This circuit was found in a 1964 Electronic Design. The circuit makes use of transistors of the time. Current equivalent transistors may be experienced.
This circuit is used with high impedance microphones, such as ceramic or crystal capsules. The...
Using transistors at the time, this circuit was found in a 1967 Ferranti documentation. The...
This circuit is from an English documentation from 1969. The circuit can be designed based on...