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Old 7th Nov 2017, 4:37 pm   #101
astral highway
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Default Re: Design-and-building a large valve Tesla coil (class C, Armstrong oscillator).

Quote:
Originally Posted by G8HQP Dave View Post
2.4kW input to an RF power oscillator in an ordinary flat (and a PSU with no overload protection)
Dave, your comment seems intended to be acerbic and offensive. You don't even know me. You don't seem to have read the thread, or indeed to have much of an idea of how I go about things.
I have a strong attachment to my life, and indeed, survived a very credible threat to it when I was seriously ill a couple of years ago. Making comments about Darwin awards so lightly seems a little crass under the circumstances, implying as it does that I am cavalier about something I take very seriously.

I put a huge safety warning up at the top of the thread, hoping that it would stay well away from scaremongering debates about safety. The mods were on board with this before I made the first post.

Of course it won't be run be run in CW with 2.4kW of RF , that's just silly. It doesn't say that, anywhere on this thread. It's intended to be a class C device with, further, pulsed operation, and with a variable pulse width. We all know that pulsed systems that are efficiently designed can have peak power that seems remarkable. I'm hoping that this is one of them; and that even at 25% duty cycle, the results will be pleasing.

And it doesn't say, anywhere, that the power supply has no protection. It never had a complete absence of protection, just not enough.

It speaks for itself that I haven't rushed to build this iteration (my fourth, ever - so I survived the previous three, note) and have been refining things carefully as I go along. I already have 50 photos documenting the progress of the prototype, as well as 12 * A4 pages of my own maths, drawings and notes as I go along.

If you want to post negative opinions that aren't well researched, please do so by PM. If you don't like what I'm doing, don't pay any attention to the thread.

The project is serious, considered, and with a wonderful meta-purpose in mind. Please leave it for those who appreciate it as it is.

Note: pictured below is the underside of the big ceramic valve-holder, with a common mode RF choke in the heater supply, and some other passive components hard wired in place.
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Old 7th Nov 2017, 6:47 pm   #102
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Default Re: Design-and-building a large valve Tesla coil (class C, Armstrong oscillator).

I can't wait to see photos of this in operation, I bet it looks dangerous (all big projects like this should, adds to their charm), making it safe* "oh I am not touching that!". Any chance of a picture or two of it in full splendour? It wouldn't surprise me that you have one of those whole body chain mail suites ready for 'first light'.

*I think it is called "risk compensation", ABS and seatbelts make for worse drivers in some cases as they rely on them.
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Old 7th Nov 2017, 7:30 pm   #103
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Default Re: Design-and-building a large valve Tesla coil (class C, Armstrong oscillator).

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Originally Posted by merlinmaxwell View Post
I can't wait to see photos of this in operation...
Thank you! your enthusiasm is highly welcome!!

Well, I hope to have it ready for display before Christmas --I need to source a new transformer and some other power supply elements.

I am rebuilding it on a new 'chassis' which allows for a more compact and lighter arrangement.

Quote:
Originally Posted by merlinmaxwell View Post
I bet it looks dangerous (all big projects like this should, adds to their charm), making it safe* "oh I am not touching that!". Any chance of a picture or two of it in full splendour?
It probably will *look* very dangerous. It will have appropriate stickers and interlocks!

For the time being, I've been working on the VCO and phase-locked loop. Success, so far, see pictures. The idea is to modulate the cathode so that the grid passes into conduction exactly in sync with the modulating pulse. I haven't seen this done before and I haven't found it on the 'net. It is, however, the favoured way of running digital Tesla coils.

Here are some early results from the circuit, showing waveforms at:


1) the Gate of a big FET (actually a 'HiperFET), yellow trace.

The FET is driven in a class E configuration by a gate driver chip (6A pulses, FET Gate needs 43nCoulombs to switch on in 23nS) but runs cold, and so does its power supply) on the same board as the VCO and PLL prototype, pictured.

