The mindkiller

 * Originally By: Se-crawshaw-at-wpg.uwe.ac.uk
 * Originally To: Richard Quick
 * Originally Re: The mindkiller
 * Original Area: UUCPE-Mail
 * Forwarded by : Blue Wave v2.12

From: SE-CRAWSHAW-at-wpg.uwe.ac.uk
To: Multiple recipients of list USA-TESLA <USA-TESLA-at-USA.NET>
Date:         Thu, 1 Feb 1996 14:21:48 +0000
Subject:      The mindkiller

Hi all, its been a very busy Tesla weekend for me, I have
completed the construction of my latest coil. I was about to fire
it up when The Fear struck. I thought I'd better check with you
guys that I'm on the right track prior to blowing up my carefully
constructed baby. So, coil specs are:

Input Filter

Ducati SFMF-6C 6 amp capacitive and inductive filter wired
backwards i.e. Line = Load


2-4 amps (I think)

Main HV transformer

25Kv spark tester
50mA (guestimate based on size)
Laminated exposed core

Primary capacitor(s)
These are across the HV output and consist of 2 caps in series to
attain working voltage.

Should I have the gap across HV bushings ? (Better for Power
supply ?)

c1 0.0015uF 12Kv  (large ceramic cap, big lugs)
c2 0.004 uF 20Kv Sangamo mica cap type g4R
( I know these are not ideal i.e. low loss but they're all I've

So that makes my cap about  0.0015 x 0.004  = 0.00109 uF
                            0.0015 + 0.004

is that a bit small? I could add the following caps in parallel,
do I need voltage balancing resistors if I do?

I also have the following caps available

4000pf -at-15 Kv unilator ceramic (big)

500pF -at-30kV   STC CHV 411p x 2 These are small 1" x 1.5"
(doorknob caps? suitable for bypass ?)

Plessey caps from radar set

200pF -at-10Kv x 4
680pF -at-10kv x 2
220pF -at-10Kv X 2
330pF -at- 10kv x 2
900pf -at-10kvx2

Spark gap
three series gaps using 1" brass rod and carbon rod (1 gap is
brass, the other two are carbon rod, should I replace carbon with
brass all round ?)
The gaps are mounted linearly on tufnol board and shielded with a
copper plate that has been bent into almost a cylinder. The ends
are open at the moment, although it should stop quite a lot of UV
/ EMI now. I plan to use this gap shield as the main terminating
point for the RF ground (more on that later)
The tufnol board is mounted on the underside of a 0.5" perspex
board. The primary and secondary coils sit on this board, I have
done this to reduce wire length and to keep the tank circuit

Primary coil

I have used copper tape for the coil. Again, I know this is not
ideal but its what I've got and I've used it before with fairly
good results. The coil is a dish / spiral type

ID = 6.75 "
OD = 19.25"
N= 22 turns

tape = 20 x 0.1 mm

30 degrees rise vertically

This coil was constructed using four 30 degree triangles of
drilled circuit board which were then slotted with a bandsaw to
accept the tape. These boards were then slotted into slots cut in
the bottom of a plastic bucket and silicone sealed in place. The
construction is not particularly robust but I think it will hold

Secondary coil

Total height 23.6"
Wound Height 18.8"
wire D 0.4 mm
No of turns 1150
4" diameter
Perspex (plexiglass) former with perspex endcaps glued on each
end (hermetically sealed)
Lacquered with corona reducing lacquer

stainless steel shotblasted 12" x 3" flat plate in middle

RF Ground
OK I dug a 4' deep hole and buried a 3'long 0.25" copper pipe in
there (total depth 7') I then bolted 2 large copper and brass
plates and a 2" strip of 1/8" copper plate to the highest end of
the pipe. About 6" of the strip sticks up above the ground. After
I had made the connection I covered it in silicone grease to
prevent corrosion. I then made a salt solution using about 1.5 Kg
of table salt and poured about a third of it in the hole. As i
filled the dirt back into the hole I added more salt solution.
Hopefully this will provide an adequate ground. We are in a river
valley so the water table is only about 6' below ground.
  I intend to connect the tesla coil RF ground (spark gap shield)
to this by means of four lengths of the copper tape used in the
primary coil, again I've got to use what I've got.

Safety / EMI

There is no filtering of the HV circuit yet. I have some 0.5 "
ferrite rod which I am going to wind 20 turns of magnet wire onto
and have one of these in seies with each HV line. Bypass caps I
can use some of the above across the HV bus, Which ones, any
idea? The safety gap I propose to run a wire from each HV
terminal to the spark gap shield. With my type of transformer
should I ground the core to the RF ground ?

All connections in the tank circuit have been made using 1/8"
copper rod insulated with clear plastic piping. Both c2 and the
spark gaps are mounted on the underside of the perspex board that
the coils sit on.

I have tried to download the design programs from the FTP
directory with very limited success, the only one I have been
able to run is TCH. If anybody can email me some programs direct,
I would be very grateful.(se-crawshaw-at-wpg.uwe.ac.uk)

The results from that were

Sec Frequency   195 KHz
Prim Cap required    0.0051uF
required primary inductance 129.55 uH
actual inductance 168.58uH

This tells me my cap is too small, anyone out there agree ?
I remember one of RQ's posts saying that it is better to have a
small cap and larger inductance in the primary (I think)

Please help me Obi Wan Quick. You are my only hope.

Also got a copy of:

Nikola Tesla on his work with alternating currents and their
application to wireless telephony, telegraphy and transmission of
power 1992

This is a fantastic book, I am sucking information from it. It is
available in the UK on Inter Library Loan although it is a
heavily requested Item (short loan)

Best regards to all coilers

Steve Crawshaw

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