This interesting circuit uses a sodion valve that we have already described in an article on the website. The circuit uses several batteries for power. The phone is of high impedance.
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...