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Old 12th Jul 2018, 5:23 pm   #61
Viewmaster
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Default Re: Bach with sparks!

The first of the two MIDI converters has been tested OK with a 'scope.
It puts out pulses at the note frequencies and can handle 3 notes at a time.
(Converter kits are from, Eastern Voltage Research, in USA. )

On a speaker a chord sounds OK so should modulate sparks. Pulse width is adjustable.

Second one being made so 6 notes can be handled at a time (3 in bass and
3 in treble clef)

Spark size is reduced now as only one GU81 each creates them.

So, will knock up sometime, a trial full wave voltage doubler to increase EHT to each valve. As current availability is reduced doing this I am getting a 3rd MOT to give it all a shot in the arm....not my arm.

Still awaiting IXDD414CI drivers from China, recommended by, Al.

Running now before I can walk ...…..just created a MIDI file with all the notes on the piano running up the scale on alternate bass/clef. This should eventually show if both sets of sparks can handle it all and what range I should set the converters to.
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Old 12th Jul 2018, 6:30 pm   #62
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Default Re: Bach with sparks!

Quote:
Originally Posted by Viewmaster View Post
So, will knock up sometime, a trial full wave voltage doubler to increase EHT to each valve. As current availability is reduced doing this I am getting a 3rd MOT to give it all a shot in the arm....not my arm.

Still awaiting IXDD414CI drivers from China, recommended by, Al.

Running now before I can walk ...…..just created a MIDI file with all the notes on the piano running up the scale on alternate bass/clef. This should eventually show if both sets of sparks can handle it all and what range I should set the converters to.
Hey Albert,

Sounds like you're putting some serious thought and resources of energy and time into this - it's a properly giant project now! I'm just adding up the weight and it must be knocking 20Kg's already.

I hope it all goes the way you imagine it to, and it would be wonderful to see your vision of polyphony realised in the way you describe.

I think if you're going to have two GU81s' like this, each with its own primary and secondary for the RF side of things, they're also better off with individual power supplies that are each properly RF bypassed.

I know it's not something that you're particularly concerned about, but a lot of the available 800W power from each MOT is just heating up your anodes
and with a bit more tuning, even one MOT per valve will be plenty with the EHT from a full-wave doubler. If you're going this route, it's also worth buying decent EHT diodes to make your bridge from.


I think I may have some candidates in my parts box (new, unused) I'll check.
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Old 13th Jul 2018, 7:29 am   #63
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Default Re: Bach with sparks!

Hi AL,
Most of the weight, of course, is in the MOT's and these are separate from the main rig so the lifting load (!) is spread between them. They are mounted on a nearby window sill. The only heavy part in the rig being the filament tx.

I used that variable HV cap to tune the primary and 1000pf seems about the right ballpark.
Recently knocked up a thick tin foil top hat for the sec, (to increase capacitance), to see if spark output was higher, but it didn't seem so.
I shall try a really big one soon.
The anodes are not running red at all, BTW.

I use BY255's in long strings for EHT rectification at present, but thanks for your kind offer, Al.

I take your point about using separate supplies to each valve. I hadn't thought of that. Silly me.

How's your project No6 coming on?
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Old 13th Jul 2018, 12:44 pm   #64
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Default Re: Bach with sparks!

Hey Albert,

Great to hear your rigs are running relatively efficiently.

I hope you make good process winding the new secondary and primary.

My project is on very slow burn - it needs me to work on the dining room/living room table in stretches of just a free hours at a time and takes ages to take everything out and put it back in an orderly fashion , and just to keep a note of where I am with progress. My teenage son is with me for a few weeks so Iíll have little opportunity to move things on for a while. Its fine , Iím not complaining! Iíll post when I have something concrete to share.

Cheers
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Old 22nd Jul 2018, 1:28 pm   #65
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Default Re: Bach with sparks!

Phew ! Problem was that I mistakenly thought I had put two midi files into stereo but having spent hours trying to do this, it's a no go

BUT, I now have a simple work around.
In a previous interest I had two small laptops.

So I shall run the bass clef on one laptop and the treble clef on the other, both now having Anvil studio software installed.

Both have USB to midi cables connected to the two midi converters.

So, I shall hit the PLAY buttons on each laptop at the same time!

Interesting experiment suggests itself now...…..Hit play button on one laptop, X number of music bars after hitting the first one !!

An Albert fugue!

I now await the next snag, but I'm getting there...…….
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Old 27th Jul 2018, 11:17 am   #66
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Default Re: Bach with sparks!

Whilst I am awaiting components to increase EHT and also changing sec. coil
(more turns), I have decided to build a half bridge SSTC in order to hear how my polyphonic midi converters sound on that system, just out of interest.
Maybe if very good, I shall eventually have 2 running for bass/treble
or just one plus a GU81 in tandem.. A kinda hybrid VTTC/SSTC.


I was afraid that using 2 laptops playing together might run Bach at different speeds but as the app seems to use the laptop clocks, on a test run, both the bass and trebled clef players finished together. So that will work OK now methinks.

