Foreword by Carey
Sublette:
An
essential component of modern nuclear weapon technology is the ability
to rapidly switch high voltage/high current electrical circuits at very
high speeds.
The detonators that fire high explosive
implosion systems (exploding wire or exploding foil detonators) require
voltages in the range of (roughly) 2-20 kilovolts, acomplete detonating
system may draw currents ranging from 10 to 100 kiloamps. Pulse neutron
tubes, used to precisely control the initiation of fission chain
reactions, require voltages of 100 to 200 kilovolts, and currents in the
ampere range. These currents must be turned on rapidly and precisely,
timing accuracies of tens to hundreds of nanoseconds are
required.
Switching devices that meet these stringent
requirements often require specialized technologies or skills to
manufacture. They are also dual use - in addition to weapons
applications they have many civilian uses too. Examples include
controlling flash lamps used in high speed photography or industrial
photochemistry, generating high power radar pulses, in high energy
physics laboratory equipment, to name but a few. Consequently commercial
sale and international trade in these devices is permitted, but it is
also regulated. Attempts to circumvent these regulations have gained
considerable public attention in a number of technology smuggling cases
in the 1980s and 90s involving one particular type of device - the
Krytron. These devices have even appeared prominently in popular
entertainment as the
"McGuffin"
used to drive espionage thrillers - like Roman Polanski's
"Frantic".
This article summarizes the basic technologies
and devices, and their principle properties.
Section 1.0:
Introduction.
Before entering into a
consideration of the individual devices that concern us, it would be as
well to explain some of the associated technology/
terminology.
1.1 Switching basics and
terminology.
The switch is possibly
the most elementary device in the field of electronics. A switch
controls the flow of current in a circuit in a manner such that either
the current flows at a value determined by the other components in
series with it, or does not flow at all, as the case may be.
However this ideal behavior is actually never exactly what is seen in
real life. A switch has it's own parameters that determine how fast it
can switch from open to closed, or how rapidly it can interrupt the flow
of current once it is has been opened. Also of course there are more
elementary considerations such as the current handling capacity of the
switch and the peak voltage it can cope with before damage or other
unwanted effects occur.
Mechanical switches such as are common in the home are
in actuality far from ideal in their behavior. The time taken to switch
from off to on ( the commutation time) is typically in the millisecond
range. Also spurious effects such as bouncing may occur as the switch
fluctuates rapidly from open to closed in the process of being
physically manipulated by the operator.
Electromagnetic relays and reed switches experience
similar problems to those seen in the humble light switch. Long
commutation and switch bounce are standard features of virtually all
mechanical switching devices.
With the advent of transistors and similar devices such
as thyristors one would have thought that these slow switching problems
would be things of the past. This is in fact largely true. But
semiconductors are limited in other ways, it is very hard to find
semiconductors capable of switching many kiloamperes especially at
potentials in the kilovolt region, and those devices that can manage
high currents such as the larger thyristors are troubled by overly high
commutation times. Whilst there are now semiconductors coming onto the
market capable of performing at these extremes of current and voltage
there are some requirements which put even these devices to shame. If
you want to switch 50 kilo Amperes with a sub 20 nanosecond commutation
time at 20kV you are going to be in trouble if you are relying on
semiconductor technology. However there is an alternative class of
devices that have been around long before the humble transistor came on
the scene. You might think that vacuum tubes and similar are a thing of
the past. But for problems of this magnitude they are the only things on
the market that will do the job.
1.2 Vacuum and Gas filled
switching tubes, introduction and terminology.
There are a great many different types of vacuum tube
in existence, however it is possible to group tubes according to some
fairly basic criteria. There are two primary distinguishing features,
the source of free electrons within the device and the gaseous filling
(or lack of it) within the tube envelope. The later of these two
concepts we have already introduced by implication. A vacuum tube is a
device with a vacuum (very low pressure gas) filling. And a gas filled
device is, as the name would suggest, filled with gas that might be at a
pressure somewhat above or below atmospheric. The type of gas used is
also an important feature, particularly in switching tubes where a wide
variety of fillings are encountered.
The source of the free conduction electrons in the
device may be either thermal such as a heated filament physically
associated with the cathode of the device - a hot cathode, or
alternatively a simple consequence of a high voltage gradient across the
device, resulting in autoemission from the cathode. A device employing
this latter method is known as a cold cathode device. In high voltage
switching the presence of high voltages, and hence the possibility of
large voltage gradients within devices means that the cold cathode
system, quite a rarity in most other types of tubes, is the norm rather
than the exception.
