Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

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
    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

    User Avatar
    Science Advisor
    Gold Member

  5. Apr 16, 2016 #4

    davenn

    User Avatar
    Science Advisor
    Gold Member

    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

    User Avatar
    Science Advisor
    Gold Member

    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

    User Avatar
    Science Advisor

    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

    User Avatar
    Gold Member


    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

    User Avatar
    Gold Member

    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

    User Avatar
    Science Advisor
    Gold Member

    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

    User Avatar
    Science Advisor

    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

    User Avatar
    Science Advisor
    Gold Member

    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

    User Avatar
    Science Advisor
    Gold Member

    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
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted



Similar Discussions: Are there purely diode, vacuum tubes?
Loading...