Theres some of these type ballasts in a broken moorlite fitting i have up in the loft.... Hmmmm.... also the fittings in the factories had some

So the longer the tube do you put a bigger capacitor in

No Danny, surprisingly it's the same components for all. The 8.4uF is normal for 5' and 6' but 8' normally used a lower value at higher voltage. I didn't want to risk a 250V capacitor so got 450V. I don't think this setup really boosts the voltage enough for 8'. It's marginal, but once started, works well.

Hmmmmmm! I may have to try this!!!

I've got a couple of these ballasts, completely forgot I owned them and I have an 8' 85w lamp to test!! I know what I'm doing next chance I get...

Wonder how well a Thorn 6' 85w SRS ballast would run a 8' 85w tube?

If it's an 8.4uF capacitor, why not try?

Still haven't got around to rigging up my Parmar ballast & 8' 85 watter. I have some SB (Thorn) 6' 85w SRS ballast's too, I'll experiment with one on 8' 85w

Most 65W 5ft 75W 6ft 85W 8ft SRS Ballasts can run each other tubes, SRS ballasts are a relatively constant current ballast (ie they keep current the same regardless of arc voltage) and 65W 5ft, 75W 6ft, 85W 8ft all share relatively close currents hence why the SRS ballasts all share the same capacitor value and can run each other tubes, I have closely monitored running a 85W 8ft tube on a 65W SRS Smart brown (thorn) ballast with no ill effects (never had any issues starting too even un earthed, gave a nice fade in)

Thanks LBF, good to know