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Old 22nd February 2011, 07:38 AM   #1
tomchr is offline tomchr  United States
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Default VR tubes, minimum current

Folks,

I'm toying with the idea of using a voltage regulator tube as the reference voltage in a voltage regulator. Specifically, I'm thinking to use a 0A3. I like the looks of it....

The maximum current of the 0A3 is about 30~40 mA if I recall correctly. But is there a minimum current that's needed to ensure stable operation?

~Tom
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Old 22nd February 2011, 07:43 AM   #2
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yes, and a minimum voltage difference too for both operating and striking (start-up). On the spec sheet usually.
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Old 22nd February 2011, 08:13 AM   #3
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Minimum current for regulation is 5mA for the 0A3, as per the Tung Sol datasheet.
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Old 22nd February 2011, 11:21 AM   #4
DF96 is offline DF96  England
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Did you choose the 0A3 for its appearance or performance? Is this art or engineering?
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Old 22nd February 2011, 04:46 PM   #5
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Quote:
Originally Posted by DF96 View Post
Did you choose the 0A3 for its appearance or performance? Is this art or engineering?
I personally use them for both, they're a nice big zener that looks great, is more rugged, equivalent noise specs (often better IME )and cost is usually about the same when purchased as surplus.


Back on the OP's question, run 'em at around 10 ~ 15 mA and you're set. For even better performance use a CCS.
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Old 22nd February 2011, 05:29 PM   #6
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A zener diode will not do as well; it will have a temperature coefficient that may bother you. VR tubes are very good in this respect.
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Old 22nd February 2011, 05:34 PM   #7
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Temperature effect of Zeners when used to power tube stages, even directly copuplet, does not bother me at all. But tubes look better.

Click the image to open in full size.
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Old 22nd February 2011, 05:46 PM   #8
tomchr is offline tomchr  United States
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Quote:
Originally Posted by DF96 View Post
Did you choose the 0A3 for its appearance or performance? Is this art or engineering?
Yes!

I love the orange glow. It's purrrdy...

10~15 mA. Oof! I'm coming down from 600+ V. That's a lot of power in the series resistor.

~Tom
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Old 22nd February 2011, 05:56 PM   #9
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5 mA is enough.
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Old 22nd February 2011, 06:54 PM   #10
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Especially if you supply it with an ultra-simple CCS, maybe with the 900V rated IXYS device (no need for cascoding), the high voltage isn't really a problem. Firing is all but guaranteed even with 5 mA when you use a CCS.
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