VECTOR: Need Help with Electrohome G05 XY monitor

This is kind of an interesting question.  I have two working 15" Electrohome G05 monitors from Asteroids Cocktail games.  One of them had a pretty bad tube so I decided to buy a replacement  from Hawkeye Picture tubes.  It works great except with this tube I can't get the brightness to come down enough.  After it warms up, I can start to see a dot in the middle with retrace lines.  Even when I have both the contrast and brightness all the way down I still get a picture.  I've already determined it's not the EHT or the deflection board because they work fine with the older picture tube.  The voltages are all correct too.

So, my question is, is there a good way to modify the circuit so the brightness voltage (G1 ?)  isn't so high?  Perhaps change the value of R516 or R518?

http://www.arcadehelp.com/manual/monitor/electrohome/G05-802.pdf

Thanks

Matt