Illuminating a Thyratron (mercury gas discharge)

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Discussion Overview

The discussion revolves around the use of a thyratron tube, specifically for illuminating mercury vapor in a novelty lamp project. Participants explore circuit design considerations, including filament heating, current requirements for illumination, and the use of resistors to control current flow.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested
  • Experimental/applied

Main Points Raised

  • One participant describes their circuit setup, including a 2.5VDC filament and a plan to apply rectified DC from AC mains to illuminate the mercury vapor, targeting a current between 0.01 and 0.5 amps.
  • Another participant questions the availability of a datasheet for the thyratron and suggests searching for its part number.
  • A participant shares a link to a datasheet for a similar thyratron model, indicating that even older models have a following.
  • One participant expresses interest in whether the thyratron can maintain operation after initiating glow and suggests using a higher anode resistor to limit anode current.
  • Another participant questions whether 120V DC rectified is sufficient and discusses the potential benefits of using a higher voltage.
  • A participant argues that more voltage may not be necessary and provides a cleaner copy of the datasheet.
  • One participant proposes using the thyratron as a regulator tube in a power supply and shares an application sheet for GE Glow Tubes.
  • Another participant suggests that the thyratron might stay lit at low current and proposes making it into a relaxation oscillator to achieve continuous illumination.
  • The original poster reports success in illuminating the thyratron but notes inconsistent operation, where it sometimes stays on without the heating filament.

Areas of Agreement / Disagreement

Participants express various opinions on circuit design and operational characteristics of the thyratron, with no clear consensus on the optimal voltage or current settings. The discussion remains unresolved regarding the best approach to achieve consistent illumination.

Contextual Notes

Participants mention various assumptions about current thresholds for different discharge types and the impact of resistor values on operation, but these aspects remain unresolved and depend on specific circuit configurations.

bwinter
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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.
 
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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 ?
 
Good to know. Do you think 120V DC rectified is enough? What would be the benefit if any of transforming to a higher voltage?
 
I don't see why you'd nee more voltage.

Cleaner copy of datasheet here

http://www.datasheetarchive.com/dl/7a2e304da0ac6860531847f5de30f97df76ae6/O/3C23
 
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
GE_Glow_Tubes_ETI-176.pdf
 

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dlgoff said:
Also I've uploaded the GE Glow Tube application sheet.

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.
upload_2017-1-17_22-11-40.png


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.
 
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I did it!
HLm9cVl.jpg

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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