This circuit was found in a Signetics documentation from the 1980s. The integrated is a PLL and the SCR is a general purpose type The pitch frequency is given by R1 and C1 as formula next to the diagram.
With this circuit it is possible to measure RF signals with a common multimeter. Signals up to 200...
Also suitable for use as a noisy alarm, this Morse Code or telegraph practice oscillator was found...
We show in the figure how to implement a current monitor circuit using only an operational...