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Old 18th Jun 2018, 5:33 pm   #21
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Default Re: Bach with sparks!

P.S

In my experience , MOT’s are designed to run hot under even the design load -all older generation ovens had a cooling fan. They even run hot with the secondary open circuit - it just takes longer.

Once you start adding extra capacitance to the doubler circuit (typical was 0.85uF) to say 5uF - and once you start taking bigger gulps out of the power supply - they start to work way harder than they can manage and fail relatively quickly.

That’s based on loads of scrapped microwave oven ‘ street-treats’over the years ...

Drifting OT but they are now inverter-based, so no big iron any more.
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Old 18th Jun 2018, 9:40 pm   #22
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Default Re: Bach with sparks!

OK Al, here come the pics I have just taken.
BTW, I am taking 8 amps from the mains when at full tilt. (2 MOT's in parallel)

The little drops on the wire are multiple coats of varnish which has cured the break out.

Sparks are 6 inches at about 2kv. DC. I've added some doorknobs cannibalised from my SGTC to increase tank cap from 600 pf to 1100pf to increase spark length so it's tuning that I must now concentrate on.

As previously mentioned will use variable cap to get right...…...I will take care not to turn the cap vanes whilst ON. !

Will keep you informed when Bach's Toccata starts sparking.
Just can't wait .

Thanks for all your useful info and help.
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Old 19th Jun 2018, 6:59 am   #23
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Default Re: Bach with sparks!

(Next door neighbour)

"I see young Albert has fitted new lights in his kitchen".

Seriously though, congratulations on your achievements. I've followed this thread and Al's in awe of the work and experimentation that takes place in this world. Amazing!
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Old 19th Jun 2018, 7:48 am   #24
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Default Re: Bach with sparks!

I wonder if he is reading his will?
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Old 19th Jun 2018, 8:43 am   #25
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Default Re: Bach with sparks!

BTW, Kentode, it's not young Albert but very old Albert...

.I'm 85.

But still a bright spark.
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Old 19th Jun 2018, 12:25 pm   #26
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Default Re: Bach with sparks!

Hi Albert,

A nice, warm glow from those big old valves there. And I like the brush discharge from the break-out point. I can almost hear the sound of it!

Quote:
Originally Posted by Viewmaster View Post
BTW, OI am taking 8 amps from the mains when at full tilt. (2 MOT's in parallel)
That's quite a lot of juice! I'll come back to that in a moment..

Quote:
Originally Posted by Viewmaster View Post
The little drops on the wire are multiple coats of varnish which has cured the break out.
Great! I'm glad that fixed it!

Quote:
Originally Posted by Viewmaster View Post
Sparks are 6 inches at about 2kv. DC. I've added some doorknobs cannibalised from my SGTC to increase tank cap from 600 pf to 1100pf to increase spark length so it's tuning that I must now concentrate on.
That's a pleasing look, but there's something not quite right, that you could address if you feel like it. A lot of that 2kW power in is going into heating the anodes, and not into that break-out.

I know that you're not making it for the length of the plasma, but if you think about it, if you're building it for the most impactful audio, you need something that's going to whack the around the plasma, so the more imposing the plasma is, the louder the sound will be.

What is the arrangement for your grid leak circuit? What R and what C are you using and what are the physical components? As you know, there's a time constant, formed by the RC combination.

So you need to know the resonant frequency of your secondary coil and it appears from the experience of many that it's best if the time constant for this circuit is about four or five times the period of one RF cycle.

Also, what is the RF bypass capacitor made from? there needs to be a really low impedance pathway for RF.

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Will keep you informed when Bach's Toccata starts sparking.
That will be fantastic! Yes, please keep us informed!
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Old 19th Jun 2018, 1:20 pm   #27
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Default Re: Bach with sparks!

Hi Al. Thanks for comments.
My grid caps are HV of course. About 5nf. The R's are two 100 bulbs painted dark blue.
Most chaps leave their bulbs unpainted but the resultant high glare detracts
from the red glow from those beautiful valves.

RF bypass is 7nf 6kv disc ceramic as I recall.

BTW, my DC smoothing is 6 off 220 uf 600v electrolytics in series, each with bleeder and 2 other bleeders across the lot. No balancing for leakage as they run well underrated at about 2kv. I know nothing about smoothing HV
but this seems to work...…….beginners luck!


Although sparks only 6 inches they do make a racket ,
when sq wave modulated, but I take your point that they could do more...

…….where's the volume control?

With no modulation the spark is very quiet due to my DC supply and that leads me to believe that musical audio might not have that awful tinny sound
that AC plasma has.

I am going to put 12v AC from a tranny onto the control mosfet to hear if the resulting sound is like a smooth sine wave or not.

If it's good and with bass I might yet get Bach's spark to sound more like an organ after all. We shall see......and hear and hope.
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Old 20th Jun 2018, 11:54 am   #28
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Default Re: Bach with sparks!

Hey Albert,

That’s great info. What’s the self-resonant frequency of the secondary coil?

You can easily find it by putting a scope probe in the air a *very* safe distance away...
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Old 20th Jun 2018, 1:39 pm   #29
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Default Re: Bach with sparks!

Confession time.
I only have a junior scope that will not be any good.
However, I have a cheap freq meter which reads 1.5 to 2 MHz, but it varies depending on EHT value ! Not reliable.

I have the variable transmitting cap now and intend to try this on the tank together with more turns (22 at present) and/or more on
feedback ( 7 at present).
I know I should do the calcs but I am but a practical man.

But I am really quite satisfied with my 6 inch spark. Quality not quantity!

A bigger one will only poison me more with ozone !