It is a beast of a device (16A, 500V) but in fact runs completely cool and draws between just 40mA and only 100+ mA at 30V, depending on the sweep frequency of the VCO, which I built to operate between 200KHz and 360KHz. The traces clearly show that the big old electronic switch spends most of its time out of conduction. Perfect! You can spot the FET is on a small alu (unnecessary) heatsink next to one of the scope probes.

( I haven't peaked the load to resonance as I don't want to destroy my 'scope). Critical are the two shunt capacitors directly on the Drain-Source pins - luckily my maths worked out ok.

The larger caps are 75nF in total. These caps are not part of a tank circuit.

2) the Drain of the FET, connected to the load. This is the primary inductor of the Tesla coil, inductance about 235uH. Blue trace, 'scope set to X10!

We can clearly see the phasing of the waveforms.

Quote:
Originally Posted by merlinmaxwell View Post
*I think it is called "risk compensation", ABS and seatbelts make for worse drivers in some cases as they rely on them.
Yes, I like the 'risk and consequences' model. Parts of this are not to be touched. It's very clear, just as no-one would touch the anode of an RF power amplifier.

I hope to have more pictures in the next few weeks or so. Next up is to sweep the completed new secondary coil with pulses from the VCO/PLL and class C RF amplifier pictured. I want to get an idea of the self-resonant frequency in this configuration, which is more accurate than testing it unloaded.

More work needs to be done on the primary coil. But you can clearly see here taps at various points for tuning of the tank circuit.

I also need to complete anti-flashover measures between the grid feedback coil at the top and the tank coil (PVC covered 2.5mm dia single earth wire, will be covered in Kapton tape).
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Old 7th Nov 2017, 8:22 pm   #104
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Default Re: Design-and-building a large valve Tesla coil (class C, Armstrong oscillator).

Note:

1) the MOSFET driver chip has two outputs. Together they can source 6A. I note from a quick mental calc that 'only' about 2A is needed to switch this HiperFET on and I'm only using one output. This is a perfect little example of peak (pulse) power versus average power, a nice metaphor for the way the whole Tesla coil will work. The power supply regulator runs cold, and so does the driver chip- peak current is intense, but average current is low.

1b) Also, peak voltage across the MOSFET is when it is switched off. This is again clearly shown by comparing the (x 10 ) blue trace (sinusoidal and square combined) with the yellow Gate pulse. The MOSFET is off for 3/4 of the time.

2) The advantage of having built a robust modulator already is that I can model the characteristics of the main resonators in detail at low voltage. This includes the design of the grid leak. Although I won't know how the power oscillator valve behaves until later, I will be able to experiment with various values of R and C to see the resultant waveform, instead of either guessing or messing around with a high voltage probe uniformed, later on. So that's all good!
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Old 7th Nov 2017, 9:12 pm   #105
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Default Re: Design-and-building a large valve Tesla coil (class C, Armstrong oscillator).

Classic textbook waveforms, I have done worse in LTSpice. Pictures of big sparks before the Solstice will be fitting!
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Old 7th Nov 2017, 9:56 pm   #106
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Default Re: Design-and-building a large valve Tesla coil (class C, Armstrong oscillator).

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Originally Posted by merlinmaxwell View Post
Classic textbook waveforms, I have done worse in LTSpice.
Thank you, MerlinM! That sounds like a compliment. I am delighted with this result. It's taken a while for me to figure out how these switches work in class E.

I intentionally started with the most challenging part of the design. The rest (fingers crossed) should now be mostly about mechanical construction.

The Christmas deadline for first light and pictures very much depends on the power supply now... as soon as I have the new EHT transformer, I can predict an completion date!
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Old 8th Nov 2017, 12:43 am   #107
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Default Re: Design-and-building a large valve Tesla coil (class C, Armstrong oscillator).

