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 circuit is from an English publication from 1965. The transistors used are rare, however, they...
This low voltage circuit was found in the November 1960 Radio Electronics magazine announcing new...
We found this circuit in a 2003 publication. The indicated coil is for capturing the signals in an...