Aug 102011

I ordered a quad of EH KT90 vacuum tubes from Jim McShane a couple of days ago to try in my Leben CS660P stereo amplifier. I was thinking that I’d tried KT66, KT88, EL34, KT77, 6L6G, 5881, 6n3cE, 350B, and 6550s, so I thought I’d better add KT90s to the list. My favorites so far have been the 350B and the 6n3cE (in the photo below, left).

I was impressed with the tonal signature of the KT90 when my friend Ron brought over his vintage Harmon-Kardon Citation II amplifier that he was using  KT90 tubes in. The KT90 tubes had a big, warm sound, that kind of reminded me of an EL34 on steroids. The more I thought about that, I thought it might be a good match for the CS660P. Today the KT90s arrived, I plugged them into the Leben CS660P, and let it warm a bit. I put on the Analogue Productions 45 RPM version of John Coltrane’s Blue Train and gave it a listen. My first impressions were very positive: warm, with a lot of timbral textures, and deeply infused tonal colors. They’re brand new out of the box, so I’ll post an update after I get some hours on the tubes and they get into their full stride. In my brief audition I’m finding I like the voltage switch set to 410 volts (switch down, indicator light green).

Update: Tonight I tried the EH KT 90 tubes in my Leben CS600 integrated amp. I have to say, the KT90 is an extremely likeable vacuum tube, it has a warmth and body to it that will delight a lot of listeners, particularly those that have speakers that tend towards being a little bright. Even with my Harbeth SHL5s I have to say the KT90 is pretty magical. Is it better than the 6n3cEs with the SHL5s? The verdict is still out. But the KT90 is enchanting, and whatever you’re running right now, I suggest you give them a try and see what you think. Be forewarned, if you decide to try them in your CS600, you will need to leave the top cover off, as the height of the KT90s exceeds its limits. Oh how I wish there was an optional Leben top cover that accommodated the more masculine tubes!

Thanks for stopping by, and I’ll report back what the results are when I get a little more time in on them.



 Posted by at 5:35 pm

  149 Responses to “The Leben CS660P Amplifier and EH KT90 Vacuum Tubes – Update: CS600 with the KT90”

  1. Hello Jeff
    I just found a leben power amp but i cannot find the model in leben web.
    The model is Leben cs 700, it is a silver amp.
    Do you happen to know this model? Is it good?
    Thanks in advance for the help/advice

    • Hi Christos,

      I have never heard of a CS-700, so I’m afraid I’m not of much help there. If you decide to buy it, do send pictures and your impressions of it, and I’ll post it for others to see.

      Kind regards,


  2. Sir Jeff,

    i have issue abt amp choice.
    currently i have marantz pm11s2 .
    some time ago i’ve choosen ( after long time of living with both) 47labs lense speakers (in comparison with harbeth shl5) .
    i’m listening 2 turntables : mono with miyajima spirit (mc) and stereo with rega master (mm) .
    currently both are commutated viw denon 320 into e.a.r.834p
    room is difficult 18 meters.
    so , currently i’m thinking abt
    change marantz pm11s2 to cs600 – canyou pleasecomment this change?
    but the problem is , that my ear phono is far away for long time noow, so i cann’t compare bith amos in equal conditions.
    so, trully looks the way is
    changing pm11s2 + ear —> cs600 +rs30eq … butthan- price wwill double.. abt sound .. advise please, will i have 1 or 10% happiness more?

    what i hear now ( cs600 + handmade phono, as rs30 is unavalbl today here) – maratnz was much powerfull , much faster, more precisely… cs600 has some … too long soundings,,,, like echo…
    but i like much more cymbals sounds in cs600

    thnx in advance.

    • Hi Andrey,

      I’m not familiar with the Marantz so I can’t help you much there. I can tell you that with every year that goes by that I enjoy my Leben CS-600 and RS-30EQ more and more, and I can’t imagine every wanting to part with it. I can’t say an endorsement like that about too many audio products. As long as the Leben is a good match to the 47 Labs speakers you own I can’t imagine you’d be disappointed with the Leben CS-600.

      Kind regards,


      • thnx, Jeff
        so, you think
        “what i hear now ( cs600 + handmade phono, as rs30 is unavalbl today here) – maratnz was much powerfull , much faster, more precisely… cs600 has some … too long soundings,,,, like echo…
        but i like much more cymbals sounds in cs600”
        it’s like habit (as i long tine lived with marantz ) ?

        and what do you think abt cs600 + rs30 in comparison with cs 28 ++ new poweramp from Leben ( smsng what will be replace 200p)

        “or may be the way is – to wait on new 200′s mono blocks from leben..
        and try cs28 (which has (as i understand) equal to rs30 phono inside) + this new amp.


