This simple step of low power audio is from a 1975 documentation. The transistor can be a BC548, and the transformer of the type found in small transistor radios and recorders of the time.
We found these circuits in a Popular Electronics from the 90s. The circuit has a simple low power...
This LED diode test is suggested by the Texas Instruments optoelectronics manual. The transformer current...
This RF monitor or field strength meter can use instruments from 100 uA to 1 mA full scale. The...