BC-221 Regenerative Receiver Conversion

The BC-221 is a three-tube frequency generator, mixer and zero-beat detector which can be used to accurately determine frequencies.

These days we use digital frequency counters and Si5351s.

So, what to do with your spare BC-221? How about converting it to a three-tube receiver?

The oscillator in the BC-221 is a 6SJ7Y in an Electron-Coupled Hartley configuration.

This schematic (from David Newkirk's website) features a 12SJ7 based regen (a 12SJ7 is the same as an 6SJ7. The 6SJ7Y is a 6SJ7 with a low-loss base). It doesn't take very many changes to change the BC-221 oscillator into a regenerative detector.

I'd leave the audio stage mostly as-is, the 450 Henry inductor will make a good filter.

The third tube can be an untuned RF amplifier and maybe an additional AF stage.

Basic tuning range is 125-250kHz in low and 2-4MHz in high. Coils might need to be rewound for more sane coverage.

• Frank Jones regen