This circuit is from a documentation from the 70s. The circuit uses logic gates of the time, which in many cases were arrays of transistors allowing use as audio amplifiers, as in this case.
Indicated by a Popular Electronics of the 90s originally to measure the light determining the exposure...
Other operational amplifiers series, such as the MC34072, MC34074, MC35071, MC35072, MC35074 d...
Found in American documentation, this circuit shows how to polarize a FET in bootstrap mode. The...