I had a few tension probs. with my main workhorse (1950's Pinnock). I now stick to Gutermann thread and metal bobbins. I always test on 100% cotton and denim (my two most commonly used fabrics). If I need to use a radically different thread/fabric I keep spare bobbins for aside for that purpose. I have also started keeping a notebook by my machine and when I get a "perfect" result, note down exactly where all the dials are at, the needle brand and size and thread/fabric details.