First post!
I’m interested in knowing about the actual materials used in construction of valves.
I know that the cathode is a metal with a special low workfunction coating which significantly increases the rate at which electrons can escape the surface for a give temperature.
What is an example of a “modern” coating material used for cathodes?
Similarly, does the anode require any special surface modifications to accept electrons?
I’m interested in knowing about the actual materials used in construction of valves.
I know that the cathode is a metal with a special low workfunction coating which significantly increases the rate at which electrons can escape the surface for a give temperature.
What is an example of a “modern” coating material used for cathodes?
Similarly, does the anode require any special surface modifications to accept electrons?
The anode is usually made from sheet nickel or nickel-coated steel, stamped and pressed into a box or roughly cylindrical shape. It may also be blackened with graphite to reduce secondary emission and to improve heat radiation. Cooling fins are often added to the anodes of power valves, while really powerful valves may have anodes of solid carbon.
The cathode is made from a nickel tube which is coated with a proprietary mixture of barium and strontium carbonates.
The cathode is made from a nickel tube which is coated with a proprietary mixture of barium and strontium carbonates.
Directly heated valves will also use an uncoated tungsten filament as the cathode, often thoriated (impregnated with thorium) to increase emission.
Thanks Merlin!
It’s a small world, I was asking you about voltage multipliers yesterday.
You post gave me something to Google,
https://ntrs.nasa.gov/api/citations/19680028529/downloads/19680028529.pdf
I was actually wondering if the cathode material was also photoelectric, and if UV, could be used. With such a low workfunction even visible light should be capable of causing electron emission. There is no practical purpose of this! But for some solar cell applications it might be useful at demonstrating interesting effects.
Euro21, it would be good to know more about ELROG, do they publish much?
It’s a small world, I was asking you about voltage multipliers yesterday.
You post gave me something to Google,
https://ntrs.nasa.gov/api/citations/19680028529/downloads/19680028529.pdf
I was actually wondering if the cathode material was also photoelectric, and if UV, could be used. With such a low workfunction even visible light should be capable of causing electron emission. There is no practical purpose of this! But for some solar cell applications it might be useful at demonstrating interesting effects.
Euro21, it would be good to know more about ELROG, do they publish much?
Many RF power DHT Triode tube's filaments are infused with Thorium.
Do not forget the 300B, 2A3, and 45 audio tubes.
Those DHT filaments are not infused with Thorium.
They are coated.
What is/are the active element(s) of that coating?
Strontium?
Barium?
Photo Electric tubes photocathodes often use caesium-antimony, or caesium on oxidized silver.
Do not forget the 300B, 2A3, and 45 audio tubes.
Those DHT filaments are not infused with Thorium.
They are coated.
What is/are the active element(s) of that coating?
Strontium?
Barium?
Photo Electric tubes photocathodes often use caesium-antimony, or caesium on oxidized silver.
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Most everything you will ever need to know about the subject is contained in:
Vacuum Tubes by Karl Spangenberg. I still have my hardcopy🙂
Vacuum Tubes by Karl Spangenberg. I still have my hardcopy🙂
Modern cathodes can operate at room temperature (no heater needed).
They use multi layer nanometer coatings on nickel (vacuum deposition).
Back in year 2000 it was found that nm titanium on nickel worked at -near- room temperature. These were easy to make even, just required electroplating.
Room temp. is for real now. The planar surfaces are quieter (less noise) and give more uniform Mu factor compared to rough oxide surfaces. Apparently, present day audio tube manufacturers can't be bothered with tubes that don't wear out, have better curves, and don't need heaters. That's why I don't buy any new issue tubes.
https://www.diyaudio.com/forums/tubes-valves/228301-diamond-cathode-tubes.html#post3337529
They use multi layer nanometer coatings on nickel (vacuum deposition).
Back in year 2000 it was found that nm titanium on nickel worked at -near- room temperature. These were easy to make even, just required electroplating.
