Double button microphone preamp (T352E)

This circuit was obtained in the 1937 RCA tube manual. Tubes are well known types that can even be obtained today. The power source is not given.

NAB Preamplifier (CB846E)
This preamplifier is intended for the use with magnetic pick-ups. Power supply must have voltages...
Power Outage Alarm (CB5952E)
We found this circuit very simple in an old documentation. The relay is high voltage sensitive, but...
Three Transistor Voltage Regulator (CB986E)
TR1 must be mounted on a heatsink in this circuit. Voltage output is 8.6 V but this value can be...