Does anyone have some info about replacing tar inside a ballast? I have a ballast that's extremely loud and buzzy. I'd like to replace the tar  with fresh tar to make it quiet again.

Where can I get new tar for this application?

This is the fixture I want to do it on. It's a top mount 2x40w HPF ballast.
https://www.lighting-gallery.net/gallery/displayimage.php?album=lastup&cat=11782&pos=13&pid=123608

The coil and other components are likely worn out as well.  You need to replace this ballast.  What type of bulbs are you using it on? 

The coil and other components are likely worn out as well.  You need to replace this ballast.  What type of bulbs are you using it on? 

I can't really replace it easily. It's a top mount ballast.

40w f40t12. The ones it was rated for.

I don't understand. You can't replace it easily? Your proposition of removing it, repotting it, and reinstalling it is a lot more labor intensive by comparison.

I don't understand. You can't replace it easily? Your proposition of removing it, repotting it, and reinstalling it is a lot more labor intensive by comparison.

It's a special top mount ballast. The wires come out from the bottom instead of the ends. The ballast is mounted on top of the fixture channel and the wires thread directly into the fixture via holes in the channel.

Looking at it from the outside, you won't see any wires.

what about drilling holes in the channel for the side wires

what about drilling holes in the channel for the side wires

I could do that but I'd like to keep it original.

I wonder if you can try reflowing the existing potting with some heat so it melts into any gaps that might have opened up over the years like what Don mentioned on your picture.

Alternately you could probably try to modify a newer preheat ballast to have either have leads coming out the back or fabricate a adapter plate to mount a newer style ballast in the existing top mount.

I wonder if you can try reflowing the existing potting with some heat so it melts into any gaps that might have opened up over the years like what Don mentioned on your picture.

Alternately you could probably try to modify a newer preheat ballast to have either have leads coming out the back or fabricate a adapter plate to mount a newer style ballast in the existing top mount.

If i remember correctly the tar is all dried up already... chunks floating around inside. Could i use some sort of roofing tar to replace the dried up tar?

Probably, I would avoid the stuff that is gooey at room temperature.

I have heard of people depotting other types of transformers by using kerosene to dissolve the old tar (obviously don’t do this indoors).

While you’re at it I would also replace the wires and capacitor.

Probably, I would avoid the stuff that is gooey at room temperature.

I have heard of people depotting other types of transformers by using kerosene to dissolve the old tar (obviously don’t do this indoors).

While you’re at it I would also replace the wires and capacitor.

Any tar brand suggestions? I've never worked with roofing tar before.

You want to soak the coils in varnish before you pour tar in. I've done it on a long jon ballast from the 40's and it did help but still a noisy ballast. I really just hope it helps it last.

Your chances are of finding that tar product are pretty slim today, they don't really use that method anymore. While potting tar is impervious to moisture, as you noticed with age and heat cycles is prone to cracking, becomes brittle, liquefies and leaks when heated and loses its integrity.

You can however use polyurethane resins, epoxy potting compounds. Both are used to pot electronics and are much more durable than tar, can take a greater amount of heat and do not lose their monolithic structure when cured. They are also a good sound insulator.

They are usually industry and large-scale manufacturing oriented. For the DIY hobbyist, if you can find them, they are pretty expensive!

If someone has more knowledge on this, I'd love to hear suggestions as well, industry electronic grade epoxy compounds aren't financially feasible for small projects.

I have a few HID ballast assemblies that used a epoxy potted ballast coil assembly. They were for Lightolier metal halide recessed downlights and they're almost dead silent compared even to the conventional tar potted F-can ballast assemblies.

Potting materials such as polyurethane and epoxy can obtained typically from electronic component suppliers. My local one sells a few different kinds from MG Chemicals but the expense of using such a product meant that I haven't really considered this option for a ballast, well and I also don't really have a reason to replace the potting.

Ironically I haven't been able to find the traditional tar potting that manufacturers like Advance still use for their magnetic ballasts. The modern polyurethane and epoxy based potting materials are much more easily available.

There's some tips here for removing the potting.