The transistor used in this circuit is uncommon today. AC124 or equivalent such as AC188K and 2N2431 can be used. The circuit is from the 80's and makes use of transformers.
This two-stage circuit has a voltage gain of 100 times, with a high input impedance. The circuit is...
Four amplifiers are used in this circuit, which uses a magnetic pickup to obtain the pulses whose...
This simple circuit was obtained in a Portuguese publication in 1979 but can be easily assembled with...