This circuit uses a feedback integrator. We found it in Ferranti's transistor manual from 1974. Transistors are general-purpose types at the time.
This circuit is from 1998 documentation. The coils consist of the number of turns indicated on...
This shield circuit was found in an American publication from the 80's. The triac is of low...
This amplifier with gains between 5 and 100 was found in the May 1988 issue of Radio Electronics...