[Amps] Glass failures Chinese tubes

[Tom W8JI]

> could see the glass softening around the anode seal, just 
> because of the conduction up the connecting stem, 
> especially if the glass was lower melting point and the 
> cooling inadequate.
> 73
> Peter G3RZP
>

Peter,

Don't let yourself get trolled OM.

The glass failures in the Chinese tubes were soft spots that 
sucked in about midway down the side walls. It wasn't 
anywhere near where the electric field would concentrate and 
displacement current through the glass would be high.

A regular propane torch would melt the glass on those tubes. 
I ran a few at 1500 volts dc (no RF at all) and biased the 
tubes at a few hundred watts dc power  and the glass would 
suck right in.

One of Paul Hrivnak's many efforts used a 3-500Z. In normal 
operation a hole would suck right into the glass.
Rich convinced Paul Hrivnak that the problem was a VHF 
parasitic heating the glass (in the middle of the side of 
the envelope no less) so Paul Hrivnak
"nichromed it up" in an attempt to stop the powerful 
glass-eating parasitic that could never be seen or measured.

The same tubes kept right on failing.

Anyone who knows anything at all would know the major RF 
displacement current stresses are not out in the side of the 
envelope, they are around the seals.

By the way, the same tube manufacturer actually glued the 
anode stem connectors on the tubes! I sent a few dozen back 
because the set screws in the connectors would not tighten, 
and they came back glued!

73 Tom