there are a couple of versions - first the simplest series choke an starter, just like a 4ft tube,  herer the cap is just accross the mains as a power factor correction, a sort of impedance match between the 230V mains and the 150 or so of the tube once struck.

Better, especially in cold weather, were the ones with the ballast more like a tapped transformer,  so the heaters had their own windings. and the strike voltage was a bit  higher. Again cap for PFC.

Then there were resonant starters, where the cap has to be matched to the series choke and tune to 50Hz - here the cap goes where the starter would. and as the series resonance builds, the voltage on the tube rises, as does the filament current, until something strikes, or the filaments blow open cct. Very fast to strike, but needed cap and choke to be a matched pair and no good on gensets with poor frequency control.

Mike

there are a couple of versions - first the simplest series choke an starter, just like a 4ft tube,  herer the cap is just accross the mains as a power factor correction, a sort of impedance match between the 230V mains and the 150 or so of the tube once struck.

Better, especially in cold weather, were the ones with the ballast more like a tapped transformer,  so the heaters had their own windings. and the strike voltage was a bit  higher. Again cap for PFC.

Then there were resonant starters, where the cap has to be matched to the series choke and tune to 50Hz - here the cap goes where the starter would. and as the series resonance builds, the voltage on the tube rises, as does the filament current, until something strikes, or the filaments blow open cct. Very fast to strike, but needed cap and choke to be a matched pair and no good on gensets with poor frequency control.

Mike

Thankyou mapj1 thars very helpful