This circuit was found in a Motorola documentation from 1975. Modern equivalent transistors such as the BF245 can be used. The circuit is powered by 9 V voltage from cells or batteries.
In the figure we have a simple way to produce tone in a piezoelectric transducer. The frequency depends...
This absolute value amplifier was found in a 90's EDN. Equivalent amplifiers can be used. The...
The integrated circuit used in this configuration for noise reduction on FM radios is not common...