Salvaging Interesting Gadgets, Components, and Subsystems


[Document Version: 1.27] [Last Updated: 05/25/1998]

1. About the Author & Copyright

Salvaging Interesting Gadgets, Components, and Subsystems

Author: Samuel M. Goldwasser
Corrections/suggestions: | Email

Copyright (c) 1994, 1995, 1996, 1997, 1998
All Rights Reserved

Reproduction of this document in whole or in part is permitted if both of the following conditions are satisfied:

  1. This notice is included in its entirety at the beginning.
  2. There is no charge except to cover the costs of copying.

2. Introduction

The purpose of this document is to help reduce the clutter in land fills :-).

Many dead appliances, and consumer electronic and computer equipment contain
parts and subassemblies which are not only neat and interesting, but useful
for various experiments and projects.

* I bet you tossed that big heavy slow 5-1/4" hard drive in the garbage when
  you upgraded, didn't you?  Admit it!  Did you know that if it was a high
  performance drive, it contained several of the most powerful permanent
  magnets you would ever be likely to find anywhere?  And, they would have
  been free!

* That big old microwave oven?  Too bad.  More magnets, nice high voltage
  power transformer, rectifier, capacitor.  Electronic or mechanical timer,
  fans, other motors, etc.

* What about that dot matrix printer?  Too bad - at least two stepper motors,
  a nice power supply, and various other electronic and mechanical components.

* More steppers in floppy drives.  Also, probably a regulated speed pancake

* Old TV or monitor?  Another mistake.  The high voltage power supply was
  probably good for 12 to 30 KVDC at 1 or 2 mA.  This is useful for many high
  voltage experiments, plasma globes, negative ion and ozone generators, bug
  disintegrators, starters for really LARGE HeNe lasers, etc.

There will be several types of information:

1. Where to obtain a particular type of part like a powerful magnet.

2. What dead consumer electronics, computer equipment, and appliances yield
   in the way of useful parts.

3. Unconventional uses for subsystems or common replacement parts or modules
   from such equipment.

3. Place to obtain sacrificial equipment

So, where do you find the equipment from which to remove parts other than your
basement, your attic, or those of your relatives or friends?  Consider garage,
yard, tag, estate, and other sales; thrift stores (which may even have a
'free' table); junk, salvage, and surplus yards (including those run by the
Department of Defense!), the town dump and other landfills if they let you
take things away, trash rooms of high rise apartment complexes, the curb on
pickup day, college campuses around the end of the Spring term, and any other
place where perfectly good equipment gets tossed in this throw-away society!

Of course, don't overlook high tech flea markets as well as ham and computer
fests.  Regular flea markets are usually overpriced (where do you think they
get the stuff??) but sometimes you will be able to negotiate a great price
because they have no idea of what they are selling!

Yes, we are a strange bunch :-).


The devices, equipment, circuits, and other gadgets described in this document
may be dangerous.  Much of it deals with potentially lethal voltages.  Getting
electrocuted could ruin your whole day.  For really high voltage equipment,
also see: Tesla Coils Safety Information.

We will not be responsible for damage to equipment, your ego, blown parts,
county wide power outages, spontaneously generated mini (or larger) black
holes, planetary disruptions, or personal injury that may result from the use
of this material.

5. Neat magnets

Two excellent sources of magnets are described below.  These are at least as
strong as the more well known speaker types, possibly much stronger, and
generally easier to remove:

1. Microwave oven magnetron tubes.  Go to your local appliance repair shop
   and ask - they just toss bad ones.  Each one has two ring shaped ferrite
   magnets about 2-1/4" in diameter with a 7/8" hole, magnetized N-S on the

   Surplus places typically charge $3 to $6 each for one of these magnets.

   Note: A few older magnetrons used AlNiCo magnet assemblies or even possibly
   electromagnets which are not nearly as interesting.  However, you probably
   won't see any of these.

2. Large hard disk drives - especially full height 5-1/4" high performance
   types - e.g., Seagate WREN series or Micropolous boat anchors (the rare
   earth magnets in these are wicked).  The magnets in small drives are even
   stronger but are, well, much smaller :-).  A typical size for a large drive
   is about 1" x 1-1/4" by 1/2".  Since almost no one wants such large slow
   drives anymore, they are often found at swap meets or yard sales for next
   to nothing.

   Surplus places may charge $12 or more for ONE of the magnets from a large
   disk drive (there are typically 2 to 6 such magnets in a disk drive)!

   For some things to do with these neat magnets, see: Neodymiumarium.

Caution:  Both these types are powerful and will squash flesh as they suck all
the bits off of your magnetic media!  I am not kidding about the part about
squashed flesh - with some you actually need a small crowbar to pry the
assembly apart!

You will find that some of these magnets are painted.  This provides some
resistance to chipping though this material may be on the verge of flaking off
or has already done so in spots.  In any case, I further recommend that you add
additional layers of a tough enamel (e.g., Rustoleum) or the plastic/rubber
dip used to coat tool handles.  Otherwise, chipping damage (at least) will
result all too easily and the chips are just as powerful as the rest of the

Disclaimer: I will not be responsible when your spouse or parents come home to
find the microwave or PC missing some key components and as dead as a brick!

