Tell us about your KT150 experience

The amps that I have heard that utilize KT120's have not been in my system, so very hard to say...I would be interested in this answer as well from someone who has had the two types in their system.

I have a PrimaLuna HP Integrated.  I've used EL34, KT120, KT150, and now Tung-Sol 7581A.  This is what I found:

The EL34 has a sweet, sweet sound.  Midrange is awesome, and they work very well for vocals and more.  But, they aren't as powerful in the extremes.

The KT120 adds more power, and wider range.  But, what I noticed after having them in the system for a while is that they have a certain "grainy" sound, particularly in mid range.  So, I could hear it around vocals.  For example, listening to Dire Straits, Mark's voice sounded kind of "fuzzy".

KT150 is a nice combination of both.  It has the power, wide bandwidth, and a nice midrange without the glare.  I like them a lot.  The problem is that they are expensive.  They definitely make the amp shine, and I thought they would be my forever tubes.

Then I found the TungSol tubes.  They are like $30 each, so the price is right.  When I plugged them in, they also have a really sweet midrange, seems have similar overall power and midrange.  Also, they have a cool blue glow at the bottom of the tube that you can see when the lights are low.  Looks cool.  I have had them in for about two months, and have not yet switched back to the KT150s.  I will do that soon, knowing I can compare two sets of well broken-in tubes.  I think it will be very close to a wash between the two.  But, given the cost, if I replace, the KT150's cost triple and I'm not sure it's worth the extra cost.

If you are looking at KT120 to KT150, I would say you'll be happy.  But, I'd suggest you try the TungSol 7581A first.  It's a lot less sunk money if you don't like them.  It says a lot to me that I haven't been tempted to go back to the KT150s so far.

Soundermn, my experience echoes yours except I haven't sprung for the big ticket KT150s.. KT120s made my PrimaLuna amp sound transitory and I've been running the TS 7581As for many months....I like them even more than the GoldLion KT77s, which are outstanding but a little analytical for my taste.

I haven't replaced my KT150s yet.I bought them from VivaTubes.They have frequent sales so no need to pay full price.They ship quickly and no issues with any tubes.I always end up putting them back in after using some other KT88s or EL34s.They are by far my favorites.I am fortunate to be able to switch my Aric Audio amp to single ended, which I prefer.I love acoustic and electric blues so these tubes are perfect for retaining the sweet midrange while cranking out the power as needed.

I have a Prima Luna Dialogue Premium. I too run four 7581a power tubes and love them. Better bottom end & sweet midrange than el34b they replaced. Not as much power as gold lion kt88.. but more musical imho. I do not feel the need to invest in 150s.