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Registered Member #4603
Joined: Wed Apr 25 2012, 07:33PM
Location: Austria
Posts: 159
When you have a 110 volts MOT the VTTC should do something with 40V ^^ Even with a bad setup it will work. Try to use a neon bulb to look if it is oszillating. Maybe you need to change the polarity of the feedback.
Registered Member #1643
Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039
Nope. i have flipped feedback / primary hundreds of times. with a 110V mot i did all my tests with 36VAC in.
I have 10 turns for my feedback I have 13 for my primary (as thats resonance)
Did all my tests with a FL tube 4 inches away, never once got a lit.
Went off of this schematic with my own cap values.
No idea..because i checked the wiring 3 times just now, and its dead on. its late though, ill play more later but idk, i cant get a thing out of this...
Maybe this is normal, but one thing i noticed is, if you short out the series caps on the mot, the mot draws a LOOOT more current off the varriac...even at 15V
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
I think you will get better output if you connect all 3 grids together. The primary should be ~30-50 turns when you run on a voltage doubler, depends on the frequencies etc. but 13 is really not enough. Recalculate the tank capacitor.
Registered Member #1643
Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039
Well, is this really even a doubler to have series caps and a diode as seen above? not the typical doubler im use to seeing. so. Right now my primary is 35 turns, and my feedback i tried 8 turns, and 25 turns.
I tried feedback 3" up the coil, 6", and even 10".
I tried every combination of phasing possible.
AB 12 AB 21 BA 12 BA 21
Noooothing, is working. maybe because its a 300khz coil of 34awg? no idea. I tested the mot before wiring, and it did spark. i tested it with the caps and diode...it sparks. i add the tube/coil stuff on, power things up, filament to 12.6V, give the mot 30VAC at max, nothing. the FL tube, 1cm off the coil, does nothing.
I putt 4VAC to the mot, and measured 72VDC on the diodes. So i know the power is FINE
Registered Member #152
Joined: Sun Feb 12 2006, 03:36PM
Location: Czech Rep.
Posts: 3384
Touch the output directly with a neon bulb. Does it light up? Have you tried swapping the grid coil connections? (probably a dumb question but) Is the cathode grounded to the transformer?
Edit: I just looked at your tank cap and 10 nF is way too much. You will need something around 1-2 nF. Calculate the cap so the primary LC tank oscillates a bit below the secondary's resonant frequency.
Registered Member #1643
Joined: Mon Aug 18 2008, 06:10PM
Location:
Posts: 1039
Okay it works. I found the capacitor on the primary had to be moved, when it's at the top, matched with the top turn, it won't work. So, moved it down, changed my grid leakage from 330 to 5000, and it FINALLY oscillates. This build was to make sure the tube works. Now that I have proof, I'm going to buy wire for a higher 600+ kHz coil.
So, with soooo many turns needed, that takes up so much space. So do you use thinner wire? Or is it okay to go so high up the secondary? Seems so wrong lol
No output, too small, I know it's wired badly, but it was just to test the tube with what I have around...
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I want to build my first VTTC...
