[miniman82]

The only thing I can think of that might have gone wrong is a hot spot on the glass, a consequence of building the tube incorrectly to begin with. If the flames are kept on the glass for too long during an operation like neck welding, the glass becomes very brittle and subject to fracture. This can be seen with a polarimeter, the glass will have a blue band around it. Can't be sure what the cause was, since I hadn't done anything to it between the time it was last used and now. It just sat up here in the apartment, no one even touched it. I suspect this is a fatigue fracture, caused by repeated heating and cooling of the area around the weak glass. The heaters were supplying the heat, and it looks like it gave way at the hottest spot- right above them. If RACS can rebuild this, it would be a simple job. Just neck glass and a gun, but I hesitate because dot plates have broken in the past and these are more fragile than a 15GP22 because the internal structures are different. A 15GP22 has a lightweight frame holding the mask and plate in alignment, and because it's light it gains or looses heat relatively fast. The proto tubes on the other hand have a heavy metal block between the dot plate and mask, meaning they have much more thermal mass. I will have to ask Filipe what he thinks about giving this a go, it's a long shot at best.