Written by Richie Burnett

The 2000 UK Summer Teslathon organised by Alan Sharp, took place at Corby on Saturday 27th May.

This year's event was host to 5 Tesla Coils, a Large Van de Graaff generator, and a display of various Vacuum / fluorescent tubes. There was also a new UK spark length record and over twenty high voltage enthusiasts from across the UK.

As usual the weather was bright and sunny on the day, so it was hard to get good conditions for photography, but there was no shortage of bright long arcs !

Bob Golding and Nick Slaymaker built this coil which uses a large secondary capped with a beautifully finished 24" spun aluminium toroid.

The coil was powered by an externally ballasted 8kv radar transformer and made use of a multiple static gap with forced air cooling.

It produced some very powerful discharges to a grounded target, which were sustained for a long time without any decrease in spark length sometimes found with static gaps.

Who needs a rotary !


The coil used a thoughtfully constructed primary capacitor of the MMC type. It consisted of a frame with copper rings at each end, into which capacitor strings could be clipped to quickly obtain the desired tank capacitance.

Each white plastic tube contained ten 47nF 1500V capacitors wired in series. There was space on the frame for up to 20 strings giving a maximum of 94nF tank capacitance.

Click here for a close-up of the connections.

Bob explained how this design gave him the flexibility of being able to tune with either the primary coil or primary capacitance.
Nick Slaymaker (left) and Bob Golding (right) considering the next adjustment to their coil…

The coil was later run with a 390BPS async rotary and performed well.

Maximum spark length was 72" on the day.

Steve Rodway pictured next to his coil.

This coil uses an inclined primary winding which is mounted on a box containing the spark gap, primary capacitors and wiring. An additional metal enclosure contains ballasts, metering, and control electronics.

The toroid of this coil uses an unusual construction technique. It consists of an internal frame which is covered with many copper wires spaced 5mm apart to form the surface of the toroid.

Steve has found this method of toroid construction to be very effective provided the wires are spaced no further than 5mm apart. The resulting toroid is very light and has a unique appearance.


This is a picture of Steve Bell's Tesla Coil.

This coil was fitted with a 24" polished aluminium toroid, which was just on the verge of breakout.

During this demonstration the coil would sporadically let-rip with very noisy discharges of 5ft or more. After breakout the streamers would slowly drift over the smooth surface of the toroid.

Very exciting to watch. (From a safe distance ;-)

This coil also triggered a car alarm outside the church hall when the breakout was suppressed !

This photograph shows the components of Steve Bell's Tesla coil.

Power is provided by a 10kv Neon Sign Transformer at the front of the base. The MMC style primary capacitor can be seen at the far left, and a multiple static gap can be seen at the back.

Grounding is via a thick copper strip leaving the right of the picture.

A long xenon tube with one end grounded was placed within striking range of Steve's coil. The blinding flashes of light which result are captured below…

Tim Davey setting up his Van de Graaff generator. The box at the base contains control electronics and a powerful electric motor. There is a belt running up the plastic tube to the discharge sphere.

The operator pulls 18 inch discharges from the sphere on top of the generator to a hand held metal target.

As the arc distance got greater his arm began to jump more at each discharge. Eventually the metal target became further from the discharge terminal than his head, and he got a surprise !

Do not try this with a Tesla Coil.

Mike Tucknott experiencing problems with fly-away hair,

Mike stood on an insulating crate and placed one hand on Tim Davey's Van de Graaff generator.

As the charge built up over several seconds his hair took on that Medusa appearance. After a round of applause he was then safely discharged.

Richie's Tesla Coil. My TC consists of a 4" x 21" secondary, topped with three toroids. The uppermost toroid is 24" x 4".

The TC is powered by an externally ballasted 9.6kv radar power supply, and uses a 200BPS synchronous rotary spark gap.

It was planned to run this TC up to 2.4kW at the Teslathon, but the absence of nearby garage walls caused long arcs to curve inward and strike the primary.

(Photograph provided by Bob Golding.)

The picture opposite was taken during setting up before the Teslathon.

Maximum spark length was around 58 inches using the synchronous rotary, although power had to be limited to 1800 watts because of severe arcing to the primary winding.

Click here for more technical details about this Tesla Coil.

During testing an arc from the left edge of the toroid, struck the rotary gap motor. This arc caused a winding to fail open circuit and the sync rotary could not be fixed. For the Teslathon on the Saturday I was leant a 390BPS asynchronous rotary. (Thanks Mike and Steve.) My coil actually hit a new spark length of 66 inches with Mike's RSG. Nice gap guys.

Alan Sharp measures the distance from his big Tesla Coil to a grounded target before an attempt at the new UK spark length record.

The entire TC stands about 7ft high, and is powered by 8kv radar power supply transformers.

The coil made use of a large asynchronous rotary spark gap, and up to 200nF of primary capacitance.

Power was supplied via a control box and variacs which were off the left edge of the photograph.

7 foot streamers from Alan's Tesla coil captured on film during setting up, late at night.

The video clip below shows more spark action from this big coil during setting up.

AVI movie (344kB) 8 seconds with sound.

For best viewing download the AVI file to disk and than play back at Double Original Size.

Alan made a few more tuning adjustments and the spectators enjoyed an 8 foot ground strike, and a lot of noise.
Power control was via two voltage variacs and two fixed ballasting inductors, in order to safely share the running current between two mains outlets.

Later a third variac and ballast were added to make the 10 foot arc a possibility.

Alan Sharp, Bob Golding and myself stood behind the table and manned the controls. All three variacs had to be kept reasonably synchronised so Alan called out "20… 40… 60… 80… 100" as he increased the variac setting. We didn’t hear anything past 40% because of the incredible noise !

Occasionally a streamer from the coil would finish quite close to the operators, so a grounded wire was arranged in front of the operators for safety.

A ten foot ground strike,

A new UK spark length record of 10 feet, (3 meters) was achieved by Alan Sharp in front of about 20 onlookers.


Corby 2000 Teslathon lineup.

More pictures from this years event (and previous events)
can be seen at Mike Harrison's web site.

Corby 2000 UK Video tape:

UK coilers can purchase a 40 minute amateur video of the event, (from which these pictures were captured,) for a cost of 5 pounds, (This includes the PAL VHS tape and postage.) If you are interested please contact Richie Burnett.

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