At OneTubeRadio.com, we’e always looking for one tube radios, and seventy years ago, QST carried these circuits for a one-tube AM transceiver for VHF. Since the war had Amateur Radio shut down for the duration, this circuit was designed for WERS on 112 MHz.
The design also took wartime parts shortages into account, since the radio has about the bare number of parts possible to make a functioning transceiver. The author notes that almost any receiving tube can be used, and includes two circuit diagrams, one showing a directly cathode, and one with a separate cathode and filament. A prototype of the unit is shown, built in a cigar box. The antenna, a quarter-wave zepp, plugs into the top of the radio. (These days, a vertical zepp for VHF is better known as the J-pole.)
The circuit is basically a regenerative receiver, with a carbon microphone controlling current to the cathode. While the modulation percentage is low, the author calls it entirely adequate for short-haul work.
The author recommends a 6J5 tube for the circuit with a cathode, or a 1LE3 or 1G4 for the filament-only circuit, but almost any tube will work. The author does not offer any details as to performance (since he probably wasn’t able to test it on the air during the war). But he notes that “for a transceiver which costs only two dollars or less, as this one does, any attainable range should be satisfactory.”
It’s doubtful whether this simple circuit would meet the current FCC spectral purity requirements for use on the ham bands. After all, even while receiving, the regenerative receiver is radiating. However, if some attention is paid, it’s likely that this circuit would be legal on 49.82 – 49.90 MHz, under sections 15.235 and 15.23 of the FCC rules.
Interestingly, this isn’t the first time that the author of this article has been mentioned at this site. The QST article was written by Gurdon Abell, W2IXK. It appears that he later moved to Connecticut and was licensed as K1EHG after the war. He passed away in 1999 at the age of 82. He was mentioned here in an earlier post, and it wouldn’t be incorrect to say that he was the discoverer of meteor scatter communications on VHF.