12-volt 1-tube Regenerative Receiver:

    This article first appeared in the Delaware Valley Historic Radio Club's Oscillator.

12-volt 1-tube Reflex Receiver:

    I was so encouraged by the success of the simple regenerative set that I undertook the design of a much more elaborate one-tube set using a "reflex" circuit.  In this receiver the signal passes through the tube twice:  first, as radio frequencies and then a second time, as audio.  Because there is considerable RF gain before the detector, this radio is far more sensitive than a simple regenerative set.
    This is not a project for beginners.  The design employs a lot of hard-to-get and potentially expensive parts, almost enough to build a rudimentary superheterodyne.  You'll probably need a sweep generator to get the tunable band-pass filter working correctly.  You should be prepared to reengineer the circuit to suit the parts on hand.