Other important terms encountered in gaseous state
switching tubes:
Delay time.
The delay
time is the time taken between the application of a trigger pulse and
the commencement of conduction between the primary electrodes.
Jitter.
Jitter is the
variation of time delay from shot to shot given similar electrical
stimulus.
Commutation time.
The
commutation time is the time taken for the conduction to reach maximum
once it has commenced. (i.e. From the time from the end of the delay
time to the time at which the maximum level of conduction
occurs.)
It should be pointed out that none of the switching
tubes we are about to consider look very much like the things in the
back of an old radio set. Many are large, some exceptionally so. Also
glass has largely given way to ceramic in the higher powered devices.
Before you go down your local electronics shop or radio shack it should
also be pointed out that many of these devices besides costing $100's
(often $1000's) a piece, and are also largely unavailable to the general
public due to their application in advanced missile and nuclear weapon
technologies. Of these devices the most 'everyday' is the ignitron which
finds much application in industrial welding situations.
The following devices are considered herein:
2.0 Vacuum and Gaseous State Switching devices
2.1
Introduction to Cold Cathode Trigger Tubes
2.2 The
Krytron.
2.3 The
Sprytron.
2.4 The
Thyratron.
2.5 The
Over Voltage Spark Gap.
2.6 The
Triggered Spark Gap.
2.7 The
Ignitron
In addition I will include a short section on some of
the solid state devices that are finally beginning to fill the shoes of
the above gaseous state device (to a very marginal extent in most
cases).
2.0 Vacuum and gaseous state
switching devices
Most of the
devices in this section switch by inducing an arcing process in a
gaseous medium. I have included in the triggered spark gap section some
mention of devices that actually use a liquid or solid substitute for
the gaseous material that is the norm in triggered spark
gaps.
The process of arc formation is actually quite complex
physically, and it will not be gone into in any depth. Anyone who wishes
to look more deeply into this aspect of device operation may contact the
author for some suggestions as to suitable text books for use in such
study.
2.1 An Introduction to Cold
Cathode Switching Tubes.
Cold
cathode trigger tubes are physically small devices designed to switch
impulse currents and voltages of relatively small amplitude. Usually
they are intended, as their name suggests, to trigger other larger
devices.
Typically cold cathode trigger tubes are designed to
switch pulses of a few hundred volts and a few hundred milliamperes.
Most trigger tubes have three or four electrodes, anode, cathode (+ve
and -ve terminals respectively), a trigger/control electrode and
sometimes a priming electrode.
A trigger tube performs in a very simple manner akin to
that of a triggered spark gap, excepting that usually the conduction is
not by an arcing but glow discharge. The glow discharge is initiated
when all of the following factors are present:
i) A sufficiently high voltage is
present across the device
(between anode and
cathode)
ii) A trigger
pulse of sufficient amplitude is present at the trigger
electrode.
iii) The gas in
the tube is primed.
Cold cathode trigger tubes rely upon some external or
internal source to ionize the gas suitably for conduction to commence
(This is called priming). This means that in theory some of these tubes
will only switch a minute or so after the application of a suitable
triggering voltage to the appropriate terminal of the device when some
natural source of ionizing radiation ionizes the gas (forming a plasma)
and hence causes conduction to commence. The triggering is basically
random- it is subject to huge statistical variation even in apparently
similar environments. Some devices incorporate a suitably ionizing
source to reduce the maximum possible time delay after trigger
application considerably. This source may be an electronic, radioactive
or photon source of some form or other. However even the standard
commercial devices often display a large variation (up to and above an
order of magnitude different) between devices fired in sunlight and
darkness, a standard commercial tube Z900T for instance displays a 20us
delay in day light and a 250us delay in darkness.
2.2 The
Krytron:
Krytrons are a highly
specialized variety of cold cathode trigger tube. They were one of the
first products developed by the US based company EG&G. The Krytron
has 4 electrodes, and is filled with a gas at low pressure. A Krytron is
distinguished among cold cathode trigger tubes for a variety of
reasons.
