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Are there purely diode, vacuum tubes?

  1. Apr 15, 2016 #1
    I am looking for a very simple and specific vacuum tube. It doesnt have to be high power. I only need a plate that completely surrounds the cathode. No grids would be ideal. Anyone have a parts number or link for something similar to this?
     
  2. jcsd
  3. Apr 15, 2016 #2

    tech99

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    Any diode such as 6AL5. Or maybe use a triode and connect the grid to anode. Then 6C4 or 6J5 would be suitable.
     
  4. Apr 15, 2016 #3

    dlgoff

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  5. Apr 16, 2016 #4

    davenn

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    why this requirement ... considering most are such ?

    well if it has a grid, it isn't a diode ! :wink: at minimum it's a triode


    Dave
     
    Last edited: Apr 16, 2016
  6. Apr 16, 2016 #5

    davenn

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    a slightly rough way to do it, specially when there are many purpose built rectifiers out there :wink:

    eg what Don has shown or here's another one

    5U4G.jpg

    The 5U4G is a twin diode, use one or use both sections, take your pick :wink:



    Dave
     
  7. Apr 16, 2016 #6

    Baluncore

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    There are so many thermionic diodes to choose from. What is the application?
    What is maximum reverse voltage and current? What is maximum forward current?
    What frequency? and maximum capacitance between anode and cathode?
     
  8. Apr 16, 2016 #7
    Now I have a question. How do anode voltages accelerate the emitted electrons if the plate surrounds the cathode? From my understanding, anything inside a conductor is uninfluenced by electric fields produced by the conductor. Do the plates truly surround the cathode?
     
  9. Apr 16, 2016 #8
    In this pin layout, is M connected to ground?
    17ax4_so.png

    This is from the 1b3gt tube dlgoff posted. Which pin; if any, is that metal cylinder wired to?
    1k3a_sockel.png
     
  10. Apr 16, 2016 #9

    Averagesupernova

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    Am I the only one who finds the above quotes by the same person a bit odd?
     
  11. Apr 16, 2016 #10
    What is odd about them?
     
  12. Apr 16, 2016 #11

    Averagesupernova

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    Ummm, well in the first post it seems very important that the plate completely surrounds the cathode. In the other post I quoted it looks as if you were not even sure that tubes are actually constructed in that manner.
     
  13. Apr 16, 2016 #12
    You can find all the answers to you questions in the RCA Tube Manual which you can download for free here. http://www.tubebooks.org/tubedata/RC30.pdf
    Page five will give a general understand of vacuum tube diodes which are used as rectifiers.

    Pretty much anyone who is experimenting with vacuum tubes will be using this manual. There will be more than a quick glance needed to understand this subject so you should expect to spend a good amount of time to get to understand what you read. As tube diodes are the least complex of the vacuum tubes, tube diodes will be not too hard too understand.

    If you get stuck and need help, post here or PM me.

    Cheers,

    Billy
     
  14. Apr 16, 2016 #13

    davenn

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    because of the big potential difference between the plate ( anode) and the filament (cathode)

    totally different situation, doesn't relate to what is happening in a tube


    Dave
     
  15. Apr 16, 2016 #14

    Baluncore

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    Probably. It is an external electrostatic screen or metal envelope. The plate or anode is, a.

    The cylindrical plate structure is connected to a small top cap, well away and isolated from the pins, marked as p on the diagram. The black bump at the bottom of the diagram is a locating index on the base socket.


    The slender filament heated cathode is mounted on a central axis. The tubular anode plate surrounds the cathode, so the heat due to the accelerated electrons impacting the inside of the anode, can be radiated from the larger area of the tubular anode, outwards through the glass envelope.
    Electric fields close to the cathode are critical to electron emission. For a triode, the control grid is placed very close to the cathode. The fields inside a capacitor or coaxial cable are all internal, similarly, the electric fields between the cathode and the inside of the tubular anode of a vacuum tube are self-screened which reduces the effects of external electric noise and so reduces interference with other nearby components and signals.
    It was Lee DeForest who first investigated the triode amplifier. He discovered the effect when placing an antenna wire against the outside of the glass envelope of a thermionic diode that was being used as a wireless signal detector. It became his “Audion” in 1905.
    It is lucky he was not using a tubular anode electrode, but something more resembling the separated anode “plate” still used in tube diagrams.
     
