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Old 21st Jun 2018, 4:47 pm   #41
astral highway
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Default Re: Bach with sparks!

Quote:
Originally Posted by Sean Williams View Post
...Have just ordered a tiny Tesla kit online, but I do have some 813s lurking that arent doing much.... I am feeling inspired to have a go
That's great, Sean! I kind of sensed that you'd get involved hands-on sooner or later!

With your professional RF engineering background, you're destined to get some pretty amazing results from a couple of 813's!
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Old 21st Jun 2018, 5:36 pm   #42
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Default Re: Bach with sparks!

Thanks Al for taking trouble on all those calcs. I shall try various light bulbs but I do seem to recall that when I first used 60w bulbs they reached max brightness well before my variac was up to 240v, so switched to higher wattage.
I was nervous about what might happen to my GU81s if the 60w blew.

BTW, I am getting an ozone mask...…
….all coilers should wear one when sparking Bach.

What with EHT, RF and ozone dangers it's safer and better audio quality just to listen to a CD!
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Old 21st Jun 2018, 6:37 pm   #43
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Default Re: Bach with sparks!

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. I shall try various light bulbs but I do seem to recall that when I first used 60w bulbs they reached max brightness well before my variac was up to 240v, so switched to higher wattage.
Hi Albert, ahah. It's worth noting what that might mean about grid current -- I've made another comment below. Obviously the bulbs aren't in the mains circuit, so their brightness doesn't directly depend on the variac voltage...but you could almost use this test to ensure that you're not passing too much grid current.

Quote:
Originally Posted by Viewmaster View Post
was nervous about what might happen to my GU81s if the 60w blew
If the bulbs blow, the feedback coil will be o/c. The circuit will stop oscillating and there is no other path for grid current.

It's possible that your valves are biassed rather above their recommended grid current as it is (this is just going from memory, I haven't re-checked the data-sheet) so it's worth doing the experiment.

Nothing bad will happen to the valves.

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BTW, I am getting an ozone mask...…
Joking apart, really worth having well-ventilated space/ a fan/ as there is tons of ozone in this set up.

Quote:
Originally Posted by Viewmaster View Post
with EHT, RF and ozone dangers it's safer and better audio quality just to listen to a CD!
True 'dat. But with these sorts of builds, there's so much investment in £££, time, and learning curve, that it's never obvious when to jump off!
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Old 21st Jun 2018, 7:14 pm   #44
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Default Re: Bach with sparks!

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It's possible that your valves are biassed rather above their recommended grid current as it is...
This isn't as clear as I meant. Obviously, we normally talk about a grid bias voltage. I just re-checked an the recommended bias voltage is between -116V and -160V, if that helps...

What I'm saying here is that as these are power devices, the manufacturer does also state a maximum grid current. It's 220mA absolute max for grid 2, from the Russian data sheet.
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Old 21st Jun 2018, 9:18 pm   #45
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Default Re: Bach with sparks!

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True 'dat. But with these sorts of builds, there's so much investment in £££, time, and learning curve, that it's never obvious when to jump off!
With an interest in music it's the challenge of reproducing it in a novel way I guess. And sparks have the added attraction to watch.

BTW, did you know that SGTCs can also play music. I'll try and dig out the reference to it.
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Old 21st Jun 2018, 10:16 pm   #46
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Default Re: Bach with sparks!

Hey Albert,

I’m sure it’s possible, only I wouldn’t necessarily class it as ‘music’🎶 with a spark-gap doing the switching! The racket from those things!!!

In any case SGTC’s have now almost or absolutely been superceded in performance by polyphase IGBT switched models in the 10kW+ class.
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Old 22nd Jun 2018, 8:08 am   #47
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Default Re: Bach with sparks!

How about a spark gap, 4 octave polyphonic organ. Al?
A bishop in Canada made it to broadcast religious music !

I would love to have heard that play.
I wonder what happened to it?

http://120years.net/category/country/canada/
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Old 22nd Jun 2018, 12:13 pm   #48
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Default Re: Bach with sparks!

Brilliant invention!! I love it. Désilets was a genius to think of this device and the method of modulation.

Thanks for introducing Désilets, Albert.

Happy construction, looking forward to when your modulator arrives!
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Old 27th Jun 2018, 5:18 pm   #49
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Default Re: Bach with sparks!

Just started building MIDI modulator kit now. Double sided PCB and very close
connections so I am taking care. Especially when I insert a 28 pin IC !