It's the musical side that I must concentrate on.
Bach is getting impatient !!

Are you making good progress with coil No6, Al? Perhaps start a new thread about it.
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Old 20th Jun 2018, 3:36 pm   #30
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Default Re: Bach with sparks!

Hey Albert,

Great to hear that youre clear about your priorities and feel on-track!

I hope the next stages with new modulation circuitry go to plan - youve definitely got my interest going.

I havent been working on project no. 6 with any intensity, rather more pinning -down and analysing an important current feedback pathway and circuit, with large gaps of inactivity in-between. Impossible without a dual channel scope and lots of patience.

Im also very practical but its totally impossible to build my current version without knowing exactly what waveforms are appearing where, in what magnitude, and seeing exactly what shape they have. Otherwise, expensive components just get smoked, in a little as 10uS!

Its taking a while to find the right materials for magnetics by trialling them individually, and to build bespoke test equipment!

But yes, ill definitely be updating my thread in a while!

Happy Bach-with-sparking!
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Old 20th Jun 2018, 4:32 pm   #31
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Default Re: Bach with sparks!

Damn !

Just this hour had the variable cap running on the tank. After some initial internal sparking to get rid of the eBay dust (!) and some adjustment, the sparks sound louder than ever before. But in daylight I cannot see how high they are.

BUT that damn breakout has started up again which does indicate higher volts.
So best tank cap seems to be about 1000pf.

Back to more varnish methinks else I shall have to remove the top turn of the coil and remake the connection.

Look forward to more news on No6. It sounds intriguing.

Will keep you posted when progress on spark musicality soon .
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Old 20th Jun 2018, 5:29 pm   #32
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Default Re: Bach with sparks!

Quote:
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Just this hour had the variable cap running on the tank. After some initial internal sparking to get rid of the eBay dust (!) and some adjustment, the sparks sound louder than ever before.
That sounds like good news!

Quote:
BUT that damn breakout has started up again which does indicate higher volts.
Hey, can you give me the dimensions of your coil, height and diameter in cm. or inches as you wish? I've got a pretty accurate formula for parallel resonance and it might be useful to calculate self-resonant frequency as you don't have a scope!

Arcing can be a pain and destructive. Where's it coming from this time?
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Old 20th Jun 2018, 10:03 pm   #33
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Default Re: Bach with sparks!

I am really enjoying reading this - 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
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Old 21st Jun 2018, 7:15 am   #34
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Default Re: Bach with sparks!

Sean, If you do go ahead I hope that you take great care and are well aware of the great dangers of EHT. It's not like HT.
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Old 21st Jun 2018, 7:24 am   #35
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Quote:
Originally Posted by astral highway View Post
Hey, can you give me the dimensions of your coil, height and diameter in cm. or inches as you wish? I've got a pretty accurate formula for parallel resonance and it might be useful to calculate self-resonant frequency as you don't have a scope!

Arcing can be a pain and destructive. Where's it coming from this time?
Arcing same place as before but have taken one turn off the top of coil and reconnected...seems OK now.

Coil dims... height is 15 inches. dia is 4.5 inches. wire dia is .02 inches
About 750 turns.....
....................749 now because of above.
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Old 21st Jun 2018, 8:13 am   #36
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Default Re: Bach with sparks!

..... That's 381mm. high, 114.3mm. across, 0.5mm. wire.
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Old 21st Jun 2018, 10:19 am   #37
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Sean, If you do go ahead I hope that you take great care and are well aware of the great dangers of EHT. It's not like HT.
No need to worry Albert, I am quite happy up to 11kV (Power Generation is my job)
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Old 21st Jun 2018, 11:38 am   #38
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Default Re: Bach with sparks!

Ooops, sorry Sean. You know more about it than I ever will.

Hope you get those 813's singing away soon. Maybe show us on a new thread.
Winding the sec coil is quite an interesting job.
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Old 21st Jun 2018, 11:43 am   #39
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..... That's 381mm. high, 114.3mm. across, 0.5mm. wire.
No it's an English coil so in inches, furlongs, poles and perches.
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Old 21st Jun 2018, 4:44 pm   #40
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Default Re: Bach with sparks!

Quote:
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Arcing same place as before but have taken one turn off the top of coil and reconnected...seems OK now.
That's good news! Drum roll, please!!!

Quote:
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Coil dims...… height is 15 inches. dia is 4.5 inches. wire dia is .02 inches
About 750 turns...……..
...................….749 now because of above.
Hey Albert,

From this, we can work out the following (approx.)
------------

Inductance, secondary coil: 16.7mH (roughly)

Self-resonant frequency of secondary coil assuming approx 10pF parasitic capacitance= 390KHz

This is likely to be rather higher in reality, as not only the break-out point but also the plasma itself has capacitance!

Inductance, primary= 170uH

(for peak resonance with parallel 1nF capacitor, as you indicate in post 31)

RF period=2.6uS

Ideal period of grid leak is 4-5 times this =say approx 10uS

With your 150W light bulb and 7nF, the period at the moment is 2.7uS

The grid leak is complicated, and of course we don't know except experimentally about the bias conditions of these triode-strapped pentodes, but it may be worth trying down to even 40W bulbs, just to see what happens

A 40W mains bulb a resistance of 1440R, compared to 384 for a 150W and the period goes to 10uS.

Grid leak period, 7nF capacitor

150W bulb =2.7uS
100W bulb= 4.4 uS
60W bulb=6.7uS
40W bulb=10uS


I'm not fortune telling and it may not have a beneficial effect, but then again, it may increase efficiency, which is always a good thing!

The best results that I've seen are when builders have an easy way to get the sweet spot for grid leak R.


Looking forward to more progress!
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