Here is my little project, of modificating old preheat FL fixture to rapid start by adding "starting transformer" Original idea by Medved. I thought maybe somebody here want to read it too so I made this site. check the link below.

http://www.arktikprospekt.com/RS/RS.html

Edit 1:There seems to be some problem with pictures. Im trying to fix it.
Edit 2: picture problem fixed. Should work now.

Good idea. I had some fittings that used to have the transformers in them, but they all fried many years ago, and were replaced with boring ferroresonant ballasts. Some were left in , but leads were cut short, leaving crispy insides to lie there.

I would guess the reason you get different voltages is the capacitor causing a phase shift, you might try using it directly across the tube, but use a lower value, like 0.22uF.

The transformer would probably be better if it was 3VAC, around 10VA rating, using 2 separate transformers preferably a centre tapped one with the power being applied to the centre tap and the tube to the outer ends. This is because most small transformers are not rated to have a high voltage between the 2 secondary windings, unless they are designed for this specially. You would wire the primary windings in parallel after the ballast choke, as this will reduce the heating of the cathodes once they are lit.

For display signs that switch flourescent tubes on and off rapidly you get a special transformer that allows the heaters to be powered all the time, with the ballast being powered separately via the flasher. This allows rapid flashing, but does not strip the cathodes, as they stay hot. It has a single high current secondary supplying the neutral of all the lamps, and separate high end windings for the lamps.

BTW, very nice ASCII art for your diagram there.

that ASCII schema is actually made by Medved.

Capacitor? What capacitor? there is only one capacitor and thats purpose is to remove any interference caused in startup not correct the powerfactor. you mean that capacitor?

Im not sure if I pictured your transformer idea right so could you draw somesort of schematic too. hand drawn is enought. If I remember right I have heart that old FL fixtures with dimmer may use separated transformer to heat electrodes and in finnish this was called hehkumuuntajakytkentä. I dont know what it is called in english but to translate it directly would mean something like heater/electrode transformer connection. Iv never seen actual connection but my old school did have couple place where they used dimmable FL. I used to play with those lights.

The reason I used this transformer is that it was only model I had right now. In here Rovaniemi there are not any shop that sells electronic components so I have to order everuthing via mail.

The 1uF capacitor across one of the transformers causes phase shift, possibly ceating a voltage disbalance on the two transformers. I don't know what is its purpose, but it should work without it and you should get the correct voltages on the filaments.

The 1uF capacitor is there to boost-up the OCV of the ballast a bit (~10..15V), to aid starting. It is connected to the transformer middle to add some serial impedance between this cap and the lamp, as discharge lamps don't like directly connected capacitors.

Project complete. Check link in first post and scrol page down to see it.