This circuit was found in a Popular Electronics from the 90s. The frequency is given by R2 and C1.
In the figure we have the circuit of an amplifier for alternating signals with 10 times gain,...
Frequencies up to just over 100 kHz can be obtained with an oscillator based on one of the four...
With this circuit it is possible to regulate a source of up to 9 A using 3 LM350. The integrated...