Hello Al. I've followed your detailed medical and technical history like a lot of other Forum Members. I note from your earliest reference to producing a continous wave output that it was always intended to be quite limited. That's about as far as I go with the circuitry I wouldn't want to suggest that I understand your theoretical approach in the same way that other Forum members clearly do [if at all] but I'm a bit fascinated by you being so interested in the Tesla Coil without getting drawn into the many and varied aspects of the NT story [impossible for me]. You indicated that the prime motivation for all this work [against a savage background of ill health that would decimate most people] is producing Kirilian images. You mention using Russian valves and I'd understood that Kirilian looked at organic matter but you seem to be examining materials. Can you say a bit more about this ie how and why?

I've come across some sensitivity on here re "non scientific" things like the 1930's Violet Ray Machine and yet the controversial Proton Beam Technology [derided in the press] seems to go directly back to Tesla and directed energy. There was a news item today re a child who had a life threatening cancer condition remitted. Christies Hospital in Manchester [not exactly radical] has just spent a fortune on importing a new Proton treatment unit. Not bad for an alternative therapy/technology that doesn't work really I'd be very interested to hear more about your motivation for developing such a sophisticated Tesla device. Do you hope to make a contribution with it and what do you think about the broader issues I mention, or am I completely on the wrong track here

PS. I'll just say that, even with all, your disclaimers/warnings and explanations, it's not so surprising that the unusually extreme nature of your electrical project might give rise to concern. A vintage TV CRT HT supply can be alarming enough!

I just think it's very likely that the comments by G8HQDave were much more intended to be light hearted than critical. Posting on a thread is like sending a txt or an e-mail, it's a representation of an apparent conversation but it's not at all the same. That's why we need to see peoples's faces and hear their tone of voice to fully understand intent. I've been misunderstood in that way and it has taught me to apply restraint-in both ways!

Best Wishes,

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Old 8th Nov 2017, 12:00 pm   #108
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Default Re: Design-and-building a large valve Tesla coil (class C, Armstrong oscillator).

Hi Dave,

Thank you for your detailed post, I really appreciate you taking the time to do this. On EHT, yes, it is a serious business and of course there’s a part of me that doesn’t feel surprised or defensive when people express a natural concern. On the other hand, I first mended a TV when I was 14, and it was a pre-War model with a mains derived EHT, so I’ve been conscious of risk and consequences unsupervised and with no mentor, from a young age.

I’ve also done hugely challenging physical things for my lifetime, including operating in savage weather conditions , climbing , mountaineering and bouldering. So I have a close and detailed relationship with risk!!

For my Chemistry O’level project, I isolated the line output stage of a TV and used that to design an electrostatic smoke chimney to analyse residues in smoke. I was really careful to house it in such a way that none of my peers or my Chemistry teacher could possibly be harmed.

I do take your point about the way it’s easy to misconstrue comments on the forum and my response does seem defensive and harsh when I look at t today. It’s a shame because I actually laughed it off at the time and was going to put a smiley and a light comment back! I’m normally pretty easy going and I prefer t take care with the way I say things. Not my finest hour; sorry Dave!! I hope Dave reads this and we can understand eachother better...


You ask what the appeal is of all this current activity, and to what extent I am interested in Tesla.

The project appeals because I need something big and complex to occupy me while I’m not able to work. I noted that many constructors report having destroyed their valve Tesla coil through over-driving it in some way, so that projects only get to lash-up stage and then go kaput! It seems a shame not to have a stable, lasting construction to display and amaze. I have also noted from my own past forays into all this that mechanical aspects of construction are more important than anything else - so it takes an understanding and appreciation of materials and is a nice invitation into how to solve significant problems with materials . I also like making things and using what I find in the street or in skips.

The circuit I’m building looks really simple (very similar to the Armstrong oscillator used in some early radio front end designs, curiously!!) but it takes a lot of experimentation to build it to survive the outrageous currents and voltages developed. I enjoy the challenge!

Also, I have been unable to do much photography at al for the last few years since my first op. Most lenses are still too heavy for me to carry without discomfort. Before things went wrong , I was planning on making a print panel for the Fellowship distinction of the Royal Photographic Society ( I have the Associateship) , and I realised sometime last year that a close-up project using a pretty manageable lens would be a pod candidate. Kirklian photography has always fascinated me; the complex fractals and sheer beauty of some of the patterns. You ask about making some kind of contribution: well, I hope people can enjoy the beauty of any images I may capture. As far as contributing to knowledge, that isn’t something I am doing.

