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Frist light achieved; is there an accepted guideline on properly optimizing/tuning a VTTC?

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Cesiumsponge

Mon Jun 01 2009, 10:12PM

Registered Member #397 Joined: Wed Apr 19 2006, 12:56AM
Location: Western Washington
Posts: 125

One benefit of not having the feedback coil up higher is you don't get the unexpected BRAAAAAAP when it arcs to the secondary

I had that scare twice, nearly needed a change of underpants since I was fairly close to the coil when it happened. I'll do more coil testing tonight. I've been tied up all day making soup.

Herr, this is an excellent observation and indeed a shallow depth of field is partially to blame for the photographic fuzziness of the 70-100VAC series. I'm running ISO100 or 200 for smoothest imaging so I had to crank my lens to the largest aperture available at that focal length,which I think was f4 or so. I set it on manual focus because AF won't work well in the dark At the same time, the camera is pointing upwards from a lower vantage point so the plane of focus isn't parallel with the center of the streamers. There is that imaginary perpendicular plane of perfect focus, but its bisecting the conical "zone" of streamers at an oblique angle which means an even narrower zone where focus is achieved on the subject. Besides the depth of streamers from the focal plane, anything above or lower than the center of the image starts to fade in sharpness as well.

Despite the shortcomings of the photos, I can say that, with personal live observation, there is indeed less definition around the "edges" of the hotter streamers than the duller purple ones. The ghost-white sections were fuzzier, like a MOT arc, than sharply defined.

If film was still readily and conveniently available, I would definitely use it in a manual SLR over a digital camera just due to ruggedness. I notice a lot of artifacts showing up on digital photos around high voltage fields and RF and I'm a bit touchy when I use my SLR around HV gear. Film grain is extremely fine, and you can easily go back and drum scan film negatives to insane resolutions. Unfortunately it's difficult to make film vs digital arguments because there are two sides that feel very passionate about it. Ultimately the argument boils down to digital vs digital because you have to scan film to put it side-by-side to a digital print and it boils down to the scanning technology. Doing some medium format film shots of a coil in operation would be plain fantastic, but expensive. It usually takes dozens of shots before you catch a streamer formation you like.

The current lens I am using is a Nikkor 18-200mm f/3.5-5.6 G ED-IF AF-S VR DX which is a "jack of all trades" lens which is sharpest at f8-f13. It has minor distortion at both extremes but this is easily fixable in photoshop. Its a convenient all-in-one that doesn't excel at everything, but does a decent all-around job. I know it's limitations, so it doesn't bug me. Usually I jump to a Tokina AT-X 116 f2.8 if I need ultra wide.

Anyhow I will post another update when I get the chance to tinker some more. I will try what Dr. Spark suggested and detune it slightly so it runs lousier at lower power levels, but should bump to Fres at higher power levels so it stops fuzzing out on me. Hopefully this process will take days and not weeks to find that happy medium.

*edit.

I think I just punched through a performance barrier. I'm making a chart of values right now but I am 1/4" away from breaking 19". I don't think anyone has managed this to date...17" seemed to be the max that I was aware of. Will do a writeup after I check out all the variables and tinker some more.

Herr Zapp

Mon Jun 01 2009, 11:46PM

Registered Member #480 Joined: Thu Jul 06 2006, 07:08PM
Location: North America
Posts: 644

CS -

You clearly understood exactly what I was talking about ...... if you were shooting at an upward angle, the "depth of field" equation would become even more complex with a conical subject.

(One of my other hobbies is photography, and I have collected quite a bit of Nikon 35mm gear, all based on the F2 body series of the late 1970s. These were the last all mechanical Nikon SLRs, and, like the Leicaflexes of the same vintage, were the evolutionary highpoint of the 35mm mechanical SLR camera. These were the "Rolexes" of the mechanical SLR world. I have a large selection of Nikkor lenses (8mm fisheye to 500mm reflex), and it pains me that I find myself using digital cameras almost exclusively because they're "convenient".)

It will be interesting to continue analysis of the "fuzzy" appearance of the hotter, brighter discharges. Another factor could be lens "flare", internal reflections between lens elements from a very high intensity light source.

However, you state that real-time human-eye observation also shows less definition of the hotter arcs. Jeff Behary's Electrotherapy Museum website has a lot of arc and streamer photos of all types, and it certainly looks like the "hot" arcs in his photos also have less edge definition.

Be conservative with plate current on your 810; those graphite plates should NOT be run with any color visible!

