This 3-tube receiver is from a 1924 publication. The circuit has 3 supply voltages and a high-impedance headphone output.
The operational amplifier 747 is old, no longer being used, but the configuration is valid for...
This circuit, from an American publication from 1971, generates a 25 Hz sinusoidal signal. Note...
In this circuit, from a 1977 publication, we have the traditional version of a filter tuned to 1...