7jp4 crt and phosphors

[Tom Albrecht]

Although it is easy to make white light green with a filter, it is not at all straightforward to make green light white with a filter. White light contains lots of wavelengths in a mixture, and the filter removes all but the green. But to fill in the missing wavelengths to make white out of green? Not straightforward at all.

I would not expect a red filter to make a good black and white picture out of light emitted from green phosphor. It must be really dark indeed.

The real solution for now is to simply recognize that there are far more TVs out there looking for a home than there are collectors to take them. If you're willing to buy a distressed set with a 7JP4 in it to harvest the picture tube out of it (and scrapping the set), you can get one for probably $50 - $100. The odds are that set will not be saved in the long run, so go ahead and get your picture tube out of it. You'll also get a bunch of useful tubes and some other good parts (such as extra HV coils). There are quite a few Motorola VT-71s out there looking for a home, as well as many of its cousins made by other brands.

In my experience, most 7JP4s are reasonably good, with only an occasional one that's simply too dark to be useable. The really bright ones are fairly rare, but that's life.

3KP4s are a bit more problematic, but even there if you're willing to keep your eyes open and buy one or two distressed TV-37s, you'll likely end up with a good tube. I lucked out when I bought a nice one a number of years ago. Original 3KP4 is nice and bright.