6. Other sources of fairly strong magnets

3. Spent laser printer toner cartridges where the entire developer assembly is
   part of the cartridge (e.g., EPS-2 for Canon engines).  These include a
   page-width ferrite magnet.  However, expect to make a mess disassembling
   the cartridge as there will still be considerable toner remaining inside.

   WARNING: The toner is a possible health hazard.  A good dust mask should be
   used while working on these.  Also, do not vacuum what remains - static can
   set off a dust explosion - use wet rags or paper towels to clean up the
   mess!  The coating on the photosensitive drum may also be a hazardous

4. Loudspeakers.

   * Smaller or older speakers use AlNiCo type magnets which are usually in
     the form of a cylinder (about as tall as it is wide).  AlNiCo is an
     extremely hard metal alloy.

     AlNiCo magnets are not as powerful as ferrite or rare earth types and are
     easily demagnetized (but just as easily remagnetized).  Passing a stack
     of these through the center hole of a strong ferrite magnet will increase
     their strength dramatically - until they are separated from each other!

   * Modern loudspeakers use ring shaped ceramic ferrite magnets (similar to
     those in a microwave oven magnetron - see the section: "Neat magnets".
     glued to the pole piece (yoke) assembly within which the voice coil moves.
     The ferrite is extremely hard but very brittle so care must be used to
     extract these from the yoke assembly - see the section: "Disassembling loudspeakers to get at the magnets".

5. Permanent magnet stepper and servo motors.  These will use ferrite or rare
   earth magnets usually in strange shapes.  Note: Removing the magnets may
   result in partial demagnetization (reduction in magnetic strength) as the
   rotor is part of the magnetic circuit.  Therefore, I do not recommend this
   source.  There is generally no practical way of remagnetizing the strange
   shapes involved.

6. Optical (laser) pickups from CD players, CDROM drives, and other optical
   data storage devices.  These may have some very tiny, but strong, rare
   earth magnets in the focus and tracking actuator.  However, it seems a
   shame to sacrifice a the beautiful mechanics in such a device just to get
   the magnets!  Caution: Tiny magnets even more fragile than bigger ones!

7. Disassembling loudspeakers to get at the magnets

For small speakers with AlNiCo type magnets (the magnets usually look like
metal cylinders), careful prying with a sturdy screwdriver will usually
break the adhesive bond and/or free them from the yoke assembly.  Note: Use
the proper tool for the job - not your dad's prized screwdrivers!)  Unlike
the ceramic magnets described below, AlNiCo types are metal and quite sturdy.

(From: Arie de Muynck (

For the normal black ceramic ring shaped magnets (and likely for some Ticonal
'iron colored') the trick is: heat the complete assembly slowly using a
paint-stripper gun, or in an oven (thermal, not microwave!). The glue will
weaken and with a screwdriver you can SLOWLY work them loose. Protect your
fingers with an old cloth. Never apply too much force, the ceramic would chip
or break.

Do not overheat them above the so-called Curie temperature or the magnet will
loose it's power irreversibly. That temp depends on the material but should be
way above the 120 C or so to soften the glue. If you want to experiment with
this effect: use a piece of iron attracted towards a magnet, heat the iron
with a flame and above a rather sharply defined temperature it will not be
attracted anymore. The effect is used in some Weller soldering irons to
stabilize the temp.

Note that the force of a bare ceramic magnet is not as strong as you might
expect, the magnetic lines of the large area of the ring have to be bundled
and guided though iron to a narrow gap to provide a proper magnetic field.

8. Scripto lighters and gas grill ignitors

Some types of disposable lighters contain a piezo electric element (instead of
a flint and wheel) which generates a spark to ignite the Butane gas.  Pressing
down on the activator drives an escapement which results in a bar hitting the
piezo element.

The result is several thousand volts on demand with its output available at a
couple of terminals.  This can be used to trigger xenon tubes or even to start
helium neon lasers (with the addition of a pair of high voltage diodes to form
a charge pump).  Or as a prod for small cattle, but I didn't say that :-).
For a discussion of the HeNe laser application, see the document: "Lasers:
Safety, Info, Links, Parts;  Diode, HeNe, Ar/Kr Ion Lasers".

Detaching the piezo assembly only requires bending back and removing the sheet
metal shroud at the top of the lighter.  The entire piezo unit then just pops

Gas grill ignitors are similar - and even more powerful.  These are available
as replacement parts at your local home center or appliance store.  (Don't
steal the one from the family gas grill - your dad won't be happy.)

9. Dangerous (or useful) parts in a dead microwave oven

A microwave oven with its power cord cut or removed AND its high voltage
capacitor safely discharged is an inanimate object.  There are no particularly
hazardous parts inside.  Of course, heavy transformers can smash your feet
and sharp sheet metal can cut flesh.  And, the magnets in the magnetron may
erase your diskettes or mess up the colors on your TV.