Room temp. is for real now. The planar surfaces are quieter (less noise) and give more uniform Mu factor compared to rough oxide surfaces. Apparently, present day audio tube manufacturers can't be bothered with tubes that don't wear out, have better curves, and don't need heaters. That's why I don't buy any new issue tubes.
https://www.diyaudio.com/forums/tubes-valves/228301-diamond-cathode-tubes.html#post3337529
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That's really interesting. I'm going to read about that, thanks for the link. What a remarkable material, it must get dangerously ionised!
I wasn't referring to the diamond point emitters. They are quite non-linear and susceptible to burn-out.
I was referring to the titanium film like planar emitters. They use an induced tunneling thin film process which is quite robust against ion bombardment and capable of high current density and are more linear. They are the result of SS quantum development.
I was referring to the titanium film like planar emitters. They use an induced tunneling thin film process which is quite robust against ion bombardment and capable of high current density and are more linear. They are the result of SS quantum development.
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To supplement Spangenberg 1948, the 1962 RCA:
Vacuum Tube Manual: RCA 1962 Electron Tube Design : Free Download, Borrow, and Streaming : Internet Archive
All good fortune,
Chris
Vacuum Tube Manual: RCA 1962 Electron Tube Design : Free Download, Borrow, and Streaming : Internet Archive
All good fortune,
Chris
Cathode coatings, material datasheet attached.
Cathodes can be coated with Ba/Sr/Ca carbonates in different mixtures depending on application. See Material datasheet bellow.
The cathodes themselves used to be made of nickel alloyed with small amounts of trace materials to give specific ductility, lifetime or economy.
In general there are passive and active cathodes, active cathodes are faster to manufacture but have lower lifetime.
The anodes of normal receiving tubes are either nickel, iron or in some rare cases nickel/copper/nickel to aid in conductivity and avoid hotspots.
Grey= aluminium coating, these anodes are shiny until you heat them with RF heating.
Black: mostly carbon based coatings, superior to nickel in therms of power handling, but runs the risk of cathode contamination.
Cathodes can be coated with Ba/Sr/Ca carbonates in different mixtures depending on application. See Material datasheet bellow.
The cathodes themselves used to be made of nickel alloyed with small amounts of trace materials to give specific ductility, lifetime or economy.
In general there are passive and active cathodes, active cathodes are faster to manufacture but have lower lifetime.
The anodes of normal receiving tubes are either nickel, iron or in some rare cases nickel/copper/nickel to aid in conductivity and avoid hotspots.
Grey= aluminium coating, these anodes are shiny until you heat them with RF heating.
Black: mostly carbon based coatings, superior to nickel in therms of power handling, but runs the risk of cathode contamination.
Oh thanks for the correction. When I was in SS research I was looking at materials which were cold but emit hot electrons internally. The idea was something like a solid state rectifier tube, but the application was photovoltaics i.e. light hits your “cathode” high speed electronics flow and because of there excess speed you can generate more power in an external circuit. It was more theoretical than anything else but was really interesting. So I follow what you mean.
Don’t know if you have come across the Nu Tube my Korg? I have not used it or heard it in anything but was applauded their creativity!
Don’t know if you have come across the Nu Tube my Korg? I have not used it or heard it in anything but was applauded their creativity!
Hi boyfarrel,
if not mentioned yet in this thread, books from Kohl or Hermann & Wagener are authoritative sources. Information content in these books from the 50's / 60's still is valid and largely up to date, except maybe for very few thermionic niche devices "invented" after that era.
You can find these books here: Technical books online
Search on that page for author names "Kohl" and "Herrmann".
Kind regards, Tom
if not mentioned yet in this thread, books from Kohl or Hermann & Wagener are authoritative sources. Information content in these books from the 50's / 60's still is valid and largely up to date, except maybe for very few thermionic niche devices "invented" after that era.
You can find these books here: Technical books online
Search on that page for author names "Kohl" and "Herrmann".
Kind regards, Tom
I have never heard of using rare-earth oxide cathode stuff as a photo sensor. And remember that talking movies and television tried about EVERYthing as a light sensor. Using existing vats of oxide would have been cheaper/simpler than developing high purity cesium surfaces.