This is the typical audio amplifier for a 1967 television. We found it in a magazine from the time. Note the use of the output transformer and the high supply voltage. The circuit is an RCA CTC21.
This circuit uses a PUT, a component not very common nowadays. Its purpose is to provide an...
We found this configuration in a documentation for radio amateurs from 1974. The circuit can be...
In the figure we have the simple way to obtain an integrator with an operational amplifier of type...