Some may feel there is nothing of interest inside a microwave oven.  I would
counter that anything unfamiliar can be of immense educational value to
children of all ages.  With appropriate supervision, an investigation of
the inside of a deceased microwave oven can be very interesting.

However, before you cannibalize your old oven, consider that many of the parts
are interchangeable and may be useful should your *new* oven ever need repair!

For the hobbiest, there are, in fact, some useful devices inside:

* Motors - cooling fan and turntable (if used).  These usually operate on
  115 VAC but some may use low voltage DC.  They can easily be adapted to
  other uses.

* Controller and touchpad - digital timer, relay and/or triac control of the
  AC power.  See the section: "Using the control panel from defunct microwave oven as an electronic timer".

* Interlock switches - 3 or more high current microswitches.

* Heavy duty power cord, fuse holder, thermal protector, other miscellaneous

* High voltage components (VERY DANGEROUS if powered) - HV transformer (1,500
  to 2,500 VRMS, .5 A), HV rectifier (12,000 PRV, .5 A), and HV capacitor
  (approximately 1 uF, up to 2,500 VAC, perhaps 3,000 V peak).

* Magnetron - there are some nifty powerful magnets as part of the assembly.
  Take appropriate precautions to protect your credit cards, diskettes, and
  mechanical wristwatches.  See the section: "Neat magnets" and the document:
  "Notes on the Troubleshooting and Repair of Microwave Ovens for more info.

DOUBLE WARNING:  Do not even think about powering the magnetron once you have
removed any parts or altered anything mechanical in the oven.  Dangerous
microwave leakage is possible.

10. Using the control panel from defunct microwave oven as an electronic timer

It is usually possible to remove just the touchpad and controller board
to use as a stand-alone timer with a switched output.  Be careful when
disconnecting the touchpanel as the printed flex cable is fragile.  With
many models, the touchpanel (membrane touchpad) needs to be peeled off of
the front plastic panel or the entire assembly can be removed intact.

The output will control a 10-15 A AC load using its built in relay or triac
(though these may be mounted separately in the oven).  Note that power on a
microwave oven is regulated by slow pulse width modulation - order of a 30
second cycle if this matters.  If it uses a triac, the triac is NOT phase
angle controlled - just switched on or off.

11. Useful parts in a non-working VCR

* Motors: 1 to 6 motors of various types.  Mostly these are cheap DC permanent
  magnet motors but the main capstan motor may be a high quality brushless
  type with electronic control on-board.  The video drum motor is likely three
  phase with its own controller.

* Power supply: Outputs various voltages and may be used intact but will always
  contain useful components like transistors and diodes, transformer(s), and
  large capacitors.

* Tuner.  Whether you can make this work without the rest of the VCR is
  problematic but worth a try.

* RF modulator.  This usually accepts a DC voltage for power, a control voltage
  to select TV/VCR, and will output on channel 3 or 4.

* Miscellaneous electronic components including crystals, delay lines, video
  and audio ICs, pots, connectors, etc.

What can you build with it?  One can never tell! :-).

12. High voltage power supplies from dead equipment

* TVs, monitors, and computer terminals all contain a source of high voltage
  for the CRT.  Depending on the particular model, up to 30 KVDC or more at
  1 to 2 mA will be available assuming the deflection/HV subsystem of your
  sacrificial equipment is in operating condition.  However, you cannot (or
  at least should not) just string HV wires from the back of the family's 35
  inch TV to your lab :-).

  - How much circuitry you actually need (and what you will have to add)
    depends on design but figure on the mainboard with the deflection drive
    and flyback, and probably the yoke (to keep the system properly tuned
    though this may not be essential).

    Some capacitance on the HV output may be needed as well (though the ones
    I have tried were happy enough with just the stray capacitance of the
    wiring).  Originally, the CRT envelope provided this capacitance.

    See the section: "Why the yoke is needed to keep the horizontal deflection system happy".

  - Power will either be the AC line (WARNING: Very dangerous) or a DC supply
    (typically 12 to 24 VDC).  They will usually operate on somewhat lower
    input voltages with correspondingly reduced output.

  - A 555 timer based oscillator or other horizontal sync source may be needed
    as well if the system doesn't free-run at close to the normal horizontal
    scan rate.  This is probably easier where the guts came from a monitor or
    terminal (since a separate TTL compatible horizontal drive input is likely
    to be available) but it should be possible to fake out a TV as well.

  - Depending on design, these may require signals like 'HV Enable' and/or a
    feedback or reference voltage to operate properly.

  - Small B/W TVs, mono computer monitors, and computer terminals will provide
    about 12 to 15 KV.

  - Large B/W TVs and Color TVs and monitors will provide 15 to 30 KV.  Even
    more from projection sets!

