This oscillator version is from an RCA documentation from the 1970s. Transistors support modern equivalents and the power can be supplied in a voltage range of 5 to 12 V. For Q2 we suggest the BD136.
The gain of the Operational Amplifier in the figure is given by the ratio between R1 and R2. In...
In the figure we have an interface using an optical coupler and the comparator LM339 or any...
This circuit uses two JFET such as the BF244 or BF245 and has an excellent gain with small...