> 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
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