        • Hi Andrey,

          If you like the Marantz you should stick with it.

          As for Leben electronics, I really like my CS-600 and RS-30EQ combination, and prefer that to the separates for my particular application.

          Kind regards,


  3. or may be the way is – to wait on new 200’s mono blocks from leben..
    and try cs28 (which has (as i understand) equal to rs30 phono inside) + this new amp.

  4. sorry for mistake: “stereo with rega master (mm)” means grado master . (rega table)
    sorry again

  5. Hello!

    Now my last “baby” from Leben ist GONE!!!

    Leben CS600 and Leben RS30-EQ have left the building.

    One tear in my eye…


  6. I love the Marantz pm11s2 with my Harbeth SHL5, can’t imagine any amp being a huge improvement but maybe that’s just me.. (I listen classical and jazz only)

    • A Marantz can not give you the emotion of music. Only very good tube amps give you the charming side of music.

      Now i own SHINDO. That’s the better choice.


      • Dude, if I get more emotion listening to the second piano trio by Shostakovich then my current system gives me, I’m afraid I’ll hang myself 🙂 Listen, we all hear different and have different taste, that’s cool, maybe I like a tube amp even better, quite possible, but don’t tell me I can’t hear emotion on my Marantz-Harby system m8..


    • do you use vinyl with phono ? which one?
      or use internal of pm11s2…

  7. What Shindo gear did you get Maik?

  8. Aurieges Phono and Montille. Both amps from the first series. With tube rectifier!!!

  9. Very nice Maik, I did a similar move, and have now moved up the Shindo lie from there. I will always love Leben though, and wish I could afford to have both!

  10. well, jeff I can only endorse your comments – I have a CS300X /401/SME audionote p/u and CD running into a pair of Proacs in the study and a CS600/linn sondek/Proac combo in the lounge and they are both absolutely brilliant to listen to. I use quad QC24P phono stages on both and also a squeezbox touch/Bushmaster DAC with the 600 and an imac/lexicon omega as a DAC with the 300X….a lot of numbers there but every hour is just pure pleasure whether its jazz, classical or a bit more rock-y…..discovering leben really revived my musical life.

    • Hi Ian,

      The Leben integrated amplifiers are really something special, that’s for sure. They are one of the easiest ways to setup a truly great sounding system and to immerse oneself into the musical life.


      Kind regards,


  11. Hi Jeff,

    Did you ever try putting a preamp in front of the CS600, using the “direct in” inputs? I am considering doing so and would welcome any insight. Any reason that it wouldn’t be similar to the CS660’s performance?

    I switched from an Audio Note Meishu 300B integrated to the Leben. I am enjoying it thoroughly but am curious if I might improve its performance with a preamp. The differences I hear on the positive side are increased clarity, tightness, and accuracy; if I can steal back some of the natural presence and emotion that to me the Meishu had a bit more of, that would be great. I’ve tried a fair amount of tube rolling with mixed results.

    The rest of my system: all analog, with a Garrard 401 in constrained layer plinth, Ikeda 407 tonearm, and SPUs; an Artemis Labs PL-1 phono stage; and Audio Note AN/E speakers.

    Thanks for any insight you can share!

    Best regards,

    • Hi Greg my 2c, if I may….
      I only use the preamp in option as I find the resolution and hence texture of music is much higher..but this does not really bypass the preamp section ie the volume pot and input tubes remain very much in the signal path..hence I would not presume a separate preamp would work well.

    • Hi Greg,

      That’s a nice system you’ve got going there!

      I haven’t tried using a preamp with my CS600, so I’m afraid I’m not much help on that question. I would tend to think that adding a preamp would degrade performance (more electronics in the signal path, etc.).

      I don’t think adding a Leben preamp will make the CS600 sound more like your 300B amp did. You could trying using warmer sounding output tubes in the CS600 like the KT90, and see if that moves it in the right direction for your tastes (although that will mean you’d need to leave the top cover off due to the height of the tubes).

      Kind regards,


  12. Thanks Arj,

    I was worried about the same thing. However the Leben CS600 product page actually refers to it as a preamp option in pretty direct language. Those same small tubes are in the CS660 as a first stage of amplification . . . confusing for sure and that’s why I’m hoping to find someone who’s tried a preamp in front of it.

