Static gaps can take several forms. The most basic is just two electrodes
spaced a small distance apart. This can be the heads of two heavy bolts
or two brass knobs from the hardware store.
This is an easy gap to implement and will serve Ok for the beginner.
The spacing between the electrodes depends on the power supply voltage
from your transformer. 9kv neons do well with about .150 inch of gap
while 12kv neons can use up to .200 inch. 15kv neons can use up to .250
inch. Wider gaps than this should be avoided as they put a great deal of
stressn your capacitor and transformer.
The single static gap while easy to build is a poor performer.
All the heat is dissipated in one area and the gap doesnt want to quench.
The hot ions in between the gap electrodes tend to keep the gap lit
at lower voltages. Blowing air through the gap with a fan or blower
will improve the operation of this type of gap by removing these hot ions.
A much better approach is to break up the single large gap into a series
of smaller gaps in series. This is called a series static gap. This divides
the arc up into smaller parts that develop less heat and operate more
efficiently. This type of gap also benefits from a little forced air to
remove hot ions.
One such gap popularized by Richard Quick and often referred to as the
RQ cylinder gap consists of multiple electrodes made from lengths of
hard copper tubing. The electrodes are usually made from 3/4 or 1 inch
copper tubing cut from 2 to 4 inches long. Larger and longer elctrodes
provide more thermal mass and handle the heat better. These electrodes are
mounted inside a piece of PVC pipe and spaced about .025-.03 inch apart.
7 such electrodes providing 6 gaps between then are normally used for 9kv neons
and 9 electrodes providing 8 gaps are used for 12kv neons.
Up to 11 electrodes with 10 gaps can be used for 15kv neons.
A small muffin fan is mounted on the end of the PVC pipe holding the electrodes
to provide cooling airflow.