The SCS, SCR, and PUT are all 3 junction 4 layer devices. The difference is the pinout. The SCS device is 4 pin and can be used anyway. The SCR uses a cathode gate to switch it on and it latches. The PUT uses an anode gate which will turn the device off when not biased. The amp in the previous post is using a PUT.
It is such a small part count I will have to build one. I will use over the counter parts which are readily available. Next post I hope to have a couple screen shots with results and a part list.