[Amps] more on rebuilding glow bottles

["John T. M. Lyles" <jtml@lanl.gov>]

Rebuilding a tube 'usually' entails more than recarburizing the 
filament. I don't recall any of ours being just re-carb'ed without 
being opened up and inspected.

The grids often need to be replaced due to high primary or secondary 
emission, from being coated during operation.They can sometimes get 
rejuvenated by running them with grid dissipation but not always. 
Sometimes there are holes in the grid from arcs from anode towards 
cathode. Sometimes the grid is warped. Sometimes there is a G1 to 
cathode short due to a loose wire.

Anode is also inspected for melting, arc craters, signs of electron 
beam cutting, unusual grain growth in the coppper. They cannot be 
reused indefinitely.

Perhaps some companies are just re-carb'ing tubes for rebuilds, but I 
would hope that they are charging a lot less than 40% of the new cost 
for just that service.

For reasons which Ian pointed out, and from experiences I have had 
with the same, it is not wise to cut and rebuild glass tubes unless 
there is an extreme need or cost is no object. In our case, the 
Machlett tubes were sold to Eimac, and discontinued from production. 
Only way to survive with them was to try to rebuild some duds or 
redesign the circuit. They ran with 90 kV of plate voltage, as a 
switch for the mod anode on a megawatt klystron.

I am not sure why Econco didn't rebuild Cermelox RCA designs, but 
maybe due to complexity, or the lack of oxide cathode knowledge for 
that design?

73
John
K5PRO
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