The Krytron is designed to switch moderately high
impulse currents (up to around 3kA) and voltages (Up to around 5kV) in
an arc discharge mode, compare this with the usual glow discharge of the
standard trigger tube. Also, and perhaps more importantly, the
Krytron is able to turn on this arc discharge very rapidly, the reason
being that it relies on an already present plasma to support the
conduction, rather than waiting for the plasma to be formed as a result
of priming etc. This plasma is created and sustained by a keep-alive
current between the keep-alive electrode and the cathode of the device.
When the trigger is applied under the conditions of a high anode to
cathode voltage, this plasma forms an easy path for the main conduction
between anode and cathode.
The fact that a conduction path is already established
prior to triggering makes a huge difference in the commutation time of
these devices compared to standard cold cathode trigger tubes.
Commutation times below 1 nanosecond are achievable with Krytrons and
the time lag between application of trigger and the commencement of
switching may be less than 30ns with an optimized driver circuit. (Note
this delay is largely due to the fact that the ionized path will need to
spread from the keep alive terminal to the anode of the device) Compare
this delay time to that seen in the standard trigger tube which is
dependent upon many environmental factors and typically 3 or 4 orders of
magnitude greater. Note that the variation in time delay exhibited by
the krytron is almost totally independent of environment, however the
time delay may be reduced up to a point with increasing trigger voltage.
Likewise the commutation time is generally decreased if the rise time of
the trigger pulse is also decreased. Given identical trigger pulses
however a krytron will have a very similar time delay from one shot to
the next. This variation is known as jitter and may be less than 5ns in
optimal circumstances.
A Krytron contains a source of Beta radiation, Ni-63.
The quantity in each device is less than 5 microcuries and presents no
significant hazard. Usually the source is pulse welded to a piece of
Nickel wire that is in turn welded to one of the electrode supports. The
purpose of this source is to increase the reliability of the krytron by
aiding the formation of the initial glow discharge between the keep
alive and the cathode. This initial keep alive current is very much
subject to environmental factors such as are seen in the formation of
the glow discharge in standard trigger tubes. It is for this reason that
a radioactive priming element is used, much as in the priming source
employed in a standard trigger tube (which is also occasionally a
radioactive source).
Krytrons typically come in a small glass envelope
somewhat similar to a neon indicator bulb with more leads.
Krytrons require a high voltage pulse (500V to 2kV) to
be applied to the trigger electrode to fire successfully. This pulse is
almost always generated by a pulse transformer fired by a capacitor
discharge in the primary (rather like a simple strobe tube firing
circuit).
The krytron often has only a short life expectancy if
used regularly (often as few as a couple of hundred shots) However when
used within the appropriate parameters and well within the expected life
time they are extremely reliable, requiring no warm up and being immune
to many environmental factors to a large extent (e.g. vibration,
temperature, acceleration).
These properties, combined with the small size make the
krytron ideal for use in the detonating circuitry of certain types of
missiles and smart bombs. The krytron may be used directly to fire a
high precision exploding wire, or alternatively as part of the
triggering circuitry for a triggered spark gap or similar ultra high
current triggering device as used in exploding foil slapper type
detonators and larger EBW circuits.
Krytrons are used in firing circuits for certain lasers
and flash tubes and also in some pulse welding applications, often as
triggering devices for other larger devices such as Thyratrons and spark
gaps.
2.3 The
Sprytron.
The Sprytron, otherwise
known as the Vacuum Krytron, is a device of very similar performance to
the Krytron. Though it generally exhibits a somewhat lower time delay
after triggering. The Sprytron is designed for use in environments were
high levels of radiation are present. The sprytron is hard vacuum
'filled' device unlike the krytron which, as noted above contains a low
pressure gas.
The Sprytron has only three leads, (no keep alive), but
is otherwise very similar in outward construction to the Krytron. The
reason for the use of a vacuum filling is almost certainly that there is
no medium present for radiation from the external environment to ionize
(such ionization could promote spurious triggering effects.)
The Sprytron requires a more powerful trigger pulse
than the Krytron, as the device works by forming an arc directly between
the trigger and the cathode, which causes the tube to breakdown (go into
conduction) by disrupting the field between the anode and
cathode.
A Sprytron is triggered in a similar fashion to
Krytron, but as mentioned requires a higher energy trigger pulse and
therefore a more powerful trigger transformer etc. EG&G makes
trigger transformers optimized for use with their various tubes, and
also make devices named Krytron-Pacs which incorporate a gas filled
krytron and trigger transformer in a single housing.
