Re: [Amps] Glass Power Tube rebuilders

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

On Jun 5, 2004, at 11:56 PM, Ian White wrote:

> Hello R. Measures

ï  Hello, Mr. White
> > On Jun 5, 2004, at 1:27 AM, Ian White, G3SEK wrote:
> >
> > > John T. M. Lyles wrote:
> > >
> > > > The problem that I have experienced with rebuilders is that they 
> > > > haven't been able to get the glass in sizes that used to be common, 
> > > > i.e., a blank in the size of a 3-1000Z diameter, from Germany 
> > > > (Shott?).
> > > > So they have attempted in some cases to re-seal a cut tube, using 
> > > > standard glass tooling/lathes, etc. The yield can be awful. I had a 
> > > > lopsided Machlett MIL LPT-44 triode made. Another one woudn't seal.
> > >
> > > The basic problem is that cutting the tube apart destroys the very 
> > > precise alignment between the anode and the grid/cathode cage.
> >
> > Ã  To restore the emission of thoriated tungsten filament,  glass 
> > envelope tube, the vacuum pump connecting tube is opened, acetylene 
> > gas is introduced, the filament is lit, and tungsten di carbide 
> > slowly reforms on the surface of the filament.  When a sufficient 
> > layer has been formed, a vacuum pump is connected, the vacuum is 
> > restored, and the pumping tube is melted closed.  Thus, there is no 
> > need to cut the tube apart.
>
> John was clearly talking about other problems where there *was* a need 
> to cut the tube apart.

ï  It's probably easier to melt a hole than to cut the glass.
> Even cutting the base seal and re-attaching a pumping tube is very 
> difficult, because it involves using open flames close to all the 
> glass/metal seals.

ï  Open flames already were used to seal the pumping tube after 
evacuation.
> All in all, rebuilding glass tubes is a very high-risk operation, and 
> the possible returns are at the low end of the market. Small wonder 
> that it's rarely done.

ï  Apparently it isn't anymore, Ian    cheerz
> --
> 73 from Ian G3SEK
Richard L. Measures, AG6K, 805.386.3734.  www.somis.org

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