  13. Thanks Jeff — I’m all for lower cost options 🙂 I’ll look into the KT90s.

    • I’m with you, Greg. Try the KT90s and see what you think … it’s always possible to spend more money later if you want to! 😉

      Kind regards,


    • Hi Greg!

      I use my CS600 Preamp “In”!!! It is better than the normal Line in. I used a Leben RS30 on the Preamp-In.
      If you want some really great tubes, try RCA 6L6GC from the early 60’s.
      They have the golden sound!!!! No other 6L6 is better.

      If you want much more….try Shindo!

      Best regards


  14. Hi Jeff
    I am running 6550EH in my 660P, assuming they are equivalent to a 6550A, but not 100% sure about it. They do sound very good but would be good to know I’m not doing any damage. Can you put my mind to rest?

    • Hi Steve,

      I do not know the answer to your question. Your best bet is to ask the Leben folks directly about any potential compatibility issues. The Leben exporter, Yoshi Hontani, should be able to answer your question or find out an answer for you. Yoshi San’s emal is .

      Kind regards,


      • Thanks Jeff, have sent enquiry on. Interested to see your comments on MC240, I have a pair of MC40’s which rotate with the Leben in the Number 1 setup, running Monitor Red 15s in GRF cabinets. Happy Days.

  15. Hello Jeff, After a lot thought and research I ordered a Leben CS600, I’ve been on the amp merry go round way to long and thought that with 600’s tube rolling possibilities I might be able to jump off and land on solid ground. I know you’ve rolled a few bottles, could list which ones in the CS600 that you have liked best in order of preference. Thank you, Christopher I was wondering if you tried the KT120s in your 600.

    • Hi Christopher,

      I think you’ll love the CS-600 – it is a wonderful amplifier!

      I’m not sure I can answer your question quite the same way you asked it – I’ve tried a ton of tubes in my CS-600 and I haven’t even come close to trying to rank them all, But I can tell you this: right now I’m using EH KT90EH tubes and really enjoying them. They’re more warmly balanced than the 6n3cE tubes, which I also really like. I’d also like to try my NOS RCA 6L6GC black plate tubes in it, I have a hunch they’d be a super match. I haven’t tried the KT120 tubes yet, but I encourage you to give them a try and report back on your results.

      Which tubes you will like best will likely be the ones that match your overall system voicing & personal tastes the best, and might not be the ones I like the best. The best thing is to experiment a little, and of course seeking advice from someone like Jim McShane on which tubes will move your system’s sound in the direction you want to go is a really good idea too.

      I hope that helps!

      Kind regards,


      • Hi Jeff, Thank you for your response. This thread about the EH KT90s was started back in August 2011, have you been using them the whole time? If so are they sounding as strong as ever? Thanks Neil

        • Hi Neil,

          I’m using the same EH KT90 tubes from back then and they’re sounding great. They get played a lot too, almost every day in fact.

          Great tubes!

          Kind regards,


  16. Hello Jeff,

    I was wondering, could you do a comparison (when time permits) between the EH KT90s and RCA 6L6GC black plates? Inquiring minds would like to know. Thanks for running these blogs, much appreciated. Thanks Christopher

  17. I’ve been thinking the same thing, Christopher, but my audio to-do list is so long I don’t know if I’ll ever get there. I’ll try!

    Kind regards,


  18. I think the RCA shows more musical texture. The modern tubes sounds too technical…
    i would prefer RCA over all other tubes

    Best regards


  19. Hi Jeff

    I got a matched quad of the EH KT 90 after reading this and also with Jim McShane’s recommendation. Can I ask what settings I should be using on my Leben CS 600?

    • Hi Swee,

      I’m running mine as I would with a 6L6, with both the cathode resistor and plate voltage switches in the forward position (

      I think you could also run it with the plate voltage switch in the other position as well, like for a 6550A, etc.

      Have fun!



  20. Hi Jeff

    Sorry for the redundant question. I missed the earlier post in which you already answered that question.

    • Hi Swee,

      No worries, I was just trying to point you to the table because it’s a little hard to find, and it’s worth bookmarking for experiments with rolling tubes.

      Let me know how you like those KT90s!

