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Tube construction materials

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I have been wondering what impact using various materials in the construction of tubes has on the performance of those tubes. I have seen ads for expensive tubes that boast various materials, but I know nothing about what effect those materials have on the functionality of the tube. For example, I have seen gold plated grids, carbonized screens, and various plate materials. What do these buy me?

If anyone could point me in the direction of some literature on this subject I would appreciate it.
 
What got me interested in this was that I was considering buying some new Genalex KT-88s. I was trying to figure out if it was worth it, as I already have EH KT-88s which look very similar.

The Genalex ad states that they have a gold plated grid, carbonized screen, and a tri-alloy plate.

I confirmed with a guy at New Sensor that the EH KT88 has a gold plated grid and carbonized screen as well. He basically said that any competently designed power tube would have these.

The plates also appear to be of the same material. Grey on the outside and shiny on the inside. Well, at least I think it is from the folded out part on the outside of the plate support posts. It makes no sense to me that the inside of the plate structure would be a shiny surface. Seems like this would inhibit heat transfer to the plate. I have yet to dissect one, though so I don't know if it is shiny on the inside for sure. Maybe just parts are clear nickel to aid in welding to the posts or something.

From reading 'Electron Tube Design', it seems like the two plate materials that would be best for power tube duty would be carbonized pure nickel and alitized aluminum clad steel. The trade-off would be that carbonized nickel can radiate heat slightly better, but alitized plates are easier to de-gas so you could get a better vacuum. If I were the designer I would probably sacrifice some radiation efficiency for a harder vacuum and then add some metal to spread the heat around a bit as New Sensor has done.

Anyone ever dissected an old GEC KT-88 or a New Sensor KT88 and care to share the details here?
 
The problem would be getting a good contact between a steel anode and nickel lead out wires; I don't think you could weld them.
I would think the anode will normally be shiny on the inside, otherwise you'll have an unevan surface on which the electrons will fall, and two metal layer with different work functions, possibly leading to secondary emission problems. Plus you don't really want to radiate heat 'inside' the anode tube!
 
I have a few power tubes here that I dissected; a GE 7591, Tung-Sol 6AR6, and a Cetron 7384. All have darkened coatings on the inside of the anode.

I would think that a dark coating on the inside of the anode would be advantageous because it would allow the anode to more readily absorb radiated energy from the grid, screen, and cathode. This would cut down on grid and screen emission. Just as black is best for radiating heat out of the anode, black is best for absorbing heat from the tube internals. A mirrored finish would keep all that heat bottled up.

Has anyone dissected a tube with a shiny inner surface on the anode? If so, was it a high power tube?
 
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I'm curious, but don't have a lot to add unfortunately. I do know that multi-layer plates are not totally uncommon.. I have taken apart a couple of power tubes in the past that were at least 4 layers. (Can't remember what they were..) Not shiny inside either, but the beam forming electrodes were..
 
Same here. I'm currently looking very hard at dropping the couple of hundred dollars on a quad of those KT88 Gold Lions, and I can't bring myself to believe they're made of any special magic mojo that makes them better than EHs or JJs.

The only things I've got that imply they're better are a small body of anecdotal and subjective evidence, and a higher price.

Of course, the Gold Lions have an illustrious history, nice boxes, and pretty silkscreening on the tubes themselves... but if the guts are precisely the same as something you can get elsewhere, I'm not interested in paying 100% premium for a nice box and good name.

The implication that I've read so far here is that the things listed in all the ad material about the Gold Lions - gold plated grid wire, carbonized screen, alloy plate structure - aren't at all special.
 
I recently had more contact with the New Sensor guy. I asked him point blank what the differences were. He basically said that more care was taken in the construction and materials were better, but he didn't say in what way. He also said that geometries are different between the EH and Gold Loin; that the new Gold Lion copies the geometry of the original. However, it obviously doesn't copy the shape of the plate. Not a big deal to me, I think that New Sensor's plate design looks pretty beefy.

He also indicated that there was more care taken in the construction of the Gold Lion tubes.

I'd still really like to dissect some of the best tubes from the past and compare to these new ones.

There's no reason that somebody shouldn't be able to make a tube superior to the tubes from 50 years ago, as long as they're willing to take the time to make it right, but it won't come cheap. I just hope that's what these are, tubes that are built to a higher standard. I don't mind paying a lot for something that is a significant improvement.
 
Honestly geometry has more effect on the properties of a tube and how it performs then the type of metal used. As far as what properties are wanted in metal is a high melting point but not conductivity, highly conductive metals have low melting points by the way.

You will find non ferrous metals and alloys as iron typically outgases in a high vacuum under heat.

Nine time out of ten aluminizing is a zinc coating or it can be aluminum which doesn't work as well for corrosion resistance.

Metals used internally in tube construction are but not limited to tungsten, tantalum, Nickel,zirconium , Gold and Graphite. There are metals used in coated cathodes that I didn't mention though which is mostly barium compounds too.

You find more refractory metals used do to there ability to handle high heat. I'm sure there are things I missed so if anyone can think of any other please feel free to add to the list.


And if there is some tube parts you really want to know what they are you can mail it to me and I can analyze it and tell you exactly what it is via xray energy dispersive spectroscopy or xray fluorescence. If you want to do this you can pm me.



Hope this helps

Nick
 
The inside of the anode would/should be coated with a material to suppress secondary electron emission. This would also ge a good treatment for thescrren grid, and in extreme circumstances, the control grid. This is one reson for gold-plated grids.

In reply to another post, zinc would most likely be a material absolutely verboten for inside a vacuum tube due to the high operating temperature and zinc's high vapor pressure (relatively speaking). It is certainly on the do-not-use list for UHV systems, especially where some sort of bake-out scheme is employed to ge rid of occluded gases.
 
SpreadSpectrum said:
For example, I have seen gold plated grids, carbonized screens, and various plate materials. What do these buy me?

Gold and carbon have very high work functions. These materials help suppress grid emmission, which causes bias upsetting currents, and is generally bad news. There are various exotic materials used for plates. These have a gettering action when hot to help preserve the quality of the vacuum. Most plates also receive an oxide coating to help suppress secondary emmission. This is why you'll find shiney plates with very low voltage VTs designed to operate from "B" batteries, where the voltages aren't high enough to cause much secondary emmission, or very high voltage types (CRTs and CRT main supply and focus diodes) where coatings won't do any good anyway.
 
Spreadspectrum you can send me a email at "(deleted- use email button)"


Pm is the little button on the bottom left side of peoples posts and there doesn't seem to be one on mine for reason I don't know because I have it enabled.

But anyways drop me a line at the above email address and we can see about getting some of your stuf analyzed.


Nick
 
Nick, I enabled your "email" button. It keeps your address secure unless you respond to any emails you receive. I edited out your email addy from your post since the bots can harvest even the way you had it worded.

If you want to disable the email button, you can do that from your user control panel.
 
SY said:
Nick, I enabled your "email" button. It keeps your address secure unless you respond to any emails you receive. I edited out your email addy from your post since the bots can harvest even the way you had it worded.

If you want to disable the email button, you can do that from your user control panel.


Thanks SY that was a quicky yahoo addres I created just for th purpose of posting but the latter is much simplier in the long run.

I wonder why it wasn't enabled in the first place. I looked in my use setting on the forum and it was enabled, weird.


Well works now thanks.

Nick
 
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