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Phillip Slawinski

Fri Sept 30 2011, 01:55PM

Registered Member #1732 Joined: Thu Oct 02 2008, 02:34PM
Location: Huntsville, AL
Posts: 112

Grenadier wrote ...

The SLR supply: I take it that each pulse you get out of the system == 1 SLR cycle to the transformer? That doesn't sound right, because you'd need huge peak currents to get anything out of it.

The peak currents are pretty massive. I've measured 400A on the primary side before.

If you aren't familiar with SLR I'd suggest reading up on it. The only major difference between this and an unmodulated supply is that I vary off time between alternating pulses on the bridge to achieve modulation.

Grenadier wrote ...

Bandwidth isn't much of an issue. A 5ms pulse == a max pulse freq of 200Hz, which is fine for bass guitar. Power might be a problem; though that's what bigger parts are for once you get something working.

You're not always switching at the maximum switching frequency, especially during the start of a ramp. Depending on your design you can actually end up with the SLR modulating the pulse rate down to the audible range. If you have inadequate filtering this will be audible.

If you want to just make ramps to simulate the sound, maybe through MIDI or something you should be okay. If you want to plug a guitar into it and play it while the coil is running essentially CW, you will probably have issues.

You might consider using a transformer isolated buck. That's what I started with. All you have to do is take a buck mode supply and slap a transformer on the output. This will provide better modulation if you want to do analog audio modulation.

Adam Munich

Mon Oct 03 2011, 01:12AM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

Alright, so if I am understanding correctly, you are varying the power and thus output voltage by increasing the spacing between cycles?

That doesn't seem right; seems like it'd toss the entire thing out of resonance!

From what I'm reading

it seems like changing loads on the transformer don't significantly affect the resonant frequency, and thus I could just use a uC to set the timing and be done with it. But I still feel that I'm getting something wrong here, since spacing in between those cycles... doesn't seem right.

EDIT: fixed stupid mistake

ScotchTapeLord

Mon Oct 03 2011, 01:19AM

Registered Member #1875 Joined: Sun Dec 21 2008, 06:36PM
Location:
Posts: 635

I believe that spacing is what prevents resonant rise, it gives time for the resonant tank to dump its stored energy back into the supply. I'm not entirely sure if that is right, but if you ran it at resonance it would ring up like a DRSSTC tank, whereas you want control over the output for this application (whereas, with a DRSSTC, out of control currents running away is desirable).

Adam Munich

Wed Nov 16 2011, 05:17AM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

Well guys, I finally have a pair of 4-1000As.

Oh5Ks

But now I think going the silicon route would be better

These things get smoking hot just running the heater, and a fan really would kill some of the awesomeness factor. I think I might keep these, or one tube to build a 1000W transmitter some time in the future to troll the fcc ...play with.

So, I'm going to build Steve Ward's DRSSTC driver

Start there, because I'm still at a loss on how to make a ramp supply for the coil, and I managed to find four 72A G27N120BN

IGBTs. Used to have more but I've got no clue where they went off to.

Marko

Wed Nov 16 2011, 05:27AM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Hi grenadier

Well, there's a russian guy on this site who has built some epic pulsed tube coils... just copying some of his designs might be a very fun start! (not sure what is the pulse rating of those tubes you have though...) I'd love to see something novel such as a coil base fed by a half bridge of tubes or something like that.

Apart from that, you should perhaps look at the thread named 'CWDRSSTC' for the newest development on the QCW coils, and within short time me or Steve Conner will attempt to reach it using delta sigma modulation technique which might even be appliable for VTTC's without the massive external SLR supply!

You will need some big energy discharge caps no matter what though :)

Marko

Adam Munich

Wed Nov 16 2011, 05:38AM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

I don't know the pulse rating, but they make special 4-1000As that are designed for pulses. Problem is those cost about $600 each...

I happen to have 40 doorknob caps coming in the mail via an impulse buy. $2.99 each for some very high DV/DT 30kV 780pf doorknobs, but even all of them in // would only give me 31nf so they are unsuitable for a silicon DRSSTC. They might work for a tube coil, but they are very nice EMP caps. 1.2 megavolts in a coaxial marx... (no clue how to build one though)

Usually these things go for about $20-$30 each

I don't know... If I go the tube route then I'll need to design a special cooling system and figure out a way to supply the 6000V for the plates, but I don't have a suitable tank cap for a silicon DRSSTC. Quite a pickle isn't it?

Marko

Wed Nov 16 2011, 05:53AM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Hi - well do you have any MOT's around? Two MOT's + FWR could do a power supply provided you have a big enough energy storage cap... (have any?)

Marko

Adam Munich

Wed Nov 16 2011, 11:35AM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

I don't have to idenical, or even two similar ones. I have two 9kV 60mA NSTs and maybe 4 30mA ones... maybe if I centertap rectify them and put them in a bus I could get something worthwhile, but now weight is starting to be a concern. :-/

Marko

Wed Nov 16 2011, 01:08PM

Registered Member #89 Joined: Thu Feb 09 2006, 02:40PM
Location: Zadar, Croatia
Posts: 3145

Hi,

Well, if you have a big pulse cap for your power supply, you can still charge it relatively slowly using your NST ... a MOT stack will get heavy as well, and not to talk about other components of the tube coil!

Marko

Adam Munich

Wed Nov 16 2011, 01:32PM

Registered Member #2893 Joined: Tue Jun 01 2010, 09:25PM
Location: Cali-forn. i. a.
Posts: 2242

I don't have any pulse caps though. Just a whole bunch of lytics that are capable of exploding things.

Hrm. I think I might just go the silicon route, though I'm going to have a tough time finding caps suitable for the tank.

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