All the various, and usual Gaps.

The Static Spark Gap

The static spark gap can take many forms, from a single unquenced simple gap to the famed quenched gap(uses perhaps a hundred gaps in succsession). For most, I think, the gap should take a less esoteric form; either an adjustable simple gap or 3 to 5 gaps in series, depending upon the transformer you choose, will do fine for most small coils. For a 6000Vac transformer, use the adjustable simple gap. For a 7500Vac one, use 3 of the "L" gaps in series. For using 9000Vac, 4 should be adequate. 12000Vac may require 5 or 6, and with 15000Vac you should use as many as you can(but don't go crazy here- remember: the greater the number of gaps, the slightly the lower the voltage accross them)

The adjustable simple gap

[gap] This a single gap whose distance can be changed by the turning of one of the terminals.

The "L" brace gap

[gap1] This gap employs pairs of steel "L"-shaped metal braces. They have 2 holes in each leg of each halve, so they are ideal, with seccuring them to the wood and electrical connection made easy.

The "Richard Quick"-style Gap

[IMAGE]
This is an example of a beautifull evolution of the static gap, and is a prime choice for any coil above a few hundred watts. I essentially consists of a series of copper pipe sections secured on the inner side of large-diameter PVC (or other insulating plastic) pipe, so the arc arcs between the pipes along their longest dimension. Most often the thing has a fan mounted at on end to pull air throught he gap, cooling it and removeing ionized gasses.

I used to use this kind of gap for my bigbaby coil.

Rotary Spark Gaps

The best style of gap, in nearly any situation, must be the rotary gap. This is a setup where at least one set of electrodes are mounted on a spinning rotor. They electrodes align at a point controlled by their number and the speed of the motor. Rotaries come in two general varieties, synchronous and asynchronous.

Synchronous Rotary Gaps are ones that use an AC-synchronous motor, usualy salient pole. This means that the speed of the motor is locked into the frequency of the input power, 60Hz in my case. This means that the electrode alignment will always occur at the peak points of power (or wherever you set it) along the sine wave.

Asynchronous Rotary Gaps are simply those gaps powered by motors that don't lock onto the 60 signal, usually, they will be driven by a variable speed motor, and the optimal speed will usually end up being where it is mimicing a sync gap. The advantage to using an asynch gap are the smaller motors needed, and the much higher rotational speeds attainable. It is muych easier to run a gap on a universal motor capable of 10,000 rpm than to try to find a synch motor of a similar speed.

As a general rule, one should not use rotary spark gaps with neon sign transformers. They stress them to usually the failure point. The one exception to this, it seems, is using 2X reso capacitance, and a gap set to fire just after peak on the 60Hz wave. This most aften referred to as an LTR system , standing for Larger Than Resonant, in reference to the capacitance. It reduces the volatges present in the primary system, with increasing the power factor, and usually increasing output spark length from the secondary.

[rotary diagram]

I've recently completed a synch-rotary, and it works wonders with the BBC.

Air Blast Gaps

-later-

"But I don't want to go to the metals room! I wanna play euchre!" Jordan, complaining as I dragged him off from lunch to help me with something HV-related.

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