On 7/24/06 at 7:48 PM Tom W8JI wrote:
>Will wrote:
>
><It's impossible to run one temperature on zirconium.
>
> I guess Eimac is lucky they quit making 3-500Z's, since the
>gray power on the anode is the getter and it is zirconium.
>
>
>>By the way, Terman on page 187 of my Third edition warns
>>about excessive resistance in grid leads. Terman states, "
>>If the resistance in the grid circuit is high enough, this
>>process can become cumulative, resulting in the control
>>grid
>>potential suddenly becoming positive and causing the
>>**destruction** of the tube as a result of excessive plate
>>current."
>
>Will wrote:
><<Nowhere in the whole paragraph about gassy tubes (Effect
>of Gas upon Tube Characteristics) which is under part 13,
>page 316 in this book, says a grid became positive! It only
>says this can cause a grid to become "less negative"!>>
>
>The text of the page in the third editon of Terman is at
>the bottom of:
>http://www.w8ji.com/fusing_and_floating_grids.htm
>
>Anyone who wants can look and see what it says for
>themselves.
>
>73 Tom
That's slightly re-worded from my edition as he never mentions positive.
However, what he's meaning about positive, and he aludes to this in other parts
of the chapter, is really the grid being less negative or more positive as
compared to another element, so it will accept electrons. It does not mean the
grid has become positive or more that 0 volts. This get's right back to the
explanation about the space charge, etc. Even after the grid gets more positive
than it once was (still negative with respect to ground or at 0 volts), and is
loosing electrons, they are being replaced by ones it's taking from the
electron flow from the cathode. I read the whole paragraph on gassy tubes, and
that's all it means. He would have caused less confusion if he had never
re-worded the text in that edition. I hope everyone with the 1st edition reads
this, or gets that edition to read. You'll see the explanation and what he
meant in it.
>
>
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Best,
Will
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