Here I demonstrate an interesting difference in behavior of two coils. One is a standard flat spiral pancake coil, the other is a Tesla bifilar pancake coil. The coils are assembled in a stack with about an inch of space between them. First I use the standard spiral coil as the “transmitter”, wired as a primary in a standard Tesla spark-gap system, with the Tesla bifilar as the receiver or secondary. The secondary develops a small spark at an improvised gap, but doesn’t fire it consistently. Next I reverse the coils, using the Tesla bifilar as the primary or transmitter, and the standard spiral pancake as the secondary or receiver. The small spark gap is set at fully twice the gap as before, yet the system has no trouble at all firing the gap consistently. The two coils are identical in wire type, length, number of total turns, and are very close in measured inductance. This result is intriguing; I will make another identical Tesla bifilar coil to use as a receiver or secondary. Will the performance improve still more if both coils are the Tesla bifilar type? EDIT to add: The smaller gap (single washer spacer) is 0.075 inch, the larger (2 washers) is 0.150 inch.
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