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Author Topic: How to getter a 3-500 tube  (Read 59253 times)
N2EY
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Posts: 5096




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« Reply #45 on: October 04, 2011, 05:25:00 PM »

I do not remember if the 3-500 is a conventioal alkali earth getter or if the anode may also be working as a sputtering pump when heated.

IIRC:

3-500Z has a zirconium-coated anode which does the gettering.

833A has a zirconium-coated anode, plain old 833 has a tantalum anode.

The 4-xxxx series of glass tx tubes, from 4-65A to 4-1000A, have anode getters but I don't know if they did the same no A = tantalum, A = zirconium thing.

Such anode-getters must be hot to work; this is why it is a good idea to rotate which tubes are used if you have spares.

It is also why it can be a bad thing to run those particular tubes far below rating - say, 250 watts input to a tube capable of 1000+. While it might seem that doing so would give incredibly long life (as it can with receiving-type tubes), the actual result can be shortened life due to no gettering because the anode never gets hot enough.

---

There was an article in QST for October, 1936 describing a 1 kW input tx that used 8 Eimac 35T tubes plus an 80. 35T crystal oscillator, 35T buffer/multiplier, push-pull 35Ts in the final. 2500 volts 400 mA! (though they usually ran them at 1500 volts 250 mA - "only" 375 watts).

The other four 35Ts were used as grid-controlled rectifiers, which permitted keying the B+.

Wanna bet those 35Ts were well gettered? With the wide open breadboard construction, cooling and seeing your way around the shack wasn't a problem...

That the authors were W6UF and W6CHE may have influenced the tube choice.



73 de Jim, N2EY       
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AG6K
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Posts: 1




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« Reply #46 on: October 05, 2011, 05:23:10 AM »

The info provided by WX7G is what I was looking for.  The plate voltage at 500 volts isn't enough to cause the gas to arc.  So I assume the tube plate will get real hot, getter the gas and then when put back into service it should not arc.  Is this a fair assumption?
 

  Since the leaky seal that allowed air to enter the envelope in the first place is still leaking, it is a fair assumption that air will continue to enter.  Rich, ag6k


Quote
Thanks for the information Dave, that was what I wanted to know.  Lou
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G3RZP
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Posts: 1321




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« Reply #47 on: October 05, 2011, 05:51:07 AM »

When a 35T dissipated 35 watts, you almost could see to read by the light! Same with some 24G. Great stuff, tantalum.
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AG6K
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Posts: 1




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« Reply #48 on: October 05, 2011, 09:42:45 AM »

When a 35T dissipated 35 watts, you almost could see to read by the light! Same with some 24G. Great stuff, tantalum.

 Indeed.   Tantalum (Ta) has such a high melting point (2,996°C) that it can be used for filaments in light bulbs.   cheers,  Rich
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GM3SEK
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Posts: 99




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« Reply #49 on: November 07, 2011, 07:41:16 AM »

I do not remember if the 3-500 is a convential alkali earth getter or if the anode may also be working as a sputtering pump when heated.

IIRC:

3-500Z has a zirconium-coated anode which does the gettering.


The 3-500Z actually has three different getters, operating at different temperatures in different parts of the structure.

The following procedure (copied from the AMPS archives) came directly from a former Eimac tube designer, who was with the company when they were still manufacturing glass tubes.


<quote>
*************************

If a tube was last used years ago, or was manufactured years ago, or is new, it's safest to assume it needs gettering. And the suggested routine is this:

Cooling is of course required throughout.

a.  Bring the filament up to rated voltage slowly.  For example, run the primary of the filament transformer through a light bulb, or similar to limit the shock of turning it on.

b.  Then after some time, bring the voltage to the specified value, and run it for about 100 hours.

c.  Then, apply the anode voltage through some current limiting means for a while, and, finally,

d.  Run the tube at a dissipation level near the specified limit for a few hours.

The reason for this is that the getter needs to experience a spectrum of temperatures, mopping up different species at different temperatures.  Furthermore, the lowly 3-500Z for example, has getters at the base of the grid and the base of the filament as well as sprayed on the anode.

While this conditioning schedule is seemingly over-complicated and ultra-conservative, it should result in no surprises when putting the tube into service.

Terms like "a few hours" are vague because different tubes require different treatment.  If we're "burning in" a monster tube that will cost us $50,000 to replace, we're going to be more conservative than with a $50 tube.

***************************
<end quote>


73 from Ian GM3SEK
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AG6K
Member

Posts: 1




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« Reply #50 on: November 07, 2011, 08:53:09 AM »

I do not remember if the 3-500 is a convential alkali earth getter or if the anode may also be working as a sputtering pump when heated.

IIRC:

3-500Z has a zirconium-coated anode which does the gettering.


The 3-500Z actually

  a key-word, N.B..

Quote
has three different getters, operating at different temperatures in different parts of the structure.

The following procedure (copied from the AMPS archives) came directly from a former Eimac tube designer, who was with the company when they were still manufacturing glass tubes.

  Ian: what is the name of this tube designer?  tnx

Quote


<quote>
*************************

If a tube was last used years ago, or was manufactured years ago, or is new, it's safest to assume it needs gettering. And the suggested routine is this:

Cooling is of course required throughout.

a.  Bring the filament up to rated voltage slowly.  For example, run the primary of the filament transformer through a light bulb, or similar to limit the shock of turning it on.

b.  Then after some time, bring the voltage to the specified value, and run it for about 100 hours.

c.  Then, apply the anode voltage through some current limiting means for a while, and, finally,

d.  Run the tube at a dissipation level near the specified limit for a few hours.

  How was it  that this critical information got left off of not only Eimac's Tech Data sheets for the 3-500Z , but it was also left off of all other Eimac glass-envelope tube data sheets?

Quote
The reason for this is that the getter needs to experience a spectrum of temperatures, mopping up different species

  now there's a new one. 

Quote
at different temperatures.  Furthermore, the lowly 3-500Z for example, has getters at the base of the grid and the base of the filament as well as sprayed on the anode.

  I've not seen any other substance on the grid of a 3-500Z that I have autopsied. 

Quote
While this conditioning schedule is seemingly over-complicated and ultra-conservative,

  to me this important  revelation is a tad suspicious due to its tardiness.

Quote
it should result in no surprises when putting the tube into service.

Terms like "a few hours" are vague because different tubes require different treatment.  If we're "burning in" a monster tube that will cost us $50,000 to replace, we're going to be more conservative than with a $50 tube.

  "Monster" tubes have built-in ion pumps.  Rich, ag6k

Quote
***************************
<end quote>


73 from Ian GM3SEK

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