[Amps] Arc distance

[Will Matney]

Ian,

My reference is the Radio Engineers Handbook by Terman. I have several other books here on getters, but I'd have to dig them up to get the names and authors.

Sure, "full of hydrogen gas" wouldn't happen in a split second, nor would it really fill up the tube. Really, I should have said it would have hydrogen gas in place of O2, etc. in some quantity. After the tube was operated over time, more hydrogen would escape. The kicker is, the anode coated with zirconium would actually absorb hydrogen gas while it was heated at 300 deg, but when it started getting over that temperature somewhere, it would start liberating it at operating temperature. It's an oddity in that type of material. 400 deg C would be where the anode would start to show red color in a dark room from heating up. Terman says you need two different pieces of zirconium heated at two different temperatures to work correctly. Accordingly he says, tantalum would be a much better, but more expensive choice. This is in the vacuum tube section of the book under the title "Getters". I have the 1st edition, but it should be in all of them I would think.

Best,

Will

*********** REPLY SEPARATOR  ***********

On 7/29/06 at 5:28 PM Ian White GM3SEK wrote:

>Will Matney wrote:
>>>>Getters like zirconium
>>>liberate
>>>>hydrogen gas when heated above 300 deg C, and start working around
>700-800
>>>>deg C to absorb O2, CO2, CO, etc. The optimum temperature is said to be
>>>1400
>>>>deg C. Tantalum though does not have the problem of emitting hydrogen
>gas
>>>>and its optimum temperature is around 1000 deg C if I recall.
>>>>
>>>Overnight I remembered some older correspondence about this. Because
>>>getter materials mop up different gases at different
>>>temperatures, some transmitting tubes have multiple getters at different
>>>locations, possibly using different materials as well. For example, the
>>>3-500Z has getters located at the base of the grid and the base of the
>>>filament, as well as the big one sprayed on the anode (information from
>>>an Eimac tube designer).
>>
>>
>>Ian, correct, that's the only way it could have ever worked. Zirconium 
>>on the anode only would have left a tube full of hydrogen gas. 
>>Something else had to be heated up to collect it. In some ways, 
>>hydrogen is worse that the other gasses because of the speed in the 
>>ions it creates.
>>
>
>What is your reference for the behavior of various getter materials as a 
>function of temperature, Will?
>
>"Full of hydrogen gas" would be an exaggeration, but I see the point 
>you're making.
>
>
>
>-- 
>73 from Ian GM3SEK
>http://www.ifwtech.co.uk/g3sek
>
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