Power Supply and Filter


The first power supply I used is a 12,000V 60mA Transco neon sign transformer. On top are PFC caps (138 mF total). Barely visible between the two flat pieces of HDPE is a line filter and fuse. A 0-140 V variac (not shown) is used to gradually apply power to the NST.


Here is the now-familiar "Terry" filter to help protect the NST.

I later added a second safety gap on the other side of the filter components.


Here is a closer look at one of the safety gaps. The larger pieces are brass bar, cut to shape and drilled to accept .125" tungsten carbide drill blanks as the gap electrodes. The electrodes can be adjusted and tightened into place with the set screws on the top.


When my NST failed after a couple hours of service, I decided to build a MOT-based supply. Here are some pictures showing the various stages of construction. It is made from four MOTs, with the outer MOTs chosen for their high secondary-to-core spacing. The primaries were connected in parallel and phased to give maximum secondary voltage. The cores for the inner MOTs were connected and grounded. The cores for the outer MOTs were disconnected from their secondaries and were left floating. The MOTs were mounted on HDPE disks cut to fit snugly inside a 5-gallon paint container. A pair of handles on the top provided a (relatively) easy way to lift the assembly (nearly 50 pounds) and place it into the container. The container was then filled with transformer oil. The wheeled cart provides easy transport around the basement and was designed to have sufficient room for mounting a line filter, switch, fuse, two MOTs for ballast on the primary side, and five 1mF MOT caps per secondary leg for secondary side ballasting. Jumpers allow the ballasts to be configured in various ways. A test of the supply (using a high voltage probe) with secondary open and no ballasting indicated an output of 8800V with 120V input.

Here is the entire MOT supply set-up, with PFC caps on the far left, ballast MOT on the left top deck, ballast caps on the right top deck, and the safety filter on the floor (far right).