>
>It has always appeared to me that normal well documented arcs
>and sparks in tubes have been used to sell nichrome.
>
Tom -- My position has always been that unless gas is subsequently found
with a high-pot., an arc is not logical. Tom's answer is that the gas
disappeared because of gettering. Is gettering very likely while the
tube is being removed from the amplifier for high-pot. testing?
>Terry's amplifier very well could have been the victim of just such a
>common effect, but since it is not nearly as well publicized outside
>engineering circles as parasites it is overlooked.
>
Barnacles that disappear?
'
>Actually the arcs stem from several causes,
Experience has taught me that when a sentence begins with the word
''actually'', it is a tipoff that a load of codswallop could be coming
down the chute. .
> and with enough
>accumulated impedance in the HV system they can damage tubes
>and other components.
Does this make sense?
>
>One problem is outgassing (the non-animal kind).
zzzz
>The materials
>inside tubes release tiny amounts of trapped gas, and this can
>cause an arc inside the tube.
>
How many arc marks have you seen inside tubes, Tom?
>A second is seal leakage (again not the animal kind). The bond
>between metal and glass or ceramic isn't perfect, and sometimes
>slight leakage occurs.
>
If this was the case, would not one find gas immediately after an
arc/big-bang.?.
>The third is dielectric failures or contamination of the tube by
>materials floating around inside.
>
Apparently in zero-g environments.
.
>A fourth problem is barnacles or whiskers. "Barnacles" grow on
>copper (I'm not sure about other materials) when it is in a vacuum.
Trying to grow vac.-cap. Cu-barnacles in a vacuum tube is a laugher. .
>
>All of these problems, if not severe enough to ruin the tube, are
>cleared or temporarily cleared by arcs.
>
>Let me give an example of how bad this problem is. Almost 70
>percent of some new tube types arc on initial turn on, or just after
>initial turn on.
>
>In the early 1970's I manufactured 50 3CX3000A7 amplifiers, and
>virtually 100% of those PA's faulted in the tube after HV was
>initially applied. I knew that because the supplies were spec'ed to
>have an instant shut down, you could take a grounded screwdriver
>and actually touch the anode and hear a loud "tick" before the
>supply faulted and dumped power into the dump load.
>
>Around the end of Eimac's run of 3-500Z's, I received a batch of 100
>tubes that arced at anything over 8000 volts. They were all bad,
>useless in PA's because peak anode voltage can be much more
>than two times the dc supply voltage under conditions of mistuning.
>
In a SB-220, it was found that the max. mistuning potential at the
Tune-C is c. 20% greater than the anode supply potential.
>Most recently, almost 70 percent of brand new 572B's arc on initial
>turn on or shortly after initial use. About 1/3 never heal, even after a
>period of anode dissipation to activate the gettering agent in the
>tube.
>
>What amazes me is no one, outside of engineering circles, seems
>to know these things happen. When someone gets a normal arc,
Sounds like page 14 of the TL-922's owner's manual. Surely you have
encountered hundreds more '' barnacles'' than any human in history, Tom.
>they blame it on a parasitic.
Your disappearing gas theory does not wash.
>
>
later, Tom
- Rich..., 805.386.3734, www.vcnet.com/measures.
end
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