A few months ago a pal asked me to look at a Vidor CN431.
One thing I was concerned about was getting the knobs off. Obviously jamming a screw-driver under them would be to invite disaster, and would probably damage the case even if the knobs survived, and the edges also looked a bit too delicate to stand the usual string/thin wire trick so I needed a different method.
I stuck an old bank card under each side and then slid others under those. After that it was a case of pushing more between these two until the knobs popped off which they did undamaged.
Click to see full size image
I thought this may of use to other people, though I'm sure somebody else will have already thought of it.
This was my first valve radio success as the main switch was jammed 'on' so was quite an easy fix.