Pye 'Fenman 1' magic eye puzzler

[Yorkie]

Thanks for your helpful tips Steve. I'm coming to the conclusion that it is the valve that's at fault, despite it being an NOS valve some months back, which worked OK when fitted. The heaters are intact and the valve warms up, all the voltages appear correct, and R37 & 38 are fine. C60 was replaced along with all other waxies, but there's not the faintest glimmer from the display.

I'll get on and build the little tester to see what that reveals!