One final point. It is interesting to note that in
application circuits (references 1 and 4) the sprytron is always shown
directly switching a load (an Exploding bridge Wire.) and a Krytron is
always shown triggering a secondary device such as a triggered spark
gap.
2.4
Thyratrons:
Thyratrons come in
several varieties. All work similarly to the semiconductor Thyristor,
one difference being that in many designs (Hydrogen Thyratrons are a
common exception) the gate must be biased highly negative in the off
state and then biased positive to achieve switching. Like Thyristors,
Thyratrons operate like a latching switch, i.e.. once you have turned
them on you can only turn off by cutting the supply to the main circuit.
Mercury filled Thyratrons are the slowest, least useful type and are
much more restricted environmentally than other types due chiefly to
problems with the mercury condensing . They are rarely used as they have
few advantages of the thyristor. Hydrogen Thyratrons are *much* faster switching than Thyristors. Some can
achieve commutation in under 20ns. Inert gas fillings tend to offer
superior performance compared to mercury filled devices, without
matching the speed of the Hydrogen filled devices.
Note that Hydrogen Filled Devices employ a hot cathode.
The actual Physical construction/ operation of the thyratron is quite
complicated compared to the other devices we have looked at and no
attempt will be made to explain it's operation. The reader is
advised to consult a wide range of books as devices employing
different fillings, or electrode heating methods operate differently. It
is not considered to be especially important to consider all these
variations here as this is merely an overview of these devices and is
not intended to be the final word on the subject. However, in order to
differentiate the thyratron form other similar devices and to define it
in at least some physical manner here follows Frungel's (Ref.4)
definition of the device:
By the term 'thyratron' there is meant a discharge
chamber in which are arranged a cathode, one or several grids, and an
anode, and which is filled with an inert gas or metal vapor.'
Some Thyratrons can handle up to 50kV(double gap
types) switch thousands of Amperes and handle very high power
outputs( e.g. CX 1154 can handle peak powers of 40MW). Typical
applications are Radar pulse modulators, Particle accelerators, Lasers
and high voltage medical equipment. Another variety of thyratron is
filled with Deuterium. These Deuterium filled devices are similar to
their Hydrogen filled counterparts but the sparking potential for
Deuterium is higher thus allowing even higher voltages to be handled.
E.g. E3213 can switch 70kV (double gap type). Specialist Thyratrons with
ceramic and metal bodies are encountered. These are designed to be
used in extreme environmental conditions. There is a wide variety of
grid configurations seen in Thyratrons, it would be impractical to
consider them all here. Manufacturers of Thyratrons Include EG&G,
GEC, English Electric Valve Co.Ltd, M-O Valve co. LTD. Big Thyratrons
often require you to get a big box full of driver/control circuitry.
Prices vary from a couple of dollars to thousands. Hot and cold cathode
type devices are encountered.
Note these ratings are the exception rather than the
rule in Thyratron devices, devices designed for sub kilovolt voltages
and only capable of handling a few tens of amps pulsed are common
enough.
Thyratrons typically come in either small multi- pin
base type packages such as are common in other vacuum tubes or in the
case of the higher current devices large tubular packages with hefty end
connectors.
2.5 The Over Voltage Spark
Gap
The Over voltage spark gap is
essentially just two electrodes with a gap between. When the voltage
between the two electrodes exceeds the breakdown voltage of the gas, the
device arcs over and a current is very rapidly established. The voltage
at which arcing occurs in these devices is given by the Dynamic
Breakdown Voltage, which is the voltage at which the device will
breakdown for a fast rising impulse voltage. Note that this voltage may
be as much as 1.5 times greater than the static breakdown voltage
(breakdown voltage for a slowly rising voltage.) how much greater than
the static breakdown voltage the actual breakdown voltage is will be
depends almost entirely on how rapidly the voltage rise, a shorter rise
time means a higher breakdown voltage. Commutation times for these
devices are exceptionally low (sometimes less than 1 nanosecond).
Overvoltage gaps are primarily used for protection. But
in combination with the other devices mentioned here they are commonly
used to sharpen the output pulses (decrease the rise times) of very high
current pulses form triggered switching devices e.g. Thyratrons.
The size of these devices is almost entirely dependent
upon how much current/voltage they are intended to switch, There is
really no limit as to the size of these devices they can be as small as
krytrons, however they can also be very big, and devices intended to
switch MA will be just that.