I had a big flash over the other day from primary to sec. My fault, in that looping the primary ends through to coil formers, thereby exposing them
to the sec coil. Another coat of varnish and all seems well again. A timely reminder just how dangerous all this can be !
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Old 6th Aug 2018, 6:17 pm   #67
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Default Re: Bach with sparks!

Latest thoughts.

Delving into SSTC's I have decided to make two small ones for treble and bass clefs.
To save time have bought 2 secondary coils from USA. A chap there winds all sizes to order and is reasonably priced.

Now this bit might not work.ÖÖ.The 2 GU81's will be reconnected as one system as before and will be modulated with the
bass clef divided by two (one octave lower) !


So the valves, will hopefully, be playing very low whilst the two SSTCs each play the normal polyphonic music.

This will not require any more MIDI converters.

So I am now teaching myself about winding my GDT's (gate drive transformers) and the rest of SSTC circuitry, which is all new to me.

It should, I hope, sound good...Ö..living in hopes.
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Old 11th Aug 2018, 4:06 pm   #68
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Default Re: Bach with sparks!

Now have all the parts for two SSTC's. (bass and treble clefs)
The first one nearly ready for assembly within a small acrylic enclosure.

Piccy shows 1,100 turns secondary with primary. Top load 8 inches dia.
Power supplies mounted on MDF. Two heatsinks for MOSFETS. and a driver board. ( PC fans will be use to cool heatsinks.)

My first attempt at winding the GDT gives waveform shown at 250kHZ with some ringing.
Will put in a ferrite bead to stop that or find better quality toroid to wind it on.

I daresay I may blow something to smithereens on this first trial SSCT but second one should be less explosive ....
...............further up my learning curve by then.
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Old 14th Aug 2018, 10:22 am   #69
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Default Re: Bach with sparks!

Here's more piccys.
I borrowed a double beam osc to adjust the o/p from the GDT secondaries to make sure they were 180 out of phase...…..if not, the Mosfets would go to smithereens, wherever that is.
(The slight difference in amplitude is the osc amp adjustment slightly different)

Also a mock up of the complete SSTC. The small blue toroid at the bottom is the feedback coil. The Mosfets are on the heatsinks in the front. All the mains power supplies are slung underneath the MDF base.

Also close up of Mosfets on heatsinks. 2 PC fans each end for cooling.
I've tried to keep all the leads as short as possible and the primary coil
will be just above with short connecting leads.

Those yellow caps (.33 mf. 2kv) were 5 quid each...….don't tell the wifey.

Blimey, if this ever works I've got to make another identical one AND get the GU81s running in tandem again...
…...I hope that Bach eventually likes it all.
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Old 20th Aug 2018, 12:07 pm   #70
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Default Re: Bach with sparks!

The first of two SSTC's is now complete and ready for first light.
I am very apprehensive and keep putting the switch on, OFF.
…..although it will be slowly wound up with a variac and video taken so I can
see exactly where the smoke came from.

There are so many stories on the net about SSTC mosfets going phutt etc.
I have taken care and have put in back to back zeners to protect the mosfet gates for example.
I have yet to put in isolation of the Midi converter i/p so that is my last job.

Started work on the second SSTC and now collecting other midi music as well as Bach.
Other than classical, Scott Joplin should sound good played across 3 sparks as well as some great tunes of the 20/30/40s. Jumping the gun, methinks.
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Old 28th Aug 2018, 3:36 pm   #71
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Default Re: Bach with sparks!

Hey Albert, I just noticed a few things:

*there doesn’t appear to be a DC bus for the MOSFETS.
This could cause a headache or worse. It needs to be really well designed .

*there are resistors in parallel with your pulse capacitor. This is unnecessary, it’s not a DC component , and turns a critical LC circuit into an RLC circuit and will cause irregularities.

*there is no RF ground plane . You need a good one and the MOSFETs’ survival depends in part on this.

At moment it looks like an audio circuit, with loads of stray inductance / long leads which will likely blow things sky-high immediately you power up.

Where is the driver for the MOSFETs and what configuration are they in?

I’m away for a few days so won’t notice any post but thought I’d share some thoughts to save a headache or two .
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Old 29th Aug 2018, 6:42 am   #72
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Default Re: Bach with sparks!

Interesting stuff I'd quite like to have a bash at something like this one day, it has the Heath Robinson -mad proffessor type vibe that appeal's and a lot of it is hand built.

It helps having Al to guide as he's come across the snags in his builds, good stuff.

Andy.
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Old 29th Aug 2018, 10:56 am   #73
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Default Re: Bach with sparks!

Thanks for your comments, Al.
Yes, it was silly of me to put bleeder R's across those caps.
Many year ago I touched a non bled 16mf at 400 v and that has influenced me ever since

My ground plane is 2 earth rods driven into the ground just outside the window 8 ft apart.
The run to these is near straight (no nasty inductive sharp bends!)

Regarding layout.
There are many great layouts to be seen on the net of course, but
look at this one built by a very experienced Czech coiler.

It's a full bridge running up to 1,400 watts and works OK.
Quite a birds nest of long thinnish wiring to his 4 IGBT's, spaced apart in each corner.

