UK Vintage Radio Repair and Restoration Powered By Google Custom Search Vintage Radio Service Data

Go Back   UK Vintage Radio Repair and Restoration Discussion Forum > Other Discussions > Homebrew Equipment

Notices

Homebrew Equipment A place to show, design and discuss the weird and wonderful electronic creations from the hands of individual members.

Reply
 
Thread Tools
Old 10th Jun 2018, 7:49 am   #1
Viewmaster
Pentode
 
Viewmaster's Avatar
 
Join Date: Jul 2016
Location: Ashby de la Zouch, Leicestershire, UK.
Posts: 127
Default Bach with sparks!

Continued from: https://www.vintage-radio.net/forum/...d.php?t=146185

I've rehashed my plasma rig, recently mentioned here, to play music through a MIDI converter which I have yet to build.
Bach toccata and fugue with sparks !

I 've had it running at 2kv, HT.
The tank coil and capacitor get warm and my electromagnetic detector shows local energy being radiated.

But I cannot get any sparks. I thought that my feedback coil was wired back to front but if this was so why all the energy and warmth !

As its DC high tension supply rather than 50 hertz, maybe it needs an interrupter to kick it off?

So some detective work is indicated.
Attached Thumbnails
Click image for larger version

Name:	BACH with SPARKS.jpg
Views:	315
Size:	73.3 KB
ID:	164335  
__________________
"Blood maybe thicker than water but it has more clots in it."
Albert.
Viewmaster is offline   Reply With Quote
Old 10th Jun 2018, 11:17 am   #2
Craig Sawyers
Octode
 
Craig Sawyers's Avatar
 
Join Date: Nov 2010
Location: Oxford, UK.
Posts: 1,439
Default Re: Bach with sparks!

I so really know what you are trying to do. Of course in the USA they seem to be able to get away with serious outdoor interference generators

https://www.youtube.com/watch?v=bbLshnfu0wY
https://www.youtube.com/watch?v=hgll-XTqcS4

Or even put a volunteer child in a Faraday cage

https://www.youtube.com/watch?v=hgll-XTqcS4

Two meter high behemoth Teslas.
Craig Sawyers is offline   Reply With Quote
Old 10th Jun 2018, 1:22 pm   #3
Biggles
Octode
 
Join Date: Feb 2004
Location: Hexham, Northumberland, UK.
Posts: 1,959
Default Re: Bach with sparks!

Shorted turns somewhere?
Biggles is offline   Reply With Quote
Old 10th Jun 2018, 6:53 pm   #4
HamishBoxer
Dekatron
 
HamishBoxer's Avatar
 
Join Date: Aug 2007
Location: W.Butterwick, near Doncaster UK.
Posts: 6,008
Default Re: Bach with sparks!

That will put out some serious interference,glad I am not near by.

In my collection I have a wooden box marked Television Interference Generator with an 807 in it but never was certain its intended use or by who.
__________________
G8JET BVWS Member and V.M.A.R.S
HamishBoxer is offline   Reply With Quote
Old 10th Jun 2018, 7:16 pm   #5
Biggles
Octode
 
Join Date: Feb 2004
Location: Hexham, Northumberland, UK.
Posts: 1,959
Default Re: Bach with sparks!

An old engineer friend of mine once told me that you can connect a motorbike ignition magneto HT lead to a long wire aerial and crank it up to blot out reception. Charming! It would probably wipe out Freeview reception nowadays as ours is very susceptible to ignition/spark generated interference.
Alan.
Biggles is offline   Reply With Quote
Old 16th Jun 2018, 8:59 am   #6
Viewmaster
Pentode
 
Viewmaster's Avatar
 
Join Date: Jul 2016
Location: Ashby de la Zouch, Leicestershire, UK.
Posts: 127
Default Re: Bach with sparks!

I have made a new coil with 750 turns and this has given me the sparks for Bach!

To try it out to see if the sparks will sound loud notes I knocked up a 555 astable sq wave oscillator and was pleased to see and HEAR the sparks sounding off when controlling the two GU81 valves o/p.

I made a cheap and cheerful winding rig to wind the 750 turns. At one point there was small overlap of turns which I didn't notice but the coil seems fine without any arcing over when running the valves at 2.5kv.