      Kind regards,


  21. Hi all, being super non technical, I was wondering if anyone had experience of running a Shindo Aurieges pre into a Leben CS660P? I know the Shindo can be tricky with its high output impedance. Speakers are Living Voice OBX-RW’s at the moment.

    Thanks for your help


  22. Hi Jeff
    I run my Leben 600 with GEC kt 88 which are very musical . I just worry when time will come to change them .
    They are difficult to find now and very expensive. I hve duplicated your system ,Harbeth 5hl,duelund cables and a digital front end EAR classic .
    EH kt90 seems a good option ,but i have read good things about kt120. And shuguang GEKT88
    What would you advice if you have experienced them
    Kind regards

    • Hi Serge,

      You have put together a very nice system! I love the combination of the Leben CS600, Harbeth Super HL5, and Duelund cables.

      I hadn’t heard of the EAR Classic until I read your comment, so I went out and took a look at it on the EAR Yoshino website, and it looks very nice indeed!

      I did like the tonal qualities of the EH KT90 valves until one of them failed, but they were too tall to keep the top cover of the CS600 on, which I didn’t like.

      I have gone back to the 6N3CE in my CS600, which has been a very rugged and good sounding tube, but not as tonally rich as the KT90, but with the advantage that its size means I can keep the top cover on the Leben CS600, which I prefer to do.

      Let me know what you decide to do and how you end up liking it!

      Kind regards,


  23. Hello Jeff,
    After months of tube rolling I always come back to the Tungsol 6550 black plates NOS,now unobtainable ,that I bought years ago
    Thank you for having helped me to put together this wonderfull system
    Kind regards

    • Hello,

      I’ve read some very positive comments about the use of KT120 in Leben CS600 and some guys got the confirmation from Leben that this poses no problems. I asked the same question to Mr Yoshi Hontani and he answers “As CS600 is not designed to use KT120/KT150, we are unable to guarantee negative effects after many years use. We also feel the sound of KT120 in CS600 is not Leben-like sound…” I already bought a matched quad of KT120 but now I hesitate to use them of course… Will try some SED Winged C 6L6GC or 6n3cE. For the moment my Leben is equipped with TungSol 6L6GC STR, not bad but are missing some dynamics and detail. My speakers are Graham LS5/9, very nice combo. Thanks for your comments.

      Kind regards,

      • Hi Marc,

        One of my favorite tubes in the Leben CS600 is the KT90 tube, which provides a warmer presentation with more body than does the 6L6GC or 6n3cE, or anything else I’ve tried, for that matter. I haven’t tried the KT120/KT150.

        I wouldn’t worry about if the sound is Leben-like, it’s more important it is ‘you-like’!

        The only down side of the taller tubes is that you have to leave the top off. I wish somebody offered an aftermarket cover with an opening(s) that would allow the power tubes to poke up through it, so you could use taller tubes and have the cover in place.

        Have fun!

        Kind regards,


        • Hi Jeff,

          Thanks for your comment. I also liked the KT90 in a previous Jadis amp. What worries me is that Mr Hontani writes “we are unable to guarantee negative effects after many years use…”
          I would not like to ruin my amp by using the “wrong” tubes…
          And there is indeed also the top cover “problem” when using larger tubes.
          Pfff, difficult to make the right choices here:-)

          Kind regards,

          • Hi Marc,

            I don’t see how you could harm the amp by using variant tubes in a particular tube family. As I understand it, all that is changing with the switches is fixed values of cathode resistors & plate voltage to adjust between 6L6GC and EL34 tube types.

            I could see how the two values might not be the best choice for a particular set of tubes, but that would be just be a tube thing.

            I did have a KT90 tube let go on me after a number of years of use in my CS600, but the amp suffered no ill effects. I’ll try to remember to ask Yoshi-san if he can tell us a little more about what he meant when he told you that.

            Kind regards,


  24. Hi Jeff.

    I already have a EH KT90 on the Leben CS600.

    The plate voltage lever can be placed in the 410v position or is it not advisable?

    Currently it is difficult to find Sylvania 6CS7.
    I only find RCA, GE and Raytheon.
    Which of these do you advise me?



    • Hi Fernando,

      You can see a guide to settings for different tubes HERE.

      Essentially, you can use either position for plate voltage with the KT90 tubes.

      It’s been so long since I’ve done any 6CS7 tube rolling in my CS600 I’m not sure I can be of much help for a recommendation. The nice thing is that 6CS7 tubes are so affordable you might as well get a quad of each and see which ones you like best.

      Kind regards,


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