This utilitarian-looking three-tube British device appeared in Practical Wireless 75 years ago this month, January 1949. It has considerable utility, as it functions as both a regenerative receiver and signal generator.

The regenerative receiver, of course, causes oscillation that can be radiated through the antenna jack. But this circuit does one better, because it turns the audio amplifier into an oscillator, which modulates the signal. Therefore, when working on another piece of equipment, you have a handy source of tone modulated RF. And when you’re done troubleshooting your other device, you can tune in programs from 3000 to 10 meters. Thanks to the second harmonic, you can use it as a signal generator up to five meters.