To increase spark length I have bought off ebay a HV transmitting variable capacitor to fine tune the primary coil

I will also have to increase ventilation more to get rid of the dangerous ozone produced!
Attached Thumbnails
Click image for larger version

Name:	VTTC new coil.jpg
Views:	197
Size:	63.8 KB
ID:	164686  
__________________
"Blood maybe thicker than water but it has more clots in it."
Albert.
Viewmaster is offline   Reply With Quote
Old 16th Jun 2018, 10:25 am   #7
dalekmoore2007
Tetrode
 
Join Date: Aug 2008
Location: Melbourne, Australia
Posts: 91
Default Re: Bach with sparks!

Need rubber gloves with this beast !are you making a singing arc Tesla coil Albert ? audio to pin 5 of the 555 will do it as you know .
dalekmoore2007 is offline   Reply With Quote
Old 16th Jun 2018, 12:10 pm   #8
astral highway
Nonode
 
astral highway's Avatar
 
Join Date: Nov 2006
Location: London, UK.
Posts: 2,610
Default Re: Bach with sparks!

Quote:
Originally Posted by Viewmaster View Post
But I cannot get any sparks. I thought that my feedback coil was wired back to front but if this was so why all the energy and warmth !

As its DC high tension supply rather than 50 hertz, maybe it needs an interrupter to kick it off?

Hello, with this might rig, you should be getting effects that are spectacular! An established rule of thumb for spark length is L=1.7 *(Sqr root power in)
Where L= spark length in inches

Or about 50 inches with 1kW in. Your two valves there can manage 2kW as a pair but I don’t know exactly if your power supply can support that.

*If you can’t get a break out, it can mean you need more capacitance in your topload or generally a mismatch between the resonant frequency of your tank circuit and the self-resonant frequency of your secondary.

*you need a very good capacitor in the tank. Strontium titanate doorknob types are the best.

*try reversing the phasing of the grid feedback coil.

* try moving the feedback coil closer to the primary, but watch for flashover as huge voltages can appear here when tuning is out.

*Also check and maybe adjust the period of your grid leak circuit. The capacitor here has to be a decent RF power type. Make sure it’s rated 2kV minimum.

*Most importantly, check that you have a very good RF bypass capacitor across the EHT power supply as the RF circuit is critical and without it, nothing will happen. The capacitor should be rated 15kV or higher.

This advice is based on multiple builds over the years with transmitting valves.


Good luck!
__________________
Al

Last edited by astral highway; 16th Jun 2018 at 12:22 pm.
astral highway is offline   Reply With Quote
Old 16th Jun 2018, 12:45 pm   #9
Viewmaster
Pentode
 
Viewmaster's Avatar
 
Join Date: Jul 2016
Location: Ashby de la Zouch, Leicestershire, UK.
Posts: 127
Default Re: Bach with sparks!

Thanks very much for that Al, much appreciated, but now sparking OK...
Made bigger coil (750 turns)...See my post No6 on this thread.

As I mentioned a variable C in the tank with or without my doorknob cap already there will soon establish tuning errors.

Eventually my spark length will not as big usual as I am using full wave and smoothed DC supply to valves.. It's 4 inches at present without any tuning.

I use DC to avoid any 50 hertz sound that is normally heard with VTTC's. It's good sound that is important not a long spark.

My 2 MOT's run cold so far.

And Dale it's not a singing plasma arc now but on/off spark at the musical notes frequencies.
A midi converter kit I am waiting to receive is polyphonic so hope to hear more that one note.

Thanks again all for help.
__________________
"Blood maybe thicker than water but it has more clots in it."
Albert.

Last edited by Viewmaster; 16th Jun 2018 at 12:50 pm.
Viewmaster is offline   Reply With Quote
Old 16th Jun 2018, 1:27 pm   #10
Radio Wrangler
Dekatron
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 10,628
Default Re: Bach with sparks!

Switched-Mode Bach?

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is online now   Reply With Quote
Old 16th Jun 2018, 1:43 pm   #11
astral highway
Nonode
 
astral highway's Avatar
 
Join Date: Nov 2006
Location: London, UK.
Posts: 2,610
Default Re: Bach with sparks!

Davis: Good old J.S Bach had a computer for a brain...

So some digital wizardry would be a fitting tribute for smashing out the famous Toccata and Fugue!

