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Old 26th December 2015, 01:29 PM   #1
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Default Can you mix glow tubes and zeners for shunt regs?

Just a quick question - can you mix glow tubes (tube voltage regs) and zeners to get the exact voltage you want? Thinking 5.6v zeners....
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Old 26th December 2015, 01:45 PM   #2
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Originally Posted by andyjevans View Post
Just a quick question - can you mix glow tubes (tube voltage regs) and zeners to get the exact voltage you want? Thinking 5.6v zeners....
Yes as long as you pay attention to current ratings. The other method is to use two tubes one higher voltage the other lower. Then use a pair of resistors or even a variable resistor and take the exact voltage from between them.
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Old 26th December 2015, 04:04 PM   #3
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What I am after is around 270v. I can get 255v with a 150v + 105v, so thinking to add 3 of 5.6v zeners.

Does this affect the strike voltage in any way? And should you wrap a .056 capacitor around the whole thing?

This is for an output tube drawing 35mA.
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Old 26th December 2015, 04:40 PM   #4
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Cap around the tubes only. Use a bigger value around the zeners. Or use three tubes, 0A3, 0B3, OC3.
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Old 26th December 2015, 05:00 PM   #5
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Yes - 0A3, 0B3 and 0C3 make 270v. Trouble is the 0B3 is only rated for 30mA while the other two are rated 40mA. I'd be using it with 35mA
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Old 26th December 2015, 05:15 PM   #6
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It will take 35 mA. But what current does the load draw?
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Old 26th December 2015, 05:17 PM   #7
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I mean the load draws around 35mA - a 4P1L tube.
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Old 26th December 2015, 06:08 PM   #8
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Originally Posted by andyjevans View Post
I mean the load draws around 35mA - a 4P1L tube.
Then set you current limiting resistor for 45mA.
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Old 26th December 2015, 06:41 PM   #9
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Thanks! You seem to know your glow tubes.

So when a glow tube is rated "30mA" - this refers to what exactly, if not the load current?
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Old 26th December 2015, 07:03 PM   #10
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It refers to how much current the tube can pass.
If you set your current limiting resistor to 45 mA, and the load takes 35 mA, then the series string of tubes is shunting 10 mA through them. Well below ratings.
I find 10mA to be a target minimum; prefer to run closer to 15 mA or even a little higher. More reliable striking and extra headroom for load swings (depending on your load).
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