1949 DuMont - issues when turned on cold

[bigaudioal]

Originally Posted by Gleb

What happens if you try to force brightness while the TV is 'cold'? If the picture degrades, looses focus, turns into a negative, then the CRT seems to be weak. If the picture fades and grows in size, it points at the weak HV rectifier tube. If nothing happens, i.e. the control just doesn't increase brightness as it supposed to, then the problem is somewhere else (the brightness control itself, the video amplifier, power issues, etc). Good luck!

The brightness control functions properly, even when the set is first turned on and you can barely see the picture. Along with the brightness slowly coming up to full when set is turned on cold, the vertical takes time to fill out as well.

This set has dual HV rectifier tubes. I will try swapping them tonight and see if condition changes.

Thx.