[Milsurplus] How Much Vacuum in "Vacuum Tubes?"

[sdaitch at mor.ibb.gov]

My problem was visualizing all this, in terms of home production 
of tubes, that is, placing the unsealed tube in a chamber, 
drawing down the vacuum, and then trying to seal the tube in
this vacuum chamber.  I could not figure out how to keep
the products of the flame from the interior of the tube,
then it kind of dawned on me, when someone talked about the
breaking the seal on the CRT for shipping.

DING DING, but then I just had to ask to confirm what 
I thought the process was. 

The typical tube with the bakelite base, and more than
9 pins in the subminuture tubes were sealed at the pin
base, while the typical 7 or 9 pin subminiature is sealed
at the top of the glass envelope.

Been away from this stuff far too long.

Thanks,

Sheldon



----- Original Message -----
From: Bob Camp <ham at cq.nu>
Date: Thursday, March 29, 2007 11:24 pm
Subject: Re: [Milsurplus] How Much Vacuum in "Vacuum Tubes?"

> Hi
> 
> That's pretty much it with a couple of refinements.
> 
> The glass pipe that goes from the pump manifold often will have a 
> vac- 
> ion gauge on it. The heat source to melt the "stem" is generally a 
> 
> hydrogen flame. The tube it's self sits in a furnace while this is 
> 
> all going on to bake it out.
> 
> The other stuff that goes on depends on just how the gettering is  
> being done. Different getters are done different ways.
> 
> Bob
> 
> On Mar 29, 2007, at 3:02 PM, sdaitch at mor.ibb.gov wrote:
> 
> > How do you seal the tube while under a vacuum?
> >
> > Is the seal stem itself hooked to a vacuum pump, and when the  
> > vacuum is down to the
> > level desired, the stem is heated by an external heat source, 
> the  
> > stem melts and seals while the vacuum is still being pulled by 
> the  
> > pump?
> >
> > I get dense on what is probably very simple.
> >
> > 73
> > Sheldon
> >
> > ----- Original Message -----
> > From: J Forster <jfor at quik.com>
> > Date: Thursday, March 29, 2007 6:20 pm
> > Subject: Re: [Milsurplus] How Much Vacuum in "Vacuum Tubes?"
> >
> >>  I read a number of articles in old (early 20s and before) radio
> >>  magazines about amateurs making their own tubes. I have a tube
> >> in my
> >>  pile of stuff that looks very crude and crooked inside, not sure
> >> if it
> >>
> >>  could qualify as 'homemade', though.
> >>
> >>  Maybe it gets down to losing skills due to progress and cost? 
> If you
> >>  can buy a new one cheaper, why go through the hassle and all that.
> >>
> >>  ~ Todd,  KA1KAQ
> >>
> >>
> >> Making tubes is not that hard. The first ones were made with the
> >> technology of roughly 100 years ago. If you can work small 
> pieces of
> >> thin metal, blow glass, and pull a vacuum, you can likely make a
> >> decenttube. Getting them to perform better and be consistent takes
> >> moreeffort, but obviously can b done.
> >>
> >> IMO, it may be easier to build a simple tube from scratch than
> >> repairingone with a bad filament. Before my time, MIT used to
> >> teach a 'Tube Lab'
> >> . They published a set of notes on how to do it which make  
> >> interesting
> >> reading.
> >>
> >> Making tubes is certainly practical in a small facility. Not so for
> >> transistors or ICs.
> >>
> >> -John
> >>
> >>
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