degen In the basement here, the previous owner installed a lot of T12 fixtures. I wasn't going to spend a cent on replacing fixtures in an unfinished basement, however, I did replace 3 of the magnetic ballasts with electronic ballasts because the magnetic ballasts were very loud, and well, a little flickery too. The new ballasts work great. I bought brand name ballasts some time ago from the hardware store that were rated to be able to drive 40W T12s so probably they are a little better than some others. There was a wagon full of ballasts outside a few weeks ago, I now regret not going back and helping myself to a bunch of them, but whatever. I don't buy fancy tubes for the basement. They're the original cheap F40 blue tubes, however what I did do (and this is an old trick) when a tube or two burnt out, instead of buying more of the blue ones, I bought the warmer red one instead. So two of the fixtures have 1 blue and 1 red tube each, and this way they're a little more balanced temperature wise. I'll keep doing that, but I use them so seldom it might be many years or never.
You could try replacing the ballast with a better one. It's not hard, just shut off the main power going to it at the breaker and unscrew the cover of the fixture to see what you have now. It'll be the same wires. Probably a name brand one like Philips that is listed as supporting both T8s and T12s will work well (though it shouldn't make a difference, but maybe it might, as there are ballasts that are rated only T8).