How long do platinum Sovtek bulbs need to break in?

I mean, I thought it would take a hundred hours or so, but the fact is, that every time I turn on my pre amp, it sounds like I have changed machines.....

This thing is totally bipolar!!!

It goes from great, clear and beautiful, to ruthless and muddy within one day!!!

Does anyone have these bulbs to tell me when this hell is going to stop?