[Amps] 3-500Z problem

[Richard]

>Hi amp fellows,
>
>I have NIB 3-500Z Eimac tube, manufacturing date seems to be 9640,
>as written on the envelope.
>
>The anode and the cathode/grid cylindrical assemblies are not perfectly
>coaxial.
>Looking at the anode bottom, the anode is closer to the grid for one
>it's side
>than the opposed  one with about 3 mm, so the the distance between
>the anode axis and grid/cathode axis, at the bottom part of the anode is
>
>to about 1.5 mm.
>
>This should affect the anode to grid/gnd breakdown voltage.
>About a similar problem I have read in the RadCom (dec '98).
>
>Anyone having experience or using 3-500Z or ZG's with similar problem?
>
This problem is caused by bad spot-welds on the anode cooler.  When such 
a tube is used, heating/cooling causes the welds to slowly weaken and 
break.  Triton, the company that bought Eimac's glass tube division 
reportedly made the same mistake -- i.e., not using enough current to 
make the spot-welds.  Chinese 3-500Zs do not have this problem.  
Graphite, instead of spot-welded metal, anodes do not have this problem.  

cheers, Traian

-  R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K, 
www.vcnet.com/measures.  
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