Bradz, if you have the money go with the 99, if not the magnum upgrade is very good. It is better than a stock 66 in all areas, you can use a number of different tubes after you done the mod to the 66. the tube I use is the E80cc, if you use this tube be sure to let Mark know so he can mod it to use that tube, you will never go back to a 12au7 after you hear it. Greg