    Last edited: Apr 16, 2016
  16. Apr 16, 2016 #15
    Thank you very much. This is exactly what I was looking for. Back to pin M in the layout. Does it stand to reason that I could turn on such a tube with a negative anode so that the electrons are attracted to the electrostatic screen? Then they would charge up the outer surface of the screen. Is this all reasonable?
     
  17. Apr 16, 2016 #16

    davenn

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    if the plate is negative, then the electrons from the filament (cathode) will be repelled and the tube wont work
     
  18. Apr 16, 2016 #17
    But this tube has an indirectly heated cathode. If I connect the cathode and the anode to the same negative potential, wouldn't all field lines will end on the screen connected to M?
     
  19. Apr 16, 2016 #18

    davenn

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    not sure
    I see absolutely no point in doing that ??
     
  20. Apr 16, 2016 #19
    Quiet source of high voltage dc current with very simply circuitry. My electrostatic generator is very loud and flybacks need smoothing caps etc.
     
  21. Apr 16, 2016 #20
    Samson4,

    Any DC current coming from a tube diode will need filtering the same as would be the case with a silicon diode. All that comes out of a tube diode is pulsating DC. Connecting up a tube in a non standard way will most like destroy the tube and perhaps blow up in you face, set the house on fire....well...those are the minor issues that could come to pass...lol

    Most tubes are high voltage devices, connected from the mains by a step up transformer designed to provide the correct voltage needed by the tube. Nothing about this is simple or cheep and has the real danger of getting you killed if you mess something up.

    Please proceed with due caution if you go forward with this sort of stuff.

    Cheers,

    Billy
     
  22. Apr 16, 2016 #21

    Baluncore

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    Quiet electrically or acoustically? Audio noise is usually generated by physical movement in magnetic components. Magnetostriction in a magnetic core or movement of windings on the core can often be a problem.

    EHT flyback rectifiers are often made from chains of diodes with parallel resistors to equilibrate the reverse voltages across the many diodes. They are called “stick rectifiers”. The 1B3GT shown by dlgoff in post #3 was designed for use in EHT generators for B&W TV. It was replaced by semiconductor stick rectifiers.
    Flyback diodes often need snubber networks made from series connected R and C. Snubbers restrict dv/dt and prevent voltage spikes that may damage semiconductor components or insulation.

    Avoid the word “screen” as that refers to an internal grid close to the plate. The black circle, M, in the diagram is not strictly an electrode. It may be a metal sleeve inside and/or outside the vacuum envelope.

    I think you are trying to use an inappropriate component do something you have not clearly specified. If you knew more about thermionic vacuum tubes you might see better ways of resolving your design requirements. It is highly unlikely that you will find neat low cost technical solutions by random assemblages of components you do not yet understand.

    There is a wealth of knowledge available from the members of PF. If you specify your project and the problems you are having, you will receive several good suggestions from members, probably along with a better understanding of your design challenge. If you could ask the right question, you could answer it yourself. When you explain a project or problem to others, you will actually get to understand it better yourself. Give it a try here.
     
  23. Apr 16, 2016 #22
    Quiet in the sense that when I power on my van de graaff, the room sounds like a textile factory. I am simply trying to replicate the mechanism of the van de graaff with a low power tube. A van de graaff deposits charges on the inside of a metal dome. I want to see if the same can be done with a simple thermionic tube.
    This is the tube I believe to be of use.
    s-l400.jpg

    198.png

    Notice that the pin M is connected to the mesh surrounding both anodes and cathodes. The filament requires .1 amps at 19 volts. I plan to connect pins k and d to a negative potential to accelerate emitted electrons to the inside of the mesh. In this regard, I only want to see if the mesh will act like the dome of a van de graaff.
    The total power input wouldn't exceed 2 watts. If I am using 19 volts and am able to achieve 100 volts at pin M, I'd consider that a big success.
     
  24. Apr 16, 2016 #23

    Baluncore

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    Surface leakage across the glass base, or voltage breakdown between the pins will severely limit the voltages possible.
     
  25. Apr 16, 2016 #24
    I agree, I'm only hoping for 100 volts. But, do you agree this could work? It will be fun to test anyway.
     
  26. Apr 16, 2016 #25

    Baluncore

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    Connect d1 and d2 to m, ground k1 and k2, heat the filament. Some electrons will be emitted from the heated k, to reach d and so drive it negative. That will repel future electron migration and so limit the voltage.

    How will you use 19V to pump charge onto the capacitance of the outer mesh ?
    Remember that the filaments should be operated at a similar voltage to the k voltage.
    What makes the vacuum tube better than a tin can ?
     
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