I have some questions and thoughts about roundies.

[oldtvman]

I will be 60 on Nov 5th, and I alos can remember seeing color when my dad took me to a tv store somewhere in South Bend. That image was embedded in my memory and even though I was only about 8 or 9 I was hell bent to have a color set in our house. I guess the round tube sets help revive that magical time when color seemed about as probable as Flash Gordon landing with Dr. Zarkov.

I was surprised to find other people just like me that had the same experience.

[compucat]

Although color tv was not completely unknown to me, I had never seen a roundie until 1974. It was in my grandparents house. It was a 1965 Zenith console, the same model that I have although not the same set. I was fascinated by the screen shape as all I knew were rectangular sets. I never forgot it and have wanted one since that time. I only have one such set, but one is enough for me as they require a lot of space and are expensive to restore.

[Carmine]

As was mentioned earlier, the extra difficulties with convergence and pincushion presented by a rectangular tube were the reasons the first color sets were round, not an inability to blow a rectangular glass funnel. As for hiding 'easter eggs', I am sure they didnt. . remember, there were millions of B&W rectangular sets watching. I dont know when the technology for adding that garbage came along, but I dont recall seeing it until the eighties.

[Kiwick]

Originally Posted by Carmine

As was mentioned earlier, the extra difficulties with convergence and pincushion presented by a rectangular tube were the reasons the first color sets were round, not an inability to blow a rectangular glass funnel.

I think a rectangular screen's surface is "spherical" just like a round screen's one... the only real difference is the shape... early rectangulars also had more or less the same curvature radius as roundies...

actually, one could say that a 21 inch rectangular screen is just a cut out section of a larger 21 inch round screen

i don't think the difficulty into making a rectangular screen is a matter of pincushion corrections, it's more likely a matter of easier shadowmask and phosphor dot screen construction...

The real challenge with pincushion correction and convergence came out with 110 degree color CRTs, earlier 90 or 70 degree tubes were much easier to drive... and for this very reason many late cheap sets are going back to 90 degree CRTs...

[old_tv_nut]

Originally Posted by Kiwick

I think a rectangular screen's surface is "spherical" just like a round screen's one... the only real difference is the shape... ..

True in part, but there are a whole bunch of considerations -
Corner convergence;
Bulb strength;
Corner purity - which is related to brightness gradation:
To make obtaining purity easier, the shadow mask holes (or equivalently, the black matrix holes) were made smaller towards the edges. This was done so strongly on some rectangular designs that people complained that there was a bright area in the center of the picture (this was not a sharp-edged area, just the gradual variation from center to edge). Due to the lack of low-frequency response in the human visual system, you can get away with some of this, especially when the picture is viewed up close - but from far away it's more noticeable.

Later tubes were designed with flatter faces, making all the problems more difficult.
By that time, stripe screens had replaced dot screens, allowing self-converging yoke designs. Since vertical beam angle does not affect purity on a stripe screen, that degree of freedom can be used to help get convergence, and the convergence circuits can be eliminated.

[Kiwick]

Some early 70s 110-degree In-line CRTs like Toshibas, the GTE-Sylvania Uniline, and the Philips 20AX weren't self converging, they still had convergence coils on their necks and required a convergence circuit with lots of adjustment knobs just like delta gun CRTs...

Self converging "Precision in line" tubes (RCA) which were the first to do away with any kind of convergence circuit in the mid-late 70s, had a finer stripe pitch in the center of the screen, and a quite coarse pitch at the sides, unlike earlier inline CRTs which had a constant stripe pitch all over their screen

as for bulb strenght, the real challenge was posed by early 110-degree B/W CRTs, as the flatter bell and increased vacuum would put a lot of strain on the edge of the screen, so early 110-deg tubes were very fragile and dangerous, but by the time the first 110-degree color CRTs came out in the late 60s, the "tensioned rimband" integral implosion protection had already been invented.

In fact, a good CRT (both 90 or 110 degree) with a serious tensioned rimband is extremely safe, and does away with the need for bonded lenses or separate safety glasses... actually, you can't get one to implode even if you smash it with a hammer... it will just break where you hit it and quietly lose the vacuum through the hole.