I have always wondered exactly how a tulamp preheat ballast works.  I wonder if they are really just two one-lamp ballasts wired in series and housed in the same unit?  I have also wondered if tulamp preheat ballasts were ever made for 20 watt fixtures.  Does anyone know?
It has been a curiosity of mine for awhile!

Hey Brain,

Preheat Tulamp ballasts are lead lag types.  Inside those things is a primary coil, two secondary coils (one lead, one lag), starting compensator (the earliest ones used an external one), and a capacitor. The capacitor is connected to the lead coil, and the lag coil just lags along on the current that is generated by the lead coil. They're parallel wired tho, that's why such ballasts can operate 1 or 2 lamps. The starting compensator doesn't directly connect to any of the internal ballast components, but are connected to one fluorescent lamp (lead side I believe). During starting it lowers the power factor for easier starting. So Tulamps are quite a simple design!

Hope this helps!

where could u get one?

I think they aren't manufactured anymore... last too long.

Hi Brian. Yes, tulamp 20 watt preheat ballasts certainly did exist. Many years ago I had a few half-pipe 2x20 watt preheat fixtures with tulamp ballasts. Unfortunately my late father who didn't  appreciate my lighting hobby tossed them in the trash while I was busy with other things.