safety. To my knowledge and to their credit, Heath never made a transformerless AC-DC radio. The GR-81 includes bandspread and the usual volume and regeneration controls. The circuit is a very simple design, but the four-band coverage, the isolation transformer, the power supply choke, and even the fuse set it apart from other sets with similar circuits.
The date on the partial manual available for download from BAMA is November 1961. The set was made from 1961 to 1972. Prices ranged from $23.50 In the 1967 catalog to $24.95 in earlier ones. An article on the set is in the Antique Wireless Association's Old Timer's Bulletin of May 1997.
This set was in mostly excellent cosmetic condition when purchased. Just a bit of cleaning of the knobs and the chassis was all that was necessary. A toothbrush and white waterless hand cleaner will get the grime out of grooves in a knob.
When received, the set was inoperative. Like most Heathkits, this set started life as a kit. Therefore all soldered connections and screws that hold down ground lugs are suspect. Sure enough, a few quick checks with the ohmmeter traced the dead set problem to a connection at the wired-in fuse. While the power cord wire had been soldered, the wire to the fuse at its terminal strip had never been soldered. A thorough check with a small screwdriver for wiggling wires revealed another terminal with 3 wires, 2 of which had not been soldered. Chances are excellent that this little set had been intermittent for all of its life. The soldering check was followed by checking to make sure every screw on the chassis was properly tightened. This was followed by applying a bit of deoxit spray to each switch, potentiometer, and tube socket. I powered it up slowly to reform the electrolytic cap and found one more bad solder joint which kept the set from functioning on band 3.
These simple regenerative sets have no alignment needs. All of the RF amplification and detection is done by one of the two triode sections of the 12AV7. Definitely a simple design. After repairs were completed, I was rewarded with a properly functioning set. Listening to short wave with a minimalist regenerative set is a fun experience that introduced many to the wonders of radio.
According to Dick Strippel, the author of the Old Timer's Bulletin article noted above, shown in the picture:
"For minimum money and building time, these sets provided a simple and fun means to explore short wave radio. Despite a simplicity of design, their overall peformance could be outstanding in the hands of a skilled operator, exceeding that of simple superhets such as the venerated Hallicrafters' S-38, and without their image problems.
One of the last tube-type kit regens was Heathkit's GR-81 'Economy SWL Receiver' of the mid-1960s. In implementation, it stood head and shoulders above its last-of-the-breed competitors such as Knight's long-lived and continually evolving 'Ocean Hopper'."
The Hallicrafters SX-62 was the previous item on the bench.