The Turn Of The Century Electrotherapy Museum
(C) Jeff Behary 2006

1/4 KW Floor Model Adjustable Frequency Tesla Coil Demonstration Apparatus:
Test I: 16" Pancake Coil

Click here to see a movie of this coil in operation.

Power Supply:  Approx. 4000V 0 - 62mA Transformer
Adjustable Condenser, .001 - .127 mfd
Optimum capacity:  .064 mfd
A. S. Aloe 3/8" diameter Tungsten Spark Gap (Thanks Frank!)

16" Pancake Coil.  Secondary approx. 14" diameter, 750 turns of 30 AWG
Electric Discharges:  8" Branching discharge
10" Spark Discharge
2 - 3" Effluves

Branching discharge was unusual in that static breezes and charging of remote pieces of metal was noticed
in the vicinity of 12" - 14" from the terminal.   Occasional single sparks would pass at these lengths. 
Nasty static shocks occurred when touching these items after the unit was powered down.
Depending on the adjustment of the spark gap, the air surrounding the terminal would also squeal and screech not unlike the sound heard
when a static machine is on the verge of discharging.

At low input power (~ 35mA) and a wide open gap (appearance of a single spark passing each second)
3" well-defined positive forked branches appeared , with the slight appearance of 3/8" to 1/2" feathery negative discharges at the ends of the branches.

At input powers of around 50 watts (~ 12-15mA) (and a silent spark gap less than .001") sparks 3/8" to 1/2" could be drawn from the terminal.

During extended operation (62mA) an unknown air-pocket located 1" from the outside of the secondary caught on fire and left a 1" black charred hole in the coil.
Discharge length dropped to 6".   Coil is now in the trash can, and rewinding will begin later on in the week.
 The new secondary will have fewer turns of wire and oil insulation.

UPDATE:  Here's the new coil in action!
Click the picture below for movie clips in operation!