[Amps] Glass melting, f, and D-factor

[Steve Thompson]

R L Measures wrote:
> It was previously stated by another denizen that the glass in early  
> Chinese 3-500Zs was melting on the sides, however, according to my  
> notes from Rus Healy, in this case, the glass reportedly softened on  
> the top in an area a couple of cm from the anode stem, a small bubble  
> formed, began expanding inward from atmospheric pressure, and popped.
> end
For clarity - what Rus reported happened to what model of tube made by who?
Did Rus see it himself?
Was it a one off or reliably repeatable?

Thanks,

Steve