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John Curl's Blowtorch preamplifier part III
John Curl's Blowtorch preamplifier part III
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Old 22nd November 2019, 09:43 PM   #30851
Galu is offline Galu  Scotland
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Originally Posted by RNMarsh View Post
The silence. Very few people have the pleasure of working on a large scale physics machine. If lucky once.
Happy retirement!

I've changed the belt on a Van de Graff generator - does that count?
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Old 22nd November 2019, 10:23 PM   #30852
scott wurcer is offline scott wurcer  United States
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Originally Posted by RNMarsh View Post
She said, i know who you are, your reputation precedes you. Wow. I didnt know. I guess she had been alerted or warned :-)
Sounds like how they describe Richard Stallman at MIT.
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Old 22nd November 2019, 11:51 PM   #30853
jneutron is offline jneutron  United States
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Originally Posted by Galu View Post
Happy retirement!

I've changed the belt on a Van de Graff generator - does that count?
Ah, but it is not the belt that is typically the problem.

VDG's work on triboelectric. The separation of two materials with different electronegativities.

A typical VDH will have felt rollers on the bottom, and plastic rollers on the top. A comb picks up the excess charge on the belt as it leaves the plastic rollers.

The problem is, the plastic rollers will become coated with rubber from the belt, so the machine stops working. I used a file to remove the outer coating on the plastic rollers to fix the one we were using here for a science show.

Trust me that fixes the problem really, really....really well. (did I mention "really"?)

Oh, BTW, I heard "through the grapevine" that after you've cleaned the rollers and put the machine back together to test it...always, always, put the grounding rod and sphere back into place. Otherwise, when you turn it on, the sparks will run 1.5 to 2 feet from the dome, and should you "ahem"....place it so that you can't even reach the plug to pull that out, can't get to the doorway...but can only cringe in the far corner of your very small office hoping those lightning bolts don't hit because you were idiotic enough to place the godforsaken thing directly in your avenue of egress...sigh.....

But that's what I've heard... not the I would make that silly mistake..no, not at all...
jn
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Old 23rd November 2019, 12:06 AM   #30854
billshurv is offline billshurv  United Kingdom
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John Curl's Blowtorch preamplifier part III
My physics teacher at school decided that std issue VDG were not powerful enough so made a bigger dome about the size of a crash helmet. That gave good spark.



I thought that was impressive till my daughter went to Daresbury for a year and told me about the biggy they used to have there.


Particle physics. Hitting small things with ever bigger rocks just in case something happends
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Old 23rd November 2019, 12:19 AM   #30855
mpeg2 is offline mpeg2  United States
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This turn of the thread really brings back some memories - eons ago (when I was a grad student) - I was licensed to operate a Van Der Graaf accelerator at Lowell Tech (MA) - it was 3 stories tall and ran at a potential of 2MeV (maybe higher). The inside was filled with Sulfur Hexafloride (to avoid internal arcing) - the control electronics were 2MV above ground & controlled by strings & pulleys from selsyn motors at the bottom (which were connected to knobs on the control panel).

All this was to simulate radiation damage in metals (I was studying nuclear materials) - after blasting the samples, I could put them into my pocket (if neutrons were used - not a great idea).

Not sure I could design one (as JN and RM have done) - but operating it was lots of fun.

Rich

Last edited by mpeg2; 23rd November 2019 at 12:26 AM.
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Old 23rd November 2019, 12:23 AM   #30856
simon7000 is offline simon7000  United States
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At the shop for Halloween we used to leave a dummy head sticking out of the press brake.

Now you guys have clued me in to something better, thinking Jacob's ladder for next year.

Did try to build a ghost generator but that is still not up and running.

I think I did mention for home use I filled some latex gloves and left pairs stick out from my front yard...
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Old 23rd November 2019, 01:30 AM   #30857
RNMarsh is offline RNMarsh  United States
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Originally Posted by simon7000 View Post
Now you guys have clued me in to something better, thinking Jacob's ladder for next year.

...
A used neon sign transformer works perfect for a J.Ladder.


-RNM
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Old 23rd November 2019, 10:02 AM   #30858
mchambin is offline mchambin  France
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A neon-sign transformer (NST) is a transformer made for the purpose of powering a neon sign. They convert line voltage from the 120-347 V up to high voltages, in the range of 2 to 15 kV. These transformers supply between 18-30 mA; 60 mA on special order

15kV 30mA is deadly.
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Old 23rd November 2019, 10:09 AM   #30859
RNMarsh is offline RNMarsh  United States
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And, a clear plastic tube surrounding the "ladder" does fine also.


-RNM
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Old 23rd November 2019, 11:07 AM   #30860
billshurv is offline billshurv  United Kingdom
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John Curl's Blowtorch preamplifier part III
An old points type ignition coil should do the trick too and gives you ability to run off a battery.
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