  - Some larger high performance color monitors may have a separate self
    contained HV module.  One particular type (found in a 19 inch workstation
    monitor) is rated at 25 KV, 1.1 mA (and produces several other voltages)
    from a 26 VDC, 2.5 A power supply.  However, by tweaking some internal
    pots, over 30 KV is available.   See the section: "High voltage power supply module from Monitronix EZ series monitors" for one example.

  One key advantage of using predesigned circuitry is that you are less likely
  to destroy power transistors and other expensive parts - and I have blown my
  unfair share :-(.

  See the section: "Sam's super-starter(tm)" for a specific example of this
  kludge, um, err, approach for starting large HeNe laser tubes :-).  

* The high voltage power supplies from plasma globes, electrostatic dust
  precipitators, photocopiers and laser printers, bug zappers, negative ion
  and ozone generators, electric fences, cattle prods, electric chairs, and
  other 'common' equipment may be pressed into service for your applications.

  Since these HV generators are not combined with anything else, they are
  likely to be self contained modules and very easily used by themselves.

  However, available current from some of these sources is generally less than
  from TVs or monitors.  Details are left to the highly motivated student :-).

  - Plasma globes: Pulsed (not rectified or filtered) 10 to 15 KV.

  - Electrostatic dust precipitators: 5 to 10 KVDC.

  - Photocopiers and laser printers: Two outputs at 5 or 6 KVDC.

  - Bug zappers: 10 KV???.

Caution: Since these power supplies were designed for a specific purpose under
specific operating conditions, their behavior when confronted with overloads
or short circuits on the output will depend on their design.  It may not be
pretty - as in they may blow up!  Take care to avoid such events and/or add
suitable protection in the form of fast acting fuses and current limiting to
the switching transistor.

Note about X-rays: Improper use of these sorts of devices may result in
shock or electrocution, but at least you will not be irradiated at the same
time unless you connect them to a something which includes a vacuum.  In order
to produce measurable X-ray radiation, electrons must be accelerated to high
velocity and strike a heavy metal target.  A high vacuum such as in a CRT or
other vacuum tube (valve) is best but there may be some X-ray production from
a low pressure gas filled tube.  There is virtually none in sparks or arcs at
normal atmospheric pressure.  However, there will be UV and ozone which are
both hazardous.

13. Sam's super-starter(tm)

This would be called a kludge by some, a Rube Goldberg by others.  But, hey,
as still others would say: "If it works, use it!".  The original application
was for starting LARGE HeNe laser tubes but there can be many other uses.

The entire horizontal deflection and high voltage sections of a long obsolete
and lonely ASCII video display terminal were pressed into service for starting
larger HeNe tubes.  A source of about 12 VDC at 1.5 A is needed for power and
a 555 timer based oscillator is needed to provide the fake horizontal sync:

* The deflection circuitry was all on one corner of relatively small board
  (about 3 x 6 inches).  The flyback transformer is a plug-in unit.  I left
  the other circuitry (vertical, video) in place since it is not powered by
  the same supply and therefore is pretty inert.  However, if you want to
  recycle the parts.....

* The horizontal deflection yoke is needed to 'tune' the system - performance
  is much better with it installed.  This wart looks a bit strange but is the
  easiest way to avoid modifying the design.  See the section: "Why the yoke is needed to keep the horizontal deflection system happy" for more info.

* Horizontal drive is provided by a 555 timer in astable mode running at about
  16 KHz (the original horizontal deflection rate of the terminal).  A 10K ohm
  pot allows me to fine tune this for maximum HV output.

  Well, it turns out there was an unused spot on the board ready made for this
  circuit (well almost, at least there was a pattern for a spare 8 pin DIP!
  So, once the thing was basically working, I built the oscillator onto the
  board to reduce the clutter!

* Power requirements are modest - 10 to 15 VDC at just over 1 A.  Over this
  range, the output varies between about 10 and 15 KV (what a coincidence!).
  Input down to about 5 VDC produces correspondingly reduced output but the
  circuit is not particularly stable over this lower range of voltages.)

I guarantee that "Sam's super-starter(tm)" - or its big brother, "Sam's
hyper-starter(tm)" using parts from a color TV or monitor - will start ANY
HeNe tube that can possibly be started!  These also make nice self contained
HV sources for other experiments :-).

14. Why the yoke is needed to keep the horizontal deflection system happy

If you unplug the yoke (even if there is no interlock), while the system may
still work to some extent but performance will be poor.  High voltage will be
reduced and parts may overheat (and possibly blow up).

(From: Jeroen Stessen (

Of course that doesn't work. The flyback capacitor is tuned for the presence
of both inductances: line transformer and deflection coil. If you remove the
deflection coil then the remaining primary transformer inductance is about 5
times as large.  So, rule-of-thumb, you would have to decrease the flyback
capacitor by a factor of approximate 5.  But that's not all:

Without the deflection coil, a lot less current runs through the horizontal
output transistor. So, in all likelihood, it will now be overdriven. So you
need to reduce the base drive. But that's not all:

If you remove the picture tube capacitance and the deflection coil then all
peak energy demand must be delivered from the primary winding of the line
transformer. Even the shortest peak load will cause saturation. The parallel
deflection coil will at least lend some temporary energy, and the picture tube
capacitance does an even better job. A good high-voltage source without the
benefit of a deflection coil is more expensive...

