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Author Topic: Development of an Avalanche Output Stage  (Read 61273 times)

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G the pulse maybe too fast dv/dt but if you are using a x1 probe i would have thought you maybe cooking your scope front end, the max my scope allows on x1 is 80V and on x10 800V much above this can do some damage (So it says in the manual), really need x100 probes for this sort of thing.

I know, but what can you do?  10x probe is more than a used scope and some are low freq.  (I have a good article on making your own.)   Even with 100X, my 300MHz scope is too slow. 

will check battery and cap effects next - give the scope a break...LOL!
   

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So far, 1500v sucks and 10kv is the only way to ride - LOL!

Negative test for rise on a battery - so far - this was with a string of 12 AA batteries to a coil wrapped outside the coil being pulsed.

Haven't tried a cap yet...

I'll keep messing with this some more and compare notes when Peter's unit is running.

I need to see what really going on:

Article: Basics of HV Probe Design

   

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I managed to pick up 2 x100 scope probes some time ago G so i should be ok, if they are fast enough to catch the pulse.

Over 1kv is not so easy, all my meters only goto 1kv, i cant even find one that goes over that, even if i could i guess the price would be high, although it is possible to buy HV meter leads with a converter built in, probably just similar to your design pdf.

So i will need to rely on my scope with the x100 probes to monitor the volts.

I am not sure how keen i am on going to high, this stuff is getting dangerous,need to think first then touch or not as is the case with a lot of this circuitry.

10KV i want to spin my coils field not make the earth spin faster  ::)

   

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With 10kv - you can feel something happening - there is no doubt about it

plus you are sure to meet the requirements and that is more voltage more effect

My trigger signal really sucks and is not always adequate - I'll pull 28v off the supply to 1.5kv supply and see if I can boost the trigger - base triggering kinda sucks as the trigger signal will effect the output shape and it takes more current - either that or go to collector triggering.

   

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increased the current to the trigger and it look really good now - 500ma setting at 15v on the supply - but still only a couple of volts after the isolation ransformer but ringing is greatly reduced and output look pretty clean from the stack

It does not appear that my delay line (10 feet of coax) is charging correctly so will take a look at this now
   

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If this pulser ends up blowing up as the fet stage did when i get the crackles, maybe the next solution is to develop a saturable inductor stage which if i remember correctly is what Spheric suggested in the first place.

Still working to getting the board done, and still have parts to order so i am being a bit slow right now, i have 2 smmt417 in the lab so i will give a 600v pulser a go while more arrive ,this should give me a feel for it.
Lots to do yet

I am going to need to buy 10 x 100pf caps for each stage, is there any preference of the type, are the blue 3kv ceramics ok for this or do they need to be more exotic?
   
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This may sound like a strange idea but is there anyway to choke the output from your fet just above the freq. required for crackles and then have another path for the energy that is killing your fet to travel like a calibrated spark gap ( surge arrestor ) that has a voltage slightly higher than what you are working with.
   
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If this pulser ends up blowing up as the fet stage did when i get the crackles, maybe the next solution is to develop a saturable inductor stage which if i remember correctly is what Spheric suggested in the first place.



If you need scans of it.. I have the only known complete unedited original copy of " Magnetic Amplifiers - A rising star in naval electronics "

   

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Cheers for the offfer Ds, not really ready  to put any time on this yet, but it maybe the next project after this one, i will give you a shout when i'm ready cheers.






   

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If this pulser ends up blowing up as the fet stage did when i get the crackles, maybe the next solution is to develop a saturable inductor stage which if i remember correctly is what Spheric suggested in the first place.

Still working to getting the board done, and still have parts to order so i am being a bit slow right now, i have 2 smmt417 in the lab so i will give a 600v pulser a go while more arrive ,this should give me a feel for it.
Lots to do yet

I am going to need to buy 10 x 100pf caps for each stage, is there any preference of the type, are the blue 3kv ceramics ok for this or do they need to be more exotic?

I use 2kv blue ones : 56pf across each transistor - they form a divider as well

I don't think I have enough current to drive a coil with this high of an inductance and still achieve avalanche at the stack.  Even with a 10 ohm load a single transistor at 200v is only providing a spike of about 50v.  You may need to match the load of the coil with a resistor after all.

Looking for another supply...hmm...do I dare use a MOT?
   

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I have hv transformers.  What is the best way to make them variable?
   
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If you need scans of it.. I have the only known complete unedited original copy of " Magnetic Amplifiers - A rising star in naval electronics "



Sorry, I just gotta bite on this one  ;D

No ya don't. The only marks mine has in it are my hand penciled notes from the class. The edited version went to the regulars but it wasn't identified as 'edited' or with an incremented edition number. What does it say about means for eliminating switching leakage for MAs in switch-mode?

