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.
Simple battery tube radio based on the PGSX crystal set.
1-Tube Regen Based on Above