This resistance meter was found in an English documentation from 1989. The operational amplifier admits an equivalent and the transistor can be a BC558 or BC559.
This is the circuit published in the August 1973 issue of Radio Electronics magazine announcing its...
This circuit can be used to add a delay to a logic signal as shown by the input and output...
This tone control was obtained in the Audio Handbook of the National Semiconductor of 1977. The...