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HeNe not working

Ttocsttammit

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Could I build a power supply using an ignition coil? I'd like to build one since I'm having trouble finding one online that matches the voltage of the one on the bottom of the circuit board.
 



Ttocsttammit

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I'm sure I would have to buy a few other parts if its possible. I'm not too entirely far from a radioshack/electronics supply store so I could make a trip there if need be.
 

Anthony P

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Found this:

I suggest you contact seller and ask him if that one will work for you, or if he has one that will. Silicon Sam is the world's leading laser expert. No LPF member would argue with that statement.

I will look through my old notes and see if I can find ignition coil supply. It would take a little transistor circuit to run it.
 

WizardG

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"And across the 75k resistor I read OL"

If your DMM was set correctly the above quote is highly suspicious. That sounds a lot like a fried ballast resistor. If that's the only issue keeping the tube dark then you just scored a $5 HeNe(y)
 

paul1598419

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I tested cont from the terminal at the front of the tube to T1 and found no resistance on the first pin with some resistance on the other two pins on the side of T1 closest to the tube. OL from the terminal at the front of the tube to the 3 pins on the side of T1 opposite of the tube. And across the 75k resistor I read OL
If this is the ballast resistor it will be attached to the anode of the tube and will likely be a 3 watt or higher power resistor. An open ballast resistor will not allow current to flow through the tube and will cause it to not operate. If it is somewhere else in a circuit, it is likely something else and, not knowing what it does, I can't say what effect it might have.
 

Ttocsttammit

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Apparently I was doing something wrong the first time I read the resistance of the ballast resistor. This time it ohm out at 75k. I'm really suspecting the power supply as some solder points look brownish and he definitely plugged a 19.2v power adapter into the power supply. I just wish there was a way to be more sure of what I need to order.
 

Anthony P

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Power supply should be similar, but does not have to be exact match. Ballast resistor may need adjusted. Start with high resistance and gradually step down till tube runs steady.

I am strictly amateur, but I would be willing to take a look at it if you want. PM me if so.
 

ultimatekaiser

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Holy! I've actually been looking for one of these. I used to play with one as a kid in the tech lab at school. Very neat to see there is one still around. They require a 12V supply at about 2A (at the HeNe supply inputs anyway, not sure about the back plug). but I don't recall what polarity, The laser is interlock protected however, so if you dont have the interlock plug you cannot run it iirc?-I doubt you need any parts... These are very robust. (and to be honest, if you were interested, I would consider trading you for another HeNe if you are interested, I have tons that I know work fine.)
 
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Anthony P

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Are you telling me you've found a way to drive a transformer with DC?

Not exactly. I have built variations of that circuit before. The only "ac" is the audio signal. It is connected to T1 low turn side. The HV from HeNe supply is fed in series though high winding side. Audio input causes enough modulation of tube output to be detectable.
 

ultimatekaiser

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of course you cant run a transformer on DC. *rolls eyes* gimme a break Cyp. The answer is indeed in the above post. As that's the only way to really modulate a HeNe. You can't fully start and stop it, as that'd be very hard on the tube and starting circuit, like you would a diode. It is analog modulated via the transformer I'd think, as it would provide isolation from the signal input. It'd be very odd to drive it off LV AC. I do remember playing with one of these when I was middle school. I'd just be tracing the circuit to see where the barrel connector goes, to get the polarity, and then put it on a lab supply and bring it up 12V at a 2A current limit and see if it draws current then go from there. I kinda wish I remember it better. I used to love watching the tube glow in the dark. I'd love to get my hands on one for nostalgia purposes/display.
 

ultimatekaiser

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Out of curiosity, Did you ever get this working? I actually just stumbled across one of these (though mine is the smaller tube version (there are two versions of the same model) I got it working with no issues. I can confirm it is indeed a 12V supply, however like alot of other lasers of this time period, for some reason it is wired atypical. the jack is center pin - instead of +. There is a diode across the input to protect it from having it wired backwards. If you tested it with a typical center pin + power supply it will not function (which is what I suspected before) I just wanted to make note of it here.

I'm pretty happy. I got this thing on a real bargain, and for me this is the laser that started it all. I'm a bit envious you have the bigger version!

You will need a 12V supply that is center pin negative at at least 2 Amps.
 
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