All in all, a very nice VTTC design, with absolutely gorgeous workmanship.

Regards,
Herr Zapp

StevenCaton

Tue Jun 02 2009, 12:21AM

Registered Member #1845 Joined: Fri Dec 05 2008, 05:38AM
Location: California
Posts: 211

CS

Have you tried changing the number of turns on the grid feedback coil yet?

I just went back to the thread about this vttc, because I never really gave it a thorought read, and I must say that you've done an awesome job. I used to not care about aesthetics too much, but now I just want to make all my coils look nice. A 19 inch spark from a piece of crap coil is definitely not the same as a 19 inch spark from a work of art.

Dr Hankenstein

Tue Jun 02 2009, 12:24AM

Registered Member #1642 Joined: Sun Aug 17 2008, 11:36PM
Location: Black Canyon City
Posts: 96

Ya, but; where's the pictures?

Hank

Cesiumsponge

Tue Jun 02 2009, 12:51AM

Registered Member #397 Joined: Wed Apr 19 2006, 12:56AM
Location: Western Washington
Posts: 125

Dr Hankenstein, my coil progress photos (sans the last week of build progress) is currently available and cataloged here:

I posted a small update on my project thread. Hit 19.25" at 120VAC but unsustainable as the 810 tube started to incandescence a faint cherry red and would have quickly gotten worse. Then the grid feedback carbonized my primary coil form when it decided to arc over. Out of action until I sand down the PVC coilform or dig up another length of PVC. Not sure if I want to get dirty today or put it off for another day.

I didn't have time to operate a camera to catch the streamers on this latest series of tests...too many things to juggle around. Since the coil is down for at least a few hours (if I even go back to it today), I'll take some photos of the essentially finished coil (minus it's final primary and grid feedback coil).

I haven't experimented with my grid feedback yet. Based on data I scribbled down, I've been getting more efficient at pushing the longer streamers at the 100-120V input at the minor expense of getting shorter streamers below 100V, but I can live with that. It'll barely create corona under 50V. I was at turn 33 when my progress stopped. I'm not sure how much further it can go. If I can get it to run at 16-17" indefinitely without overheating the tube with occasional "amp to 11" runs to hit 19"+, I'd be completely satisfied.

Dr. Drone

Tue Jun 02 2009, 01:23AM

Registered Member #290 Joined: Mon Mar 06 2006, 08:24PM
Location:
Posts: 1673

teravolt

Tue Jun 02 2009, 01:58AM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

I was thinking that not only frequency may afect the shape of the spark but also whether the spark is hot. I have noticed that sparks that are more violet are sword like and sparks that are orange aruond the exit point of the secondary are spiral in nature. I don't know if this comes with more power or less frequency. can sombody confirm this

Dr Hankenstein

Tue Jun 02 2009, 03:27AM

Registered Member #1642 Joined: Sun Aug 17 2008, 11:36PM
Location: Black Canyon City
Posts: 96

I must apologize. Looked at your extensive photo colaboration...very cool! I was actually refering to Herr Zapp! We have been giving him kind of a hard time waiting for his photos of the Teslaton. Sorry for the confusion.

Hank

teravolt

Fri Jun 12 2009, 07:59PM

Registered Member #195 Joined: Fri Feb 17 2006, 08:27PM
Location: Berkeley, ca.
Posts: 1111

Hi Cesiumsponge what was the outcome of your endever to fix your vttc. I am curous if the recomindations fixed the detuning

Cesiumsponge

Tue Jun 16 2009, 01:07AM

Registered Member #397 Joined: Wed Apr 19 2006, 12:56AM
Location: Western Washington
Posts: 125

Hello teravolt. I've been swamped with attending birthdays, graduations, and relatives flying in to visit in the last couple weeks so I haven't had much time.

I've since slathered some polyurethane on the tickler coil when I'm in the garage to grab stuff from the freezer so it's got a few layers on there now, better than before! I should be able to pick back up where I left off sometime this week or next weekend on the coil. Definitely more primary turns gets me better tune at longer streamer lengths but you really need to crank the variac past 50-60V before you even see the faintest brush discharges because it's now fairly detuned on the low end. I'm hoping to finish the coil entirely by the end of this month (though I said that back in April too).

Unfortunately it means I need to order more wire for my final primary coil. I ordered a 50' spool of cotton braided wire which works to right about 30 turns. I guess I need a 100' spool now.

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