Tell us about your KT150 experience

By now, there must be quite a few folks who own amps that utilize the Tungsol KT150 tube. ( I own a pair that do).
As such, i would like to hear the experiences that you folks have with re-tubing the amp with new KT150’s...what dealer did you buy from, how well were the tubes matched, how long have they lasted, any problems with the set or old set? What amp(s) are you using them in?...and lastly do you believe that they are superior to other Pentode power tubes...and why.
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. 
I have a Primaluna Dialogue Premium HP amp and have used EL34’s, 7581’s, and last week installed KT150’s. I have not tried the KT120. I totally agree with everyone’s comments about the 7581. Fantastic tube for 30 bucks. Deeper and tighter than the EL34 which I don’t use much anymore even though they have a wonderfully liquid midrange.

I’m only one week in with the KT150s but they do everything that the 7581’s do well but better, particularly soundstaging and depth. I wasn’t at all expecting those changes to the degree I have experienced. Imaging is better too. Everything I have read about the KT150 talks about the fullness, bass depth, tightness, which I agree with, but I was surprised with the rendition of space.

Again, I only have 25 hours or so of actual listening time on the KT150’s so we’ll see what they do over a longer period of time and the honeymoon period has worn off. I’ll wrap up by saying this though, if you are a bit hesitant to slap down 100 bucks per KT150, the 7581 is a fantastic alternative, kind of a KT150 lite. But I really do like the KT150s (all $800 worth, yikes!) 
For what it’s worth...

Comparing, re-tubing an older KT88 based amp that will "accept" KT150s vs. an amp which was designed day-1 (with larger transformers, and higher plate voltages) to natively run KT150s optimally, "can" "sometimes" yield a different listening experience. I’ve run across this with 3 different amps.

While I really enjoy the KT150s in my current mono block amps, they were originally designed to run them. Sounds great. However, a good friend just removed KT150s from his older amp, and he went back to KT88s as his amp was originally designed for them. In his case, I too preferred the KT88s in his amp. His upgrade to KT150s was a waste in his particular situation. Found out later his amp had much lower plate voltages, and (apparently) was not able to fully drive and take advantage of the more expensive TS KT150s.

It seems the amp/design/circuit has something to do with it as well. Probably worth checking with the amp designer to see if it’s worth it. A case of bigger or newer may not always be better.  

I have stated before that it it is not usually wise to simply roll in KT150 tubes into any tube amp. If the amp was not designed from the start to utilize the new KT150's...damage to the transformer can result! The KT150 needs a lot higher voltage to drive it.( therefore an inability to bias the tube is also a factor).  Best to check with your amp designer to see if the amp can accept KT150's with no damage.

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