One of the triode time relay circuits

One of the triode time relay circuits

It uses triode control. According to the component parameters shown in the figure, the delay time is about 40s, and the error
does not exceed 2s.
    When the power is turned on, the transistors VTi ~ VTa are turned on one after another, the relay KA is closed, and the load circuit is turned on. Once the charging of capacitor C3
is completed, all transistors are cut off, KA is released, and the load circuit is cut off. The process from KA suction to release is
the delay time. Thermistor R. It plays a role in stabilizing the work of VTi.