The WR/7AU7-80 Regenerative Receiver

Figure 0—The WR/7AU7-80 regenerative receiver covers the Morse-code-friendly portions of the 80-, 40- and 30-meter amateur radio bands with the help of SA602/NE602-based 40- and 30-meter converters built in Wrigley's gum cans. Aside from its inability to serve as a monitor for the transmitted signal (as a result of detector overloading due to the difficulty of shielding the detector against strong-signal ingress), the WR/7AU7 is entirely practical for two-way Morse code amateur radio communication.

Figure 1—Front view of the WR/7AU7-80 regenerative receiver for 80 meters. The front-panel rotary controls are, from left to right, are FAST TUNING [FT], REGENERATION, and SLOW TUNING [ST]. The toggle switch selects L (LOW, approximately 3470–3538 kHz) and H (HIGH, approximately 3533–3601 kHz) tuning ranges. The ST control varies the tuning about ±2 kHz from the center frequency set by FT. The WR/7AU7-80 is a variation on the 40-meter Watch Receiver scaled to 80 meters; the detector is a 7AU7 dual-triode synthetic tetrode Hartley, and the circuit's grounded-grid RF buffer and AF voltage amplifier triodes comprise a 6C8G dual triode. The utility audio amplifier/filter box brings the WR/7AU7-80's audio output up to headphones or speaker level. The big cans shield the set's vacuum tubes.

Figure 2—View inside the WR/7AU7-80 receiver tuning head showing the trimmer and tuning capacitors, tuned-circuit inductor, RANGE switch, and REGENERATION control. The soldered-on box cover has been temporarily removed.

[to be continued...]