This circuit is from a Radio Electronics from February 1959. The circuit has a speaker output and good sensitivity. Power is supplied from a 9 V battery.
This sequential circuit appears in other versions on this site. This is from American...
Suggested by a 1965 Electronic Design, this circuit has a gain of 15 dB at 45 MHz and can be...
Using 5 transistors, one of which is a unijunction, this circuit was found in Radio Electronics magazine...