[Amps] Glass Power Tube rebuilders

[Ian White, G3SEK]

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.

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