Hi Marcus,

I will admit that I was expecting a somewhat high number for output from javatc. Seems to be a common thing that I have noticed sometimes by others too, even though I have never used this program, I suppose this is caused by some missing or incorrect inputs somewhere.

Yes, my opinion is not enough power in, especially to charge up a 15nf tank capacitor.
The tank capacitor is usually matched in a certain range for power input.

And okay on verification on toroid size, yes quite big for your current power input.

Okay on the lead for more power... :^)

Got to "run" here... going to be spark gap coiling in my basement myself experimenting this afternoon for me here in my time zone.

Chris

Hi,

Yes, some more details needed here.

What are you getting for spark output? Did you design this with paper and pencil? Or did you use some computer program? Even still...if design work was calculated some way, my experience is that old school tuning is still required for best performance. There are in my opinion aways real world variables out of our control when you actually build a Tesla coil, unless if you possibly control everything to be perfect, again hard to do , especially if one is "budget building" a coil. (Well...you did spend on the good caps, unless you got lucky on good prices for these somewhere. We discussed this recently of good possible prices somewhere in a different thread here.) Test equipment measurements are required along the way to verify if it is within what was designed to begin with, and this requires a lot of time and work. If none of this was done, then most likely quite out of tune. Even if you follow something with the extra work I said, tuning is usually still required, but you are much closer to optimum tuning. Reducing losses in parts of the whole circuit helps some too.

Also I am going to assume your ZVS does not have a whole lot of power output possibly. You did not say what it is. A coil's input power is directly related to minimum power out (spark length) expected.
So it is possible you are getting what is expected for your power in.

Just some rambling thoughts here for not having many details.

Chris

Hi,

I just did a search at Octopart and the current prices for less than 100 are quite jaw dropping I will admit.

Here is a screenshot I did:

https://photos.app.goo.gl/ocvuWvKLUyGBESK2A

So definitely if less than 100 needed you will have to explore elsewhere with some just luck involved too.

Chris

Unfortunately, as you may know, the same 4 pictures again have posted.

Here is some information near the bottom of this, read closely what it says:

Site rules/forum guide, must be read before posting! (Updated August 13th 2021): https://highvoltageforum.net/index.php?topic=31.0

I am not sure what is happening at your end, again can not see what you are trying/doing.

Maybe someone else will chime in with more maybe.

You can just also just post a link only to the picture(s) from a host site if it is already uploaded to the internet somewhere.

Chris

I got one of the "newer" Spellman 10 kV power supplies, those flat 19" versions, properly from the 1980-1990's. It has the exactly same coil design, just uses transistors for the driver instead

Hi Mads,

Just to add to this a little bit more of interesting history, here is another different Spellman catalog page from 1965-66 that I have in some very big older master catalogs I have in my collection.

https://photos.app.goo.gl/oUGBCKgPhreYsfjW9

Some more transistors use. And still using tubes in the rectifiers for that time though...a hybrid at the time.

Chris :^)

Hi Steve,

No, I did not do a sliding provision or taps but probably a good idea.

Me, I always did it the hard way. I would just make a slightly calculated judgement from past experiences to position the feedback (# of turns also). Then if I could not get to work good...strip off the wire and reposition it. Some coils, I had some wiggle room to move primary up or down a little instead. Then when it came to turns...I usually start with too much and cut off a turn a time and testing. And yes, I go too far sometimes removing too much and have to strip off and rewind again, but now I know from notes I took along the way where it was best for this particular VTTC. Like I said the hard way. That said I am planning something different on my 304er finalizing project for the feedback... been gathering and searching for parts that I want to try.

I actually thought about your first VTTC late last night, built way back in the day...I remembered the "pies" and yes the very top feedback "pie". This is a lower power VTTC and uses not very powerful tubes so yes it works here of course.

I have an old from about the 1960's Spellman high voltage power supply. Spellman also made these little "pies" type coils/little VTTC's and used them in these now old power supplies. The "pie" coil  form in this much higher voltage and current supply and using larger more powerful tubes...they cut this top feedback "pie" right off...I can see the cut marks...

They then did feedback  ...completely different...   I have not had the time yet to restore this PS and look at it closer on how they did feedback and study and understand what they did.

I will try to find a few pictures I took and post a link later...

Chris

Hi all,

:^) Yeah, the 833 is a weird tube with grid and plate pins both on top. Bad thing is several people in the past have accidentally mixed the connections up when they are adjusting/changing things since pins are same size.
Very bad outcome of course!

I also feel that this high voltage negative peak may also be very possible, but overall driving power low.

