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Registered Member #397
Joined: Wed Apr 19 2006, 12:56AM
Location: Western Washington
Posts: 125
Be careful and don't crank the power up too fast when first troubleshooting it. I was tuning mine and it had a breakout point, but it did not breakout and I had an arc leap from the feedback coil to the secondary and it scared the crap out of me.
I also concur on it having a dedicated breakout point. The secondary wire is just so thin, it has too little mass for thermal dissipation and I'm sure you could accidentally melt it even at low power levels and charring your secondary coilform is never fun.
You could simply take some solid 12awg wire, run it about 1" above the secondary coilform, bend it into a circular loop as field/gradient ring (or imagine it as a very anorexic looking minor diameter toroid), then bend it upwards into a sharp breakout point from the center.
Registered Member #105
Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408
Yes, I was planning on making a topload, I just hadn't gotten that far yet. But otherwise, power worthy ? I can but 3/4 inch flexible tubing from home depot, then cover that with aluminum tape and then add a breakout point for the toroid, and it should look nice. Updates to come!
Registered Member #397
Joined: Wed Apr 19 2006, 12:56AM
Location: Western Washington
Posts: 125
If you have some copper bus bar and flexible copper tubing handy, just solder some together. I got the idea from some ham's website as corona rings but I went an extra step and tinned mine so they won't tarnish. It's cheap and can be modified to fit any number of situations involving high voltage. The following image I attached should illustrate it pretty well.
Registered Member #105
Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408
Heres an updated picture of the layout. The thing on the heatsink in the back is the grid leak resistor- made from 6 20Kohm resistors- 2 in series to increase the voltage rating, then 3 of these pairs in parallel for 13.3kohm. Each resistor is rated for 35W, and they are heatsinked, so I think this will work Suggestions welcome, I decided to use my home wound transformer for the filament, its heavy but if i want to i can add another tube to the coil, and add one more turn on the transformer to keep the voltage right around 6.3V, maybe a bit higher. One switch is for the filament, and one is for the MOT. And there is the secondary with the copper pipe fittings toroid and breakout. EDIT: Also grounded prettymuch everything metal thats not part of the circuit including the filament transformer core, the on/off switches, and the MO caps metal body.
Registered Member #105
Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408
Ok, decided to make this a dual 811A coil, so I am making a few changes. First, the new secondary is 14 inches long. This should prevent flashovers to the nearby tubes Also, do you think that 4 inch PVC (4.25 o.d.) would be sufficent for the primary form? I was using three inch, but looking at other coils this seems way too small- even 4 inch may be to small. Im modeling this one after steve wards coil, and he uses 6 inch PVC- is this neccessary?
Registered Member #56
Joined: Thu Feb 09 2006, 05:02AM
Location: Southern Califorina, USA
Posts: 2445
I found that with really tight coupling things didn't work (too tight of a feedback caused my tubes' grid to ark over) but I didn't really try too much... I use 6" for my single (or dual, I run it both ways) coil with a 2" by 5" secondary...
Registered Member #105
Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408
I know "..." has had success with a doubled MOT supply and 2 tubes, but anyone else try this with success? I think I might go with just the MOT rectified and filtered unless there are HUGE improvements that can be made by level shifting the MOT.
Registered Member #105
Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408
Ahh, awaiting some sockets and plate caps for first light, but everything is ready and waiting. I got my other tube yesterday in the mail, and everything is wired. The primary cap is almost directly under the primary coil, so there isn't much extra wire inbetween them. First light as soon as the other stuff arrives Suggestions welcome!
Registered Member #105
Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408
First Light! It makes an aweful squealing noise, but it works! Sparks are about 4 inches long or so. Do all VTTCs make that horrible squeal? Im gonna try a couple things- removing filter capacitance (2uf on the output of the MOT) as well as lowering grid leak resistance. The feedback coil is the right polarity if I am getting these sparks, right? Other suggestions welcome!
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Starting a new (first) VTTC First light!
? I can but 3/4 inch flexible tubing from home depot, then cover that with aluminum tape and then add a breakout point for the toroid, and it should look nice. Updates to come!