2.6 Triggered spark
gaps
The triggered spark gap is a
simple device, a high voltage trigger pulse applied to a trigger
electrode initiates an arc between anode and cathode. This trigger pulse
may be utilized within the device in a variety of ways to initiate the
main discharge. Different spark gaps are so designed to employ one
particular method to create the main anode to cathode discharge. The
different methods areas follows-
Triggered spark gap electrode configurations:
Field distortion: three electrodes; employs the
point discharge (actually sharp edge) effect in the creation a
conducting path
Irradiated: three electrodes; spark source
creates an illuminating plasma that excites electrons between the
anode and cathode.
Swinging cascade: three electrodes; trigger
electrode nearer to one of the main electrodes than the other.
Mid plane: three electrodes; basic triggered spark
gap with trigger electrode centrally positioned.
Trigatron: trigger to one electrode current forms
plasma that spreads to encompass a path between anode and
cathode.
The triggered
Spark gap may be filled with a wide variety of materials, the most
common are-
1) Air
2) SF6
3) Argon
4) Oxygen
Often a mixture of the above materials is employed.
However a few spark gaps actually employ liquid or even solid media
fillings. Solid filled devices are often designed for single shot use
(they are only used once- then they are destroyed) Some solid filled
devices are designed to switch powers of 10 TW (10 000 000 000 000
Watts) such as are encountered in extremely powerful capacitor bank
discharges. Except (obviously) in the case of solid filled devices, the
media is usually pumped through the spark gap. Some smaller gaps do not
use this system though.
Usually Gas filled spark gaps operate in the 20-100kV /
20 to 100kA range though much higher power devices are available. I have
one spec for a Maxwell gas filled device that can handle 3 MA - that's 3
Million Amperes! But then it is the size of a small car!! More commonly
gas filled devices have dimensions of a few inches. Packages are often
shaped like large ice pucks though biconical, tubular and box like
structures are also seen.
Sparkgaps are often designed for use in a certain
external environment (e.g., they might be immersed in oil). A system for
transmitting the media to the appropriate part of the device may
sometimes be included. Common
environments used are:
a) Air
b)
SF6
c) Oil
Typical spark gap device no.'s are: TG7, TG113, TG 114
etc., etc.
Spark gaps are damaged by repeated heavy discharge.
This is an inevitable consequence of such high discharge currents.
Electrode pitting being the most common form of damage. Between 1 and 10
thousand shots per device is usually about what is permissible before
damage begins to severely degrade performance.
EG&G make miniature triggered spark gaps specially
designed for defense applications. these devices are physically much
smaller than normal spark gaps (few cm typical dimensions) and designed
for use with exploding foil slapper type detonators.
Laser switching of spark gaps. The fastest way to
switch a triggered spark gap is with an intense pulse of Laser light
which creates a plasma between the electrodes with extreme rapidity.
There have been quite a few designs employing this method, chiefly in
the plasma research area.
Triggered spark gaps tend to have long delay times than
Thyratrons (their chief competitor, at least at lower energies) However
once conduction has started it reaches a peak value exceptionally
rapidly (couple of nanoseconds commutation.)
2.7
Ignitrons
The ignitron is mercury
vapor rectifier in which an arc is switched between a (usually graphite)
anode and a mercury pool cathode. The discharge is initiated by an
ignitor electrode which dips into the mercury pool cathode. On
application of a suitable impulse current/voltage to this ignitor an
electron emitting source is formed at the point at which the ignitor
contacts the pool. This initiates the arcing between the anode and
cathode.
It is important that the ignitor should be triggered
correctly. The ignitor requires a certain energy for successful ignition
and also an 'ignitor characteristic' application of this energy in terms
of current and voltage with respect to time. Misfiring or ignitor damage
will otherwise occur. It is also vital that no significant negative
voltage should appear at the ignitor with respect to the cathode else
ignitor destruction will be the inevitable result.
There are two main ways by which the trigger can be
biased:
Anode excitation: common in resistance
welding applications here the anode bias is connected to the ignitor by
means of a switch (thyristor, thyratron etc.) and a resistor/fuse
network. The ignitor current drops rapidly on ignition as the
anode-cathode voltage drops very low during conduction.
Separate excitation: as the name suggests, here the
ignitor circuit is largely independent of the main circuit.
Ignitrons are often used in parallel for AC power
control applications.
