Antique Tesla coil with tubes - Page 1
Forum section: electronics / rf-microwave

author: Physikfan
author_rank: Regular Contributor
timestamp: November 12, 2017, 12:57:24 pm
content: Here are pictures of a commercial antique Tesla coil with tubes,probably built around the year 1950.Please, who might have a schematic for such or a similar device?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 12, 2017, 01:50:39 pm
content: Ah, hmmm, probably would've been relatively cheap to make then -- fresh WWII surplus put to entertainment use!Tim

author: medical-nerd
author_rank: Regular Contributor
timestamp: November 13, 2017, 07:34:29 pm
content: That is just beautiful.

author: Photon939
author_rank: Regular Contributor
timestamp: November 13, 2017, 08:23:27 pm
content: Are you looking for general schematics or specifically the circuit used for that tesla coil? Just google "VTTC schematic" and you should get lots of results. Including the tube numbers may help to narrow your search.

author: floobydust
author_rank: Super Contributor
timestamp: November 13, 2017, 08:24:48 pm
content: Where is the rectifier? I'm expecting some 866'sB+ must come from another board and the small power transformer just for 250TH filaments.Eimac 250TH triode datasheet.Plate voltage 4kV DC, 350mA, 250W.I can't see the primary winding, where is it.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: November 14, 2017, 06:58:09 am
content: If it's not external plate supply, I would figure self-rectified.Tim

author: Physikfan
author_rank: Regular Contributor
timestamp: November 15, 2017, 11:46:11 am
content: More pictures:

author: @rt
author_rank: Super Contributor
timestamp: November 24, 2017, 04:28:48 pm
content: It looks like there are brackets and terminals for the primary, but it’s gone missing.Are you planning on trying to fire it up?

author: Physikfan
author_rank: Regular Contributor
timestamp: November 25, 2017, 07:59:08 pm
content: Hi @rt"It looks like there are brackets and terminals for the primary,"Please, at which picture and where you have found these brackets and terminals for the primary?"Are you planning on trying to fire it up?"If we could restore the Tesla coil we will try to do so.

author: Cyberdragon
author_rank: Super Contributor
timestamp: November 25, 2017, 09:45:20 pm
content: There are several open connections, the terminal on that green thing (resistor? Capacitor?) next to the main coil, the alligator clip below that, and that dangling white wire. You may not find a matching schematic as it may have been engineered from scratch, so the only way to be sure is to trace out the circuit (noting broken connections) and we can figure out what goes where. The primary probably screwed onto the brackets that hold the main coil up.P.S. Look how far that green wire on the green thing below the clip has been stripped!I would cut and resolder that.EDIT: Those green things are probably capacitors, given that big pile of them looks like the main tuning tank. The primary does probably connect across them on those two open connections, which leaves that white wire as a mystery.

author: chris_leyson
author_rank: Super Contributor
timestamp: November 26, 2017, 12:49:20 am
content: QuoteThat makes a lot of sense. I wonder what the mains transformer next to the two-pin Bulgin style connector does, maybe for the 10A heaters ? and perhaps the vitrious enamelled wire wound resistors connected to the transformer are for grid bias, sort of makes sense if it's self-rectified. Are those "rheostat" resistors behind the mains connector, wonder what they control ? I think it might have been built pre 1950 a lot of it looks pre WWII and the wiring and construction style looks for 1930's. I like the lonesome crocodile clip next to the bank of capacitors must have been used for tuning and those big green things are tubular ceramic caps but I can't remember where I've seen them before. Looks like the anode leads go to the bracket that held the primary coil which must have been center tapped. Grid feedback coil would have been mounted there too I guess. Not sure about the large white ceramic components next to the valve bases, I think they might be resistors. You could maybe date it from the components used but that isn't going to be easy, it will take a lot of research, sorry for stating the obvious. Wiring diagram would be helpful it would fill in some of the blanks.

author: Cyberdragon
author_rank: Super Contributor
timestamp: November 26, 2017, 01:27:23 am
content: Quote from: chris_leyson on November 26, 2017, 12:49:20 amThe tranformer is for the filimants and the HV B+. If those terminals on the tuning caps are just there for adjustment, then what are those blue/green wires going to? Is the primary actually inside the main coil?

