With the capacitor used, this circuit provides delays of 40 to 60 seconds. Larger capacitors can be used, and the SCR supports an equivalent. The circuit is from the 1977 RC semiconductor manual.
This oscillator, which can be used as a signal injector, was found in a Popular Electronics from the 90s....
This circuit was found in a Dutch documentation from 1970. The circuit makes use of semiconductors that...
This circuit is from a publication from the 70s, but it can be assembled with any diac and a Triac...