Tube construction materials

[SpreadSpectrum]

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.

[SY]

For a amateur-level overview, Robert Tomer's book "Getting the Most of of Vacuum Tubes" will explain a lot; it's available on-line. So will Morgan Jones's "Valve Amplifiers."

For a more advanced treatment, the RCA classics "Electron Tube Design" and "Vacuum Tube Design" are available at Pete Millett's site:

http://www.pmillett.com/technical_books_online.htm

[SpreadSpectrum]

Thanks Sy,

I got 'Electron Tube Design' and it looks like exactly what I was looking for.

[SpreadSpectrum]

Well, this reading brings up another question. Is the typical gray colored plate coating alitized aluminum cladding on a steel plate?

[HollowState]

Another interesting read is the Eimac book "Care And Feeding of Power Grid Tubes. Some pdf links can be found here.
http://www.coutant.org/eimac/index.html

[Merlinb]

Originally posted by SpreadSpectrum
Well, this reading brings up another question. Is the typical gray colored plate coating alitized aluminum cladding on a steel plate?

The anode is usually nickel, as are most of the chunky parts inside a valve. The grey coating may be electro-less nickel plating, but I'm not sure.

[SpreadSpectrum]

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?

[Merlinb]

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!

[SpreadSpectrum]

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?

[SpreadSpectrum]

I can't be the only one here interested in tube dissections...