The circuit is from a June 1995 Electronics Now. The relay is power-dependent and both R1 and R2 should have close resistances in operation.
We found this 4W transmitter in a Mullard transistor manual from 1960. The circuit is powered by...
The response curve of this circuit has a maximum boost of around 6 kHz. The vertical scale is in...
Using the 555 this circuit was found in a Popular Electronics from the 90's. The circuit directly...