If you *must* get rid of the 'ugly' deflection coil, then you may want to
replace it with an equivalent 'pretty' coil.  But:

* It must be able to carry the peak current without saturation (a deflection
  coil has such a huge air gap that it can not possibly ever saturate, but a
  smaller coil can).

* It must have a low enough dissipation so you might have to wind it with
  litz-like wire (multi-stranded isolated), do not underestimate the losses in
  high-frequency coils,  mostly due to skin- and proximity-effect. 

* Yes, it can be done, good luck.

And you might want to add a discrete high-voltage capacitor.  How to isolate
the wiring (corona discharge!) is left as an exercise to the reader... (We
pot them in convenient blocks).

15. High voltage power supply module from Monitronix EZ series monitors

This is a self contained module (separate from the deflection circuitry)
which makes it very convenient for your HV projects.

It is fully enclosed in an aluminum case about 1-7/8" x 6" x 5" with a
9 pin connector for the low voltage wiring and thick red wires with HV
connectors - suction cup and Alden type - for the CRT 2nd anode and focus
voltage respectively.

Manufacturer: Toyo, Corp., Japan

Model: HVP-1208A1-26L.

Input: 26 V, 2.5 A max.

Output: 25 KVDC, 1.1 mA
        Focus, 4.5 to 7.65 KVDC, 15 uA
        G2, 200 to 1000 VDC, 5 uA
        -200 VDC, .5 mA

There are 8 pins installed on the 9 pin connector of which 6 were used.
I wonder if the other 2 have any function other than spacing off the G2

     /          \
   <  o3  o6  o9 |
    >            |  View of connector on case.
   <  o2  o5  o8 |
    >            |
   <  o1  o4  o7 |

Pin 1: -200 VDC (-184 VDC measured)   White or yellow
Pin 2: V+ in 26 VDC, 2.5 A max.       Green or brown
Pin 3: Power Gnd                      Black
Pin 4: Shield Gnd                     Bare or black
Pin 5: NC
Pin 6: NC
Pin 7: Enable (low) TTL               Orange
Pin 8: NC
Pin 9: G2 (+200 to +1000 VDC)         Red

I assume the NCs are truly not connected to anything and simply serve as
clearance for the up to 1000 V G2.

In addition to the Focus and G2 pots, there is an unmarked adjustment
accessible via a hole in the case.  At first, this appeared to have no
effect on any output.

When I opened the case, 2 additional pots come into view.  While I do not
really know their exact function, by advancing them clockwise, the HV could
be boosted significantly.  With both fully clockwise, the externally
accessible control will vary the HV between about 27 and 32 KVDC regulated
(only HV probe meter load).

16. High voltage transformers

* Neon sign or luminous tube transformers (same thing): 10 to 15 KV at 15 to
  60 mA, current limited.  Some may be higher.  There are also smaller ones.

  Current limited means that the transformer will deliver the rated current
  (Io) into a short circuit and produce the rated voltage (Vo) with no load.
  This is somewhat similar to being in series with a resistor equal to Vo/Io
  but implemented as a loose magnetic coupling so there is no additional power
  dissipation.  (It isn't really this straightforward but will serve as a
  first approximation.)  Therefore, a short circuit on the output will not
  blow a fuse or trip a breaker.

  Sources: Your local sign shop, demolition company, or salvage yard.  New:
  $100 or more.  Used: $5 to $50 or free.

  WARNING: Though current limited, the available current from neon sign
  transformers - especially the larger ones - is far into the range where
  lethal consequences are likely under the wrong circumstances.

* Oil burner ignition transformers: 8 to 10 KV at 10 to 25 mA, current
  limited.  (See description for neon sign transformers, above.)

  Sources: Your local HVAC contractor probably for the asking as they are
  thrown out along with old oil burners when they are replaced.  However, you
  will probably have to take the entire icky smelling disgusting burner
  assembly as part of the deal :-).  However, there is will be a nice motor
  and small oil pump in there as well ;-).

  WARNING: Though current limited, the available current from oil burner
  ignition transformers is still more than enough to kill under the wrong

Both neon sign and oil burner ignition transformer generally have centertapped
secondaries connected to the case - which MUST be grounded (via a three wire
cord and properly wired outlet) for SAFETY.  Therefore, it is generally not
possible to construct a totally isolated HV power supplie with these devices.

* Microwave oven transformers: 1.5 to 3 KV at .25 to .5 AMPS.

  Sources: Dead microwave ovens (the transformer is rarely the problem).  Try
  your local appliance repair shop.  However, you will probably have to cart
  away the entire oven - but other useful parts inside :-).  See the section:
  "Dangerous (or useful) parts in a dead microwave oven".

