KT 170

I've had them for about 400 hours now in a primaluna evo 300 power amp. Not much increase in power (PL is a little to gentle on them, I think they might like to be driven a bit harder) but a discernable increae in control of the speakers (dhalquest dq-20's are behaving very nicely). Best way to describe them is as a GL kt-77 on steroids. Not the ones that make you grow hair, the ones that make you all sexy and stuff. Or something. Just not hairy.

It's very linear and tight with wonderful bass - very SS like in that regard but you won't mistake it for SS - at least not on my system but dayum, is it frigging nice. Very nicely extended highs and a surprisingly pleasing midrange to boot.

I really like it.  

NOS amprex in gain stage and NOS sylvania in driver stages. 

They hit the xformers on any PL that uses 8 output tubes.

I contacted upscale audio a couple months ago about them: "We’re testing, buy kt-150’s". Screw that, you advertise as "future tube proof" so we’re gonna test. They are :)

EDIT: total cost for the 170's from viva tubes was 20 bucks less than 150's from upscale. Sure, it isn't much but thats 2 good grams of (legal) weed here.

That's from the Facebook PL group, think someone measured and verified with upscale but it wasn't me. I have no way of actually verifying if it's true or not but it would be a major concern. 

All I can say for certain is that they work extremely well in an evo 300 power amp.