Hi #12
I was running this in simulator (Falstad), and after a while capacitor voltage gets to a point where it doesn't move. Is it just simulator or in real world I would see oscillation?

 

I just logged in because I realized that I didn't give the gate enough current to turn on. (I messed up again.) I'm looking at an SCR called S201E. It requires up to 15 ma for the gate to turn on and the hold current is somewhere less than 30 ma. Point is, "somewhere" less than 30 ma. It is possible that the triac needs 15 ma to trigger and if the hold current is that low, it will be stuck on.

That's why diacs were invented. The typical diac does not pass current until it has about 32 volts across it, then it collapses and lets a surge of current start the SCR.
Lets try a different way.

ps, please forgive my sloppiness. This circuit is so fundamental that I assumed I remembered how to do it.

 

#12

Thanks for your help. After googling I found another circuit which achieves what I wanted. It was using positive feedback to discharge capacitor to start cycle all over again.