Unusual MasonLITE neon tube PSU (with schematic)

Masonlite was an iconic British supplier of neon equipment when the neon sign industry was at its peak. I think they may still exist in Dubai, but their UK base seems to have faded.

This is a very unusual power supply for short neon tubes. When I say "neon" I actually mean the argon/mercury variant, as the mercury vapour seems to ride out the sine wave zero crossing point better than pure neon with this style of power supply. (Pure neon starts to cut in and out when it has warmed up.)

Note that during this video I did have my hands in the vicinity of high voltage mains referenced electrical connections. Making contact with the output of these units will (in the words of Dirk Boonstra) "Blow all the hair out of your head." I have always been aware of the position of my hands with respect to the live connections to avoid testing this theory.

When I first came across these modules I was intrigued to know what was in a wall-wart style plug-in power supply. I managed to get a hold of one and then explored it thoroughly. I also managed to restore the faulty tube I got it with, since it had been affected by mercury migration due to the use of DC current. It lattery turned out that Masonlite sold these bare resin potted modules for use in freestanding neon ornaments. I'm not sure if they were designed in-house or rebadged.

When I'd sussed out the operation of the units it launched me on a very long and ongoing neon obsession, making my own minimalist multiplier power supplies and getting custom tubes made at a local Glasgow company called The Neon Workshop. It's notable that the manager of the workshop (Donald) was a veteran of the sign industry who had worked for Glasgow's equivalent to Las Vegas's YESCO - namely Franko Signs. In hindsight it would have been good to record our conversations as they painted an interesting image of that era in signage.

The number of higher value multiplier stages dictate the length of tube that can be powered. The original could drive a few feet (about 1m) of tube, while my simpler single stage version is good for about 2 feet (600mm) of tube. I also made a few animated versions which had several multipliers and a control circuit to allow one PCB to power and animate several tubes.

While running argon/mercury tubes on DC is very simple, it does have some disadvantages. The tubes can take a while to bed into a DC supply, starting off flickering slightly but quickly settling in and working fine. The mercury will gradually migrate from one end of the tube to the other, resulting in one end of the tube darkening over time. That can be fixed my shaking the mercury droplet back, or swapping the polarity. The extra slim version of this power supply for illuminated posters has a polarity reversal switch for that reason.
If using with a vertically mounted tube the orientation can be chosen so that the mercury always drops back down to the bottom under gravity.

I think the main joy of these power supplies is that you can rough a power supply together from standard components with no fancy high frequency transformers. This also makes them VERY reliable.

An interesting effect of running tubes on DC is that one electrode (the cathode) does all the work. It's the only electrode that gets warm.

With the proliferation of linear LED based light sources, it's become harder and harder to get custom neon tubes made. The process is a specialist art and requires complex and expensive equipment including high vacuum pumps, gas dosing manifolds and very dangerous high voltage bombarder units that heat the tube by passing high current through a near vacuum.
It has become an art medium, and any working tubes you find should be treasured accordingly.

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