KT150 to KT120..or KT120 to KT150

@decooney  Remind me again as to what amp you are using with these tubes.

I ask the question in my OP because there is a well known and respected (justifiably so, IMO) amp designer, who believes that the KT120 is superior sounding to the KT150. This has NOT been my experience, but i am questioning if others have experienced the same results as the designer claims.

@dsholl1 I don’t want to tell who the amp designer is, but I really like his gear and I respect his opinion ( generally). However, my opinion is that he is mistaken when it comes to the differences. @decooney What you posted about the quality of the driver tube is exactly my experience as well. Right now,I am using stock EH driver tubes in my amp, but I have rolled in a variety of NOS vintage tubes...and the difference is not slight. The KT150’s really seem to light up bass on what is upstream. Since the amp designer I am talking about doesn’t believe in NOS vintage, I would strongly suspect that this is where he is basing his finding on..a mismatch between th driver tube and the KT150, leading to his favoring the KT120.( in his particular amp). Nonetheless, @dsholl1 in what context( amp..driver tube etc) did you find the KT120’s better?

@dsholl1  Unfortunately, I don't believe that you can lay the differences that you heard between these two designs, the i50 and DA88sMk2, at the feet of the power tubes utilized by these amps. There are signifiant differences in amp abilities as you go up the Jadis line, just like most other manufacturers. There is a reason for the price differentials. 

The varying opinions of the KT150 tube seems to be primarily dependent on whether the amp was designed to utilize the KT150 in the first place. Since the KT150 needs a more stout transformer and has to run on a higher voltage, i would question if those who are not pleased with this tube are simply seeing the results of swapping in the KT150 into an inappropriate platform! 

@fsonicsmith   You are using the KT150's supplied from ARC? They do seem to have good QC, better than most. In the past, ARC has told us that rolling in tubes from other vendors is dicey, regardless of the tube type.

What amuses me a little with the amp designer in question, is that not only does he preach that the KT150 is worse than the KT120, with no proviso that it could be in his circuit, but not others; but also the fact that he did not believe in tube rolling or NOS tubes until recently and was known for telling everyone he was in contact with about this. ( wherein his new marketing manager must have told him that this could be another profit source, and apparently magically changed his mind!). We really do have a lot of 'interesting' fellows in this hobby on the manufacturing side, IMHO.

@decooney  I do agree that the design of the circuit is a major factor in whether the KT150 or KT120 is going to be preferred. The amp designer in question is absolutely convinced that the KT120 is superior to the KT150 in SQ. i think while this might(?) apply to his particular amp circuit, it certainly is not a universal. ( even though this guy would like everyone to believe that it is!) 

@vinylvalet  Do report back once you receive and have run in your new Zesto amp. I am particularly curious as to the difference between the KT150's and the new KT170's.

I would expect the amp to be basically idling when driving your Fyne's...with all the tube choices.

@decooney   Intersting point. I tend to agree that ic's can make or break your system, depending on a number of variables. Your findings above do not actually jive with mine, as I am very impressed with a pair of OCC Ohno Continuous ic's with my KT150's. However, I am fairly sure that the design and make has a lot to do with the ultimate results. So, no real generalizations are possible here. 

Wonder how many amps out there that are running KT150's were actually originally designed to run on KT88's, then modded to run KT120's and finally KT150's? 

Interestingly, my old ARC amp running GE 6550's was super sweet sounding, the NOS GE 6550's were a superb sounding tube; but these days, I believe the newer KT150's and 170's are more resolving and offer better power in the bottom end.

@decooney No doubt that combo works well. Question is whether these amps were originally designed for KT120’s or KT150’s?...my money says KT120’s, which would lead to your observations.