[Test-Equipment] tube question

[rbethman]

The modern getters are going to be made of Barium.

That patch on the side of or top of the tube is directly adjacent to the 
getter.  You'll see, (if you look closely.), that the getter has a 
"single" support that is energized at the very last stage(s) of production.

I use one of the Western Electric testers, made by Hickok.  It is a 
KS-16XXXX, ( Don't remember all the numbers.), and I find it does better 
than all the others I've either had or used.

It is usually best to let a tube sit in a tester.  You may even need to 
press the test button for a couple of minutes.  It needs to FULLY heat 
up.  (That would be the elements.)  It will/should begin to feel warm.  
It won't usually be as hot from running for several hours.

The heat takes awhile to get through the vacuum.

Bob - N0DGN

> *
>
> The getter
>
> *
>
> We want a good, hard vacuum inside a tube, or it will not work 
> properly. And we want that vacuum to last as long as possible. 
> Sometimes, very small leaks can appear in a tube envelope (often 
> around the electrical connections in the bottom). Or, the tube may not 
> have been fully "degassed" on the vacuum pump at the factory, so there 
> may be some stray air inside. The "getter" is designed to remove some 
> stray gas.
>
> The getter in most glass tubes is a small cup or holder, containing a 
> bit of a metal that reacts with oxygen strongly and absorbs it. (In 
> most modern glass tubes, the getter metal is barium, which oxidizes 
> VERY easily when it is pure.) When the tube is pumped out and sealed, 
> the last step in processing is to "fire" the getter, producing a 
> "getter flash" inside the tube envelope. That is the silvery patch you 
> see on the inside of a glass tube. It is a guarantee that the tube has 
> good vacuum. If the seal on the tube fails, the getter flash will turn 
> white (because it turns into barium oxide).
>
<snip>
> <snip>
>
> Hi, it could very well be grid contamination.  That shows up
> when the grid is hot.  The grid "contamination" is barium and strontium
> that evaporated from the coated cathode during normal operation.
> What heated up the grid is the "cathode emission" test.  In that test,
> the control grid, screen and plate are connected together,
> and the tube acts as a strange diode.  The tube tester puts
> around 30 VAC across the series combination of the "strange diode"
> a current limiting resistor in the plate circuit, and a 200 Ohm
> "Load" pot in the cathode.  The panel meter is connected as a voltmeter
> connected from the slider of the pot to one side of the pot.
>