This two-tube circuit, one being a double, was found in Radio Electronics magazine from July 1958. The distance to the microphone depends on noise and losses. The cable must be shielded.
This reaper has the signal limit determined by the zener voltage. We found this circuit in a 1980...
This unity gain circuit was found in the February 1995 Electronics Now magazine. The frequency is 10 kHz,...
This reinforcing stages from a 1960s documentation. No information is given about the transformer...