I’ve tried the latest blue belts on Lingo 4 and Radikal and both adjust the speed perfectly.
I had problems with a Naim Armageddon/ standard modern motor and so cannot get the speed slow enough (set via a strobe and disc). Not enough adjustment in the motor tilt mechanism unfortunately. I think the belt is too short. Haven’t yet tried it on other configurations like a Valhalla but I will when I get time.
Same set up but opposite issue for me- I can't get it fast enough, maybe we should swap belts!