The transistors of this circuit found in an English 1980s documentation may be the modern BC548 equivalents. The circuit is battery powered and the earphone must be crystal.
Suggested by Sprague in the 1980s documentation, this circuit can control three-phase AC motors....
This circuit is from a 1977 publication for radio amateurs presenting a crowbar protection. The...
The coil L2 has 64 turns of wire 28 or thinner wire in a 1 cm form coreless and L1 10 turns on L2....