Need help with tube selections

The options that are avaliable to you are either the 6550, or the KT-88. Getting Old Genelex/MO Valve KT-88s will be QUITE expensive, and they will probably be used. Sylvania 6550s could be had for some folding money, otherwise you are looking at mostly Chinese tubes. There is still some black art to making tubes, so eventhough some chinese KT-88s are 6550s in a bigger bottle, there is a difference. As to the driver tubes in this amp, stick with what the lettering says, or the industrial equiv.
I would strongly urge you to stay away from the KT-90, it is an unfinished product with a lot of hysteresis.
Happy listening.

The best sounding tubes for your MC-75 will be the GEC Goldlion KT-88 tubes. They are expensive both they worth it.
A set of four will last your life time!!!!

call andy at vintage tube svcs (no i do not work for him). he has always given me good advice and tubes. and if i do not like them....he will take them back! i am buying tunsol 6550s from him for my rogue 120s. i have heard electro harmonix has a good kt88 (per mark obrien at rogue). rogue also sells kt88 selects with thier name on them that go in their magnum up grades. i would buck up and go nos tubes. the difference in my equipment (pre-phono pre- amps; tuner etc) have been big. i am sure there are other good nos tube dealers out their too.

good luck

Thanks for everyones help.

sovtec kt88 end of story. if you like i will try to locate some.