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New to the hobby




From: 	Kevin Radtke[SMTP:umradtke-at-cc.UManitoba.CA]
Sent: 	Thursday, September 04, 1997 6:14 AM
To: 	Tesla List
Subject: 	New to the hobby

Hi All,
	I just subribed to this mailing list a few days ago and am happy to 
find my mailbox swamped with very interesting (although at times 
difficult to follow :) mail all the time.  I'm a third year Mechanical 
Eng. student, so while I have a pretty good understanding of the tech 
jargon you guys use, I must admit its quite often above me.  But I love 
to tinker and learn and thats exactly what I hope to do.  I started a 
Tesla coil project for my high school physics prof about four years ago 
but haven't had any success with it until recently.  I've got lots of 
questions so please bear with me.  I got the plans from a book on 
electronic projects in our local library.  The primary circuit consisted 
of a rectified 12V xsfmr running a 555 chip through a power transistor 
and an auto ignition coil.  That part of the circuit always worked fine.  
The design suggested using 15pf "doorknob" caps available from an old TV.
The problem is the whole thing won't work at all when I connect these 
caps to the circuit.  I have no fancy equip. at home ie. oscilliscope 
etc. so I have no way to measure Q's and Freq. etc.  My secondary is 3" dia
ABS pipe with 28 awg mag. wire approx 18" in length. I'm leaving out Most of the details 
of this design because I've sort of abondoned it.  I just wanted to know 
if anyone has ever heard of a design which used a primary circuit such as 
this to drive the coil.  I guess it sort of resembles a Flyback circuit.
A friend of mine who is into making neon signs and I got together and 
have built a new coil using a 15kV 30mA neon sign xsfmr.  This is the 
first time either of us has gotten a coil to REALLY work.  I want to 
better understand how to improve the output of our coil.  Right now we 
are getting 12-14" discharges off of a 5/16" bolt terminal.  (we don't 
have a sphere or torroid terminal yet)  
	I apologize for the long-windedness of this e-mail.  I'll get to 
the point.  I'll describe our setup as best I can without measuring equip 
and I'd appreciate any comments as to how to improve it.  Everything we 
accomplished so far has been by trial and error. :)


xsfmr = 15kV 30mA neon sign

2 rf chokes (one on each lead from the xsfmr) = 28 awg mag wire around 
1/2 wood core approx 100-110 turns)  we just guessed but put this in 
after we blew two 5kV sign xsfmrs :(  There is also a safety gap in 
parallel with these (just big enough so that 15kV won't arc across)

cap = Al foil with ldpe  dimensions: Al 4"x51" with 8x6mil pe sheets 
between layers.  submersed in oil and pumped down.  We have built at 
least 5 or six caps of varrying Q's  going smaller than this doesn't work 
well and doubling, trippling quadrupling the size decrease performance 
drastically.  We lucked out here.

spark gap = rotary type 12v motor 3" plastic disc with 12 points.  
Changing from a single gap to the rotary gap DRASTICALLY improved 
performance.  We built a varible power supply to see if the disc speed 
would have an influence on the coil performance.  It did, but it works 
best at the max speed.  The faster you go the better?

primary = #8 Al ground wire 15 turns.  Tuned at 14.  Now here is a question.
our first primary was a cylinder dia. about 12-14" (can't remember) we 
had problems with the secondary arcing to the primary.  I saw a picture 
of a coil on the net with a bowl shaped primary and this made sense to me 
so our primary is now bowl shaped.  We no longer have arcing problems but 
this leads me to wonder what sort of mag. field a bowl shape produces and 
how does it affect the performance of our coil.  Which shape is best.  
can you use an isulator like a 6" PE pipe over top of the secondary?

secondary = 28 awg mag wire 18" in length and 3.5" diameter around 3" ABS 
pipe.  Is ABS OK to use or should you use PE or PVC?  I have read that 
short "fat" secondary's are better than tall thin ones?


We tried wrapping a basketball in Al foil and using that as a terminal 
but the spark lenght was reduced to about 1.5 to 2 inches. :(  would that 
have something to do with the fact that we suspended the B-ball on the 
bolt terminal using some thin string attatched to the rafters of the garage.?
Can the HF HV discharge along the string to the rafters?

Up till now we had been using the same ground that my friend has his 
bombarding xsfmr (for neon) hooked up to.  This I believe is also his 
house hold ground.  I understand this is a bad thing.  What lenth of pipe 
would we need to drive into the ground do get a good ground?  What type 
of pipe.  Also none of the elements of our circuit are grounded (not even 
the neon xsfmr) is this wrong?  We are very aware of the dangers involved 
in coiling.  We are taking the precautions that we know of ie. hearing 
protection, UV protection.  The coil is operated at a distance using an 
extension cord to power the neon xsfmr.  Does puting a 100W light bulb on 
the output terminal of the secondary produce X-rays?  It looks cool.  

Anyways thanks for your patience in reading all this.  In the future I 
will only ask one or two questions at a time, but I felt that an initial 
introduction was necessary.  I would appreciate ANY input or suggestions, 
I do NOT know it all and am willing to learn.  Thanks again.


sincerely,

Kevin, & Ernst