This circuit was found in a 73 magazine for radio amateurs from the 90s. The circuit uses high voltage transistors and the relay is high voltage as well.
This circuit sensor is an NTC with a resistance of the order of 2k. The SCR can be from the TIC...
The load current can be adjusted up to about 1 A. The transistor can be TIP32 or TIP42. The...
This oscillator with common general-purpose transistors appeared in Radio Electronics magazine in...