I recently bought this ozone generator (enaly OZX-300AT - 220 volt version) of ebay - it uses 2x  4" long stainless tubes acting as anode/cathode - one inside the other. The air is pumped into the gap between these tubes exiting on the left outlet.

There is no forced cooling on this unit & the transformer is is small cast iron horseshoe design.

Ive posted this because Im interested in the design and may be helpful for others looking at buying a cheap ozone generator (cost me £55 new) and would at some stage like to build my own based on a cold cathode oxygen fed design after reading through this and Hv's forum.

So far, I'm getting a lot of use out of this generator and its proving reliable. Its great for ozonating water and disinfecting appliances, clearing odors from rooms, cars and deodorizing footwear and clothing and I love the smell that remains afterwards - concentrated fresh air!

could do with a more powerful unit though!

The downsides to this unit is that it uses lots of plastic & pvc tubing rather than silicon tube , the pump is one speed - a variable speed pump would be more useful.