If this method to restore emission is to work, how do you keep the filament
from burning up and the acetylene gas from igniting while in a non-vacuum
filament on time? What`s the rest of the story Mr. Measures? Jim.
----- Original Message -----
From: "R.Measures" <r@somis.org>
To: "Ian White, G3SEK" <g3sek@ifwtech.co.uk>
Cc: <amps@contesting.com>
Sent: Saturday, June 05, 2004 3:46 PM
Subject: Re: [Amps] Glass Power Tube rebuilders
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.
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.
cheers
>
> And then it takes extraordinary skill to re-join large-diameter,
> thin-wall glass tubing without losing the whole thing. Glass cannot
> be welded like metal - the two melted faces have to be pushed together
> and then pulled apart again, while very gently blowing into the tube
> to prevent the glass from sinking inward. It all has to be done on the
> fly, with an amazing combination of boldness, delicacy and feel for
> 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
> with the top and bottom ends of the tube aligned just right. Therefore
> the tube will never have the same electrical characteristics as
> before.
>
> The very best you can hope for will be like Nature's repair to a
> broken bone - never exactly the same as it was before.
>
>
> --
> 73 from Ian G3SEK
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>
>
Richard L. Measures, AG6K, 805.386.3734. www.somis.org
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