Albert: Bass response can be underwhelming with plasma; Id be interested to see how this goes and I hope you get the results your hard work deserves!
__________________
Al
astral highway is offline   Reply With Quote
Old 16th Jun 2018, 4:02 pm   #12
Viewmaster
Pentode
 
Viewmaster's Avatar
 
Join Date: Jul 2016
Location: Ashby de la Zouch, Leicestershire, UK.
Posts: 127
Default Re: Bach with sparks!

Quote:
Originally Posted by astral highway View Post
Albert: Bass response can be underwhelming with plasma; I’d be interested to see how this goes and I hope you get the results your hard work deserves!
Al, my rig isn't plasma now but square wave modulated sparks.
The audio is not put into a plasma flame to give that very high freq tinny noise but turns a tesla spark on/off at the frequency of the musical note.

For example, A above middle C would have a spark freq of 440 hertz.

Here's a good example of 2 tesla coils playing Beethoven together !

https://www.bing.com/videos/search?q...88AE&FORM=VIRE
__________________
"Blood maybe thicker than water but it has more clots in it."
Albert.
Viewmaster is offline   Reply With Quote
Old 16th Jun 2018, 5:34 pm   #13
merlinmaxwell
Dekatron
 
merlinmaxwell's Avatar
 
Join Date: Jul 2008
Location: Maidenhead, Berkshire, UK.
Posts: 7,641
Default Re: Bach with sparks!

Quote:
to get rid of the dangerous ozone produced
You smell the nitrogen oxides produced by the very reactive ozone, still not the best thing to inhale.

Quote:
Switched-Mode Bach?
Brilliant!
__________________
Cats have staff, it's dogs that have owners.

Last edited by merlinmaxwell; 16th Jun 2018 at 5:34 pm. Reason: spelling
merlinmaxwell is offline   Reply With Quote
Old 16th Jun 2018, 9:18 pm   #14
julie_m
Dekatron
 
Join Date: May 2008
Location: Derby, UK.
Posts: 6,815
Default Re: Bach with sparks!

This set me wondering .....

Could you modulate the arc of an electric welder as you ran a bead along, then hear a -- probably weak and scratchy -- reproduction of the original sound by running the corner of a plastic 10 note, or some similar acoustic diaphragm type device along it?
__________________
Julie {formerly known AJS_Derby}
julie_m is offline   Reply With Quote
Old 16th Jun 2018, 11:12 pm   #15
Radio Wrangler
Dekatron
 
Radio Wrangler's Avatar
 
Join Date: Mar 2012
Location: Fife, Scotland, UK.
Posts: 10,628
Default Re: Bach with sparks!

Yes.

If you TIG weld steel with DC polarity, it's pretty quiet.

To weld aluminium, you have to use AC polarity to get some scouring action to bolw oxide flakes off the weld-pool. Boy is it loud. My welder is essentially a 9kW function generator. I can swithc it between sine and square waveforms, slew the frequency from 20 to 200Hz and I can vary the mark space ratio. All very audible!

Tenners would melt anywhere near the business end. The argon costs a fair bit without burning banknotes.

David
__________________
Can't afford the volcanic island yet, but the plans for my monorail and the goons' uniforms are done
Radio Wrangler is online now   Reply With Quote
Old 17th Jun 2018, 2:02 pm   #16
astral highway
Nonode
 
astral highway's Avatar
 
Join Date: Nov 2006
Location: London, UK.
Posts: 2,610
Default Re: Bach with sparks!

Quote:
Originally Posted by Viewmaster View Post
Al, my rig isn't plasma now but square wave modulated sparks.
Hey Albert!

Pix of your coil operating, please?

If you cathode modulate the two transmitting valves with a digital audio signal, you're simply switching them on and off at the frequency of the note, as you observe.

That doesn't change the nature of what pops out at the antinode of the secondary coil. It's still ionised gases - AKA plasma - including nitrogen and oxygen. It's hot! On my first valve Tesla coil, I had a 2mm brass wire as the break-out point. It vapourised the metal.

Quote:
The audio is not put into a plasma flame to give that very high freq tinny noise but turns a tesla spark on/off at the frequency of the musical note.
I think this is just a (harmless) confusion of terminology. I don't know what a 'Tesla spark' is...

