This circuit that has a response from 10 Hz to 700 kHz was found in Philips documentation from 1968. Dual transistors can be replaced by matched pairs.
This simple metal detector was found in a 1960 Sylvania transistor manual. The phone must be high...
This is one of the many versions of this type of indicator that the reader can find on our...
Found in an English publication from the 1980s, this circuit can be built with equivalent...