Continuous switch with transistors (NOT gate loop)
There is the Uni-junction Transistor like(2N2646) configured as a Relaxation Oscillator. The timing can be set with emitter side components using the usual RC time R/C calculations for output load controlling the on/off stages. The time period of the oscillation T2 and the discharge time T1 can be configured with components but you have to make sure that the resistance is not too high or too low or the oscillation or trigger will not happen. Schematics can be found for these. Good luck.