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Cherenkov Radiation in a Vacuum Tube

  1. Apr 12, 2014 #1
    Someone on another forum shared with me that a 6L6 vacuum tube exhibits a blue dot when in operation that is supposed to be Cherenkov radiation. I say nay, as I have worked out the relativistic velocity using $$KE={ m }_{ 0 }{ c }^{ 2 }\left[ \frac { 1 }{ \sqrt { 1-\frac { { v }^{ 2 } }{ { c }^{ 2 } } } } -1 \right] $$. The plate voltage is 500V max, so I used 500eV for the KE. This works out to $$8x10^{-17}$$Joules. Solving for v, I get v=$$1.3x10^{7}m/s$$. If the speed of light in glass is $$\frac{c}{n}$$, where n=The index of refraction of glass (I will assume 1.5). Then these electrons are not fast enough for Cherenkov radiation. Am I on target here?

    Chris Maness
  2. jcsd
  3. Apr 12, 2014 #2


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    Its more likely some sort of ionization - and the spectrum is blue because the photon energies are around 4-4.5 eV.
  4. Apr 12, 2014 #3


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    Most of the blue in good power tubes is from FLUORESCENCE, sometime near or surrounding the anode plate or glass envelope.

    If it's more pinkish and near or inside the plate structure then it's ionization and that's usually the sign of a gassy power tube.
    http://www.amplimo.com/index.php/electron-tubes [Broken]
    Last edited by a moderator: May 6, 2017
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