[Amps] Glass Power Tube rebuilders

[R.Measures]

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=20
>> haven't been able to get the glass in sizes that used to be common,=20=

>> i.e., a blank in the size of a 3-1000Z diameter, from Germany=20
>> (Shott?).
>> So they have attempted in some cases to re-seal a cut tube, using=20
>> standard glass tooling/lathes, etc. The yield can be awful. I had a=20=

>> lopsided Machlett MIL LPT-44 triode made. Another one woudn't seal.
>>
>
> The basic problem is that cutting the tube apart destroys the very=20
> precise alignment between the anode and the grid/cathode cage.

=F0  To restore the emission of thoriated tungsten filament,  glass=20
envelope tube, the vacuum pump connecting tube is opened, acetylene gas=20=

is introduced, the filament is lit, and tungsten di carbide slowly=20
reforms on the surface of the filament.  When a sufficient layer has=20
been formed, a vacuum pump is connected, the vacuum is restored, and=20
the pumping tube is melted closed.  Thus, there is no need to cut the=20
tube apart.

cheers
>
> And then it takes extraordinary skill to re-join large-diameter,=20
> thin-wall glass tubing without losing the whole thing.  Glass cannot=20=

> be welded like metal - the two melted faces have to be pushed together=20=

> and then pulled apart again, while very gently blowing into the tube=20=

> to prevent the glass from sinking inward. It all has to be done on the=20=

> fly, with an amazing combination of boldness, delicacy and feel for=20
> the material.
>
> (I used to watch it being done... you can probably tell.)
>
> It's impossible to do all that necessary manipulation, and wind up=20
> with the top and bottom ends of the tube aligned just right. Therefore=20=

> the tube will never have the same electrical characteristics as=20
> before.
>
> The very best you can hope for will be like Nature's repair to a=20
> broken bone - never exactly  the same as it was before.
>
>
> --=20
> 73 from Ian G3SEK
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>
Richard L. Measures, AG6K, 805.386.3734.  www.somis.org