We found this circuit in the 1964 RCA transistors manual. The transistors used are uncommon today, but they can be used equivalent. The circuit controls the operation of a heating element.
In this circuit found in the December 1972 Radio Electronics magazine. R can be from 1k to 22k,...
This circuit can operate between frequencies from 1 to 15 MHz depending on the coil. For 3.5 MHz...
This metal detector circuit uses an AM radio as an indicator. The radio is placed off-station and tuned...