Rebuilding electrostatic CRTs

[N2IXK]

Originally Posted by Sandy G

I wonder if that great big, ginormous 30" tube was electrostatic, or magnetic, & if it was, maybe that's why it was so short lived... Always heard those things were kinda primitive & a bit crude, despite their huge sizes...

The DuMont 30BP4 used electromagnetic deflection. DuMont did make electrostatic tubes up to 20", though.

The reason for the short life on 30BP4s was insufficient gettering. The tubes were not aluminized, so getters could only be used in the neck to avoid contaminating the phosphor with patches of barium. Unfortunately, neck getters alone weren't sufficient for a tube with that much evacuated volume and that many linear feet of glass to metal seal to potentially leak air molecules into the tube.

Once aluminized tubes became the standard, additional gettering could be used inside the funnel area to improve the vacuum integrity.

[bgadow]

Good info, N2IXK!

Somewhere I have an old article from Antique Radio Classified (or maybe it was Don Patterson's Radio Age?) about having a 3KP4 rebuilt; this was in the late 80s or early 90s, and the rebuilder was a former DuMont employee in NJ. The gentleman was getting up in years back then.

[Sandy G]

Yeah, Thanks for the info ! I THINK I've seen a pic of the 14" & 20" Dumont tubes... There's a pic from like 1938, w/this rather odd-looking gal sitting on a table, holding the both of 'em up... She's smiling, as if she was BORN to do that, one wonders if she knew how much DANGER she had, mere inches from her face/chest.

[jr_tech]

Like this?


http://www.videokarma.org/attachment...8&d=1301008843

jr

[Sandy G]

Aye-Yoop... Dat be De One..

[N2IXK]

I know a green phosphor 20" tube was used in a classroom demonstration oscilloscope that DuMont sold. Pic here:

http://www.myvintagetv.com/Scope/dum...cope%20233.jpg

[rca2000]

Originally Posted by Sandy G

Aye-Yoop... Dat be De One..

NOT very likely those tubes were evacuated...

[jr_tech]

Originally Posted by rca2000

NOT very likely those tubes were evacuated...

I would hope not, but on the larger tube I think that I see a couple of oval getter flashes on the neck, about an inch above the base cap.

jr

[N2IXK]

How would she even manage to hold on to those tubes like that? They would seem WAY too top heavy to be held vertical from the base end with screen up.

Early "photoshop" job? Or are the tubes actually supported by rods on the backsides of the necks?

[Eric H]

Those are thin glass, so even though large, they don't weigh all that much.

I think they'd have no problem standing up like that if plugged into a socket that was attached to the table, she also has he hands near the base, possibly to stabilize them a bit?

[bgadow]

Looks like they might use a unique base with edge contacts? So the end could be flat, might not balance too bad. The glass does look awful thin, not much more than a big light bulb.

[Dave S]

Originally Posted by wa2ise

Was wondering if a green phosper tube's cathode and other guts could be a doner to rebuild a white phosper tube?

I'm still a 'dumb guy' when it comes to all the hands-on details on this stuff, but as far as I can see there'd be no reason a green tube couldn't be re-phosphored as a white tube. Hadn't thought of that before. Everybody save those dud 3KP1 'scope tubes!

[N2IXK]

Unfortunately, once you let the green phosphor tube down to air to replace the phosphor, the cathode coating is destroyed by contact with the air so the cathode (or entire gun) will need to be replaced, as well...

[timmy]

or we could send a whole lot of crts that need something done to them to outter space with the astronauts and during a space walk they can perform what needs to be done since space is vacuum and upon taking the gun out, well it wont be contaminated. i know its wishfull thinking , lol,lol....

[N2IXK]

Sounds like a plan, but settling new phosphor screens might be a bit of a challenge in zero-G.