Hi, I've been using C106D1, Vmax 400, IE(A) 4, VF(V) 2.2, IG(uA) 200, VG(V) 0.8, Hold In(mA) 3. If u can get an industrial rated C106D1 SCR they r much better quality & have way better thermal characteristics, but just an ordinary old C106D1 will b fine usually. I havent had 1 fail & dont heatsink them. I was going 2 put 1 together over the weekend but the local outlet is outta polypropylenes so it'll b a couple of days. Cheers