None of my inter mosfet wiring is longer than 2 inches. as you can see.
(The long leads in my pics are, of course, the 12v supplies for the 2 cooling fans. )

Regarding driving the mosfets. I'm using a dual mosfet driver, UCC27425, driving via the GDT.
The GDT is only 2 inches from the mosfets so leads are, again, short.

BTW, my driver board is shielded from the sec coil.


I did blow a mosfet but that was due to an incorrect connection.
There is a fault on the driving board as no signal comes thro' to the GDT from feedback.

I have just finished making another board for the second SSTC and this is working OK.
So will do a swop for the dud one, then the sparks may fly.
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Old 30th Aug 2018, 3:36 pm   #74
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Default Re: Bach with sparks!

Al, Re DC bus. I have a 4 inch straight run from DC supply to the mosfets in 4mm cable.
Maybe too small?
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Old 7th Sep 2018, 11:14 am   #75
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Default Re: Bach with sparks!

10 minutes ago it sprung into life!
I have been struggling this week trying to get the feedback to work but the SSTC was dead.
The waveform from the GDT was good and the circuit board had been checked and rechecked.

If something doesn't work I try to sidestep and go around the other way

So I injected a sq wave at approx. 250 KHz into the feedback connection and wound up the variac

Nothing.


Then I slowly adjusted the sq wave freq and suddenly hit the sweet spot of the secondary's resonance freq.
A big flash over from the primary to the sec. Put some temporary paper between them and tried again...……

6 inch sparks now from the break out point and only slight warming of the mosfet's heatsinks after 5 mins.

If I cannot get feedback to work I shall drive the SSTC's with a 555 set at the sweet spot freq and switch it on/off with MIDI signals.

HT is a bit low so if I get that sorted the spark length should increase.

Will now start making second SSTC but first thing now
is a relaxing cup of coffee.
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Old 13th Sep 2018, 1:26 pm   #76
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Default Re: Bach with sparks!

Whilst building SSTC No2 I have been experimenting with No1 !
.
In my excitement of having it running I let it run in continuous wave for some minutes.
So stupid of me.

The secondary became extremely hot, not being able to touch it !
Fortunately I noticed this before any harm was done to the windings.

Now running with an interruptor for experiments, set to a short duty cycle.
Secondary only gets warm now.

I have not blown any mosfets, both running cool and no more flash overs so my layout cannot be too bad.
I am very pleased with the results so far after all my efforts.

I haven't yet MIDI modulated it yet. Waiting to get No2 up and running so I can hear all the poly notes in one glorious fanfare.

More anon.
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Old 16th Sep 2018, 12:06 pm   #77
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Default Re: Bach with sparks!

More change of plans.

Two SSTC's now being built plus the big VTTC valved tesla (for bass notes) is going to take up too much room !

So the VTTC will be replaced with this very small tesla full bridge unit I bought from China.
All it needs is a power supply, sec and primary coils. The feedback coil is on the left. 4 mosfets at the top.

I now have the pitch changer to lower notes an octave or part of for bass.

Also an echo unit I shall experiment with to hear how sparks sound when put through though it! I wonder if anyone has ever tried that?

So the 3 teslas will now be quite a compact system, playing the 9 poly notes,
my built SSTC's each side with the smaller Chinese one in the middle.

Will it all work? Place yer bets.
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Old 16th Sep 2018, 1:08 pm   #78
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Default Re: Bach with sparks!

Quote:
So the VTTC will be replaced with this very small tesla full bridge unit I bought from China.
Available from Madscientist.com.

Keep up the good work Albert, looks like you're getting closer.
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Old 18th Sep 2018, 11:49 am   #79
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Default Re: Bach with sparks!

Quote:
Originally Posted by Viewmaster View Post

So I injected a sq wave at approx. 250 KHz into the feedback connection and wound up the variac

Nothing.


Then I slowly adjusted the sq wave freq and suddenly hit the sweet spot of the secondary's resonance freq.

Hey Albert, youíre really pulling all the stops out here!


Itís not advisable to bypass the feedback mechanism by injecting a signal here. The purpose of the current transformer that you removed to inject a signal instead is to control the phasing of the breakout as well as to limit instantaenously any overcurrent. Simpler designs place the current transformer in the secondary coil base, more complex ones in the primary coil where it directly delimits the max current in the full bridge/ half bridge with logic circuitry. You can see some SMD logic circuitry on the Chinese board you e posted .

The logic switches in nanoseconds and then only switches on again via flip-flop at an appropriate moment, , whereas if you reach for a switch because you notice something is warm or burning, thatís a timescale millions of times longer.

Anyways, just sayiní

You seem to be enjoying yourself and trying every resource to reach your goal!
Great enthusiasm!

Good luck !
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Old 21st Sep 2018, 12:59 pm   #80
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Default Re: Bach with sparks!

OK on all that Al.
I shall heed what you say and try to get feedback to work soon, when I have SSTC No2 running...Ö..it's nearly finished. Interesting to see if the feedback on No2 runs OK or not.

The China one will have a spherical top load running between my others with their toroids. Look a bit like Brighton Pavilion !

How's your new project coming on, Al? Is it making interesting sparks?
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