What problems are you having on pin 8 exactly. to start, once everything is wired in take a reading from test point 1 to ground. try to get it around the 430R of the original schematic by adjusting the pot. if you can’t get it to that point then something is wrong. also do you still have it wired with the elevated heater voltage because that will throw off your reading. cut the wire between pin 7 and 8, and see if you are still having voltage issues.