This circuit was found in a documentation of the 80s, having didactic purpose. For R1 values between 10k to 1M can be used. Transistors are general purpose types.
The oscillator shown in the figure can generate signals between approximately 3 and 15 MHz,...
This circuit uses unusual operational amplifiers, but equivalents can be tried. FETs can also be...
In the figure we have the circuit of a clamp-type microammeter described in the Radio Electronics...