[ohohyodafarted]

Tom,
I have to agree 100% with your thesis about the safety of the FB vs the FJ tube. Upon thinking about the reasoning for the manufacturers to transition from the air gap to the bonded resin face plate, I think this may have been more a mater of not having to clean the dirty inner glass surfaces of the FB type, and less a mater of safety.

Even though the FB type had a gasket at the circumference of the face-plate, it does not create a perfect hermetic seal. The action of heating and cooling the air between the safety glass and the surface of the crt, causes the air to "breath". In a similar fashion, changes in atmospheric pressure will cause the air in the gap to breath. As a result, especially in homes of the 60's when cigarette smoking was still commonplace, that polluted air was drawn into that air gap and could create a film of smoke on the glass surfaces in the air gap.

Manufacturers may have decided that it was time to eliminate the possibility of degrading the image via dirty glass surfaces of the crt by "bonding" the safety glass to the crt face, and thus moved to a bonded configuration. In the end I think this bonding was more about keeping the dirt off of the face of the crt and retaining a factory fresh crt image. This way anyone could take some Windex and clean the face of the safety glass and have a fresh clean image again. There may or may not have been some additional safety attained by the bonding, but it is my opinion that it was more of a selling feature to be able to tell the potential customer the set had a "bonded safety glass" and the picture tube would never need a service call to have the glass cleaned. (though I doubt many people had a special service call for cleaning alone)

But I do remember at least one service tech who asked if mom and dad wanted him to clean the glass (on a B&W set). And when he showed them how much smoke film was on the face of the crt and the inside of the safety glass, mom and dad were astonished. And the picture was visibly much sharper and brighter after the cleaning.