Any use for 21FBP22 with poor emission?

[jhiesey]

When I got my CTC-10 set from Maguns at Stellar Electronics, he told me that the CRT (a 21FBP22) was in ok but not great shape, so he sold me an extra 21FBP22 as a spare.

I finally got around to testing the emission on both CRTs, and found the one that came in the set was pretty poor, while the spare was much better.

Just for the heck of it I bought a brightener for $10 and tested it out with the old CRT, and it did help quite a bit. But I did decide to put in the fresher tube anyway, especially since I wanted to install the safety glass that was missing when I got the set. The picture looks much better!

At 6.3V on the filament, using -50V on G1 and 50 microamps at cutoff and 0V on G1 for emission, I got the following test results on the old tube:

Red: cutoff -285V, emission 575 microamps
Green: cutoff -382V, emission 382 microamps
Blue: cutoff -315V, emission 460 microamps

Especially the green gun looks very weak (the spare tube measures almost three times better emission on all three guns, and consistent cutoff voltage on all guns of around -275V). Boosting the filament voltage up to 9V does improve the emission on the old tube significantly.

Is the old CRT a candidate for rejuvenation? Would anyone want a tube like this?

Or should I just recycle it?

[rld-tv01]

Where are you located. I have a CTC5 in Southern California with a necked 21axp22. I believe the 21FBP22 could be rejuvenated since it has a vacuum. I think it could also be substituted for a 21axp22 with some modifications to the sets circuitry.

[old_tv_nut]

21FBP22 can be subsituted for 21AXP22 with only mechanical adaptation - no circuit changes are needed. I ran one in my CTC5 for a long time until I found a good 21AX.

[Electronic M]

I keep the weak ones that are under vacuum. If there ever is rebuilding at the ETF having a tube that is under vacuum and you know has no dead phosphor and a good shadow mask (I've seen ones that got knocked loose) is the only safe dud to gamble rebuild money on. Also if you ever are given a necked console and need to sell it a weak tube that makes a picture is a heck of a lot better for making it sell.

[madlabs]

If the pic is OK with a brightener on the weak tube, I would use it until the picture sucked and then pop in the fresh one. Waste not want not!

[Electronic M]

Originally Posted by madlabs

If the pic is OK with a brightener on the weak tube, I would use it until the picture sucked and then pop in the fresh one. Waste not want not!

+1

I rode the weak jug in my Zenith 29JC20 till it took 30min to warm up to a bright balanced/stable color picture...soon I got to find time to swap it to the better CRT or throw a brightener on and use that to set guns to hyper-dead.

[Steve D.]

I have a CTC-5 Wingate Deluxe chassis model. It has a 21FBP22A/21GUP22 replacement tube. Fortunately it has an RCA metal to glass tube mounting conversion kit. This allows the installation of the new tube to the existing mounting receptacles w/o using the 21AX plastic shield. The original yoke was retained.These kits are extremely hard to find and other various homemade mounting hardware has been used for installing later model 21" round tubes.

-Steve D.

[old_tv_nut]

The plastic shield for the 21AX fits its cone-shaped metal bell, but not the bulge of a glass tube. On my CTC-5, I made mounting hardware out of a combo of threaded rods, with hinged brass connectors to connect to the CTC-7 harware straps. I removed the edge magnets.

By not doing any major mods to the cabinet, and saving all the 2AX mounting pieces, I was able to restore it all when I finally got a 21AX.

[jhiesey]

Originally Posted by rld-tv01

Where are you located. I have a CTC5 in Southern California with a necked 21axp22. I believe the 21FBP22 could be rejuvenated since it has a vacuum. I think it could also be substituted for a 21axp22 with some modifications to the sets circuitry.

I am located in San Francisco. If you'd like the 21FBP22 and are willing to pick it up I'd be happy to give it away!

[jhiesey]

OK I'm definitely going to keep the tube for someone who wants it.

A few more things about it: the base is cracked and a bit loose. I attempted to fix it a while ago with some epoxy, but it came loose again when I disconnected the socket to test the emission and put on the brightener.

Here's the label on the tube:


Does the "RE" indicate it was previously remanufactured?

[Tom9589]

RE indicates that it has Rare Earth phosphors. On the left side of the label it states: "Grade AA- Description -All new components and materials." Definitely not a rebuild.

[Electronic M]

High temp automotive silicone caulk seems to be a good way to reattach the base. The heaters won't degrade it as readily and it has some flex absorb force to prevent cracking loose under mechanical force.

[rld-tv01]

Thanks Jhiesey. San Francisco is a little over 800 miles round trip from my place so I'll have to pass. I'll probably drive to ETF in Ohio this year so maybe I'll find a CRT there. I got a Muntz 721 CTC5 a couple years ago for free. It was sitting outside for some time so the cabinet needs a lot of work.