Several years ago, in the first tube coil of mine that I tried a tall primary I experienced the first time of noticable strange feedback winding behavior. Performance was sub par this way also despite a few changes I tried. Any changes I tried seemed to not be very responsive at all. Very little change, when it should be much more. I then immediately realized since the feedback is up so high now on the secondary that it was now influenced by the voltage rising on the secondary, instead of the primary winding that we want. And since the feedback is grounded...arc over problems too...and I see the arc shield done here, which others have resorted to also when having this problem.

Me, I knew we want to stick to feedback off of our primary. So I just took the whole primary and feedback form and I literally with no changes, just turned it upside down as is so feedback is now on the bottom. Since bottom of secondary is mainly all current, arcs to feedback problems gone. And now we always have the wanted feedback from primary only. I feel this is key to best performance possible.

If you flip this around, experiment slowly to get things tuned up correctly for the feedback. Also feedback leads may need to be switched around for correct phasing after this change.

Ever since I have run into this problem my first time, I now always build my tube coils with the feedback on the bottom below the primary, whether a short primary or tall one. My experience shows that it works much better this way once adjusted correctly of course.

I agree a variable rheostat is the way to go on the grid leak... being able to adjust on the fly is key also to best performance. I sometimes also in conjunction with the rheostat, have a fixed smaller ohm value "safety" resistor with it. That way you do not accidentally turn down to zero resistance. But these days...I mostly run just rheostat only and remember about not doing this.

Chris

Hi,

Sorry about the bad news of being too close.

I went to Steve's website to get a better look at what your are trying to copy.
This was an early first one he did. His MOT is too close having the same flaw. But his MOT happens to be turned 90 degrees by chance I guess. I suppose if you try this...it can help some I think. Still too close from what I know...but it is your best option since you do not want to redo whole mounting board to larger.
This will maybe get you closer to the 6" you are hoping for eventually.

I did say much earlier, tube coils are "tricky beasts at times". Efficient proper layout of certain coil components is necessary also. This is one of several reasons I achieved 12"+ on a dual 811 on a straight MOT only.

Adjustment of primary capacitance is the next important thing to do, while kind of the same time...experimenting with the number of feedback turns and changing grid leak resistance values and grid capacitor values are necessary also for best performance. My good running T200 VTTC took dozens and dozens of tries to get this area at it's best. Even though I usually from experience can "tell what a coil wants" it still can take me a while at times myself, especially if I want the best possible.

Otherwise you need to look at what Steve did again in his pictures and REALLY COPY what he did and do not stray at ALL if you can on ANYTHING. I can see several things you did different. These things which may not seem that big of a difference in reality can be much larger than you think.

Again really sorry to give bad news here and you will have to decide.

Chris

Thanks Mads,

Even though I am fairly new here, I am glad to be a part of this great resource and community here.

Chris Reeland

Hi,

Starting to show even more signs of life...

You are lucky you only ran for a short time with the very low filament voltage before...glad to see you have corrected this and tubes still seem usable. Your filament voltage is just a little hot now, but much better than very low.

I can not see whole layout of your coil...but yes watch distancing. Again sounds you got lucky overall with damage which could have been much worse.

From the schematic did you follow this very closely?
If you did you really need the top load toroid.
I see in the picture you have attached in the next post is just a long skinny extended secondary wire. This is bad... never will get good arc length this way, it just doesn't work this way...toroid with center straight up break out point about 3 inches long is required. The original plans have this toroid figured in... without your are most definitely likely way out of tune.

Also feedback winding needs adjustment most likely... your negative grid seems too high now.

Even with toroid, the original circuit will require some tuning, but you will be much closer to tune. There are always variables out of our control...no matter how closely you try to copy someone else's work.

It seems counter intuitive...but sometimes...high current draws happen when greatly out of tune. The extra power drawn is just wasted elsewhere in the circuit, instead of being put into the desired spark length.

And actually... when all is in "harmony" current draw will go down to reasonable expected levels when in properly tuned and it will have decent spark length also.

Going from past memories/experience on a dual 811 tuned up real good will see maybe from 12-14A @ 120VAC (I am in the USA) when using a MOT output only...just like your current schematic (NO level shifter). I achieved 14" arcs. (But this was a much different coil form setup and running frequency.)

They are not really efficient to begin with and are even worse from my experience with newer MOTs on tube coils.

Tube coils are actually "tricky beasts" at times.
Keep at it and be careful with your components with changes and you too... remember... even though lower high voltages here...they can be deadly if a mistake is made. Treat it with the same respect as a spark gap type coil.

Chris Reeland