Found in a 1949 Radio Electronics, this 4-tube circuit was fed directly from the mains with a half-wave rectifier.
Here is a simple source without a transformer for currents up to 50 mA. The voltage depends on the...
We found this circuit in an old QST magazine. The circuit is powered according to the thermostatic relay...
This simple field strength meter is from a transistor book from the 60's. The transistor is made...