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Radio tube mystery

  1. Feb 24, 2017 #1
    I recently got a 5 cm high radio tube from a old radio in my house. It has 9 pins ,arranged in a C shape at the base, a getter at the top and parallel metal plates inside.

    I decided to use my GMC-300E plus ,Geiger counter to check if it had a thoriated cathode. It did not. Just for fun, I two of it's pins to a 1 Kv power supply. I expected a nice show of plasma inside the tube. When I turned on the supply ,purple eruptions came from the plates.

    The Geiger counter was still on and sitting beside it. The Geiger counter's display whited out and the light at the side which flashes when the counter registers a click, just glowed constantly, the buzzer did the same.

    I instantly moved the counter away and turned off the supply. What made the counter do this? Was the tube interfering with the Geiger counters circuits, which seems unlikely. Or was the tube emitting an amazing amount of X-Rays ? The supply was only 1 Kv so this seems impossible.
    Last edited by a moderator: Feb 24, 2017
  2. jcsd
  3. Feb 24, 2017 #2


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    1 kV is a lot for a radio tube.
    Any descriptive text on the thing ? Is it reddish or is it goldish ?
  4. Feb 24, 2017 #3


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    Staff: Mentor

    Do you routinely put 1kV across components and circuits that you don't have a schematic for? Where did you get the 1kV? DC or AC? Source impedance?
  5. Feb 24, 2017 #4


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    A GM tube detects charges freed by the ionisation of the inert gas in the tube. Maybe UV radiation from the 1kV discharge penetrated the GM tube window sufficiently to generate ions within the tube.
  6. Feb 24, 2017 #5


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    a photo of said tube would be extremely useful
  7. Feb 25, 2017 #6

    jim hardy

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    Geiger counters make small electrical pulses that get amplified and counted inside the instrument.

    I suspect your detector acted as an antenna for old fashioned 'static' from the arcing.

    that's specuation, you could check by making some sparks from a lower voltage source like a six volt lantern battery and see if it counts them.

    If you do it with a car battery use long jumper cables because you don't want sparks near a car battery The hydrogen inside them can explode and spray acid everyehere.
    That happened to me, my glasses saved my eyes but i lost a dress shirt and trousers.
    I doggone near got blinded and that's no exaggeration. Stay safe.
  8. May 10, 2017 #7
    I am sorry to be so slow getting back, I had some minor account glitches (forgot password :headbang: ) , but I did more research and with your contributions I am now sure of the static/UV interpretation.
    Thank you all very much
  9. May 10, 2017 #8

    jim hardy

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    Thanks for the feedback !
  10. May 10, 2017 #9
    Don't use a car battery without a current limiting resistor. A few hundred amps through e.g. a wrist watch strap generates a lot of heat.
  11. May 13, 2017 #10
    Yes. Or better yet a fuse, and not slow blow one. Also, eye protection recommended if you go applying 1 KV to a glass component. Remember P = E**2/R.
  12. May 14, 2017 #11
    If you're looking to make sparks, then an inducer would be the thing to use
  13. May 15, 2017 #12
    Wire meshs moved over each other work well too.
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