Found in a 1967 Electronics World, this preamplifier uses an integrated circuit from that time, difficult to obtain today. The maximum frequency is 15 kHz.
This circuit is from a 1995 Electronics Now. The sensor is a 10k to 220k NTC. R2 must have the...
This circuit adds the voltage from the secondary of a transformer to an outlet connected to the...
This circuit of 1965 documentation makes use of a tunnel diode to retard a pulse without...