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Author Topic: Light Up A Vacuum Tube (How?)  (Read 5211 times)
Hatefly
Deck Hand
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United States United States


« on: November 07, 2012, 10:56:52 pm »

Hi Folks!

I am working on a project - A Ray Gun - and I wanted to know if it is possible to light up a vacuum tube with a momentary switch and a small battery or two, say 9V or AA batteries.

I know these things take a bunch of power, but I'm not looking for constant light. Does anyone have any experience with this?  Huh
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oldskoolpunk
Zeppelin Captain
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United States United States


WWW
« Reply #1 on: November 08, 2012, 07:32:39 am »

You apply the rated voltage across the heater pins and it lights up. 

Tubes usually have a standard type number on them, like "6AL5" or "5U4" or "12AX7". The initial digits are conventionally the heater voltage in volts. Normally, one looks up the data sheet for the tube number, which shows which pin does what. However, if all you want to find is the filament, just use an ohm meter to find two pins which have a resistance between them which is neither zero nor infinity. If you find several pins which seem to be interconnected with nonzero resistances, you have found a tube with a center-tapped filament.  Find the pair of pins with the largest resistance between them.

If you don't have an ohm meter, try hooking 4 AA batteries in series with a 6V flashlight bulb, and bring two wires out of the circuit  (The bulb prevents you from shorting the batteries.) Touch those wires to pairs of pins until the tube lights up. This will produce some glow for tubes from 5V to 12V. Once you've found the correct pair of pins, hook up the appropriate number of batteries for the rated voltage (1.5V per battery) and leave out the flashlight bulb.

9V and AAA batteries will not power a tube for very long.  Consider D batteries.

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Hatefly
Deck Hand
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United States United States


« Reply #2 on: November 08, 2012, 03:57:49 pm »

Awesome, thanks very much!

I found a data sheet on one of my tubes - RCA 22BW3 - but still trying to figure out what these letters designate. Does "H" stand for heater?

Somehow I am thinking by the numbers on this tube, I might need more battery power than would be workable in a handheld weapon prop, lol. Then again, I'm still learning this stuff, so I am prob wrong.
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oldskoolpunk
Zeppelin Captain
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United States United States


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« Reply #3 on: November 08, 2012, 11:23:28 pm »

RCA 22BW3
22 volt heater, on pins 1 and 12, the two pins on opposite sides of the pin gap. Draws about 1/2 amp.
It's a 4-terminal device in an 12 pin package.

If you're planning on running on battery power, find a tube with a lower heater voltage.  Look for something which begins with "6".  Those are common and run on 4 AA batteries. This one requires 15 AA batteries. 

Some tubes produce a nice glow, and some barely glow visibly at all, depending on where the heater is located.
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Hatefly
Deck Hand
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United States United States


« Reply #4 on: November 09, 2012, 07:32:29 pm »

OK, it is as I feared!

I guess I can look for a couple others or just go with the easier to use LED route. I have a really nice two piece stock I have designed, but it does have it's limits on what I can fit inside of it and still keep it strong.
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celephicus
Officer
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Australia Australia


Mensura ergo sum (I measure, therefore I am)


« Reply #5 on: November 13, 2012, 11:51:54 pm »

Just mount a LED so that it shines into the glass, much easier to engineer and you have a choice of colours and it will run off a tiny battery.
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Dr. Celephicus -- amateur (gentleman) mad scientist
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Angus A Fitziron
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United Kingdom United Kingdom

Research Air Ship R.A.S. 'Saorsa'


« Reply #6 on: November 14, 2012, 12:01:45 am »

Yes, absolutely - use LEDs. If you are mounting the tube in a proper valve base, you may be able to drill a hole in the base to accomodate the LED without it being obvious. The heater elements do not give off a great deal of light anyway and would probably be invisible from a few feet away in bright sunlight! An LED will run off a 3 volt source and there is no problem with a simple switch. Check the data sheet though because you will need to insert a small resistor in series to limit the load current.

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