I'm working a predicta pedestal, which is going fine - re-capped it and replaced most of the resistors and some of the tubes - more tubes to come. The contrast control has almost no effect though, so I was wondering what might cause that.

The CRT is a 21FDP4 which tested OKish - I had to renovate the filament though, and the tester manual says that contrast is one of the things to go on well used CRTs.

I guess I should also check that the pot is OK.

Anything else I could look at?

Apparently tuning it in properly helps a lot!