Finally finalizing my 304er VTTC

[304er]

Hi all,

Fairly recently, I have decided it is finally time to get this finalized, inspired by others here :^) and will share this. This project will take some time and will update as I go. This is a single tube Eimac 304 and a single MOT with a level shifter with 120V input from a variac. This has been a great running little fella.

Some goals also so far are:

- To have this completely and very easily portable and light as possible.
- Very simple setup, just a single plug to any 120V outlet, to power everything. One slight exception is the accessory 120V cord plug coming out the unit to power my several different kinds of interrupters I have and the "trigger" wire connector from the interrupters. I do not want to be limited to one type built in.
- To have this coil be as high performance as possible, but very reasonable power draw. VTTC's can be horribly inefficient vs. arc length output.
- To take advantage of the heatsinking capabilities of the whole aluminum enclosure and use a single fan to help take this heat away cooling stuff on the way out. I want to be able to do VERY extended run times, with everything staying "happy".
- To take advantage of some of the shielding this enclosure should provide. It will be at ground potential. Everything thing iron/steel will be inside. This will also greatly simplify several connections.
- And of course, look great hopefully!
- Still thinking of others :^)

I will admit that I am torn some here on an enclosure, I normally prefer everything out in the open at times, but the advantages that I want outweigh the "open". I am planning to make sure that I can get the top cover off with the minimum of hassle to show off "under the hood".

Here is a link below to some pictures of it's current state after a quick run testing it before starting to taking it all apart and the new aluminum enclosure nearby.
Also a video taken oh... about a month ago...I did not take any video today, but nothing has changed, so this is how it runs with one of my interrupters now. Yardstick hanging in back as a reference.

There are going to be some changes here also... this is not a direct transfer of everything...so the hope is not to have less performance!
I will try not to mess things up with some ideals I have.

And well, this is also a repair project, as the secondary is slightly damaged for quite some time now. Down in the primary area the windings are buckled some. Got over heated some, during some extreme testing I did. The acrylic is now warped some. The epoxy coating can only do so much...
Kind of bummed to retire the coil form...been in use since about the early to mid 1980's. For those that don't know, this VTTC has changed quite a bit over the years especially the last 3-4 years from it's origins in the 80's. Several different tubes, transformers, variacs, capacitors, secondary rewound several times, primaries, etc. Somewhat surprised the secondary works pretty good still with damage, even if though not really much voltage in the windings here.
I will take some close up pictures when fully apart.

https://photos.app.goo.gl/CqugwKFGQjLn3pdb7

Oh...this is all I can think of currently...and I will think of more as I go and post. There will be some tests along the way and I will also give some numbers and specs.

Oh...a few numbers to start, the new/old surplus enclosure I found is 17"x17"x6". The old platform board is 20"x20". (Actually, this platform board is the second one for this coil. Original much smaller, ran out of room with changes. It has a lot of "bullet holes" as does this current board from several changes experimenting as seen in one picture of the underside.)

Make some Sparkys all if you can :^)

Chris Reeland
Ladd Illinois USA

[304er]

Hi all,

I have just a few updates on the tear down and the board is now down to just the core components and the secondary removed for closer damage inspection. I have "roasted" this a bit more than I could see when in place on TC. The wire insulation and the epoxy handled the high temperatures fine, no signs of any discoloration can be seen. Acrylic not so...look at the straight edge pictures of one side and it's opposite side. And the ripples inside the tube. Again, surprised some still worked as well as it did. You also can see some notes of mine on the specs when this was wound.

I am going to do some frequency measurements of this damaged secondary out of curiosity and will post results later.

https://photos.app.goo.gl/AbvGszTCESuyAYHV8

So just a minor update...

Chris Reeland
Ladd Illinois USA

[304er]

Hi all,

Okay, here is some measurements out of curiosity of the damaged secondary. There is really what I call no real changes here. Not completely sure what to make of this. While I was not expecting a huge difference, I was expecting some. Not what I consider "peanuts". Now under running conditions it could definitely be different. Will never know now, since I do not have any measurements of coil running with this damage. I do have some before this. I will let the few pictures speak for themselves. FSA on my note, stands for secondary Free Standing Alone (no toroid and break out point) for my starting frequency here on this coil.