( nope - wasn't in the Navy. Also took training from other branches at the demand of uncle Sam).
   
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I have hv transformers.  What is the best way to make them variable?

this is fairly cheap...

use a variac on the 120v side of the mot

you can use smaller caps for what you are doing

This just uses computer buss capacitors

The power resistor limits the current draw from the MOT on an empty cap bank - go big Watt if you can

and if you want to tune it down to 1200v you can put a stop on your variac as a high limit or a power resistor in series

This is basically what i did with 811 driver

http://www.overunityresearch.com/index.php?topic=211.msg2558#msg2558


OR...

If you find that you need a super quiet dc and the MOT is too noisy - try one of these - http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=370189794492

   
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Sorry, I just gotta bite on this one  ;D

No ya don't. The only marks mine has in it are my hand penciled notes from the class. The edited version went to the regulars but it wasn't identified as 'edited' or with an incremented edition number. What does it say about means for eliminating switching leakage for MAs in switch-mode?

( nope - wasn't in the Navy. Also took training from other branches at the demand of uncle Sam).

Ok i stand corrected 2  ;D
   
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I guess this means we are two of the biggest geeks  ???

Edit>>

Oh! On your 2500V PS schematic, above... you got away without balancing resistors across the caps? For me, that is like (doing you know what) into the wind. I had a whole bank go off like a string of firecrackers.
   

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It's not as complicated as it may seem...
If you need scans of it.. I have the only known complete unedited original copy of " Magnetic Amplifiers - A rising star in naval electronics "



What are the differences with the edited version? I don't seem to have either version...could you pass it along?

Thanks,
.99

ETA: Is this the same as "Magnetic Amplifiers - Another Lost Technology"? That one I do have. It appears to be a re-packaging of the original material from 1951. This one was re-issued in 2000. http://www.powells.com/biblio/7-9780970961853-1
   
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I think that one is missing about a hundred pages. The one I have in my attic is about an inch thick. The photos of the German documents, in German, of course, aren't in the unedited edited one.
The only text I found interesting was the method of controlling the V2 guidance. '51? I thought it was '47.

I don't think the magnetic bridge rectifier is in the latest, EMDevices found a document from the 1880's describing that and shared it.
Magnetic switching, not spoke of commonly but used in inductive reactive load banks (added to resistive load so test can be ran somewhere beside unity P.F.).
Nothing in the book will make OU.

I want the one from the Army that details the same functions using dielectric amplifiers. It had the same big red letters ink stamped on the cover - back in the '70's. Never got to read it. Didn't have the 'Need to Know'  :(
   
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I guess this means we are two of the biggest geeks  ???

Edit>>

Oh! On your 2500V PS schematic, above... you got away without balancing resistors across the caps? For me, that is like (doing you know what) into the wind. I had a whole bank go off like a string of firecrackers.

Good point - the diag. is not a complete build diag. its missing and rf filter , fuse on the 120v side, balance / bleed resistors , and a hf choke on the output side to kill anything coming back.

And it would be quite spectacular if it unloaded  :o
   

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OK

MOT's are readily available and this puts it in the hands of more people.

Dumping 1500v to a high impedance load of say 250uh takes a few ma.

I had hoped to avoid the variac and go with some sort of oscillator for the MOT primary using MOSFET's or transistors.

You all know where this is going, so lay it on me.
   
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Like a pwm driving a mot?
The mot can really suck up the amps.
I have never seen that done

you will need to limit the current - or even put another mot in line with the 120v side with its secondary shorted to act as a magnetic ballast to the main mot..

You could try a (pwm) dimmer for a low voltage lighting magnetic transformer - those are good for about 6-10 A - must specifically say for magnetic transformer!

Like this:

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=180493912689

here is the mfg page for the above unit:
http://www.leviton.com/OA_HTML/ibeCCtpItmDspRte.jsp?item=22329&section=13608

or

http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=230492024291

   
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Sounds like you ultimately need a 500w 1500v inverter circuit
   

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It's not as complicated as it may seem...
I think that one is missing about a hundred pages. The one I have in my attic is about an inch thick.

Apparently the bibliography was over 40% of the original document, and was removed in this issue. It can be purchased as well. These may be the missing pages to which you are referring.

.99
   

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Sounds like you ultimately need a 500w 1500v inverter circuit

500W ? Ouch!
   
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Apparently the bibliography was over 40% of the original document, and was removed in this issue. It can be purchased as well. These may be the missing pages to which you are referring.

.99

Probably. The first part read more like a history with some short stories inserted. Right now, my attic is probably about 130 deg. F. I'll wait till it cools down and dig for the book.
   
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@WW

That's the problem with attics. Either too hot or too cold and when it is just right, you don't feel like go'in up, so you say "ahhhh, maybe next year". lol


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