What about output tubes...KT-88, KT-77, KT-120, KT-90, KT-99

I would be interested in your results with different Russian output tubes, sound , quality , price........All around ??
Depends on the circuit, I have Rogue m180s, with Revel f208s and have tried kt77s, kt88s, kt90s, and kt120s, in my system the kt77s sounded tonaly the best, while the more powerful tubes sounded "bigger" 
I'm fortunate, my amp will take most common output tubes.  It came stock with EL34,  the EH EL34 are a great tube for the money....

I have also used Gold Lion KT66 which are pricey but great,  I think my favorite tube and currently in use is the Gold Lion KT88....again, pricey but excellent sound.
Be careful of the heater currents the KT120, are up to 500mA each more than a KT88 times this by 8, and you can cook the heater supply, and it probably sagged below 6.3v because of it. My bridge rectifiers crack in two on my Rogue's when I owned them.

Cheers George 
George, what rogues did you own? I own m180s and was told by Mark Obrian 120s would be no problem. 
From memory they were the 150 monoblocks. It took a couple of months before the bridge rectifiers went, then I put in some much lager 35amp ones and all was fine. Not fun though when they go.

Cheers George
PS: something that slipped my attention, is that you also need to look at the power transformer’s filament (heater) winding to see if it can handle the extra current as well and without sagging.

Cheers George