TV Treasures

[Jeffhs]

Originally Posted by Tubejunke

It looks quite a bit bigger than a 19" to me. There were some large round tubes made, mostly used by DuMont. The 19AP4 does seem to get a bad rap. I wonder if other metal/glass crts are as troublesome. The issue is vacuum loss at the seam. If that were the case they all would be trouble.

I wonder why they ever made the metal tubes.

I once had a Majestic TV (1951 model) which had a round 16GP4 CRT (metal cone). Never had one bit of trouble with the tube losing vacuum or anything else. Also, I did not realize that round CRTs had seams anywhere in or on them; in fact, I don't recall seeing a seam anywhere on the 16GP4 in my set. (I learn something new all the time reading the posts in these forums.)

Round metal-cone CRTs: I agree with you one hundred percent. Those tubes worked well enough, but the metal cone created the heck of a HV shock hazard, as I think the cone was one half of an HV filter capacitor, the bell of the tube being the other (this technique, IIRC, replaced doorknob HV caps in many if not most 1950s sets with round CRTs). IMHO, the best thing ever to happen to television CRTs was when the manufacturers gave up on metal-cone tubes and switched to glass exclusively, which all but eliminated the shock hazard.

[Eric H]

Originally Posted by Jeffhs

I once had a Majestic TV (1951 model) which had a round 16GP4 CRT (metal cone). Never had one bit of trouble with the tube losing vacuum or anything else. Also, I did not realize that round CRTs had seams anywhere in or on them; in fact, I don't recall seeing a seam anywhere on the 16GP4 in my set. (I learn something new all the time reading the posts in these forums.)

The metal cone tubes have a seam where the glass face is bonded to the metal cone, they also have a seam where the neck is joined to the other end of the cone.
That said I have a 50+ year old 16AP4 that is still holding vacuum as was the worn out tube it replaced.
I think the bigger tubes (19", 24" 30") probably had more problems because of the larger joint surface and the extra expansion contraction problems.

The metal tubes don't hold a charge on their own but I guess you could still get shocked with the set off if the doorknob cap was charged up.