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Illuminating a Thyratron (mercury gas discharge)

  1. Jan 17, 2017 #1
    I found a thyratron tube at a yard sale recently and I want to build a circuit to heat the filament and illuminate the mercury vapor for purposes of building a novelty lamp.

    The filament is just 2.5VDC at 7 amps and I have a transformer for that.

    To light the vapor I will apply DC rectified and smoothed from the AC mains.

    The illumination is related to current, and to achieve maximum illumination of the electrode I want to achieve something on the order of milliamps, above the current for Townsend discharge but below that of arc discharge. I don't know what those values will be so let's say, between .01 and .5 amps.

    So V = IR
    120 = 0.01R
    12000 Ohm = R1

    120 = .5R
    2400 Ohm = R2

    So my load resistor in series with the thyratron will be a 10K rheostat in series with a 2.4k Ohm resistor.

    Hoping for any input from someone with tube experience, if this might work.
  2. jcsd
  3. Jan 17, 2017 #2

    jim hardy

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  4. Jan 17, 2017 #3
  5. Jan 17, 2017 #4

    jim hardy

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    I'll be interested to see if you can hold off the avalanche after initiating the glow. I've only used 2D21 , fifty years ago.

    Try severely limiting anode current , ie higher anode resistor ?

    Keep us posted ?
  6. Jan 17, 2017 #5
    Good to know. Do you think 120V DC rectified is enough? What would be the benefit if any of transforming to a higher voltage?
  7. Jan 17, 2017 #6

    jim hardy

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  8. Jan 17, 2017 #7


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    Maybe you could use it like a regulator tube in a power supply like the one I built. Also I've uploaded the GE Glow Tube application sheet.

    tubesupply A+B.jpg


    Attached Files:

  9. Jan 17, 2017 #8

    jim hardy

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    What a great find !

    That thing just might stay lit at low enough current.

    If not, perhaps make it into a relaxation oscillator at a few hundred hz, fast enough to appear continuous.


    We used to do that ^^^^ with NE2's and a 90 volt B battery. I found that some resistance in series with the lamp prolonged its life.
  10. Jan 25, 2017 #9
    I did it!
    Funny operation though. Sometimes it will stay on without the heating filament and sometimes not, even if the current is the same. I have it connected through 168VDC and a series resistor (~2k).
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