Graham...testing SCRs is easy, do it as below
The +12 needn't be that high, for small SCRs it can be as low as your multimeter on diode test (then omit the bulb as the multimeter will limit the current) as Peter suggests. The light bulb could be a LED and resistor for small SCRs, and RG might be just your fingers across the terminals. The theory is to leave Rg open and you should get no current (ie bulb shouldn't light). Trigger the SCR with a suitable Rg and the bulb should light, even after you remove the Rg. For anything except the smallest SCRs you'd probably need a small 12V bulb, and you'd probably need a resistor as your Rg (try a 1k, but you may need less).SCRs have a trigger current (the smallest gate current that will trigger them ON), and a minimum holding current (the lowest anode current that will keep it turned on). Get these figures from you data sheet and if you can do Ohms Law calculations you can calculate the Rg and anode load resistances. For really big SCRs you might need car headlight bulbs and Rg of 100 ohms or lower, but for your little SCRs you would only need smaller components.On your SCR CP106D, trigger current is 60-200uA, from 12V that's about 200k or less. You just might do this with wet fingers. Holding current is 5 mA, not sure if the diode test range on a multimeter will supply that much, but a LED with a 1K resistor would do.