I prefer to make it clear the huge difference between 1) mild corona 2) the spark you might get out of an ignition coil or a LOPT, and 3) the spectacular discharge from the antinode (top of the tesla secondary) that is going into free space and not to a grounded object -- but that's just to emphasise how high the voltage at the antinode of a Tesla coil is. And also there's an aesthetic component...

Quote:
Here's a good example of 2 tesla coils playing Beethoven together !
Those are big old coils, with a distinctive, unusual topload (it's normally a toroid, as you've likely seen repeatedly elswehere.) They are probably (from what I know of the typical size of the electronics encased under the primary) 1.5 metres or more tall.

Most digital coils this big use a 3-phase power supply, 10kW in isn 't unusual, although it's not possible to see in this case if those cables draped along the ground plane are thick enough to be three phase. It takes a lot of skill to build a solid-state coil that can survive repeated ground-strikes like this. It puts a gigantic amount of current through the switching devices.

Some people like to cycle these sorts of spectacular, solid-state exhibition coils through various modes - 'burst', with a repetition rate between 40-400Hz or so, and audio modulated, and sometimes (much, much more rarely) CW

I do find the typical, prominent, very 'buzzy' sound that accompanies this kind of modulation (you can hear it clearly in the clip you've posted) a bit of an unwanted distraction and full of distinct harmonic impurity. But that's probably because I play the piano/keyboards, and prefer the complex resonant properties of notes produced this way. Also, I find that when there's a moment of intentional, obvious polyphony with an orchestra, this doesn't develop with sounds produced this way.

But it sure makes for a spectacular display if people haven't heard it before!

I'd love to see more of your coil, so yes, pix of it in operation, please!
__________________
Al

Last edited by astral highway; 17th Jun 2018 at 2:22 pm.
astral highway is offline   Reply With Quote
Old 17th Jun 2018, 5:49 pm   #17
Viewmaster
Pentode
 
Viewmaster's Avatar
 
Join Date: Jul 2016
Location: Ashby de la Zouch, Leicestershire, UK.
Posts: 127
Default Re: Bach with sparks!

OK AL, I will get some working pics when I have overcome an annoying break out in the top connection to my main break out point, a 2 BA threaded length of brass rod.

It seems the enamel coating has been fractured where the coil runs across to the 2 BA rod in my winding the coil, exposing the copper and break out occurs there. I've added coat after coat of new varnish on it but it still breaks at that small area when my variac is wound up to 240v. No sharp bends in it either.

I understand problem you had with your brass break out, it is very hot.
You say, "On my first valve tesla...." How many have you made then?
Did you musically modulate any? I would be interested to know.

Well Al as a pianist, music by spark must be a terrible noise for you to listen too, but somewhat compensated by the display, as you mentioned.
......you can't get electrical sparks out of a piano.

I was contemplating changing the spark length for high/lows notes to add to the display.

Pics to follow soon.
__________________
"Blood maybe thicker than water but it has more clots in it."
Albert.
Viewmaster is offline   Reply With Quote
Old 18th Jun 2018, 11:25 am   #18
astral highway
Nonode
 
astral highway's Avatar
 
Join Date: Nov 2006
Location: London, UK.
Posts: 2,610
Default Re: Bach with sparks!

Hey Albert,

That sounds like an annoying problem with the flashover. I can’t quite visualise what you mean - not between turns on the secondary at the top of the winding? Can you post a pic?

I’ve made five Tesla coils over the years. Yes, my first was Ulrich Haumann’s plasma tweeter using an old TV line output valve: small but beautiful!

The second was a design by John Freau using a Svetlana 572B transmitting triode, the typical microwave oven transformer doubled circuit and a simple cardboard postage tube coated with 20 coats of yacht varnish over the secondary winding . I got 22cm sparks in CW but the design was poorly tuned and could only run for 10 seconds without overheating the valve.

The third was a better design using a second valve and a better grid leak circuit and RF design. I took it apart when my son was starting to toddle around and left coil building until after a few years ago. He’s now a mid-teen and leaves all my work well alone.

My fourth was similar to your design, only with one GU81M. However I was by then really incapacitated by the multiple surgeries I’d unexpectedly had, which really limited how much I could safely carry and even a few Kg seemed a lot, suddenly. This really threw me as I was strong as an ox before they started dissecting and separating bits of my core and major leg muscles repeatedly in a short time!

