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.
We found this preamplifier for recording heads in a 1980s documentation. The circuit can be used...
An advanced motor control software plug-in for Microchip’s MPLAB® X Integrated Development...
This circuit is from Delco Radio found in a 1968’s documentation. The transistors are of the time...