Questions on KT150 vs KT120

I preferred the upgrade to 150s over 88s that came standard with my Amps.  As I recall it was a short breakin period, maybe  a 100 hrs on my QS V4 monos to open up the high frequency that’s about it.  Signal tubes were whatever NOS RCA or Sylvania it came with. Not sure how the new stuff would sound?  So I purchased an extra set inputs when I got the amps many years ago, they do last almost forever unlike the new stuff. Thanks to Mike Sanders stock piling for his customers.

I have VAC Phi 200s… Which were designed around KT 88. Kevin from VAC tells me that I could run KT 150s on them, but he doesn’t prefer them. I have not tried yet. Are you running KT 150s on your VAC? Which VAC amplifier do you have?

@paulcreed for whatever reason and comparing to my local audio shop friend’s same amps, driving back and forth several times to compare, I found his same amps with KT150s were notably smoother and more musical than mine brand new when I got them. With my brand new KT150s I noticed slight changes at 100-150hrs, and he kept telling me "nope" try again at 250-300hrs and see if they smooth out and sound better, and they did at 300hrs.  I’ve sinced boxed them up and went back to KT120s again, yet I do like both sets and the KT150s can sound good with the right front end tubes in the preamp and with the amps too. It can be a balancing act.  

FYI, what I did finally realize with others, some amplifiers are NOT actually designed to run KT150s properly, with insufficient plate voltage.  My amps are designed to run KT50s, KT120s, and I cannot run KT88s as the plate voltage is too high and will burn them up prematurely. 

Ask your amp mfg what the plate voltage is on the amps to see if they are actually optimized to run KT150s or not.  Many tend to ignore this because they will plug in and play, maybe not properly though, fwiw, worth asking your amp designers.  

Great advice @decooney 

I run KT150’s in my mono block amps, which were designed with that tube in mind. The KT150’s sound great, but you have to balance them with the preamp and the driver tubes. They are very sensitive as to what driver works best, I am still experimenting with drivers even after a few years. So far, the KT150’s seem to prefer a robust tube, the RCA clear tops are good, as are the NOS Telefunken’s, The newer reissue tubes can work, but i find them to have less life when driving the KT150’s.

Peter have not tried 150’s on VAC, I found the 150’s tipped up on the Audio Hungary so it may ever be worse on the VAC.
 

decooney I contacted Audio Hungary and a75i class A is shipped with both 120’s and 150’s depending on customers preference. Why did you end up preferring the 120’s, at this point I’m in the same camp. They do have big bass but at times it’s a little too much. Also agree on front end tubes play a big part on tube I found was Mullard work the best, Telefunkens,RCA, Mazda and others did not play as well.

I prefer the 150s over 120s in my Quicksilver V4 monos 

"@paulcreed Why did you end up preferring the 120’s, at this point I’m in the same camp."

I may have an unhelpful answer, in my case.  First, has to do with my custom built speakers.  Secondly, old habit, familiarity, maybe. I'm an old EL34 fan too.  I like KT150 & KT120s for different reasons. I end up tuning the system to be a tad more rolled off on the top end, slightly, always focusing listening pleasure more on midrange frequencies.  It's partly a preference kind of thing as I've aged. I cringe hearing uber-detailed systems. Piercing horn speakers hurt my ears, for example. I grew up listening, building, electrostatic AMT hybrid speakers.   

My speakers generate a lot of sound output above 1200hz in my particualar listening room. Revealing.  Some of my more neutral front-end and power tube combinations can be too much of a good thing to my ears.  I might have some hearing sensitivity in upper midrange and high frequency ranges, so I tend to lean towards a smooth dac, smooth interconnects, tubes (input our output) that tend to recess high frequency, slightly. I have the same challenge and preference with my solid state amplifiers. Got that dialed now too, to my preference.   If I decide I want a tad more detail and depth, I pop in the KT150s, but i've been stuck back on KT120s again past few years. Bought three quad pairs of them as spares. I may try the KT150s again over the holidays. When I replaced the main power capacitors and coupling capacitors with really nice upgraded units, even more detail came through - back to the balancing act.  As my buddy says, "its all preference at the end of the day for each individual".  I tend to agree.   Its all good. :)

Thanks decooney for explanation, I’ve always been a fan of el34’s and el84’s but these 150’s are very detailed with big bass but that doesn’t make me want to listen for very long. I’m going to put the 120’s back in this weekend just to enjoy listening again. I’m hoping with more time they may come around and become enjoyable to put in every once in a while. Anyone know how long this break in period can be.

I like the KT150 tubes, the KT120 tubes sounded a little tipped up in the treble to me with a touch of grain. 

When I had the Audio Hungary a50i, I too preferred KT120s over the 150s. They just sounded more musical and engaging. Makes sense because the designer voiced the amp with KT120s. 

@paulcreed ...I’m going to put the 120’s back in this weekend just to enjoy listening again. I’m hoping with more time they may come around and become enjoyable to put in every once in a while. Anyone know how long this break in period can be.

I just remembered something.  When I first bought my new QS Mono 120 amplifiers, the Co founder-designer told me that if I liked EL34s, to try the KT120s instead of the KT150s the amp originally came with. So, my local dealer gave me a discount on the amps if I'd give him the KT150s for his parts surplus, and he'd been running KT150s in these same amps original designed specifically for KT150s. 

I then picked up a quad of new TS KT120s.  Tried them for 30 hours and did not like them.  I had a return policy guarantee with my tube supplier at the time.  I STUPIDLY returned them. Later learned I did not give them enough time to settle in. Long story.  Then tried KT150s a while. Nice, powerful, detailed. I still wanted more musical midrange. So, I went back and repurchased a quad of KT120s. Checked them at 100, 150 hrs, and they started wearing in nicely, and I've kept them playing since.  Saved the KT150s stored, and then bought other quad sets of KT120s as spares liking them more after giving them more play time.  Re-check at 100, 150, 200hrs play time.  See if you start to like them more. I  sure did. :) 

I put the 120’s back in few days ago but put them 150’s back in last night to break them in during the week. Soon as I did same thing bright just not natural. I’ve been using a Z Cable/Clarity Cable Clear Focus power cord on Streamer and Dac. I Decided to try a Audioquest Hurricane and was a very nice improvement then put in a Clarity Cable Red Lightning it was even a little better from AQ. Will continue trying to make 150’s work, but was pleasantly surprised with results.

I forgot to mention I also tried a Snake River power cable which I also find on the warm side just like the AQ and Clarity Red Lightning. The Clarity Clear Focus is one of the most transparent cable I’ve ever owned it digs so deep and pulls out things in the recording you normally would not hear. So far not a good match with the 150’s, maybe too much of a good thing. Tubes are also a Problem with the 150’s I couldn’t pull the Telefunkens, Tungsgrams and Mazda’s out fast enough.