Is there such a thing as an insulated gate SCR or anything fitting that description?
Electronic – Insulated gate SCR, does it exist
fetscr
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Isn't the current enough? Is it important to have this 0.6V or 1.5V supplied to the gate?
The SCR gate needs 1.5 volts to guarantee a 32 mA drive - the gate has a non-linear input impedance and, as far as I can tell you'll need to account for the 1.5V needed by the device's gate when the gate is drawing 32 mA.
If 32 mA is passing thru the 10 ohm resistor then this means that the input voltage to the left side of 10 ohm resistor is 1.5 volts + 32 mA * 10 ohm = 1.82 volts. If the zener is 7 volt rated then the circuit will crowbar at 8.82 volts.
As an aside - why are you putting a crowbar circuit on a 5V linear regulator like the 7805?
As everyone told you the SCR is not a current amplifier as a bipolar transistor. It is a latch-up component; put enough current on the gate and it will switch on, and it will remain ON until the load current is more than Ih (holding current)
Graph from wikipedia: https://en.wikipedia.org/wiki/Thyristor
Best Answer
Apparently MOS-controlled thyristors were commercially available briefly, but were withdrawn due to performance issues.
The structure looked like this: