This circuit using the CK722 among others came out in a September 1950 Radio Electronics. It was one of the first circuits of this type published with transistors that started to reach the market.
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...