As we all know...the 21AXP22(and the "A") is a metal CRT, wherein the neck and screen are glass--but the bell is all metal--and is the anode. MANY BW tubes were this way...but i KNOW that the 15GP22 is glass(most of it, anyway, it DOES have that "flange" behind the faceplate, so it might be considered a "hybrid"), and I KNOW NONE of the color tubes that followed the AXP were metal, the 21CYP22 was glass--and so were all that followed, to the best of my knowledge.

But by the time the AXP was in production--(54-58 or so) metal tubes were already OUT for BW--so WHY was the AXP metal, but not the 15GP22, or any others(AFAIK)?

The 19VP22 was also a tube with metal flange, as were several of the limited version tubes made by Zenith and Philco. But as you mentioned mass-production, I can't think of any others besides the 21A, 15G, and CBS 19V.

There are a few metal-coned projection tubes from the 1980s & 90s, which were used in very high-end big screen projectors.

Charles

Maybe it way a technology they were familiar with at first?

After Corning Glass works developed *devitrifying frit* and the frit-seal process was introduced for the all-glass 21CYP22 (1958), most color CRTs have been assembled in that manner. The frit-sealed glass panel and funnel quickly surpassed a variety of less successful methods of color crt assembly. If this process had been developed a few years earlier, my avatar might be displaying a picture, as the primitive but complicated panel to funnel seals are the main source of leaks in these CRTs.
When RCA went back to the metal funnel for the 21AXP22 the troublesome glass funnel-to flange and panel-to-flange seals of the 15GP22 were eliminated.

jr