author: floobydust
author_rank: Super Contributor
timestamp: November 26, 2017, 05:52:50 am
content: I tried to sketch a draft schematic of this Tesla coil but the pics are a bit fuzzy and everything is brown, lol.The large green things are probably inductors, but they have a middle terminal.Not sure what the orange inductor is doing on B+, it looks grounded on one end but would have several kV on it.I only see one primary winding (no center tap?) and no idea about the oscillator feedback winding, if it's one or two windings etc.It is a self-bias circuit, so the large wirewound variable resistors.edit: Dec. 2, 2017: updated schematic with green things being RF capacitors. Just need feedback winding wiring details to add.

author: Beamin
author_rank: Super Contributor
timestamp: November 26, 2017, 11:28:17 am
content: Doesn't JAN mean joint army navy?Imagine what that would cost to make nowadays? That was probably considered cheap back then. They had no idea how cheap china could make things in 70 years.Soon when you buy a product it will come with a Chinese person as labor/warranty/tech support because labor is so cheap in that country. Just don't use your device in high buildings as you might find your warranty has jumped off the roof.

author: Cyberdragon
author_rank: Super Contributor
timestamp: November 26, 2017, 07:53:26 pm
content: Quote from: floobydust on November 26, 2017, 05:52:50 amNo, those tubular things have to be capacitors, as that schematic makes no sense. The primary of a tesla coil is usually part of a resonant circuit. Putting inductors in series with an inductor (the transformer primary) makes no sense, it would just be needless load, and probably wouldn't oscillate very well (if at all). But capacitors there forming a tank circuit at the plate would make more sense.For the feedback, is that tiny separated part of the yellow winding actually part of the primary or is it on a different circuit?EDIT: There might be a center tap (B+) with each side connected to a tube, and two cap groups across each side of the coil forming a sort of double primary. Not sure what would keep the tubes 180° out of phase, but it would be some form of astable. Or they could be in parallel across the primary, but then it would need a feedback coil.

author: floobydust
author_rank: Super Contributor
timestamp: November 27, 2017, 12:59:19 am
content: I was thinking this is a push-pull design- or is it single-ended with both tubes in parallel? I saw no need for parallel triodes here, each 1kW...If we figure that out I can fix the schematic. Tesla did push-pull with dual-spark gaps.Those are RF power feed-through capacitors! The middle terminal I think connects to GND.So looking at the pics, the tubes are in parallel.pic from4HV forums; looking for a push pull schematic for VTTC

author: Physikfan
author_rank: Regular Contributor
timestamp: November 27, 2017, 04:03:12 pm
content: Hi T3sl4co1l, medical-nerd, Photon939, floobydust, @rt, Cyberdragon, chris_leyson and BeaminThank you very much for all your comments.Special thanks for all these who tried make a circuit diagram.We are planning to take new pictures of this antique Tesla coil.Are there special wishes for certain details?

author: Cyberdragon
author_rank: Super Contributor
timestamp: November 27, 2017, 08:32:27 pm
content: Quote from: Physikfan on November 27, 2017, 04:03:12 pmYes, the connections and wiring under and around the main coil (including the cap bank), and if you can, inside it.

author: floobydust
author_rank: Super Contributor
timestamp: November 27, 2017, 09:01:45 pm
content: A few more high-rez pictures to show the wiring would be good, to finalize a schematic.If you can mention any text on part values i.e. kV, pF, ohms etc and on the panel meters, that would be good I'll add it in.I suggest adding a jumper wire across the two HV binding posts or across the (can) filter capacitor, as there is a little hazard.This is probably what the dangling white wire is for. I would carefully short the cap and then connect the other end to that screw terminal.Older high voltage oil-filled capacitors are stored and shipped with shorting jumpers across them. I was told this is to prevent them from accumulating stray (static) charge, which can bite (and from dielectric absorption, but this has not been powered up for a very long time, so not a concern). Modern caps (i.e. microwave oven) have a built in bleeder resistor to prevent this- but not in the 1950's.I think this VTTC was to be a push-pull design but stayed wired-up at lower power as a single-ended circuit, probably to optimize things.I would say it is built from scrap parts from a high power radio transmitter.