This circuit triggers an LED when the input signal exceeds the peak, or the value set in RV1. The transistors can be the modern equivalents BC549.
This circuit is from Popular Electronics from the 90's. The circuit discharges the battery with a...
We found this time base circuit in a timer project from the August 1972 Radio Electronics...
This sonic switch, vox or sonic relay uses a Darlington of the time that has a gain of 10,000. The...