I had ordered a bespoke 2.5kV, 2kVA, transformer wound by Ed, but when it arrived, I couldn’t even lift it off the floor as I couldn’t bend that far. (It’s 26Kg) . That’s now been bought by Chris on the forum, along with the valve and base and some huge caps for the power supply (collection pending).

Undeterred, I switched my attention to high-power solid state designs and with the overall rule that the resulting build should be modular, light and yet still spectacular.

My fifth was a small sub-project using a power MOSFET in a class E RF amplifier for about 40W of output

So I’m now on my sixth build. It’s slow progress as I have limited space in a flat after my marriage ended in 2012.

I have no dedicated workshop and have to do all cutting and fettling on a small picnic table on my balcony. Soldering and test equipment (‘scope, bench power supply, components) are systematically and in a logical order laid out on the dining room table and everything goes away after each session. You can imagine how this limits the pace a bit!

It might take me three days to get organised to build a simple assembly that would take 4 hours with a permanent workshop. However, I’m just delighted to be back in the game.

I’m also building some bespoke test equipment along the way and winding my own magnetics - this is complex and it’s often not possible to copy someone else’s design.

The purpose of the current build is linked to a big photographic project that I will describe in the future when I have made appropriate progress.

Hope to hear more from you soon!
Attached Thumbnails
Click image for larger version

Name:	C1BBFE48-CE19-4D61-BC63-EC704DB2C1D7.jpg
Views:	58
Size:	36.7 KB
ID:	164838  
__________________
Al

Last edited by astral highway; 18th Jun 2018 at 11:32 am.
astral highway is offline   Reply With Quote
Old 18th Jun 2018, 2:18 pm   #19
Viewmaster
Pentode
 
Viewmaster's Avatar
 
Join Date: Jul 2016
Location: Ashby de la Zouch, Leicestershire, UK.
Posts: 127
Default Re: Bach with sparks!

Well Al, many thanks for your sparking history. A big variety of designs there.
I salute your perseverance in the face of all your difficulties and health problems. Especially not having a workshop.
I do have one outside but do most of my work on the kitchen table.....I'm not allowed to use the dining room table as you do.

I wonder why you had to have such a heavy single transformer when MOT's
can be stacked in series and parallel to get high volts and amps as required?
Each one is not too heavy if handled as units.
But I daresay I am missing something here...…….as is usual with me.

I did follow your progress when you had a thread about it here on this forum.

I wonder what the photographic project is? Best not describe it here as we will get in the Mods bad books for going off topic,

So back to Bach with sparks !...…….my break out is cured with many coats of varnish at the top of the coil, on the wire connection to the brass break out point.

My rig is in a small conservatory without curtains so hope to take some pics of my spark tonight when it gets dark. It certainly makes a racket when square wave modulated ! No AC interference with my DC supply.
__________________
"Blood maybe thicker than water but it has more clots in it."
Albert.

Last edited by Viewmaster; 18th Jun 2018 at 2:36 pm.
Viewmaster is offline   Reply With Quote
Old 18th Jun 2018, 4:48 pm   #20
astral highway
Nonode
 
astral highway's Avatar
 
Join Date: Nov 2006
Location: London, UK.
Posts: 2,610
Default Re: Bach with sparks!

Hey Albert,

Re MOT’s: they are actually quite heavy, as you know, and they’re also really inefficient unless they’re seeing the right impedance load, which is a magnetron with doubler circuit.

I have a lot of experience with them and they served me well for years , but I ended up wanting to improve efficiency, so after an approach from me, Ed designed and wound one on suitable lams. It was /is fit for bigger start-up currents as I stepped away from the small, oil-filled caps from scrapped microwave ovens and towards larger ones. As Ed drily noted, it would make a good electric chair.

It’s a moot point now as even two MOT’s would be an unwieldy and unwise lift from floor level now.

I’m glad you fixed the arc and am looking forward to seeing your progress.

Take care!
__________________
Al

Last edited by astral highway; 18th Jun 2018 at 5:14 pm.
astral highway is offline   Reply With Quote
Reply

Thread Tools



All times are GMT +1. The time now is 5:47 pm.


All information and advice on this forum is subject to the WARNING AND DISCLAIMER located at https://www.vintage-radio.net/rules.html.
Failure to heed this warning may result in death or serious injury to yourself and/or others.


Powered by vBulletin®
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
Copyright ©2002 - 2018, Paul Stenning.