I'm going to be stripping this wire off. I was originally not planning this. But I want to better see where all the rippling is located on the whole form. Has me curious now. But first I am going to do some measurements with a new device of mine which I have had actually almost a year now and have not gotten around to using it. I will post details of it when I get there. I have to learn some on using it also.

https://photos.app.goo.gl/anYAXJwMFtiTryQr6

Chris Reeland
Ladd Illinois USA

[304er]

Hi all,

I have made measurements with my new device.
My device is a NanoVNA-F Vector Network Analyzer.

This is nice a small compact device, but not too small to use. It has a decent screen size that is very readable and usable for the touch screen functions by your finger. It also has a very decent capacity battery.

The reason for the extra comments, is that I also have, before I bought this one, I purchased the original NanoVNA. (The "F" was not out yet.) Now this one is much smaller and thinner. The screen text is hard to read. Touch screen hard to use by finger. Stylus is nearly required. Battery life not great, which is no surprise, since so small and thin, just no room for a decent battery. That said, it does work. When I saw the "F" version come out, I purchased this and what a great improvement and pleased.
The original while neat that small, it is just not that realistic in my opinion.

I have not kept track of these "Nano's" recently, so there are probably new models and improvements.

These are very reasonably priced for what I feel you are getting.
As some may know...the real bench top/rack VNA 's are out of reach for normal people. Can get extremely expensive.

While I know this will never be as accurate as the "real ones", I feel these are plenty accurate enough for us coilers, and others in the several other uses possible.

But I will also hazard to say, this is probably more accurate than my recent secondary measurement with my function generator, scope, and LED's.
Again while still plenty accurate for our uses, it still is pretty tough to adjust for the final 1000's as LED's intensity differences harder to see now. And the hanging scope probe trace to help "see", "wavers" around some, so a little bit of guessing here.

The screenshot pictures of my results are after I have narrowed down the start and stop frequencies, to "zoom" in and get a better look at the  resonant frequency. It is really nice to be able to "see" this here.

I am still learning things about this device, but I would say I got decent results here in comparison to my original and recent measurements of this secondary.

I have some more thoughts on this secondary buckling damage. The buckling of wire is under quite a bit of tension. I would have thought, the wire insulation was compromised in some areas, causing some shorting, but this seems not the case.
But under these test conditions, nothing has really changed with my function/scope/LED method because the what I call "visual" error in this method in the slight frequency difference.

I have found the main culprit for the buckling. The winding height was originally 13 3/4. It is now 13 5/8 measured just before I stripped the wire off. The ripples that I can see inside, I now realize is bulges from the tube form shrinking in height.

I have taken a couple of pictures of the bare form. I was hoping to see something on the outside, but I can not see much at all. And I took another of the inside...sorry this is hard to take this picture...

So I have satisfied some of my curiosities and hope maybe some find this interesting :^) or not :-D

Pictures link of measurement result and form.

https://photos.app.goo.gl/Qju6FvDeBocSmSG49

I have a new plan for the new secondary, and will post when I am ready and have time...

Chris Reeland
Ladd Illinois USA

[304er]

Hi all,

Been a while since any updates on this project of mine.
I have gotten busy on so many different things and hopefully will get back on track on this soon.

Going to share some occasional pictures I took a while back during initial construction and some recent pictures of it as it is now. Some things could possibly change when I do again move forward on this.

I have decided on several changes already as can be seen in pictures.

I will no longer be using a main variac on the plate supply transformer.
I will use a temporary external variac during first light though...then if all well...and if initial tuning is good enough for now...it will be removed.
This will save 11.34 lbs on 120V in/out variac originally planned.

I have found a near perfect for the 304 tube, a 5V CT (2.5V CT 2.5V)@ 30A Stancor NOS filament transformer at a Hamfest unexpectedly earlier this year. This is very hard to find. Previous one was a 12V@16A Triad control transformer set with a small variac for 10V. For those wondering now...the 304 is a weird tube in many ways. This single tube is actually four 75T's in one. Four filaments total wired in pairs internally. There is four filament pins on the base. These four pins can be wired parallel (5V@25A) or series (10V@12.5A).  The Triad was the closest I could find back then and is a little bit overkill. A 10V filament transformer near those amps is hard to find also. Going to save some weight here now...the Stancor @ 5.71 lbs vs. the Triad @ 8.03 lbs.

