I just built 3 of the 12volt conversions for the 40w tubes. These are the ones Bt Humble was talking about. They seem to work well enough. I got to thinking, I really want inverters for 8ft bulbs. In my storage box I had a 555 timer circut connected to a irf640n mosfet that I'm using for various experiments. I took the circut changed it to 18Khz @ 20% duty cycle approx and hooked it up to a modifyed ferrite switching transformer from I think an old tv. Next I hooked up an 8ft bulb applied power and I have a nice soft white light. I don't remember what the turn ratio on the transformer was but I will try to figure it out. I think this setup is as easy to build as the other and mosfets will keep going long after a transistor has died.
Cool! I've got vast numbers of ferrite transformers from old PC power supplies, but the windings are all wrong for what I'm trying to do with them.
2 2n3055s died in the first attempt to get the 40watt units going somthing about the ferrite transformers was out of whack. I think this is a good circut idea but could probably use some input from sombody who knows more about designing circuts than I do.
The trick is in the "feedback" winding. If it doesn't light immediately when you connect the power, you need to reverse the way you've connected it to your circuit. You also need some good heatsinking on the transistors, or they'll suffer badly.
I've since discovered that the TIP31C I was using on the 15W versions doesn't work for the 40W ones. I've now got a pair of 40W tubes lighting my shed, using some unknown transistors salvaged from a PC power supply. They're only drawing 2A, but they get pretty hot.
Thanks for the news, I'm glad that my work was of some use! ;-)
BTH