Regen receivers of the past.

[Reece]

A very popular set in the early twenties was the Radiola III two-tube, one stage of regenerative detection and a stage of audio. The III-A added two more tubes and could drive a speaker. I have a III from 1924 and it easily picks up anything an ordinary superhet can all over the eastern U.S. at night with just fifteen feet of wire. It doesn't like too much antenna which tends to load it down and keep it from regenning.

There are countless versions of regen circuits and much written about them. They were popular with amateurs even into the 1930's due to the great sensitivity possible with few components. The touchiness in operation can be reduced with proper shielding and often a regenerative detector tube "likes" a particular B+ voltage for smooth operation: often voltages from 12 to 22 volts work better than higher voltages.