This 1924 receiver uses a battery for the tube filaments and a high voltage battery for the amplifier and detector circuit. The speaker is kind of high impedance era.
Capacitance to voltage converter (CB6075E) This Texas Instruments circuit can be used on a...
The signals from this circuit obtained from the 1965 Radio Shack documentation are picked up from...
Found in Popular Electronics from the 1980s, this circuit uses two operational amplifiers from...