CTC-19 Lost Brightness, Help!!

[classicradios]

Thanks for the tips Ian,
But I already tried all the things you mentioned. I pulled the chassis last night and spent a few hours checking for loose connections, tubes etc.. No luck at all. Can't see where anything is touching or grounding to cause a problem either. The CRT tests strong and I can get an arch at the cap of the horizontal output tube. I hope it's a simple fix, If I can get the schematic I'll trace the leads from the 3 taps on the brightness control and try to solve the problem. I've tested all the resistors in the high voltage section and didn't find any problems. All bad tubes have been replaced also.
It's a mystery but aren't these vintage electronics always a work in progress?
Jim