  WARNING: The electrocution danger from microwave oven transformers cannot be
  overemphasized.  They are not current limited, and even if they were, could
  be instantly lethal given the least excuse for a suitable path through your
  body since the rated current is a substantial fraction of an AMP at several
  thousand volts.  Normally, one end of the high voltage secondary is bonded
  to the core - which must be grounded for safety.  However, it may be
  possible to disconnect this and construct an isolated HV power supply (which
  will be only marginally less dangerous).

* Automotive ignition coils: 25 to 75 KV (depending on model) at low current.

  Sources: Your 1997 Honda.  Just kidding :-).  Auto repair shops or parts
  stores, salvage yards.

  WARNING: While unlikely to be lethal, the HV output of an ignition coil can
  still result in a seriously unpleasant shock and possible collateral damage.

* Flyback transformers from TVs, monitors, computer terminals, or other HV
  power supplies.  Little teeny ones in CRT based camcorder viewfinders and
  older Watchman TVs.  Output from less than 3 KV to over 30 KV at 1 to 2 mA
  depending on model.  Most include a high voltage rectifier though some may
  use an external one or voltage multiplier (also a useful and neat device).

  For many hobbyist uses, the only portion of the flyback that is important
  will be the high voltage winding (and rectifier, if present).  It is a
  simple matter to add your own drive and feedback windings on the flyback
  core.  This eliminates the uncertainty of determining the number of turns
  and wire size for the existing windings.

  Sources: CRT based equipment tossed for failures NOT caused by a defective
  flyback.  However, sometimes even a bad flyback can be used for HV projects.
  This will be the case if the problem is:

  - Shorted primary windings.  With some flybacks, the primary windings are
    on a separate bobbin and can be removed.  Even when buried, they can
    sometimes be extracted without affecting the HV winding (just don't lose
    the HV return!).

  - External arcing due to cracks or pin-holes.  Try coating with RTV silicone
    or HV sealer (allow ample time to dry completely).  Plastic electrical
    tape may work temporarily at least.  Note: Try to get the type of RTV that
    is non-acidic.  The normal kind (that smells like viniger when curing) may
    be corrosive to the wiring.  However, I haven't seen problems with this.

  - Breakdown in focus/screen network.  This section may be removable with
    a hacksaw or small chisel!  Then, insulate the exposed HV terminals as

  - Shorted HV rectifier (rare).  Just add an external HV rectifier if needed.

    If you really want AC, this is an advantage!  In fact, it might be
    possible to deliberately short the HV rectifier where you want an AC
    source by passing excessive (DC) current through it and/or violating its
    PIV rating (but that may be tough as other parts are likely to fail

  - Broken or cracked core.  Substitute the core from another flyback or glue
    or clamp the pieces together (broken edges in close contact).  Don't lose
    the mylar/plastic spacers and replace them (if needed) when the repair is

  No one actually buys flyback transformers for experimentation!

  WARNING: Flyback transformers are capable of producing shocking experiences.
  However, when run at high frequencies, your first hint of bodily damage may
  be via your sense of smell - from burning flesh.  Keep clear!

Note: Ignition coils and flyback transformers can generate very high voltages
but must be driven by a pulsed or high frequency drive circuit.  These cannot
be plugged into the wall socket directly!

Also see the section: "Driving automotive ignition coils and similar devices".

17. Driving automotive ignition coils and similar devices

"I have some questions about automotive ignition coils.  I'm referring
 to the cylindrical "universal" type which has two 12 V terminals and
 one HV terminal in the center of the cap.
 What is the typical peak output voltage and current?
 What is the maximum average power input that such a coil can tolerate?
 I'm aware that the cross-sectional area of a transformer core dictates
 power handling capability.  Judging from the skinny core in a spark
 coil, I'd place the maximum continuous duty input at around 50 watts.
 Am I in the ball park on this?
 Is there an optimum pulse rate?
 Do ignition coils employ any sort of current limiting?
 Do "high-performance" coils with 45-75kv outputs offer significant
 increases in output power, or just higher voltage?"

(From: (John Freitag)).

First, be aware that the coil does not act as a transformer as such, even
so called "Hot Coils" have only a 1:100 turns ratio which would give only
1,200 volts from a transformer. If you were to energize the coil with an
AC voltage like you would with a transformer this is what you would get. 
An automobile ignition is more properly referred to as an "induction coil"
Its output voltage is defined, not by the turns ratio but rather by the
differential equation:

 V = L di/dt


 V is the output voltage
 L is the inductance in Henrys
 di/dt is the rate of change of current flow as the field collapses in the

V into an open circuit, will essentially rise until a spark jumps. When
the air ionizes and the spark occurs the remaining energy in the coil
sustains the spark.

Hot coils have a heavier primary so that they can pass more current, hence
a higher di/dt.

The maximum pulse rate is determined by the time taken for the current to
build when the points close (due to L it rises slowly until it reaches a
steady state) and the time for the field to collapse when the points open.
(the voltage to generate the spark occurs only after the points open and
the field is collapsing)

I have never thought about the power in the spark but I suppose it would be:

P = (L di/dt) ^2 / R  where P is the power in watts and R is the total
resistance of the coil secondary, the plug wire and the ionized spark
gap.  (Some Professor of EE is welcome to comment here).

