Found in a 1924 Gernsback publication this circuit uses 4 batteries for power and loop antenna. Listening is over a high-impedance type earphone or loudspeaker common at the time.
This circuit was obtained from General Electric documentation from the 1980s. FET operations are from...
This circuit is from an American documentation from 1976. The FET can be the BF245 or MPF102 and...
This amplifier has a few Watt output, using old transistors. The speaker is 45 ohms, but with...