brightening CRTs

--- David Griffith <dgriffi at cs.csubak.edu> wrote: There are numerous ways of brightening old CRT's, all having to do with the filament. Some people "zap" the filament with a sudden jolt to "revive" it, others raise the operating filament voltage, and another trick is to run the tube's filament at a higher than normal voltage for several hours, to "cook" it. Basically, you're trying to get the filament to have a higher electron emission by stripping off the coating of old material. Cooking the tube overnight seems to work pretty well - just hook up a small AC transformer or DC suply of a volt or two more than the tube's filament (for a 6.3 volt filament, try 7 or 8 volts). You might need to build something to supply that voltage. Unhook the tube's neck connector, and connect the wires directly to the filament pins of the tube (aligator clips and tape or something), and run the filament at the higher voltage for a while (this is where a variable DC bench supply comes in handy). Be careful not to burn out the filament. Try it for a few hours, then see how it works. I've heard of people cooking tubes for a couple days (really weak ones) and had them come back well. Another thing I have found is that sometimes if a tube sits for a long time, it will be dim at first, then begin to "wake up" after just letting it run. You might try this first, just turn on the terminal, leave the contrast all the way down so it doesn't burn, and let it run all day. That might even be enough to improve emissions. This is typically something I see on really old TV's though, don't know if a fifteen year old terminal is old enough to have sat long enough to do that. But before you go to the tube brightening stage, I'd look at the terminal. There might be a pot you can adjust inside, or possibly even a bad component causing this - It seems as if I have seen a couple Wyse terminals with this type of failure - might not be the tube. Good luck. -Ian