Need help with tube selections

On my Sonic Frontiers Power 2 I took out the 6550's & replaced with KT 88's. The improvement was dramatic. The Kt 88's were Tesla & then I tried Svetlana's. The Svetlana's are, in my system, a bit more musical than the Tesla's. But not really significantly. The only way to tell is to give them a try. If you don't like them sell them on this web site.
Good Luck.

We have tried the KT 88's with numerous amps that come with the 6550's and we have always considered the KT 88's to be superior from top to bottom. We have also tried the KT 90's and have still found the KT 88's to be overall the superior tube.

You are now experiencing one of the advantages of tube equipment and that is that you can change the sound of your system by changing the tubes. Changing the input tubes can also tune the sound of the system although usually not as much.

We have tried the various brands on the market and like the KT 88 STR's by Ruby Tube.

Good luck and have fun!

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.