We found this circuit in a 1964 Electronic Design. It provides 0.5 V signals from 4 kHz subcarriers. Transistors are from the era.
This high quality circuit with complementary symmetry was found in an Electronics World of 1966....
This circuit was obtained from an American documentation from the 1980s. The T1 triggering...
This circuit appeared in a noverber 1962s Practical Electronics. The magazine is no more, but the...