Right Fedi, if there's anywhere which can probably answer this vintage radio question... I have a pile of NAB/Fidelipac carts, and a 1978 player. Most play fine through the player, BUT the Scotchcart ones with the tensioners won't. I've tried twiddling the tensioner, etc. but the tape doesn't run. Are these incompatible systems (original Fidelipac vs Scotchcart)? I can't seem to find a definitive answer on that, although both are the same dimensions and method. Please RT for reach.