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Old 1st January 2009, 01:34 AM   #1
athos56 is offline athos56  United States
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Default Switch box using VR glow tubes

So I'm going to build a switch box to switch between my CDP, Phono, and Reel to Reel (yet to be aquired). It will also have a switch to shift my main speakers between the Home theater and my tube amp. While in idea central (the bathroom) I had a "great" idea. Why not use one of the switches poles to change between glow tubes to indicate which component is selected. I'm thinking of using a 120v isolation transformer and a few diodes for the b+. The switch would select beween dropping resistors, then the VR tubes, followed by a some sort of current regulator to draw the proper current for each tube. The switches for the inputs and outputs would be totally passive, and the tubes just for show.

Here is the qwestion, what should I use after the tube? All I would need is something that could handle more than 5ma or more than 10ma depending on the VR tube. Would an LM317 be sufficient?
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Old 1st January 2009, 02:43 AM   #2
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I don't think you need any load after the reg tubes.
Just size the resistor(s) so that the current is within the tubes spec's.

I did that on an amp I was tinkering with,just for show.One side-benefit was that it helped to keep the B+ from soaring at switch-on,before the power tubes warmed up.
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Old 1st January 2009, 02:50 AM   #3
athos56 is offline athos56  United States
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I drew this up, so you think I wouldn't even need resistors after the tubes?
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Old 1st January 2009, 04:37 AM   #4
Colt45 is offline Colt45  Serbia
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no, you don't need resistors after the tubes.. just dial in the dropper for 20mA or so.

why is there 5 tubes...?
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Old 1st January 2009, 04:45 AM   #5
athos56 is offline athos56  United States
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Ok! thanks.

one for each input and 2 to indicate which amp the speakers are going to.

Now I have to find which tubes glow the best... I'm thinking 0A3, 0B3, and 0C3...
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Old 1st January 2009, 06:46 AM   #6
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Or use a different tube for each input,get some color variety!
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Old 1st January 2009, 09:11 PM   #7
Merlinb is offline Merlinb  United Kingdom
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Since the indicator circuit is entirely separate from the audio you don't even need a transformer, you could power them directly from the mains live, as long as you're using an earthed metal chassis.
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Old 1st January 2009, 09:24 PM   #8
athos56 is offline athos56  United States
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You mean: A standard hammond steel chassis, 3 prong power jack with the safty ground attached to the chassis at the plug, and then run the other two to the tubes.

Ok, that cut the cost in half...
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Old 1st January 2009, 10:06 PM   #9
athos56 is offline athos56  United States
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Hmmm I'm concerned about tube brightness. Will the glow tubes be bright enough to make it worth it? Or would a Nixie tube rigged to show 1 to 3 be cooler....
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Old 1st January 2009, 10:15 PM   #10
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Quote:
Originally posted by Merlinb
Since the indicator circuit is entirely separate from the audio you don't even need a transformer, you could power them directly from the mains live, as long as you're using an earthed metal chassis.
This is a terrible idea. The transformer is there for your safety which is particularly relevant on something you are likely to touch.


Quote:
Originally posted by athos56
would a Nixie tube rigged to show 1 to 3 be cooler....
Yes.
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