Differences in 21FBP22 CRTs

[Tomcomm]

I'm running a 21FBP22 crt in my reactivated (not restored) RCA 21CT55. The matrix has been changed to the original CT-100 original I / Q chroma demodulation system from the 21CT55's R-Y / Q system. Color Bars reveal that the RED and BLUE are acceptable, but the GREEN is very much yellowish green. This causes YELLOW to be more brownish yellow.

I've got a second 21FBP22 that I think came out of my Dad's Zenith. It has a definite muddy green inactive phosphor tint where the present 21FBP22 is almost white or very slightly grey. I think its OK, but the neck pin cap is shattered and leans to one side so I can't slide the yoke and stuff over it. Maybe this CRT has better GREEN? Does anyone know anything about this CRT? I'd like to know more about this "greeni-roundi" before I go further...Tom

[RetroHacker]

That muddy green color is probably the tinted/frosted faceplate/safety glass, bonded to the face of the tube. FJ's have a bonded faceplate, that sometimes develops mold or gunk underneath it, leading to what has become known as picture tube "cataracts". The 21FBP22, however, has no bonded faceplate, and was intended to be installed in sets that have safety glass in front of the tube already.

Now, if you got your first FJP from a picture tube rebuilder, then it might be missing it's bonded faceplate. On most non-Zenith tubes, the faceplates come off when it's heated enough, which is a part of the rebuilding process. The faceplate isn't really needed, so probably gets left off a lot (AFAIK). Cataracts on these tubes is cured by carefully heating the faceplate with a heat gun to soften the glue, getting it off, cleaning off the glue, and taping the faceplate back on with packing tape along the edges.

Zenith tubes, OTOH, have a bonded safety glass that's affixed to the tube with something that doesn't really respond to heat. They tend to get a "green halo" when the bonding agent deteriorates. I think the procedure for removing the faceplate from one of those involves nichrome wire and a car battery.

-Ian

[bgadow]

Here is a good old thread that will give some information:

http://www.audiokarma.org/forums/sho...d.php?t=105491

[3Guncolor]

There were a lot of sets that used the 21FBP22 with the same faceplate that would be bonded to the 21FJP22 they just used a gasket to hold it in place. I really don't think any rebuilders would leave off the face plate / safety glass on a 21FJP22.

[Tomcomm]

Both my 21FBP22s have no safety glass, so the screen color is due solely to the phosphor. Both are original RCA, not rebuilds. The only numbers I could find were on the pin-caps: the gray screen that's installed has two gray and one green phosphor dots #N JE63619 while the green screen in attic has two green and one bronze phosphor dots #L GA45493. Both are aluminized. Do the cap numbers mean anything? I can slide the yoke over the greeni's broken pin cap so I can repair it with JB Weld then wrap it with thin plastic wrapping tape and try it in the 21CT55. I would still like to know the detailed differences in phosphor between the two.....Tom

[andy]

...

[bgadow]

Sometimes you can scavenge one from an old picture tube brightener.

[old_tv_nut]

Originally Posted by Tomcomm

Both my 21FBP22s have no safety glass, so the screen color is due solely to the phosphor. Both are original RCA, not rebuilds. The only numbers I could find were on the pin-caps: the gray screen that's installed has two gray and one green phosphor dots #N JE63619 while the green screen in attic has two green and one bronze phosphor dots #L GA45493. Both are aluminized. Do the cap numbers mean anything? I can slide the yoke over the greeni's broken pin cap so I can repair it with JB Weld then wrap it with thin plastic wrapping tape and try it in the 21CT55. I would still like to know the detailed differences in phosphor between the two.....Tom

This would indicate that phosphor formulation was changed without changing the tube type number. The green-green-bronze tube undoubtedly has an all-sulfide screen. Not sure about the other one - can you find date codes on the tubes?

see
http://www.audiokarma.org/forums/sho...d.php?t=105491

[sampson159]

whichever one you dont want,i will take!!!!

[Tomcomm]

I hobbled-up the Green CRT with the CTC2B chassis and checked it out. It's GREEN color bar seemed slightly more vivid then the Gray CRT but the RED color bar seemed slightly less vivid then the Gray. Both produced virtually the same quality pictures. I'll probably run with the Gray and keep the Green as backup. Only numbers were on the pin cap and I assume they were serial #:
Gray- two gray dots and a green #N JE63619
Green-two green dots, and a bronze #L GA45493.
Seems the Gray is a later number? The May,1961 21FBP22 RCA data sheet indicates all Sulfide Type, aluminized. Is there some CRT guru that can decipher the meaning of the SR# and screen # on the Green CRT?

[old_tv_nut]

The 21FBP22A (note the "A") had a vanadate rare earth red phosphor, according to an old paper in the IEEE Transactions on Broadcast and Television Receivers. Might your "gray" tube be a 22A?

[Tomcomm]

The Greeni 21FBP22 is definitely the older (lower SN) of the two and red stamped "21FBP22" on its pin cap. Its tri-dots are two green and one bronze, the red one. RCA data sheet identifies the 21FBP22 as all sulfide. It seems the majority of 21FBP22 crts screens are green, only a few are gray. Is this your impression also?

My gray is newer (higher SN) but has no type stamped on its pin cap, only its SN. Its tri-dots are all gray. Does anyone have a verified 21FBP22A? What color is its inactive screen?

I tend to agree with Old TV Nut, my newer, unmarked gray crt may possibly be a "rare-earth" 21FBP22A?? The picture quality of both 21FBP22.. are very good, but the gray will stay mounted in the 21CT55 as I start aligning the dynamic conversion system, hope its not that painful.....Tom