This circuit is from a Radio Electronics from October 1963. The transistor is a power transistor of the time, and two transformers are used. The input has 10k impedance and is powered by 12 V.
This encoded lock circuit with alarm for use in homes was found in a publication from the 90s. The...
The circuit shown was found in the 1994 National Semiconductor Linear Applications Handbook. The...
This circuit is from a 1979 documentation. The FET can be the BF245 or MPF102 and the bipolar...