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Re: the geek group

Original poster: "Mark Broker by way of Terry Fritz <twftesla-at-qwest-dot-net>" <broker-at-uwplatt.edu>

This is starting to get off topic....  so, I'll post the solution!

The Geek Group runs its own email list off of Yahoo Groups (it's reliable and
free).  *ANY* topic relating to The Geek Goup, be it projects (no matter how
bizaar, fantastic, or routine), funding (donations of time, expertise,
equipment, MONEY, etc), or Geek Life in general are fine.  Since the list is
really slow lately, I'll even let you discuss your theories on Cold Fusion and
Faster Than Light Travel (though Chris and I are both, to a degree, physicists,
and love to argue (debate?).....).

To join, send a blank email message to

Then, start sending messages to

If you have a Yahoo ID, you can link your Email address to your Yahoo account
as an option on the yahoogroups page.

Everyone here is a geek, and therefore encouraged to join.  If you can't admit
that you're a geek, you should find a less "geeky" hobby (HV is as "geek" as

> Mark came out for the weekend and we had a blast. We had Mark, Alia, Tink, 
> Tim, Ben, Mini-Me (Little Chris), and Myself all stuffed into Little St for 
> 4 days. I'm happy to have my little 600SqFt apartment not littered with 
> bodies sleeping everywhere again. 

Don't forget about Adrian and his lady-friend for a night.... 

> Over the weekend Mark Broker (Geek#10) worked his butt off on the Thumper 
> project. 

Mini-Chris helped immensly, too.  Betsy even had a small part (bought washers,
and helped un-twist wires)

>  We now have a small (if you can call 1.7kJ small) 

Actually.....  5.3kJ  (30x2200uF caps -at-400V)  1.7kJ was for the string of 10.

>  module prototyped 
> and functional. It sounds like a quarter stick of dynamite going off and you 
> can feel the shockwave in your chest 30' away across the room. We tried Can 
> Crushing (with moderate success) but found Can Exploding MUCH more fun :). 
> We learned quite a few things about cap-discharge setups. 

Need higher voltage to get coins and cans to crush successfully.  It BARELY
worked (slight hourglass-shape to the can) with a 12-turn coil of #12AWG wire. 
The PVC insulation on the work coil partially fused together after one bang.

> 1. We need some 30A diodes. 

We were using a 40A diode bridge that we scavenged from a 30A DC PS.  Two fried
(on the last firing, of course) when we discharged the bank.  I have no clue
the voltage rating, but I guess 600V.  We were charging to 400V, the max our PS
would handle (and the max we felt the caps should be pushed) - too bad, the
extra 50V would have increased the bang size to 6.7kJ!

> We also worked on Sam a bit. With a large (think the furnace in your house) 
> Squirrell Cage blower on Crap-Gap-III the coils performance improved 
> markedly. We are getting consistant power-arcs to a grounded rod 51" away. 

Was it really that far?  Looked much closer than that.....

> It still sucks, but it's getting better. 

Yes, a "standard"  "TCBOR" or Scot-gap would help a lot.  A RSG would help even
more.  Chris' kludged gaps (hence the name "Crap Gap") don't work well at all.

> There was much rejoiceing Saturday evening and now we have 2 cases of Mikes 
> Hard Lemonade bottles to make some more SW caps. 

For which Mark was never reimbursed (remembered around St. Joseph on the way

> 4 large switches/breakers, each 3 pole, rated 600VAC 400A 

Weight:  approx 40lbs each.

> Several X-Ray transformers, varying sizes. 

1 x 50kV (100kV anode to cathode), around 400 pounds
2 x 75kV (150kV anode to cathode), 800 pounds each
   both have tube rectifiers, and are PCB free.  We can drain the oil to reduce
weight, but you'll need to fill it with HIGH QUALITY transformer or mineral

> Some BEEFY power supplies and such. 

a 30VDC -at- 30A, 100V input (the hard part),
a couple voltage regulators/isolators.  Ratings unknown, other than 220-240V in
to 230V out.

> X-Ray tubes, complete, some with housings/cooland tubes,etc 

There are a couple tubes for an XDR-5 and XDR-7.  They are worth on the order
of $1000 in working order, as the system has been discontinued.  burned out
tubes can be repaired....

> and various other goodies. If you're looking for something let me know. 

some short lengths of 500MCM cable (max length ~ 10ft)  Stiff as solid 1"
diameter steel bar, but perfect for "Project Thumper", and similar.
tons of buss fuses in various sizes and amperages.

> I'm looking for help on a triggered spark gap that can handle some MASSIVE 
> current for the Thumper project. Basically I need a resetable crowbar for a 
> 50kJ cap bank. The downside is I need it to work at as little as 400V. This 
> is impossible in a spark gap as far as I know, ideas? 

Triggered spark gap with a gap width setting feature sounds the best to me.... 
those 1" D tungsten carbide disks that Marc sent way back when are flat to well
within .001" (probably .0001"), and could be brazed to a 1"D piece of

Mark Broker
G-5 Geek #10