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How small can a VTTC be?

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ragnar

Wed May 23 2007, 11:42PM

Registered Member #63 Joined: Thu Feb 09 2006, 06:18AM
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Posts: 1425

Good to see you around, Reaching.. and that VTTC is cute, too!

Vaxian

Thu May 24 2007, 12:21AM

Registered Member #635 Joined: Tue Apr 10 2007, 01:56AM
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Posts: 85

My coil now has breakout in the 1/2" range and still working on it.

The trophy will probably be a tube with lit filament on a lexan base with some wordz of encouragement. (I have lotys o lil tubes)

I am in AZ right now, will get a pic of the coil with breakout on ASAP

EDY19

Sun May 27 2007, 12:26AM

Registered Member #105 Joined: Thu Feb 09 2006, 08:54PM
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Posts: 408

OK, I've started mine now, the TC bug bit me

Here's the primary with 25 turns, the last 20 are tappable. The grid coil is not wound on the former yet. The secondary is 1.25 inches in diameter wound with 28 gauge wire. The power supply is done, but I need to make a nice base for it before i start final assembly. Pics will be up in a little bit!

Steve Conner

Sun May 27 2007, 10:39AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Tetrode tubes like the 6146 should be so easy to drive, you might get away with no grid coil at all, and just use an antenna on the grid pin to pick up some RF from the secondary coil. That's how all the old plasma tweeters worked.

If you do that, you need to provide a large resistor from the grid pin to ground. A plasma tweeter schematic should show this.

EDY19

Sun May 27 2007, 01:59PM

Registered Member #105 Joined: Thu Feb 09 2006, 08:54PM
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Posts: 408

I just might try that- i found one site that uses a ~20k 5W resistor for that application, so I'll try that out, I was struggling to find suitable wire for the feedback, anyway, and I'm thinking that moving the antenna closer or further away will be easier then making the feedback tappable

Anyway, also on that site is a 1nf poly capacitor in series with the antenna. Must this also be included? Is there an acceptable range for the value of this capacitor- im assuming its just so the antenna voltage does not start "walking" up, so any small HV cap should work alright there. Its coming together, and the tank caps are in the mail!

ShawnLG

Sun May 27 2007, 05:39PM

Registered Member #286 Joined: Mon Mar 06 2006, 04:52AM
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Posts: 399

I hope this contest is not over yet. I just picked up a nice tube with a screw terminal mounting base today.

uzzors2k

Sun May 27 2007, 06:49PM

Registered Member #95 Joined: Thu Feb 09 2006, 04:57PM
Location: Norway
Posts: 1308

No, we'll let it run for a while yet, seeing as the interest is starting to pick up. The coils are looking good!

Vaxian

Mon May 28 2007, 03:55AM

Registered Member #635 Joined: Tue Apr 10 2007, 01:56AM
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Posts: 85

Awesome!

As soon as I get back from Arizona I will start work on the trophy.

I will also work on my coil! Been working on it some, getting about 1/2" of spark right now, going to wind a better secondary, the one I am using now only has about 400 turns.

Been subbing in different caps, I have allot of old Military surplus Micas.

Just bought some 30 guage wire on ebay, going to use 2 1/2" PVC to wind a new secondary about 6" long or so. This will add some size to my coil but I am not happy with the coils output as is.

I am very happy to see more interest in this contest.

Steve Conner

Mon May 28 2007, 08:35AM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

Given that the antenna couples capacitively to the output anyway, I don't see any point in putting another cap in series with it. anyway good luck, this contest looks great

EDY19

Wed May 30 2007, 07:40PM

Registered Member #105 Joined: Thu Feb 09 2006, 08:54PM
Location:
Posts: 408

Alrighty! First Light is here- 650pf capacitor, voltage quadrupler with 560uf 400V capacitors, 1N5408 diodes. 1 6146 tube, and antenna feedback. Sparks are about 1 inch long, making a little bit of a hissing sound. I kinda want to try adding another capacitor, we'll see what happens once i get a little more familiar with the setup right now. Any things to check before i add on another 650pf capacitor?

I also want to interrupt this so the tube isn't seeing quite as high of an average current, and that way i can add another cap for sure- i know i can't use stacatto because i am using filtered DC- could I just put a mosfet from the cathode to "ground" and switch that? I'm thinking that the ratings shouldn't have to be too extreme, I have some 15A 50V mosfets, would that be sufficient? I guess I'm just not sure of the voltage that will develop across the tube cathode and ground. Also, what kind of current limiting should i have on the 110VAC going into the voltage quadrupler? I have a 10 ohm 10 watt resistor in series with the line voltage on the input of the quad. right now, but it gets quite (ok, really very) warm

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