This receiver was found in a Popular Electronics from the 90's. Its different configuration shows a tuning circuit after the tube that works as an aperiodic amplifier. Observe supply voltages.
This traditional configuration of astable was found in a 1965 documentation. Transistors can be...
This variable frequency oscillator generates signals that have a recurrence frequency determined by...
This is an old circuit, using operating equipment of the time, modern operational amplifiers can...