As for current limiting, many coils employ a series resistor in the
primary which limits current and is shorted out during starting.

(From: Mark Kinsler (

I use a 12 volt battery and it works pretty well.  Probably the best
high voltage power supply for careless amateurs is the one I designed,
which could be found on my Web page if I knew how to do schematics but I
don't.  But it's simple enough.

I've been driving my old 12 V coil (bought as a replacement for the one in my
Econoline but never used) through a buzzer-type interrupter made from an old
relay.  I put a capacitor across the contacts for good luck, and for the most
part it works pretty well.  It'll give me about a 1/2" spark, which is all I
need for my illegal spark transmitter and the spark plug in my famous "One
Stroke Engine" demonstration.  However, it yields some amusing effects, to
wit: blue sparks dancing around on the battery lead and the battery itself,
extremely strange noises, copious production of ozone, and the occasional puff
of smoke.  I have the whole mess mounted inside a plastic 2-liter cola bottle.
On the advice of my friend Dewey King, who restores old gas engines from oil
rigs, I've purchased a Chrysler ballast resistor to put in series with the
battery and thus keep the coil healthy.

All you need to do is make a trip to the local auto junkyard:

Buy a used but fairly viable car battery, an old-fashioned ignition coil
(i.e., before electronic ignition came out in the '70's), an ignition
condenser (capacitor) from out of a dead distributor, and the heaviest 12
volt spdt relay you can get from Radio Shack.  DPDT is okay, too. 

1. Figure out how to connect the relay so it buzzes. 

2. Connect the capacitor across the contacts

3. Connect the primary winding of the ignition coil in parallel with the relay

If you do this right, the relay contacts will give a pulsating current through
the ignition coil primary.  You'll get a several hundred Hz, 12,000 V between
the secondary (the central tower of the coil) and ground.  It'll give you a
big surprise but it won't kill you unless you're pretty determined to do
yourself in.

I've found that only a car battery has sufficiently low internal resistance to
run the thing: my big old bench power supply won't do it.  So keep a trickle
charger on the battery.  It seems capable of giving a 3 cm or so arc depending
on conditions. 

(From: Pamela Hughes (

I did something like that only it plugged into the wall.  Don't remember the
circuit but it was a 33 uF, 630 VAC mercury vapor ballast cap connected to a
rectifier in a linear fashion (much like using a cap for an AC resistor only
the rectifier prevented bidirectional current flow...).  This was connected to
an 800 V, 6 A SCR and a neon lamp for a diac in a trigger circuit.  Adjusted
the trigger point so the scr would fire at a certain point in the AC cycle and
discharge the cap through the primary of an ignition coil.  If you adjusted
the trigger point right, you could get about 3" to 4" sparks.  Connected that
to a 40 KV TV rectifier and a cap made from a window and some aluminum foil
and to a 2" spark gap.  Wouldn't fire unless something was placed in the spark
gap, but then it went off with a bang that would put any bug zapper to shame.

BTW, I took the ignition coil apart, disconnected the common lead connecting
the primary and secondary and then used the secondary and core for a giant
sense coil for monitoring changes in magnetic fields... thing would make the
volt meter jump if you brought a magnet anywhere close to it, but mostly it
just fluctuated with atmospheric effects like lightning.

(From: Pierre Joubert

1. Use a monostable-based circuit which gives the maximum 'on' time for
   current in the coil.  As revs go up, many older systems produce reduced
   spark energy simply because the rate of rise of current in the coil
   prevents full current from being reached before the current has to be
   switched off.

2. Use one of the coils which is designed to operate normally with a
   series resistance, which is conventionally bypassed during cranking to
   help get a better spark on the reduced battery voltage.  But instead,
   limit the current in the coil to a safe value by setting a current limit
   around the switch transistor.  This prevents the coil overheating (which
   it would if you used it without the resistor in a conventional system.

3. Look around for the 'best' coil you can find; you might find a better
   match to your needs by using a coil from a different model or even make
   of car.  If you know the R and approximate L you can model the current
   buildup and estimate the energy available.  Generally the more energy
   the better, assuming that the transformation ratios of most coils are
   roughly the same, which was true way back when.

18. Mark's comments on high voltage lab conditions

(From: Mark Kinsler (

So how do you make your high-voltage laboratory safe?  Well, you just
assume that anything you build is likely to catch fire and/or arc over,
and design your lab space accordingly.  Stay out of the way of capacitor
strings, though when these blow up the shrapnel is generally pretty
harmless.  I've gotten stung by exploding carbon resistors, but again,
it's no big deal if you're well away from them.  In general, take the same
precautions with high-voltage or high-current components that you would
with small fireworks: avoid flammable environments and stay well away from
them.  If all else fails, take the stuff outside. 

