Operating at a frequency of around 180 kHz, this transmitter was found in a Science & Electronics of 1970. The coil has 34 turns of 22 wire. The transistor can be the 2N2222.
This circuit was found in a 1973s Japanese publication. The power transistors used are of the era...
This circuit from an old 1978 publication uses germanium transistors but can be implemented with...
The figure shows how to implement an amplifier with gain 10 using the operational amplifier LM41....