In the meantime that premature break out has started up again in the same place.
Started again when I turned up an unmodulated spark to max so may have to reposition the main break out to avoid the gentle bend where break keeps occurring.

Just found Bach's organ music on square wave on the net but it doesn't modulate the spark. The square wave amp o/p must be too low as my 555 modulates OK. So will have to sort that out.

More news when it all works!
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Old 27th Jun 2018, 9:27 pm   #50
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Default Re: Bach with sparks!

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Originally Posted by Viewmaster View Post
How about a spark gap, 4 octave polyphonic organ. Al?
A bishop in Canada made it to broadcast religious music !

I would love to have heard that play.
I wonder what happened to it?

http://120years.net/category/country/canada/
It mutated into the Hammond tonewheel organ (sort of).
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Old 28th Jun 2018, 4:43 pm   #51
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Default Re: Bach with sparks!

Hey Albert,

That's great news about your modulator. Good luck with the build.

I'm not quite sure where your break out is happening, can you send a pic? If it's some way down the secondary, that's often a tuning issue. But yep, pic will help.

I don't quite understand what you mean by 'Bach on square wave.' Can you clarif - I love Bach but this is an alien concept and sounds like it would have all sorts of harmonic impurities.

(I know that we can square up a signal with a Hex inverter chip with Schmitt trigger, like 74HC14 - this is often done with digital Tesla coils and current feedback. So it's not I don't know how to do it, rather I don't know why in this case.)
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Old 28th Jun 2018, 5:35 pm   #52
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Default Re: Bach with sparks!

Al, I did send a previous pic of unwanted breakout point, but here it is again. It breaks out just on the bend.

Bach on square waves is exactly what it says in the tin. The single notes should modulate OK but the chords will sound iffy I'm sure although my modulator can handle 2 notes.

The square wave Bach can be found here...….if you can bear listening
to a square wave rendition.
Only squares listen to square waves

https://www.youtube.com/watch?v=eN2VjU-BZ6E&t=58s

If you save it and run it on Audacity, you will see that all the notes are square waves, ideal for spark modulation. As I said, I tried it but I need more volts o/p to modulate my rig.

Happy sparks.
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Old 28th Jun 2018, 6:26 pm   #53
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Default Re: Bach with sparks!

Hey Albert,

Hmm, thanks for the link. It's not that I don't understand how a signal can be squared up (see my last post.)

What I'm saying is I'm still not sure why you need a square wave version to modulate your coil (with a MOSFET in the cathode, IIRC?) It seems a shame to bring in all those unwanted harmonics when you could use the original version. You don't need to hard switch a valve Tesla coil.

If I understand you correctly, your new modulator (under construction) needs square waves, and you won't then have the problem of needing a higher voltage signal? It's still not clear to me why you need that version...

Thank you!

Re the breakout, yes, best to avoid sharp bends. I'd remove that insulating disk at the top and run the wire the shortest distance under your breakout point. That should fix it!

Alternatively, there's no reason why the breakout point needs to be in the centre with this design, so if that doesn't work, why not have it at the side?
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Old 28th Jun 2018, 9:39 pm   #54
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Default Re: Bach with sparks!

The modulator I am making will use midi files or a keyboard for the tesla. As I understand it the o/p is sq wave at 5v ( again not enough to directly turn my mosfet in cathode on/off)

Forgive me, Al, if have the wrong of the stick but as I understand it with musical teslas, one can do one of two things.

1. Modulate a continuous plasma flame with the actual music (non sq wave). The result being that awful tinny tiny sound very severely lacking in bass.

2. Modulate a non flame plasma system where square waves at the musical frequency turn a spark discharge on/off to produce a note.

It is the latter that I am working towards. So that is why that sq wave version of Bach is of interest to me...……..

………. or can one really reproduce something better with teslas that I am not aware of

Have I got this all wrong? It's what I have gathered searching the net for info.

Yes, the main breakout point at the side will probably cure it but I do like a central looking display so I will persevere.
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Old 29th Jun 2018, 12:54 pm   #55
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Default Re: Bach with sparks!

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The modulator I am making will use midi files or a keyboard for the tesla. As I understand it the o/p is sq wave at 5v ( again not enough to directly turn my mosfet in cathode on/off)
Hey Albert... you could put a MOSFET gate driver chip in there to improve gate drive. IXDD414CI is perfect and I've used it up to 4MHz. If your other plan doesn't do what you want, I can give you more deets later down the line.

Quote:
... as I understand it with musical teslas, one can do one of two things.