It’s possible that few people have tried putting a phase locked loop into a valve Tesla coil to peak efficiency. I certainly haven’t found any documented reports, so that may be the extent of my ‘contribution’ - not very significant at all!! So something inside me feels very happy to have made the waveforms I put up yesterday . Also I haven’t come across the use of a high powered class E modulator to test out the main inductors at low voltage and to prove and deeply understand the complex waveforms in three windings that are inter-related. So i’m happy with that decision and it is already rewarding!

There is something in me that loves making beautiful things; it’s just an urge.

As far as Tesla’s free energy legacy, I usually encounter phoney beliefs and misguided claims with no evidence behind them. I think Tesla’s emphasis on transmission is interesting and was ahead of its time : he is of course the inventor of the polyphase motor and AC power distribution systems.

Do you have an interest in Tesla’s achievements?

Thanks again for posting ...
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Old 8th Nov 2017, 2:49 pm   #109
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Default Re: Design-and-building a large valve Tesla coil (class C, Armstrong oscillator).

Just a note to say that Al and I have exchanged PMs and made apologies to each other.
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Old 8th Nov 2017, 3:32 pm   #110
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Default Re: Design-and-building a large valve Tesla coil (class C, Armstrong oscillator).

Thank you, Dave!

Progress. I've been using my modulator to analyse waveforms in the grid feedback coil. This is usually a huge guessing game for people who power up at EHT without knowing what's really going on in the feedback or 'tickler' winding. It can put the power oscillator valve under unusual and indeterminate conditions.

It seems crazy to me, now that I have made the same mistake in the past.

I have clearly been able to demonstrate that loading the grid feedback coil also substantially loads the primary. Current consumption in my MOSFET modulator increases vastly at some frequencies, showing that coupling is rather close.

The photos keep attaching in a random order, how ever many times I try! So please excuse the confusing numbering, this is how they uploaded!

2) Blue trace x 10V shows the Grid feedback coil waveform with RC components (variable 20K resistor and 680pF 2KV capacitor) at 205KHz. Note the extreme symmetry of the kink in the blue trace and the kink in the yellow trace. The waveform is nearly sinusoidal at resonance.

4) Same as above at 376KHz, RC components only, no damper or 'recovery' diode. Current in the modulator rose to 140mA from 40mA as I swept up frequency.

1) Using a flyback damper diode. My idea, in this application! I found this paper by Dr Hugo Holden, who happens to be forum member Argus25! It is relevant and extremely detailed. The diode is in series with the RC components and is a Schottky diode. It does seem to have a pronounced effect on the waveform here.

(If I reduce the output voltage of the modulator, the ringing in the waveform disappears) The top of the wave becomes almost flat, like a square wave, and its shoulders are also squarer.

The waveform goes negative with a slope that much more closely matches the falling edge of the MOSFET drain square wave - way faster than the sinusoidal decay without it. Because of the RC components, it starts oscillating again when the MOSFET is still switched off, and continues to resonate until the end of the next cycle. That ringing is really very pronounced, right?

3) Same as above, flyback damper diode, but at 376KHz.

In other news, I've just heard back from Richard (Mole42UK) who has done a superb job of lathe-winding the secondary inductor. I can't wait to see it in person. Thank you, Richard!

I haven't heard back from the other Richard yet. Ed Dinning, our resident transformer expert, is also on the case to price up a bespoke wound transformer with various taps. Thanks also to Ed!

I'd be interested to hear comments on these waveforms and my observations.

Thanks folks!
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Old 8th Nov 2017, 4:45 pm   #111
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Default Re: Design-and-building a large valve Tesla coil (class C, Armstrong oscillator).

