12UP4 condition

[cluelessgame]

Originally Posted by EdKozk2

I was able to get the brightness control to vary the crt's brightness. I disconnected the existing crt filament leads from pins 1 and 12. I then taped them off. Then connected a 6.3 volt ac @ 600ma transformer to the filament pins. The existing brightness wire on crt pin 11 is unsoldered, then connected to pin 1 or 12. This was an easy to be able to vary the brightness on a most likely broken internal cathode connection. Thanks again jr_tech. The filament transformer output leads can not be grounded, it should float. I tried this with a 6 volt battery, a 6 volt dc wall wart and even a 7.2 volt dc wall wart. All of the filament sources worked. The higher voltage produced a brighter picture of course.
Ed

does this mean you're turning the filament into the cathode itself?
I may have to try this with the 21ZP4 in my Admiral. I think it has the same issue

[EdKozk2]

Originally Posted by cluelessgame

does this mean you're turning the filament into the cathode itself?
I may have to try this with the 21ZP4 in my Admiral. I think it has the same issue

I would have to say yes to your question. The method I used is basically the way a battery operated tube radio from the old days was wired. Only this method must be isolated or you will burn the crt's filament. Also note that if you have your video and brightness being input on your cathode this may not work. The Zenith set I have has the video on grid #1 of the crt.
Ed