I will still control filament voltage with a small variac to avoid current inrush to be nice to my four filaments and to better set proper required filament voltage accurately. And this variac is going to change also thanks to another Hamfest find...found a smaller one @ 1.63 lbs vs. 2.98 lbs of the previous.

I am also going to replace the "sort of big" older Advance MOT @12.47 lbs. This one is still much better than the "newer" MOT's. At least has some more "iron" and has real copper wire (not copper plated aluminum wire).
Though, it still is not that great (still better than "newer") at "idle" current.
At no load idle current it is 5.18 A and it does get quite warm after awhile.
My "new" plate duty transformer is an "even bigger looking MOT", but it is not one actually. This is a Canatron @15.58 lbs, made in the UK, found on eBay in the USA. Seller said it was removed from an older Varian ion pump power supply. The build quality looks much better vs. older and newer MOT's, which is expected. I would say also that a much higher quality grade of lamination steel is being used here also. This fella is going to add a little weight to my project...but is worth it. And I have already saved weight in other areas. A no load idle current check shows 0.15A...ahh :^)...so much better!!! And of course stays cool after awhile leaving on, unlike the old MOT. (Just for a comparison...the NOS Stancor fil. trans. at idle is 0.13A)

I am also going to get a voltage boost from this Canatron. Nameplate says 2600V and has multiple input taps. I will be using the 117V tap input.
Checking with no load, with my Sensitive Research electrostatic voltmeter
with 123V input (voltage at the time here), got an expected higher voltage of just under 2800 V. For comparison, the old Advance MOT (nameplate does not give output) I got 2125V no load.

I will also on this Canatron once again be utilizing a lever shifter and I will take FULL advantage of the longer "ramp" this waveform offers in addition to the even more voltage this offers of course, with my several Interrupter/Staccato controllers I have.

I have decided on the replacement for the original secondary acrylic tube.
I am going to try a piece of G10 thin wall tube that found. Got the new wire already, so hopefully will wind this soon.

Okay...I think I covered "most" things here on this update finally...I will let pictures cover the rest...ask if curious on other things and I will try to answer...I am still working out several other things on the top deck in my head, got most of it so far...

Here is the pictures link:

https://photos.app.goo.gl/UCR5hZdTnVttPbVKA

Chris Reeland
Ladd Illinois USA

[MRMILSTAR]

Hi Chris,

I really like the look of this chassis! That new "MOT" looks really beefy and it looks like the core is actually bolted together instead of being welded. That should help a little more in the eddy current department. Is the plan to always have that outrigger fan attached?

[Mads Barnkob]

Indeed is a very nice chassis. Did you cut, bend and weld the aluminium yourself? That is some nice weld seams.

Why are the meters upside-down? That had me puzzle for a bit.

If you are going to remove the variac, add some other kind of passive softstart with a relay, timer or NTC. I have seen tubes flashing-over from initial voltages into a "cold" circuit.

[304er]

Hi Steve,

Thanks for the kind words. You are one of the few people who have inspired me for construction styles.

Yes, the steel laminations are interleaved, so definitely much better on this former ion trans.

Yes, the "squirrel cage" blower on back is going to stay. I want a high volume of cooling air, with a reasonable amount of noise. This is pretty quiet. I tested some large 120V AC box fans and was not satisfied with the air flow and the noise was quite annoying. A lot of box fans have an annoying to me in my opinion a higher pitched noise to them also, in the total overall noise emitted.

This "bump" on back will "blend in" with the coming "real bumpy fun stuff " on the top deck of this enclosure.

Chris :^)

[304er]

Hi Mads,

This enclosure is a surplus fiber optic storage box I found. The surplus dealer used to have several of these. I tried to order a few more for other future projects.
When he checked, he realized I got the last one previously and removed the listing on his website.
Wish I knew of these a few years ago. This enclosure was very reasonably priced surplus for a high quality aluminum box.

I knew this was coming...these small meters are upside down because when this is on the ground they are actually easier to read as you are nearly tilting your head upside down when bending down and looking at them. Even when on a normal height table this greatly helps bending down and tilting your head. I tested this out and it definitely works for me here.

Since no variac, to limit inrush current, and there is also the level shifter capacitor to charge, I am using a SSR (solid state relay). The one I am going to use for this here is a DC control by toggle switch with optical isolation. This SSR also has AC zero crossover detection built in to eliminate "hard" switching, so it will minimize current inrush to everything.

Chris