Ignitrons must often be cooled when used continuously
(i.e.. Not single shot as in capacitor discharge) Water cooling is
commonly employed. It is vital that Ignitrons must be used in the
correct temperature range to hot or too cold can be very bad news for
these devices- (cold leads to mercury vapor condensing on the
anode.)
Ignitrons are very limited with regards their physical
orientation. This reason being simple that they rely upon a pool of
liquid at one end of the device that must be correctly positioned for
the ignitor to function correctly. Positioning the device so that it
leans over at an angle of more than 2 or 3 degrees from the vertical is
fatal.
Most ignitrons operate at most currents between 5 Amps
and 100kA and may be suitable for voltages from a couple of hundred to
20 000 Volts.
Thyratrons and Krytrons are sometimes used in ignitron
triggering circuits along with the familiar thyristor.
Ignitrons are suited to applications were power control
of high voltages or currents is required. Welding is probably the most
common application.
3.0 Solid State
Devices.
(Note this section may well
be considerably expanded following further research by the
author.)
There are now a few commercially available transistors
on the Market which can switch many tens of kV. There are also a few
transistors about that can handle pulsed currents above 5kA. These
devices may match for example Krytrons and Sprytrons in terms of
electrical performance, but not in terms of size and (in the case of the
Sprytron) radiation hardness.
Thyristors are widely available in designs that can
handle upwards of 10kA pulsed at several kV. They are however very slow
switching devices and are not capable of achieving even low microsecond
switching speeds.
A new class of devices is at present showing great
promise in the R&D sector. These devices are optically (usually
LASER) switched devices employing GaAs or Diamond film technologies. The
reader is advised to consult the appropriate reference below for more
information relating to these devices.
Final note to the reader:
Some
of the devices I have mentioned are subject to strict control due to
their military applications. None of the above information is however in
any way restricted or controlled. For clarity switching devices that are
restricted by dual use guidelines are as follows: (courtesy Oak Ridge
National Laboratory)
(a) Cold-cathode tubes (including gas krytron tubes and
vacuum sprytron tubes), whether gas filled or not, operating similarly
to a spark gap, containing three or more electrodes, and having all of
the following characteristics:
1. Anode peak voltage rating of 2500 V or
more,
2. Anode peak current rating
of 100 A or more,
3. Anode delay
time of 10 microsecond or less, and
(b) Triggered spark-gaps having an anode delay
time of 15 microsecond or less rated for a peak current of 500 A or
more;
(c) Modules or assemblies with a fast switching
function having all of the following characteristics:
1. Anode peak voltage rating greater than 2000
V;
2. Anode peak current rating of
500 A or more; and
3. Turn-on time
of 1 microsecond or less.
Acknowledgments:
I would like to thank the following for their help and
assistance:
Carey Sublette for providing
a great deal of help and encouragement.
Roy Schmaus for providing the original site for this
information.
References: (in
alphabetical order by title)
1) EG&G Catalogues/ Material. (RE:
Components)
2) Exploding Wires Vol. 4, Proceedings of
4th Conference on Exploding Wire Phenomena. Ed. Chace and Moore - Plenum
Press (RE: EBW's)
3) High Power Optically Activated
Solid State Switches, ed. Rosen And Zutavern- Artech House (RE: Solid
state devices)
4) High Speed Pulse Technology by Frank
Frungel -Academic Press. (RE: EBW's, FCG's, components)
5) High Velocity Impact Phenomena by Ray
Kinslow-Academic Press. (RE: Foil Slappers)
6) IEEE
publications (please contact author for more details).
7) Maxwell Catalogues. (RE: spark gaps)
8) Mullard Valves and Tubes Book 2 Part 3 (RE:
components)
FURTHER INFORMATION PERTAINING TO THE SUBJECT
MATTER WILL BE MUCH WELCOMED
BY THE
AUTHOR.
Information regarding the author: I am not an
expert in any of the above technologies and I will welcome any
corrections. However please could anyone providing information also
provide references to either the material
they
present or as to themselves so that their contribution may be given due
weight.
Anyone who would like to contact me (the author) for
whatever reason should mail:
John Pasley [kc76@cityscape.co.uk - current email
address not available...]
Disclaimer: I the author assume no responsibility for
anyone who injures/kills themselves trying to implement any of the above
technologies. High voltages are generally exceptionally dangerous, and
none of the above is intended or should be used to provide instruction
in the correct procedures for building or constructing high voltage
circuitry of any description. High voltage is used here to describe any
voltage which may cause death i.e., anything above 50V.
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