>>>So then if all of the tube isn't evacuated, none of it is evacuated.
>>>
>>The evacuated space acts as one entity. The space is pretty well
>>evacuated and sealed at manufacture. If a glass to metal seal has a
>>microscopic imperfection, the vacuum fades as air invades.
>>
>Right. In other words, the entire tube inside the glass is "evacuated"
>space. So the glow from the beams striking the glass envelope is in the
>evacuated space.
no. The glow is from within the glass.
>Other people have pointed out that if the tube is gassy
>I would see the blue glow *inside* the anode assembly.
Seeing inside the anode is difficult. The glow I see is typically in the
space between the lower outside of the anode and the grid or screen
collet.
> In other words
>look in between the holes in the plates and see if the blue glow is in
>there. This explanation made the most sense to me.
>
>So there is no difference between one area inside the tube and another in
>terms of the vacuum. Either it's all gassy or it's got a good vacuum.
>
semi-yes. Less than 10 or so uA @ 8kV of cold leakage in 3-500Z means
the vacuum is good enough. However, new ones often measure less than 1uA
@ 8kV.
>Perhaps we are saying the same thing and I am misunderstanding what you
>were saying...
>
>>>But you said that one blue glow is from electron beams striking the
>>>envelope. The other is in the "evacuated space." How do I know which
>>>from which?
>>>
>>By observation.
>
>Well, since the glow from electrons hitting the envelope does occur
>inside the evacuated space, it's kind of confusing by your definition. I
>think what you are trying to say is that if the blue glow happens at the
>surface of the glass envelope, then it's not a problem. If the blue glow
>happens in the middle of the free space inside the tube, then it's gas.
>
yes
Rich...
R. L. Measures, 805-386-3734, AG6K, www.vcnet.com/measures
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