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Old 31st May 2009, 12:03 PM   #1
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Default 0B3 Glows Orange

Hi all,

I am playing around with a bunch of 0B3 tubes (brand, Electronic Enterprises) and they glow orange. I was under the impression that the 0b3 had a blue/violet glow. The tube seems to be regulating OK. Does anyone know if this particular brand glows orange or do I have a problem with the tube?

Cheers,

Rob
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Old 31st May 2009, 12:12 PM   #2
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You don't have problem : the colour of the glow depends on the mixture of gases inside the valve. Most British 85A2s that I've come across glow orange.
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Old 31st May 2009, 12:34 PM   #3
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Thanks Barretter - Then I do have a problem as I am looking for that violet glow!! I achieved this briefly when I removed the shunt resistor and powered up the tube. It flashed blue, popped and then tripped the circuit breaker Unfortunately it does not glow at all now. Looks like I might have to look for some sylvanias.

Thanks again for the information.

Rob
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Old 31st May 2009, 01:17 PM   #4
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Do you mean series resistor? There should always be a resistor from the raw supply to the anode of the regulator valve. What are you using the 0B3 for? Direct supply of regulated voltage to a circuit or as a voltage reference in a more complicated regulated supply. If you're using it in the first role you can only supply a maximum of 30mA to the circuit from a single 0B3.
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Old 31st May 2009, 02:14 PM   #5
kevinkr is offline kevinkr  United States
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Barretter is right, you pushed that tube into the arc region of operation which destroyed it. The regulated output voltage is a function of the gas mixture and the geometry of the tube. My understanding (perhaps mistakenly) is that gas mixture and pressure plays the dominant role.

I would be more concerned about the functionality that the tube provides than the color of the glow. All of the 10 or so OB3 I have on hand IIRC are orange glow types.
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Old 31st May 2009, 09:08 PM   #6
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Yes Barretter, the series resistor, sorry. I have about 20 of these tubes and wanted to see just how long the tube would last without the series resistor - not long. I am planning to use it as part of a bias circuit, so current draw wont be a problem.

Hi Kevin, you are correct of course but I was hoping for both functionality and looks. Obviously, the tube mentioned above now has neither.

Rob
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Old 31st May 2009, 09:37 PM   #7
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Well you're going to have to have a minimum current of 5mA otherwise the valve will extinguish. Are you using them to feed screen grids?
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Old 1st June 2009, 03:39 AM   #8
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Yes, will have a power across the output of the tube in order to satisfy the minimum current draw. Interestingly, with respect to these tubes it was my understanding that they could supply a higher current to the circuit as long as the maximum current rating (in this case 30mA) was not exceeded through the tube. Some designs that I have seen show these tubes being used to supply circuits well in excess of the tube current rating, with the series resistor used to limit the current through the tube - I don't think that I have got this wrong but at least for my circuit, it's academic as the bias current is very small.
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Old 1st June 2009, 05:56 AM   #9
chrish is offline chrish  Australia
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Hmmm, what are you building now Rob
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Old 1st June 2009, 06:12 AM   #10
Colt45 is offline Colt45  Serbia
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I've got some ST shaped sylvania and.. dunno, some other brand. They glow a kind of purpley white.. not as purpley as an 0D3, though.

Then I've got a couple raytheon -GT types, they glow orange (and reg more like 95V rather than 90ish..)
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