My advisor at Mississippi State University observed that if you never 
damage any equipment and you don't have fairly catastrophic failures, 
you're probably not doing any research.  That helped justify the 6" crater 
I blew in the concrete lab floor (a record that still stands--his crater 
was only 4", though there were several of them produced at once.)    

19. Cheap sources of magnet wire

It has been suggested that transformers, inductors, and TV/monitor deflection
coils are inexpensive or free sources of magnet wire.  This may be OK for
antennas or similar applications where the insulation isn't critical.  However,
unwinding those coils may result in damaged insulation as the wire is peeled
apart since they tend to be impregnated with varnish. This makes the wire
unsuitable for winding new coils.  Unless, you have a way of dissolving the
varnish without destroying the insulation, the risk of a random shorted turn
or two (or many) buried beneath several thousand nice separate ones isn't
worth it!

However, a nice source of fine magnet wire is relays and solenoids - many
have very fine wire - #40 for example - and miles of it (well thousands of
feet at lest).  These are very often not varnished so they unwind easily
(just don't let them unwind all over your junk drawer!).

20. Plasma globes

A 'plasma globe' is  one of those things sold at Radio Shack and gift shops
which have a glass sphere containing a partial vacuum sitting on a power
supply base which is a high frequency inverter.  The pressure is such that the
discharge tends to take place in streamers rather than as a diffuse glow.  The
resulting display is supposed to be neat, nifty, interesting, etc.  When you
place your hand(s) on the globe, the patterns of the discharge inside change.

Recent Sci-Fi movies and TV series seem to have latched onto plasma globes
as high-tech replacements for the old-fashioned Jacobs Ladder :-).  (E.g.,
certain episodes of "Star Trek the Next Generator" and "Star Trek Voyager".)

One such product is called "Eye of the Storm".

It should be possible to construct these gadgets with salvaged flyback
transformers, power transistors, and a few other miscellaneous parts using a
large clear light bulb - good or bad, doesn't matter - for the discharge
globe (However, I don't know how good these actually are for this purpose).

Of course, purists will insist on fabricating their own globe (and official
ones can also be purchased at exorbitant prices as well).

As far as I know, these will work with just regular air (though the expensive
ones no doubt have fancy and very noble gasses!) and the vacuum is not that
high so a refrigeration compressor should be fine.

See The Electronic Bell Jar vacuum technology articles for info on
using refrigeration compressors as vacuum pumps.

However, since large clear light bulbs may also be satisfactory (though I
don't which ones to recommend), there is may be no need to mess with a vacuum
equipment :-).  And, of course, you have a wide selection of inexpensive types
to use for experiments, and dropping one or blowing it up isn't a disaster!

Excitation is usually from a high frequency flyback transformer based inverter
producing 12 to 15 KV AC at around 10 kHz.  Its HV terminal attaches to the
internal (center) electrode of the globe or light bulb.  The HV return is
grounded.  Ionization of the gas mixture results from the current flowing due
to capacitive coupling through the glass.

For a power source, either the "Simple High Voltage Generator" or "Adjustable High Voltage Power Supply" would be suitable.  See the document: "Various and
Diagrams" for circuit ideas.

However, note that its output must be AC so there must not be any internal HV
rectifier in the flyback transformer (which may be hard to find these days
since most flybacks have internal rectifiers).  (If a flyback with an internal
rectifier is used, the globe will just charge up like a capacitor which is
pretty boring after a few milliseconds!)

(Portions from: Steve Quest (

A $20 air conditioner repair hand-pump is fine.  If the colors of plain air 
are not 'pretty' enough, let me recommend what is used in commercial units: a
mixture of low pressure argon and neon.  If you want to be extra fancy, try
all the inert gasses, or a mixture of them all, helium, neon, argon, krypton,
xenon, radon. :)  Of course, radon may not be safe/legal, or even available.
You could just toss a chunk of radium into the globe, it will generate the
daughter isotope Rn(222) thus slowly, over time, enhance the color of the gas
mixture.  Just a thought.

The power supply needs to be dielectrically isolated (using the glass as the
dielectric), otherwise you'd have direct emission from the metal, and it would
be more of a light bulb than streaks of color.  Plus, people touching it would
feel a tingle while the dielectrically isolated is less likely to shock.  What
this means is that a direct connection to the filament lead wires is not that
great as you really want glass in between the driving source the center as well
as the outside globe.

* If you are making your own 'globe', one way to do this is to fuse a glass
  test tube into the center and coat its interior with conductive paint.  This
  then becomes the center electrode.

* For a light bulb (which isn't really recommended anyhow), you can try to use
  the filament directly or cut the lead wires as close to the glass as
  possible and insulate them with RTV or HV putty.  Then coat the remainder of
  the interior of the glass filament support structure with conductive paint
  to use as the center electrode.

If you cannot locate a suitable flyback, wind your own.  Tesla-style air core
transformers work.  :)

Written by Samuel M. Goldwasser. | [mailto]. The most recent version is available on the WWW server [Copyright] [Disclaimer]