Ok Dave and thanks for that Al-a very generous response. Yes I've been fascinated by Tesla for years but I'm not alone in that-including yourself of course-even if it's just the Coil. I think it's the loner aspect as well that interests me or when it seems that someone gets dealt a bad hand by the "establishment" eg Professor Laithwaite. Only today I was commenting on Theremin in the current thread and the possible similarities with Tesla's personality. I'm glad that I seem to have [inadvertently] brought about a "cease fire" although I doubt that there was ever [really] any dispute. Good luck with "The Project" Al.

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Old 9th Nov 2017, 11:56 am   #112
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Default Re: Design-and-building a large valve Tesla coil (class C, Armstrong oscillator).

Hey Dave,

Yes, me and Dave had a PM thread going for a while and I feel we both understand eachother a lot better and things are clear and easy now. Thanks for prompting us to be the best version of ourselves.

As I'm not working at the moment, still recovering, the project has taken on a greater significance for me than it would normally -my problem-solving capacities need exercising, like an enthusiastic border collie chasing endlessly after a ball! So my whole focus can sometimes go right down to this one thing... I expect others are familiar with this feeling?

All: more progress. I put a 10,000uF electrolytic right across the power supply pins to the MOSFET modulator -- far beefier decoupling. Performance is even more impressive than before. There is now 400V across the primary inductor at a supply voltage of 29V. There is noticeably less ringing in the waveform of the grid feedback winding.
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Old 15th Nov 2017, 2:21 pm   #113
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Default Re: Design-and-building a large valve Tesla coil (class C, Armstrong oscillator).

Good morning folks. PROGRESS!!!

Please see pix.

1) First off, Richard (Mole42UK) has done an incredibly beautiful wind of the main inductor, the secondary coil. It is air cored and he lathe-wound it with adjacent turns, over the entire length of 41cm. It is wound on a PVCU tube.

It has an aspect ratio of approx 4:1 (length to height) and an inductance of around 25mH. DC resistance is 50R.

I'm incredibly impressed by Richard's craftsmanship. Richard used two pieces of circular stock to hold the coil in position and I will be able to use these to hold it in place on the base. It is also beautifully varnished to an incredible standard.

2) I finished work on the primary coil. This is the fatter coil at the base of the secondary. It took more work than is obvious - it contains metres and metres of 2.5mm dia single earth wire, with taps, and then at the top is the grid feedback winding. There is an anti-flashover guard between the windings, several turns of silicon sleeving with epoxy binding.

3) See pics showing a corona brush discharge at the top of the secondary coil. This is around 1cm long. The coil is just being driven by the MOSFET modulator I built specifically for test purposes. This draws 800mA at 30V for the result shown, so let's call it 20W RF in as the switch is nearly 100% efficient. The MOSFET runs completely cold on its tiny heatsink. Resonant frequency is 322KHz.

This is incredible, as the design frequency was 0.3MHz, and the plasma loads the coil (it has some capacitance). The Q is around 400.

Blue trace on scope, pictured, shows the waveform of the secondary coil. The scope probe is at x 10 and is hanging in the air a distance away from the coil. We can see that there is a zero volts crossing point: the rising edge of the sine wave is at the end of the MOSFET switching cycle. The MOSFET is still switched off, hence remains cold; it switches on with the rising edge of the sine wave. The phase locked loop is working!

As I say, this is only around 20W in. This is 50 to 80 times less power than the design power in, when the power supply and oscillator valve circuit are rebuilt. Hopefully, 50 centimetre plasma will be achievable.

Next steps:

This won't happen much before Christmas, but in the meantime, I will use the existing modulator to build an EHT power supply, already under construction, with an output again of only 20W or so.

Once I have the bespoke transformer back from Ed (Dinning), I will be able to do incremental testing of the valve power oscillator circuit.

Also pictured is an EHT probe under construction. This is following a design by Argus25 and should be good to 70Kv. It won't be able to test the voltage at the antinode at the top but it will be able to look at waveforms in the tank circuit (20KV plus at HF RF) and grid feedback circuit (800V plus).


