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 circuit of various uses on the bench was found in Radio Electronics magazine from January 1960....
This circuit is from a 1957 Japanese magazine, showing the use of OC19 in a high voltage inverter. The...
The integrated circuit used in this power supply is no longer very common in power supplies today....