We found this circuit in the October 1987 Radio Electronics magazine. The triac must be controlled according to the heater. The transformer has a low current, of the order of a few hundred mA.
This Japanese radio is from the 60s, presenting excellent sensitivity and an output power of 100mW...
Found in a Popular Electronics from the 90s, this circuit uses components that are still current....
This circuit consists of a simple capacitance bridge. The handset can be high impedance from 500...