alf638
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- Joined
- Dec 10, 2010
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Hi guys, I recently got my first HeNe and have just finished building a power supply based on the following schematic (from The Professor's Homebuilt Laser Page)
I know its not the most efficient power supply, and it's definitely not going to be permanent, but I happened to have all the necessary parts on hand, so I thought I'd give it a go.
I connected the cathode of my tube (the big metal can electrode, according to the FAQ), to the ground/centre tap and the ballast resistor (2 megaohms!), to the anode, and all was working nicely, although the beam seemed a little dimmer than expected.
After letting it run for a while though, I noticed a drop in power output, down to the level of nothing but a very faint dot, barely visible on the opposite wall. Being paranoid that I'd managed to get the polarity wrong, I swapped the anode and cathode, grounding the electrode without the can, and connecting the output of the rectifier to the metal can electrode. I switched it on (for no more than about 5 seconds, just in case), and I noticed a BIG increase in power output, from a faint dot, to something several times a commercial cat-teaser (and of a much nicer colour!).
I also noticed that with the metal can electrode (cathode?), connected to ground/the centre tap, the other electrode got quite hot, which of course, the cathode is supposed to do! The metal can electrode stayed totally cool, while the other electrode got quite warm to the touch.
So, I guess my question is this, is there any way that either the metal can electrode is actually the anode, or that I've been stupid and ground is effectively positive in this circuit?
Also, I'm sorry if this is a stupid question, I just really want to make sure I keep my new HeNe nice and healthy!
EDIT: I realise I left out the details of my setup. I'm running from a rectified 15kV neon sign transformer to give 10600VDC, assuming around 1600V operating voltage for the tube, that leaves around 9000V being dropped across the 2 megaohm ballast for a tube current of around 4.5mA, this is on a 30mm by 240mm tube. My filter capacitors are a touch over 0.5uF.
EDIT 2: I did another quick test run in both polarities, just long enough to take a photo of the beam. I really don't want to run it for more than a few seconds at a time unil I've got this polarity issue figured out, but I thought a few pictures might help.
The first picture is the low, barely visible output when the metal can (cathode?), is connected to the centre tap/ground which. The second much brighter dot is that produced when I reverse the polarity, attaching the metal can electrode to the ballast resistor side.
I also noticed a slight ghost beam in this polarity, and a rather significant amount of light output from the HR.
Thanks in advance for any and all help, this laser is absolutely hypnotic!
I know its not the most efficient power supply, and it's definitely not going to be permanent, but I happened to have all the necessary parts on hand, so I thought I'd give it a go.
I connected the cathode of my tube (the big metal can electrode, according to the FAQ), to the ground/centre tap and the ballast resistor (2 megaohms!), to the anode, and all was working nicely, although the beam seemed a little dimmer than expected.
After letting it run for a while though, I noticed a drop in power output, down to the level of nothing but a very faint dot, barely visible on the opposite wall. Being paranoid that I'd managed to get the polarity wrong, I swapped the anode and cathode, grounding the electrode without the can, and connecting the output of the rectifier to the metal can electrode. I switched it on (for no more than about 5 seconds, just in case), and I noticed a BIG increase in power output, from a faint dot, to something several times a commercial cat-teaser (and of a much nicer colour!).
I also noticed that with the metal can electrode (cathode?), connected to ground/the centre tap, the other electrode got quite hot, which of course, the cathode is supposed to do! The metal can electrode stayed totally cool, while the other electrode got quite warm to the touch.
So, I guess my question is this, is there any way that either the metal can electrode is actually the anode, or that I've been stupid and ground is effectively positive in this circuit?
Also, I'm sorry if this is a stupid question, I just really want to make sure I keep my new HeNe nice and healthy!
EDIT: I realise I left out the details of my setup. I'm running from a rectified 15kV neon sign transformer to give 10600VDC, assuming around 1600V operating voltage for the tube, that leaves around 9000V being dropped across the 2 megaohm ballast for a tube current of around 4.5mA, this is on a 30mm by 240mm tube. My filter capacitors are a touch over 0.5uF.
EDIT 2: I did another quick test run in both polarities, just long enough to take a photo of the beam. I really don't want to run it for more than a few seconds at a time unil I've got this polarity issue figured out, but I thought a few pictures might help.
The first picture is the low, barely visible output when the metal can (cathode?), is connected to the centre tap/ground which. The second much brighter dot is that produced when I reverse the polarity, attaching the metal can electrode to the ballast resistor side.
I also noticed a slight ghost beam in this polarity, and a rather significant amount of light output from the HR.
Thanks in advance for any and all help, this laser is absolutely hypnotic!
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