Tandy CRT swap

[lnx64]

Not a television, but couldn't decide which section to put this in. Asking for a friend.

He's trying to swap out the CRT to a Tandy 80 model 4, but he can't get an image on it. He has the heaters lighting up, but there's nothing on the screen.

The CRT in the Tandy 80 model 4 is usually a 12VCMP31

The CRT's he's tried are:
1. MN1215H8AU - CPJ310N1U (Two numbers on the same CRT)
2. MP1433H8AU - CPJB340AHE (Two numbers on the same CRT)
3. 310KLMA

He has found that if he puts the Tandy's monitor in where the replacement CRT's are pulled, it produces an image that's far too bright. I was thinking maybe a G2 control on the Tandy's flyback could help? But he says there's no G2 control.

Hopefully anyone can help! Thanks in advance.