This circuit uses a lamp driven by the Hertz loop and measures its brightness with ordinary photovoltaic cells. The circuit is from a Radio Electronics from February 1964.
This low-frequency oscillator was found in a 1963 documentation. Capacitors determine frequency. The...
This circuit uses a triac to detect the level of a reservoir, and a sensitive SCR connected to the...
Found in a 1964 Electronic Design this circuit compares two signals by providing the inverse of the...