This Japanese transistor radio was manufactured in the 1960s in Japan. The circuit of 6 transistors is for the medium wave range and is powered by a 9 V battery.
This circuit for frequencies from 1Hz to 100 kHz was found in the June 972 Radio Electronics...
This circuit generates short pulses. The transistor can be a 2N2222 or BC548 and the frequency is given by...
We found this filter in a Popular Electronics from 1993. The operational amplifier can be the 741....