I use 5V and the current is limited to about 25 mA with a resistor of 180 ohm and the SCR triggers really good. The voltage at the SCR imput falls to 2Vpp max. Probably it will run OK with less current.

A good and easy way to invert the pulse of a hall device is by using an optocoupler. 4N25 device can do the work, but we're still working on.

Best Regards