# Illuminating a Thyratron (mercury gas discharge)

1. Jan 17, 2017

### bwinter

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. Jan 17, 2017

### jim hardy

3. Jan 17, 2017

### bwinter

4. Jan 17, 2017

### jim hardy

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 ?

5. Jan 17, 2017

### bwinter

Good to know. Do you think 120V DC rectified is enough? What would be the benefit if any of transforming to a higher voltage?

6. Jan 17, 2017

### jim hardy

7. Jan 17, 2017

### dlgoff

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.

GE_Glow_Tubes_ETI-176.pdf

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8. Jan 17, 2017

### jim hardy

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.

9. Jan 25, 2017

### bwinter

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).