1. Modulate a continuous plasma flame with the actual music (non sq wave). The result being that awful tinny tiny sound very severely lacking in bass.

2. Modulate a non flame plasma system where square waves at the musical frequency turn a spark discharge on/off to produce a note.
I see what you mean, only I've only ever seen (2) applied to solid state coils. These are 'hard switched', by which I mean, simplifying a bit, that the switching transistors are really close to being like a mechanical switch, either on or off.

So the square wave is relevant and essential here because it has vertical edge and also because it biases the gates off really quickly. They are usually in pairs or a quad of two pairs. If one of the pair wasn't off when the other one was switched on, it would be up in smoke in a few microseconds.

I have never heard of digitised audio files being used to drive a valve Tesla coil on the grounds of musical fidelity. It doesn't make sense, as square waves are full of spurious harmonics that aren't in the original. Also, you will have sounds that originally dwelled/decayed slowly being chopped harshly, and to me, that sounds like a robot playing a keyboard.

Quote:
Have I got this all wrong? It's what I have gathered searching the net for info.
I do think there may be some confusion there.

However, when you describe 1) above as tinny and lacking in bass, that's also true. So you can choose that, or your in my opinion robotic-sounding square wave, which as I say I haven't previously seen married with valve Tesla coils because the over-engineering involved may not be worth it in sound quality terms.

But no harm done if you experiment away, only a caution again with audio signals coming from a PC or a mobile - isolation, isolation, isolation!
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Old 30th Jun 2018, 11:05 am   #56
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Default Re: Bach with sparks!

OK on all that Al and the IXDD414CI mention.

I think that my rig is a first in that few now build VTTCs and when they did,
musical modulation was not popular until SSTCs were built.

Of the many coils I have seen running on the web, VTTCs, none use modulated sparking for music, only plasma producing the non bass stuff.
That is what I first started building for, but changed horses ( or sparks ) in mid stream and wound a new coil.

I wouldn't put my laptop anywhere near or connect it, when the sparks fly!. Only a cheap portable CD player. I don't know what the possibility is of a flash over from the GU81 anodes to the centre tapped filament but so far all has run OK.........….Beginners luck?

Of all the many interests I have had and have, this sparky lark is the most
dangerous of all, but so, so intriguing.
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Old 30th Jun 2018, 2:43 pm   #57
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Default Re: Bach with sparks!

Have you seen this bar graph score of Bach?
Interesting to ponder on what the great man would have thought of this.
https://www.youtube.com/watch?v=ATbMw6X3T40
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Old 1st Jul 2018, 8:33 am   #58
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Default Re: Bach with sparks!

New thoughts......

I have a MIDI version of Bach's TandF.
Using studio 2 app the bass and treble clefs can be displayed and then saved as two separate MIDI tracks.

Now convert each to MP3 and save bass and treble clef versions as stereo on left and right channels and save to CD.

Now play each track via 2 Schmitt triggers switched alternately at 30 hertz.

(notes in a chord played alternately at 30 hertz sound very much 'chordal'.)

All this should enable tesla to handle chords, with increased clarity, spread over the bass/treble as they are handled separately.

ALTERNATELY, split my two GU81 into two separate teslas (new pri and sec coils required), and play bass clef though one and the treble clef through the other.
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Old 2nd Jul 2018, 12:44 pm   #59
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Default Re: Bach with sparks!

I have now decided to have two teslas running side by side, one slightly higher that the other as I have 2 valves running anyway.
The higher coil will be for the treble clef and the lower the bass clef.

I have discovered on my music app that I can easily shift bass notes to the treble clef and treble to the bass clef. (still playing the same note of course)

This means that where single notes are sounded I could shift alternate notes to another clef and make the two tesla alternate between them for display purposes! Tremolos have never looked quite so good !!

I have found out how to put two independent tracks (bass and treble clefs) as a stereo pair so one step forward.


I don't think that there are any snags to my ideas but the proof will be in the
sparking pudding.
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Old 7th Jul 2018, 5:44 pm   #60
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Default Re: Bach with sparks!

I have now split the two GU81 valves that were in parallel into two separate teslas for the bass clef and treble clef systems and wound the primary coil for the second one. On the left in piccy.
The primary coil formers I use are acrylic flower pots from you know where.

Awaiting more wire to wind another 750 turn secondary...….
.........not looking forward to that !

Have decided that as I have already built (not yet tested ! ) one MIDI converter
kit I would build a second one to serve both of the teslas.

Maybe my EHT will need a boost to drive the two independent systems.
We shall see.
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