i was wondering if i could make a slimline ballast by winding a 230->600V (or more) transformer or auto transformer and then connect to the transformers output some 3 230V ballasts in series and then light up a slimline lamp (or if someone can help me with the theory behind this i could also make a specific high voltage ballast for this project)
thank you very much

You definitely have to start with finding out the exact tube parameters - like burning voltage, OCV required, heater voltages & currents.

RRK: i would like to make a F42T6 ballast which if i’m not wrong operates at 200mA 125V. heating cathodes isn’t required (and isn’t possibile) since it is a single pin slimline fluorescent tube. i think OCV is something between 600 and 900V

230/230V isolation transformers are useful to make multiples of line voltage. You connect primaries in parallel to the line, and connect secondaries in series with hot (live) wire of the line, adding a bootstrap voltage. You need to get phasing right. If not right, the voltages will subtract, but nothing will blow. With a single transformer you will get 460V, 690V - with two.


For the ballast, a staple is to use some series/parallel combination with off-the-shelf chokes like 18 or 30 or  36W ones until you get an approximately right impedance. Confirm this with tube current measurement. You should not saturate the chokes with overvoltage. Approximately this means if you use triple line voltage, you need 3-4 of standard 230V chokes in series.

Be careful! Multiplying line voltage makes things really dangerous!

Here is a quick Kicad sketch of what I mean. Points at transformer windings show phasing. Connecting a capacitor to somewhere in chokes series midpoint can make the circuit somewhat series-resonant for even more OCV, but is rather tricky!

Again, be careful with this!

Here is a proper spec sheet for this strange tube. It needs only 405V for instant start, so a single bootstrap transformer will be enough. I would start with four 36W chokes in series, three will be probably about right. No need for a resonant capacitor, but with proper tuning it will probably make this circuit to start f42t6 tube even without step-up transformer at input.
 

Here is a quick Kicad sketch of what I mean. Points at transformer windings show phasing. Connecting a capacitor to somewhere in chokes series midpoint can make the circuit somewhat series-resonant for even more OCV, but is rather tricky!

Again, be careful with this!

thank you very much RRK  i think i’ll try by winding a 230 to 460V transformer and using 2 36W ballasts in series

ahhh this brings back memories, something along these lines is how many years ago I lit 2 F72T12 slimline tubes I was kindly given by James

in that case I used a 180W SOX leakage transformer to provide me with the the 600V OCV I needed (I was lighting both them in series) and additional chokes for current limiting of course





as for the F42T6, its a 120mA-300mA tube with a nominal current of 200mA

ANSI specifications for a reference ballast choke call for a "mains" voltage of 405V and a ballasting impedance of 3200 ohms 1960 ohms 1350 ohms respectively for 120mA 200mA and 300mA operation


so I think you will want 3 or even 4 F36T8 chokes in series rather then just 2


BTW dont forget that you can add some PFC across the output of the transformer to reduce the total apparent power of the inductive choke circuit being connected to it, this will let you get away with using a smaller transformer if cost/space is a concern

as an aside I recall you have an electronic F72T8/F96T8 ballast, that should also work for an F42T6 tube unless its shutting down due to the lower arc voltage of the F42T6?

36/40W choke is about 390 ohms, so 460V + 4 chokes looks spot on.

As I understand, larger American slimlines run at 425ma, so basically, large 96 inch slimline is two 40W T12's in series, 72 inch is about 1.5 of them)

Using F96T12 electronic ballast will certainly overdrive that small 17mm tube by current.

Do note I said F72T8 F96T8 not T12!

theres an import distinction to made there, the *original* American single pin tube was T8, 120-200-300mA, which the FxxT6 tubes are a family derivative of (the F42T6 and F64T6)


this is why the whole thing is called Slimline, even tho T12's are not what one would traditionally think of as slim

The easiest (and likely cheapest) solution for running a F42T6 lamp would simply to get an electronic instant-start F32T8 ballast.

Yeah that would probably be the easiest solution. Another one would be to look up whatever Fullham Work Horse ballast is rated to run them and then get the 120-277v 50/60hz version.

Yep, in USA/Canada. @Rafaf777 is in Italy. And he probably wants to play with some DIY magnetic.

In Europe, it will be likely easier to get some HE T5 or CFL electronic ballast of suitable OCV and current. Most of them will work with electrode out pairs shorted for single-pin tube.
 

If the original slimlines were T8, why did they make T12 versions later?

Do note I said F72T8 F96T8 not T12!

theres an import distinction to made there, the *original* American single pin tube was T8, 120-200-300mA, which the FxxT6 tubes are a family derivative of (the F42T6 and F64T6)


this is why the whole thing is called Slimline, even tho T12's are not what one would traditionally think of as slim

oh that’s interesting. i should try with that ballast but ii think it will refuse to stay on due to low arc voltage. btw as RRK said my goal isn’t only lighting an F42T6 lamp but also making a DIY magnetic slimline ballast
edit: oh no i forgot that my F72-96T8 electronic ballast doesn’t work, i only have a F72-96T12 one