We found this circuit in Mullard's 1960s transistor manual. No information about transformers is given. Transistors are germanium types of the time.
In figures 1 and 2 we have two current drains that can be made with operational amplifiers and...
Great sensitivity for the circuit can be obtained with a Darlington amplification step for the...
The used diode is an unusual component today. We found this 12 V regulator in documentation from the...