... tell me about it; that's why I always had to *improvise, or borrow (scrounge) someone else's test kit.
But, if we are starting with "essentials" here, obviously the first thing you need is something to quickly show if the tube is actually exposing (that is, producing the magic rays). A bit of intensifying screen from an old film cassette should do.
Anyway, Good Luck.
By the way (as you may have already learned), the travelling x-ray service engineer also needs to carry a step-ladder!
*
Which is not always a bad thing, as it forces you to "get back to first principles".
