Interesting RF air-core transformer construction

[MRMILSTAR]

My first tesla coil was a small VTTC. It used a commercially-made air core RF transformer for the primary coil, secondary coil, and feedback coil all combined into a single assembly. It is a Miller 4526 which is called "High Voltage RF Transformer".  I bought this one in 1969. They are no longer made. I am not sure what the intended use was. Possibly it was used in place of a flyback transformer in some TVs but that is only speculation. Coincidentally this part has all three of the coils that you need to construct a small VTTC.

I have attached some pictures of its construction which I find very interesting. Notice the winding method used for the various coils. All 3 coils use an overlapping zig zag pattern in their windings to reduce stray capacitance. The secondary coil uses a stack of separate winding sections with space between them to prevent the HV from arcing between turns. An arc suppression shield can be seen between the top of the secondary coil and the feedback coil. The entire coil assembly is about 6 inches high.

[304er]

Hi all,

I recently came across some interesting coils from my 1965-66 EEM Catalog that I have also fairly recently aquired. Aquired several years actually. What tremendously wonderful huge catalogs these are. I am still going through them a little at a time. Just all kinds of wonderful information of stuff past. Been meaning to post this, and now finally got to it.

I came across this Spellman section stuff and I was "stopped dead in my tracks".

And instantly thought of Steve White and his Li'l TC. I remember him commenting somewhere along the lines, there was not much information on the coils, specifically the Miller coil form itself and it's interesting construction. While these are Spellman's, a couple models look very close. And there are a couple other interesting models here. And he questioned other possible uses. The Li'l TC article says for large TV screen use, but I am not sure this was completely accurate at the time. Maybe as direct replacements for much older TV's. I am pretty sure 1965-66 TV's made were all flyback transformers, even before this date. I know they used these types of coils in the very early TV's, but flybacks got delvoped not too long afterwards and I thought pretty much phased these types out. Well Spellman had other uses as seen in pictures for high frequency (RF) rectified DC power supplies. As true for the time most are vacuum tube circuits.

But check out one page, an early transistor type coil!

Recently I tried looking for more information online and there is still not much out there at all on the Miller version of these coils. Very little. And I could not find anything on these Spellman's.

Well I hope some find this interesting as I did.
Pretty cool that you built a VTTC using one of these coil types "actually back in the day", Steve.

A couple of pictures links:


Li'l TC:

https://photos.app.goo.gl/mPnxKyig4K3NXX3P6

Spellman's:

https://photos.app.goo.gl/XLnzkiP6sgi1U6Vy9

Chris Reeland
Ladd Illinois USA

[MRMILSTAR]

Great info Chris on the Miller 4526 RF transformer. I have since found a picture of one actually installed on the chassis of a Dumont model RA-102 television so it turns out that at least one application was indeed for TVs. I believe that it was made in the late 1940s which was pre-flyback. I posted a picture of the chassis below. I also posted a picture of a Dumont RA-103 TV which is very similar to the RA-102. It cost $525 in 1948. That would be thousands of dollars in 2021 dollars so obviously it was a luxury item back then. I also have the data sheet for the Miller 4526 which I also posted below. It includes a suggested circuit application which looks very similar to that of many VTTCs. 

I still have my Li'l TC coil and it still works great with all the original parts 52 years after I built it. I also still have the Popular Electronics July 1964 edition that I bought new when I was 11 years old. This is where I got the plans and idea for building Li'l TC. This is what got me started with the HV bug.

Great memories!

[304er]

Hi all,

Have a bit more to add here on something that happened pretty fast recently. I came across one these "TC" power supplies from this era.
Price was right and driving distance to get was not too bad. So last weekend, I went to Flint, Michagan to "save this fella". "I had to have it!" :^) Especially being mainly a VTTC guy. After all it will be a great piece of test gear to use. Seller did power this up, and in pictures I saw, meter did go up and down when he advertised it. Me, I have not powered up yet. Going to go through everything and check things 1st. Also will be changing power plug cord. It is shot. Wrapped by someone quite a while ago with electrical tape from one end to the other. But the high voltage cables looks to be in great shape. I will test cables with equipment I have to be safe. Overall physical condition is great!

So here is a link to pictures of my find:

https://photos.app.goo.gl/Pt3PqAdfWgyrkQwD7

The paperwork I got with it do not photo well at all, flash or not, good room lighting. They appear to be "ditto" machine copies, which are quite yellowed now. This "TCPS" changed "hands" for whatever reason right away (was at Iowa Ordinance Plant)... looking at paperwork. Went back to original vendor of Klaus Radio in Peoria, Illinois. And then who knows where next? Not sure were seller got, did not ask and truthfully, I don't think he used it. He seems to be a seller of stuff which is fine. This paperwork brought me back to when I was very young in the late 1970's. We had a Klaus Radio branch store in La Salle, Illinois and I remember going there with my father several times. We lived at the time in neighboring Peru, Illinois.
While maybe not quite like Steve White's great memories...this was still cool for me :^)

I will eventually take more pictures and post the little TC and rectifiers tubes under the protective cover, when I get it apart. This is fairly heavy and a bit large. This TCPS is mounted inside a nice BUD mini rack mount enclosure. The protective cover will not come off inside the enclosure, which is for well high voltage of course, but also to shield RF and the lower level x-rays being produced by rectifier tubes.

Okay for now...

Chris Reeland
Ladd Illinois USA

[MRMILSTAR]

Is that the same Miller 4526 RF transformer shown in your picture of the schematic?

[304er]

Hi Steve,

I am not really sure what model Spellman coil this is yet, from the schematic. Kind of odd it is not identified. At least I can not find it...looked several times...just in case I am missing it somehow.

I would say it will be quite similar to your Miller coil, once I get it exposed.
And it is just an assumption, but maybe one the coils on the Spellman catalog pages I linked. But who knows, could be "custom" to this TCPS.

We will have to see...

Chris Reeland
Ladd Illinois USA

[304er]

Just to add a little more directly:

Here is a link again of one page having coil models from Spellman. Currently my guess would be the middle ones in the page...

https://photos.app.goo.gl/FhJK87S5rL9n2NSW7

[304er]

Hi all and Steve,

Sorry, I kind of "dangled a carrot with a brown bag over it" :-D

So I have done it early for Steve, since I have him wondering now.

Only has taken me 6 days to actually open this area up, since I got it  :^)

I am quite patient with some things. I was not going to open up until I was actually ready to do a proper complete restoration of this. Already loosely planning with my Father on this to bring to his place and work on together in about month or so. I also do not have a tube tester yet for these kind of small tubes. He has several. Also, 2 "can" caps so far should wisely be replaced.

Currently busy working on several coil projects, related interrupters modifying again...and testing at my place.

So here is an early peek after all at the little beauty of TC  :^)
Pictures link:

https://photos.app.goo.gl/adrpec9MSGqJBpbS9

Commenting on what I saw inside, nothing in condition surprises me. Overall really clean for age. Worst visual thing, which is no big deal is the mildew on plastic sleeves over high ohm resistors.

On the coil model from Spellman, it looks to me a customized stock coil. It appears to me, and I can see the cut marks at the top of the coil where they cut off the original "tickler" coil. Feedback is done completely different as can be seen under the high voltage rectifiers. Interesting filaments supply coils also. Lots of "pies".

I have not opened the under deck yet. Happen later. I right away put it back in the mini rack mount enclosure.

Okay, I will eventually get to this project in near future. Will scope stuff and test output and will hook up an eletrostatic HV meter also and give updates here.

Chris Reeland
Ladd Illinois USA