Is it worth trying to fix the Ampliphone monitor?
No it's not. Put it in a crate and send it to me so I can finaly build a Vector Mame.

This is one of the best Vector monitors. The CRT has medium resolution, which gives a much smaller dot than the other color vectors. It's also "quicker" than the others. (Higher slew-rate).
You can bet your life on that HVT being dead. At least that's what I read, and that's exactly how mine was.
Even IF it would be working, I'd replace it anyway. You can get a brand new replacement here:
http://www.cinelabs.com/amp/ for just 99 bucks. That's a more than half the price of the other (Wintron replacement) that also needs a lot of re-wiring.
Drop Mark a mail, great guy.
The Amplifone FAQ refered to above is fantastic and helped me understand the workings and how to fix it.
Remember that if the HVT is dead, it took other parts out as well. But these are minor ,cheap parts. Start by visiualy checking the HVT PCB on both sides. Mine had a bad burn on one of the large resistors.
The Amplifone has a bad name, but most of it because of that poor quality HVT. If you follow the Amplifone FAQ, you get a very reliable vector with the best picture possible.
It's great you have that extra box with the WG, so you can test the PCB set separately.
Again, read this:
http://forum.arcadecontrols.com/index.php?topic=68094.0Lot's of references there too, pics and even vid's on YouTube (which are still only an indication of the REAL picture

).