The 30W T8, isn't a retrofit tube. It is just a reglar T8 argon lamp, that intended to operate on a 30W T8 ballast.

The 30W T8, isn't a retrofit tube. It is just a regular T8 argon lamp, that intended to operate on a 30W T8 ballast.

What I mean is F30T8 retrofits F30T10, which is rarely being used in here nowadays
F30T10s were everywhere several years ago, but most of them are being replaced by F30T8 now

I'm pretty sure that they also had something like the f30t10, but for 40w tubes. The f40t10 tubes were better and brighter on preheat ballasts. Once rapid start became hip, f40t10 tubes all but faded from existence.

Thanks to all!
What about T10 lamps? What were their purpose?

Dont know. But i have a few F40T10's from the early 2000s, made by the same Chinese manufacturers that make the emitter-less T12s with the misshaped end caps that band up and EOL within a few years

Thanks to all!
What about T10 lamps? What were their purpose?

I think T10 was kind of improved version of T12 with better efficiency but still maintaining compatibility with RS gear (unlike even more efficient T8)

Roi is right. You could find more f40t12 preheat ballasts rated for t10 and 12. I have several ballasts like that. Now I need to get my hands on some t10 tubes.

Here we only have limited choices of retrofit tubes in Hong Kong

Tubes currently available here (T8, T10 and T12): (retrofit tubes are marked with "#")
F10T8 (330mm, 0.23A)
F15T8 (450mm, 0.31A)
F18T8 #
F20T10
F20T12
F30T8 # (900mm,0.36A)
F30T10
F36T8 #
F40T10 (1200mm, 0.45A)
F40T12 (1200mm, 0.45A)
F58T8 # (F65T12 is long gone)
All type of T12 Slimline tubes (interior lighting for public buses with Duple Metsec DM5000 bodywork only, no one uses Slimline tubes for general lighting in their home )

Tubes NOT available in Hong Kong:
All standard G13 tubes longer than 5ft
All HO tubes, excluding T5 HO
All VHO tubes

list updated 

You guys still have t10? They are rare ish here in the US.

Can I ask what is a starting compensator? What does it do?

Solanaceae :
We had here few off batches of 40W T10's Daylight Halophosphor in the early 2000's, all from cheap Chinese manufacturers. I have a couple EOL ones somewhere

Hannah :
The ballast determines the lamp current. It have to supply the correct current in 2 different modes :

 - Normal working of the lamp : At the normal arc voltage drop on the lamp, the current have to be what the lamp is made for. The current in this mode got to be quite precise value for correct brightness and long lamp life

 - Preheating : At about 0V drop on the lamp (shorted starter), the current have to be what is required to heat up the cathodes to thermionic discharge, but not too high to not overheat them and burn off the emitter coating. Here it is not required to be precise, but still in the acceptable range

The ballast is designed along the lines of what happens in normal working mode. The wanted current determine the inductance of the choke, the secondary coil in the lag side of a lead/lag ballast, or the coil & capacitor parameters in the lead side

Then when the ballast parameters are determined, the preheating current will just be what it comes out to be..... It so happens that for chokes and lag circuits it usually is in the acceptable range, so its left at that

In the lead circuits it sometimes ends up being way off, and a "correction" is required. The correction could be by adding or subtracting few turns off the secondary coil to get the correct preheating current. The extra turns can be wound in the same direction as the coil to add or backwards to subtract

For the added or subtracted turns to not change the normal working current (which we allready got right), the coil of the additional turns is wired in series with the starter, so only has effect in the preheating mode. When wiring the ballast up, the starter of the lead side goes through the ballast as well (to the wires intended for it) and not straight from end to end of the lamp

The last t10s I've seen were Westinghouse on here. Interesting that my magnetek RS ballasts from the 90s are rated for them as well as the t12 counterpart.