This circuit is from a 1976 publication, but it can be assembled with modern components. For the SCR we can use the TIC106 and for the unijunction transistor the 2N2646. The diode can be of any type. We can increase the capacitor C1 to about 2 200 uF and R2 to 1 M to obtain timings that exceed half an hour. The load can be a relay or other low voltage device, in which case B1 must be changed according to the controlled load. D1 is a 15 V zener diode.
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