This is a 6500K Octron 13 watt 18 inches. Wonder what the CORRECT ballast would be to run this on ?  I am using this in my manual preheat desk lamp. I am sure it is some over driven, but the aging looks normal, and it sure is bright !!!!

Also I have a HF ballast that will run F17 through at least F32 T8 lamps.  Will a F20T12 run on it acceptably? I may have to make a test fixture if I can't find out.........   

This is a 6500K Octron 13 watt 18 inches. Wonder what the CORRECT ballast would be to run this on ?  I am using this in my manual preheat desk lamp. I am sure it is some over driven, but the aging looks normal, and it sure is bright !!!!

Also I have a HF ballast that will run F17 through at least F32 T8 lamps.  Will a F20T12 run on it acceptably? I may have to make a test fixture if I can't find out.........   

Try following:

1) Connect one of the filaments to 3.5V voltage source and measure the current Ifil.
2) Multiply this by two and you hen a raw approximate of the designed lamp current Iraw = 2*Ifil
3) Estimate the arc voltage: Vraw = 13W/Iraw/0.9
4) Find a ballast capable to feed the desired ballast voltage with a current between Iraw and Ifil.
   - If the estimated arc voltage would be below 60V, F15T8 series choke ballast would be good, in series with the lamp and in a "manual preheat" circuit.
   - If the voltage would be between 50..90V, use a combination of F4..8T5 choke plus 2.7uF/250VAC capacitor in series, all in series with the lamp and in a "manual preheat" circuit
   - If the voltage is 80V or above, use F13T5 ballast, connect as "manual preheat"
  This should light the lamp after few "preheat" trials. If the lamp electrodes glow, but the lamp only flash when opening the "starter" switch, go to "one step higher voltage" setup and retry.
5) Start the lamp in one of the previous circuit and measure the arc voltage Vnom by a "true-rms" AC V-meter.
6) Calculate the nominal lamp current as Inom = 13W/Vnom/0.9
7) Find a ballast feeding the nominal lamp current (you may use one of the previous circuits, if it feed the correct current, but check with an A-meter). The ballast current may be in the range of 60..110% of the lamp nominal current.

You should post a picture! Is it an energy saver lamp or something!?

Q1 lamps can tolerate inexact power, driving ~15-16w (its not as simple as that but close enough) into 13w lamp is not too bad, but it might last somewhat less than if driven at 13w

Q2 I think the F20 will be fine

Q1 lamps can tolerate inexact power, driving ~15-16w (its not as simple as that but close enough) into 13w lamp is not too bad, but it might last somewhat less than if driven at 13w

Q2 I think the F20 will be fine

Knowing the wattage alone is by far not enough, as you have to pretty well match the current and have sufficient OCV.
The F20 ballasts belong to the higher current ones, so are of higher risk to significantly overdrive the filaments...
If it is 0.16A lamp, the F15 ballast would overdrive it quite a lot during preheat (there the current could rise up to 0.4A)...

The 3.5V test show, what current the filaments could safely handle, at least for short term.

From the description the lamp is overdriven, so the current in it is highre than supposed to be. How much hihger ? The arc v on the lamps is probably not too far, so the vdrop on the ballast is close. As such the current in hte 13w lamp would be about same as in hte 15w lamp. Maybe 16w for the somewhat higher current due to increased vdrop on hte ballast

This appears quite consistent imho with what we know about the aging of the lamp - its not aging fast so not overdriven much

1000 bulbs says the bulb draws 265 ma. I will try the 20 watt bulb on instant start for F17

1000 bulbs says the bulb draws 265 ma. I will try the 20 watt bulb on instant start for F17

Then use the "PL-S 13W" ballast, it is about 0.21A, what is not that far...

Is that the energy saver version of the f15? I've also seen a 24in 15w lamp as an energy saver version of the f17/18t8.

actually its the electronic version with 4.5V RS cathodes instead of preheat cathodes 9V
..I have one in my collection

I've also seen 21W 3FT T8s

Would it work with a f15 choke that is rated for .3a? Those are the chokes from the goodwill lamps.

0.3A is about 15% overdrive (compare to the 0.261A rating), it may work.

I'll have to check, but will a 13w pl choke run this too (on 120v)?

I'll have to check, but will a 13w pl choke run this too (on 120v)?

The PL-S13W is a 0.22A, so it should be spot on...

Thanks. I also have several ballasts that are rated on 12-22 t5/8/12 ballast, so I think it would work.