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Registered Member #9711
Joined: Sat Jan 19 2013, 03:27PM
Location:
Posts: 65
Ok, the silicone tubing arrived yesterday and I slid the 7mm copper core wire through it. Just after that, after some thought, I decided to just silicone the one end of the wire to the tube end. I found the prior silicone was fairly easy to cut away and I was no longer apprehensive about applying it again. That way, an elbow or other end doesn't stick out far enough to make contact with the inner metal shielding. For the other end of the wire going to the multiplier, I cut the remaining original multiplier wire about 6" from the multiplier then used a couple of boots to form a sort of press fitting connection between the spark plug core and the HV multiplier wire end. I soldered the wires together, then coupled the rubber boots together.
Early testing found blown 3055's (they blew out a lot anyway even before the mods), so I replaced those with more rugged 2N3773's. Took a while to make sure there weren't shorts, then a 2nd power up. As I carefully started adjusting the HV pot upward, I knew there was HV as I could hear spraying, although not near what it was before the mods. I adjusted to the max and spraying was somewhat more BUT so far my PC has not frozen.... a good sign. I carefully placed my hand up against the wire and couldn't "feel" any static, unlike before, except for one area where I actually got a bite: where I used the rubber boot couple. I think this may need some of the silicone grease within. Only other issue is that I have to make sure I still ground the metal shelving to the HVPS ground, otherwise I get a small bite everytime I touch the shelf. I guess I never will figure out the cause. Since the HV side is so well insulated now, my guess would be the flyback transformer or flyback circuit itself, but since I don't get the shocks when everything is grounded, I won't test any further. Final test will be to check output of the tube later today, but I don't expect any issues.
Thanks again for all the help, and especially Ash for helping address the issues.
Registered Member #4074
Joined: Mon Aug 29 2011, 06:58AM
Location: Australia
Posts: 335
With regard to the metal shelf:
The HV circuit is capacitively coupled to its surroundings, so if the shelf is isolated from earth it will be floating at a relatively high voltage. Since it has a rather large surface area, its capacitance is high enough to deliver a painful shock. Grounding the shelf removes this issue. This is pretty normal behavior for HV circuits, especially when higher frequencies are present. Grounding, shielding/filtering and insulation are usually fairly high-priority in hobby HV builds.
Registered Member #9711
Joined: Sat Jan 19 2013, 03:27PM
Location:
Posts: 65
Thanks, GrantX. I guess being the first time using my own HV circuit in this fashion, I wasn't aware of how much coupling can take place.... obviously a lot! I think I mentioned that I used the circuit before, but at that time the shielding was all leaded acrylic, so arcing and other issues weren't much of a problem. However, the acrylic didn't shield the x-rays well enough which is why I decided to use my current shielding. Switching from the acrylic to metal and lead meant a lot more detail to HV insulation and grounding, so hopefully all good to go now.
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best ways to minimize HV arcing/ spraying?
