hi members, i ordered a Philips HF Regulator electronic ballast for my Philips TL5 HO 24W tubes and it uses the 1-10V dimming protocol. How can i dim this ballast without a pre made dimmer? Can i just use a DIY variable power supply and connect it to the 1-10V connections on the ballast? or the system is different? thank you 

The system "feeds" the dimmer by a current about 1..2mA and expects the "dimmer" to clamp the voltage to the desired level (the 1..10V).
One of the easiest things is to made such clamp using about 100kOhm pot, a small signal transistor, a 5.6kOhm resistor and optionally two trimmers (if you really want the control spread exactly across the whole travel of the pot, but normally that is not needed):

Assume you have an NPN transistor (BC547, 2N2222,...).
The emitter is connected to the negative side of the dimming terminal, collector to the positive terminal.
The CW end of the pot is connected to the base, the wiper to one end of the resistor, the CCW end to the collector.
The other end of the resistor you connect to the emitter.

This contraption will allow you to set the voltage in about 0.56..12V range, which overlaps on both ends so you have the complete dimming range available.

If you want to make the range exact, you connect one 5K (or a 4.7kOhm) trimmer (its center and one end) in series with the CCW ebd of the pot, plus you reduce the resistor to 4.7kOhm and put a 2.5kOhm (or 2.2kOhm) trimmer in series.
The "2.5k" sets the 10V for a full brightness, the "5k" one the 1V for minimum brightness. Both pots partially influence the other end, so you have to adjust them in a few multiple cycles.
To me I wouldn't spent effort with those trimmers, even without them more than 70% potenciometer range falls into the 1..10V.

Actually, a single potentiometer of about 100 KOhms across ballast 10V input is enough. Can't be more simple

It is useful to read manufacturer's application notes sometimes.

The thing is, the bias current is not that standard to allow just a simple potentiometer. Yes, you may be right for a single ballast brand, experiment out a value that works for the ballast you have, but different ballast brand wmay yield different optimum pot. Some are even differing piece by piece or temperature or the exact lamp condition. The tolerance of the bias current the standard allows is just very wide and some ballast designs really exploit that.
The transsistor circuit suppresses that so the same control unit works properly with any ballast, yet it is not that much more complex.  Plus it allows to connect a few ballast u its to a common control box, when the bias currents add up together, so another variable.

I believe the idea of small current flowing out of 1-10V control inputs was specifically designed to allow a single potentiometer to be used in a minimal setup. Rafaf777 asked what can be used with his single ballast in a test setup, why overcomplicate things?

And we are talking Philips ballast, right?
So why not to read a nice application note which says it all, page 67?

http://www.docs.lighting.philips.com/en_gb/oem/download/Technical_Application_Guide_Fluorescent_Gear.pdf

A simple 100K potentiometer WILL DO for this ballast, period.
As for most of 1-10V circuits, too.