[AMPS] Rocky Point effects

[measures]

>
>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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