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some progres on the coil. Actually a lot of progress . Everything on the second "floor" is completed. The only big thing left is to mount the resonant capacitor on the 3rd floor and start wireing. Here some pics:
Registered Member #1025
Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566
Hi Huben, what is the red thing which looks like fire-extinguisher miniature? Some kind of cap? BTW: The set of MOT caps looks insane!!! Keep us updated…
Registered Member #477
Joined: Tue Jun 20 2006, 11:51PM
Location: Seattle, WA
Posts: 546
Looks real cool, Huben. I can't wait to see it go! With 20kV on the plates, you've got room to grow, definitely. A bunch of 15/60 NSTs in parallel might make a nice plate supply for this sucker! Somewhere, I've got a radar tube with very HV plate like that, but it's a much smaller tube than what you've got.
Mates - the "fire-extinguisher miniature" (good comparison by the way ) is a capacitor. It is 5kV 2nF 15kVAR. I will be using it for the feedback circuit. You don't see such caps everyday . For the bank of MOC - they really look good, but i am concerned - will the pain cause some insulation issues (the connectors and the "hats" aren't painted). But we will soon find out
Hi Aaron - thenks for the repply.
"With 20kV on the plates, you've got room to grow, definitely." -well ... yes and no. I don't have capacitors (for the resonant one ) that are more than 30kV (the one that i use now is the biggest i can get). So for using 20kV on the plate will requite some really high voltage caps.
"I've got a radar tube with very HV plate like that, but it's a much smaller tube than what you've got." - my tubes are also from a radar. It was a real luck to get them
And now one question. Because of the relatively small resonant capacitor (2.8 nF ) and the low resonant frequency of the secondary (around 210khz with topload) I need to put about 40 (estimated) turns on the primary. Is this TOOO much, or will it work OK ? . And if i use so many primary turns, how will the number of feedback turns change ? (The basic circuit that I am using is Steve Ward's 833A )?
Your Fo may be a bit low. 883’s like about 350khz to 405khz, anything under that and the tubes start to choke and lose spark length/sword appearance. Suspect with your high plate voltage and smaller plate size, those tubes will like a bit higher freq.. This will also reduce your primary inductance by 10 turns or so. Maybe a secondary about 450khz without top load is a good starting point.
Good luck sir, looking great!
I agree but my buget is tight (the whole coil is built from what i have on hand) so first I will try this secondary . The last time when I run the tubes at that frequency, there wasn't any obvious problems (the coil was in CW mode !!! and i was using bigger resonant capacitor ). Here some pics of the progress - the resonant capacitor is mounted, the primary is winded (about 44turns so i can remove after that) and the "sled" for the feedback is done (missing the windings). So the question - if i use SO MANY turns what will be the problems that i will face . PLEASE WRITE.
"Project is looking good, getting me the momentum to pull the Quad VTTC out and finish the project. A bit of welding and powder coating and will update the post." - this project is inspired by your coil - so PLEASE start working on it agian - we all want to see some sparks from that beast
Registered Member #1025
Joined: Sun Sept 23 2007, 07:53PM
Location: Czech Rep.
Posts: 566
Huben Panev wrote ...
So the question - if i use SO MANY turns what will be the problems that i will face . PLEASE WRITE.
Hi Huben, I'm not familiar with tube based circuits but I would be afraid of so many primary turns. There must be very high voltage induced on a primary with so many turns... I think you should add at least some safety spark gap to protect your resonant cap (and the tubes).It is just an idea - maybe stupid but very cheap on the other hand...
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4Kva Dual GMI-7 VTTC - FIRST SPARKS
. Everything on the second "floor" is completed. The only big thing left is to mount the resonant capacitor on the 3rd floor and start wireing. Here some pics:
Somewhere, I've got a radar tube with very HV plate like that, but it's a much smaller tube than what you've got.
) is a capacitor. It is 5kV 2nF 15kVAR. I will be using it for the feedback circuit. You don't see such caps everyday 
. For the bank of MOC - they really look good, but i am concerned - will the pain cause some insulation issues (the connectors and the "hats" aren't painted). But we will soon find out 
) that are more than 30kV (the one that i use now is the biggest i can get). So for using 20kV on the plate will requite some really high voltage caps.
. And if i use so many primary turns, how will the number of feedback turns change ? (The basic circuit that I am using is Steve Ward's 833A )?
. The last time when I run the tubes at that frequency, there wasn't any obvious problems (the coil was in CW mode !!! and i was using bigger resonant capacitor ). Here some pics of the progress - the resonant capacitor is mounted, the primary is winded (about 44turns so i can remove after that) and the "sled" for the feedback is done (missing the windings). So the question - if i use SO MANY turns what will be the problems that i will face 
