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My first SGTC (AKA the Howlin' Mad Murdock SGTC MarkI)

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HM_Murdock

Wed Sept 01 2010, 02:26AM

Registered Member #3075 Joined: Fri Aug 06 2010, 02:44PM
Location: Athens, GA
Posts: 148

After some studying, I think I have the design layout for my first SGTC...

If I can get the eyes of the wise on these and validate my components, I would appreciate it.

NST - 9kV, 30mA

Multi pipe spark gap (copper pipe)

Safety gap

4" spherical top cap, with a capacitance of 11.36 pF

3" x 13.5" secondary on PVC

26 AWG enameled wire on secondary, 780 turns, 612 feet, and 401.14KHz resonance

1/4" copper tubing, 1/4" spacing, flat coil for primary. 10 turns. Expect to tap somewhere between turns 6 and 7 to attain resonance with secondary

0.0136 (1.7 x resonance of NST) primary cap. 11 942C20P15K caps, giving 22,000 V peak.

So, do my parts and measurements make sense...good, efficient use of the parts? Sizes, caps, turns, and wire gauge all look good?

HV Enthusiast

Wed Sept 01 2010, 12:25PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Just some thoughts . . .

1. Go with longer secondary. Maybe 20" would be a good size for that NST. 10" seems really short for a 9kV/30mA.

2. You could probably use 10AWG (or even 12 AWG) wire for the primary. 0.25" is overkill. 1/8" tubing if you want to keep it tubing.

As comparison, i use 1/4" tubing for a 14.4kV/240mA transformer powered SGTC.

HM_Murdock

Wed Sept 01 2010, 12:41PM

Registered Member #3075 Joined: Fri Aug 06 2010, 02:44PM
Location: Athens, GA
Posts: 148

Oops!

Don't know where I pulled that number from, but I meant to say the secondary is 3" x 13.5". That follows the 4.5 rule of thumb. When you say go 20", do you mean also to increase the diameter to stay in ratio, or to go with a 3" x 20"?

I went with tubing as it was the norm, had not really considered solid core (figured tubing would be more efficient since it uses skin effect on the primary anyway). I could get 10 or 12 AWG off the roll by the foot though, so that may work out to be more economical regardless. I assume there is no loss in using solid core 12AWG Vs. 1/8" tubing?

Thanks for the feedback so far! I do plan on making this a start to finish thread btw...

HV Enthusiast

Wed Sept 01 2010, 01:41PM

Registered Member #15 Joined: Thu Feb 02 2006, 01:11PM
Location:
Posts: 3068

Maybe go 3.5" OD Secondary (standard 3" PVC) with 20" height and 18" winding length. This will give you unloaded fres of about 455 kHz.

For the power levels you are running solid wire 10 AWG should be fine. If you have 1/4" tubing you want to use thats fine too - it does look good IMHO. Just not needed for that power level. So its more just a personal choice.

HM_Murdock

Wed Sept 01 2010, 02:01PM

Registered Member #3075 Joined: Fri Aug 06 2010, 02:44PM
Location: Athens, GA
Posts: 148

Thanks!

Will re-do the specs tonight when I get home and change the Secondary to 3.5" x 20" and 18" winding.

I do not have the tubing already, and in fact (unless I am mistaken) the 10AWG solid will wind up being less (Vs. buying an entire roll of tubing), so that works out even better.

In fact, the only part I have currently is the NST...everything else is going to have to be either purchased or scavenged...so feel free to make suggestions or changes if you see something that can be improved or tweaked.

HM_Murdock

Tue Sept 07 2010, 01:11AM

Registered Member #3075 Joined: Fri Aug 06 2010, 02:44PM
Location: Athens, GA
Posts: 148

Primary coil is done...

Lessons learned:

1- 20 feet of 1/4" tubing is not enough to wind out to go 12 turns at 1/4" spacing
2- easy on that last tiny bit when drilling through plexi (especially near the edge of the hole)
3- it's not easy making a pretty spiral

Luckily, I am going for function on this first one...I think I would use a cutting board next time (this 18"x18" 1/4" plexi was a $2 scrap piece, so I decided to go with it). She aint' exactly pretty, but it should work.

Xplorer

Tue Sept 07 2010, 05:49AM

Registered Member #2416 Joined: Sun Oct 04 2009, 04:23AM
Location: Oceanside, CA
Posts: 91

I made a small TC with a 9/30. Make sure you solder 10M ohm bleed resistor across each cap. I use 1/4 watt and they're fine.

-Tony

HM_Murdock

Sat Sept 11 2010, 02:45PM

Registered Member #3075 Joined: Fri Aug 06 2010, 02:44PM
Location: Athens, GA
Posts: 148

progress made...finished my secondary last night, and covered it in Envirotex Lite epoxy. Left it to rotate overnight, and am quite pleased with the result.

Primary platform is now attached and adjustable for height.

HM_Murdock

Sun Sept 12 2010, 02:58AM

Registered Member #3075 Joined: Fri Aug 06 2010, 02:44PM
Location: Athens, GA
Posts: 148

We have first light!

The visible output was better than these pics, but I had a heck of a time capturing the sparks and corona with my digital camera...

Considering it's my first coil, it's a single segment spark gap, my cap is a bunch of plastic plates and tinfoil, I haven't made a proper toroid for it, and about half of the thing is joined by alligator clips, I am happy to get this much to start with. Will be improving and building the proper parts and connections for it next.

And yeah, ironically, that is a Mountain Dew Voltage can in the pic (realized the name of it as I was taking it down)...

HM_Murdock

Sun Sept 12 2010, 04:25AM

Registered Member #3075 Joined: Fri Aug 06 2010, 02:44PM
Location: Athens, GA
Posts: 148

(sorry for the triple-post...if there's some secret way to add attachments in edit, please let me know)

Broke out the older digital camera, and got decent video this time...also got a better pic using a screen capture of the video

]voltage_can_2.wmv[/file]

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