I have just purchased a set of Mobern preheat strips from eBay. They are F15T8 preheat with the starter mounted at the end of the fixture. They are similar to the small 4-8 watt strips which are popular with some members here. They are equipped with Robertson choke ballasts, that are long and thin. The problem is that I intend to install them under the cupboards in my kitchen, but they are too noisy. I installed one just to see how it would be, and the noise level is too high. I don't want to install all four of them just yet ; I want to take care of the humming first.

Here are the two questions :
1. Is there any way of reducing the noise in the present ballast ?
2. Has anyone tried the Vossloh Schwabe ballasts for that wattage (preheat, 120V 60Hz) ? I am considering trying to get them from Semperlite if they can still get them... They are model number 165374 on the Semperlite website.

Thank you very much.

hello there

there is some potted sylvania ballast that is nice and quite. I just cant almost feel the humming. there is hard to find. i am going to restore check again to see what around if i can get some more. then i dont mind shareing them with other members on LG.

Thank you, funkybulb.

I think I saw a picture of those in your gallery. Unfortunately, I don't think they would work because the ballast channel in the fixture is only about 1.25 x 1.25 inches. I need a long thin ballast instead of the more usual short fat ballast.

I have a pair of them that came with this low profile fixture.  They seem to be very quiet and work quite well.  I did have an issue with lost continuity (compounded by failed starters) but it was easy enough to fix.

The existing ballasts must be Robertson finger ballasts.

I notice why on stemperlite site I notices the sound rating of C for those slim ballast

funkybulb : Yes the Robertson are sound rated C. The VS, however, have no sound rating as they are open coil.

icefoglights : Never mind the question about the ballast repair. I read your description and answered my question.

does ballast reduce hum when isn't mounted in the light fixture?
if reduce noise, try to separate ballast from fixture using an spring, or some plastic material.

You can try rubber washers between the fixture and ballast.

I wouldn't want to put rubber washers between the ballast and the fixture as the ballast heats quite a bit. As soon as I can sort out the availability issues with the VS ballast at Semperlite, I will order some and work from there.

Thanks to everyone who helped.

With the European ballast style (used by the VS) I've never seen any case, where the noise originated directly from the ballast. But what create the noise is the external magnetic field (escaping from the ballast), vibrating the thin iron sheets of a fixture.
The solution to this is to shape the sheet metal below the ballast so, it becomes rigid structure (so could not move underneath the ballast), or using aluminum mounting plate (aluminum is not affected by the field).
Or use nonmagnetic material for the fixture body.

In any case (but mainly when the fixture isn't from a nonmagnetic material), make sure all bolts between the ballast and the fixture body are installed and tight (and secured against loosening by a drop of some heat resistant paint), so the fixture body can not vibrate, so cause the hum.

All humming ballasts I've seen had loose bolts holding the ballast, or the sheet metal was thin and somehow bended, so had the play to vibrate in the ballast magnetic field. Mostly tightening the bolts eliminated the hum...