Re: [Amps] more on rebuilding glow bottles

[R.Measures <r@somis.org>]

\
On Jun 7, 2004, at 10:11 AM, John T. M. Lyles wrote:

> 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.

  John --  The tubes you use at work are somewhat different than the 
tubes used in Amateur Radio.
> 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.

  Re-builders / re-carburizers charge c. 50% whether any repair is 
needed or not..  In some cases, a new Svetlana tube is less than the 
cost of a rebuild.
> 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.

  I have never heard of any re-builder doing such with glass tubes.

> 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?

  As I understand it strontium / barium oxide cathodes are not 
refurbishable because the emissive layer is bonded mechanically, not 
epitaxially.

cheers, John. 
 
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