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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!

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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 Yesterday, 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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Last edited by Viewmaster; Yesterday at 1:38 pm.
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