This amplifier with the EL84 tube is a European commercial type from Corpim mounted on a printed circuit board. The diagram appeared in a September 1958 Radio Electronics magazine.
Another way to increase the sensitivity of the circuit with the amplification of the sensor...
We found this circuit in the Radio Electronics magazine of January 1986. The frequency is given by the...
This circuit was found in the September 1984 issue of Radio Electronics magazine. The circuit is...