http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=2184578382&category=3638
is that a cover glass or is it shot?odd way to crack.

No cover glass, it's shot.
You can see the white getter in one picture.

All metal cone picture tubes use a separate safety glass. This includes round & rectangular b&w types as well as color types.

It's amazing how thin the screen is on these tubes!

I have an article somewhere about them, apparently they are made from very precise tempered glass.

The article touts their lack of distortion compared to conventional tubes, as well as their very light weight.

The tube on eBay is pretty rusty, I wonder if corrosion is what cause it to crack, or perhaps some temperature extremes in that attic?

Eric,

The glass faceplate in those tubes is under compression at the edges, which greatly increases its strength and makes possible the use of such thin glass. The first tube of this type was the 16AP4 introduced in 1948. By 1952, 27" rectangular tubes with a metal cone were in production (27AP4 & 27MP4). :cool:

Bill, interesting, I didn't know they went that big!
I have one set with a 16AP4 (I got a NOS one from eBay)

They seem to have disappeared suddenly like the Dinosaurs though.

Was it just easier to make glass tubes at some point, or maybe the shock factor had something to do with it ;)

Seems like the weight savings would have been worthwhile in itself.

Originally posted by Eric H
. . . I didn't know they went that big! . . . They seem to have disappeared suddenly like the Dinosaurs though.

Eric,

Surely you haven't forgotten Du Mont's round metal 30BP4, used in the Royal Sovereign! :eek:

I have a book on picture tubes that states the metal tubes were easier to manufacture on high speed machinery, had lighter weight, and were expected to cost less. The cost saving did not materialize, and once the all-glass rectangular tubes were being produced in quantity, they were cheaper to make than the metal ones. :(

Originally posted by wvsaz
Eric,

Surely you haven't forgotten Du Mont's round metal 30BP4, used in the Royal Sovereign! :eek:


I remember though I've never seen one in person :(
There is a picture on Steve McVoys Site:

http://www.earlytelevision.org/dumontra118.html

I suppose it's fortunate they went to glass since most rebuilders won't touch a metal tube. also because of the sealing problems, though that doesn't seem to affect the B&W tubes.