I'm really happy to answer any questions!
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Old 15th Nov 2017, 3:23 pm   #114
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Default Re: Design-and-building a large valve Tesla coil (class C, Armstrong oscillator).

Hi Al, congratulations! In telescope building circles we call this "First Light".

I'm following this thread avidly, with no hope of recreating it(unless you plan to market it in kit form!).

I look forward to the day when your workshop looks a little like this!
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Old 15th Nov 2017, 4:29 pm   #115
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Default Re: Design-and-building a large valve Tesla coil (class C, Armstrong oscillator).

Quote:
I look forward to the day when your workshop looks a little like this!
"Honestly constable, I was reviving her"
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Old 15th Nov 2017, 6:11 pm   #116
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Default Re: Design-and-building a large valve Tesla coil (class C, Armstrong oscillator).

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...congratulations! In telescope building circles we call this "First Light".
Thank you, Ken! It's a small but significant first step in the right direction. I've uploaded another photo, this one after-dark. The plasma is a beautiful indigo colour. One thing, even at this tiny wattage from the modulator alone, it produces tons of O3.

It's quite a feat of efficiency, pretty much the same output as a line-output transformer in a vintage black and white TV, but from just 25 volts supply.

Quote:
Originally Posted by Kentode View Post
I'm following this thread avidly, with no hope of recreating it(unless you plan to market it in kit form!).
That would be *interesting*! It would be possible to do the modulator in kit form. And with a beefier MOSFET, even just the modulator could produce 100W of output. But far too early days to consider this...

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Originally Posted by Kentode View Post
I look forward to the day when your workshop looks a little like this!
Ahaha! Perhaps it does already! Actually, my 'workshop' is two places - a little picnic table on the balcony, where I do all cutting, sanding and brazing heavy joins. And pictured is just my dining room table. So usually, the whole lot has to go back into drawers at the end of the session... it's one of the most challenging things with any project, takes a lot of patience!
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Old 15th Nov 2017, 8:23 pm   #117
mole42uk
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Default Re: Design-and-building a large valve Tesla coil (class C, Armstrong oscillator).

I am very pleased to see the coil working! It looks well on your bench too.
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Old 15th Nov 2017, 8:32 pm   #118
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Default Re: Design-and-building a large valve Tesla coil (class C, Armstrong oscillator).

Hey Richard, I feel happy that you can see the fruits of your labour in action!
You really did an amazing job.

I was able to re-use the stock that you put in to the ends to turn the piece - they're back to back at the base, one inverted and partially inside the pipe and the other turned upside down. They're glued together and when cured, I can plug the whole unit into a base and unplug it as I wish, for transport, exhibition (eventually) and storage.

I've permanently attached a thick, strain-relieved ground wire to the base (high RF currents) and a copper corona-guard with the other lead-out wire soldered at the top. You can just about make this out in the photo.

How did you apply the varnish so absolutely immaculately without even the slightest run? I can do this on a flat surface but I would struggle with a tube...

Were you slowly turning the lather at the time?

Anyway, beaut job. Thank you again. Stay tuned and I hope you'll be seeing full power before New Year!
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Old 15th Nov 2017, 8:49 pm   #119
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Default Re: Design-and-building a large valve Tesla coil (class C, Armstrong oscillator).

I expect an announcement on the bbc news of "a mysterious hole in the ozone layer above London" shortly!

Does the dining room smell like the dodgems at the fair?
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Old 15th Nov 2017, 9:09 pm   #120
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Default Re: Design-and-building a large valve Tesla coil (class C, Armstrong oscillator).

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Originally Posted by Kentode View Post
Does the dining room smell like the dodgems at the fair?
Ahaha! Burning rubber? Nope, mostly just the faint and familiar smell of solder, sometimes a solvent like acetone, or at the moment, the whiff of Wellseal, which is pretty pongy for a living environment, but the balcony door is wide open, and so are the windows.

There's a very quiet integral extractor fan in the ceiling, which operates at night and does a great job of restoring the room to odourless by the morning!
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