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MC75 - KT88 or 6550 ?

Discussion in 'McIntosh Audio' started by ofery, Oct 1, 2018.

  1. ofery

    ofery Active Member

    Messages:
    189
    Hello All,

    Which power tubes (KT88 or 6550) are the best for two MC75 monoblocks ?
    If KT88, then I'm considering Electro Harmonix or Genalex Gold Lion Reissue, which one is better ?

    Currently I have Electro Harmonix 6550 on the MC75s.
    My pre-amp is C11.

    Regards /Ofer
     

     

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  2. clinic-audio

    clinic-audio all on YAMAHA untill 1990

    Messages:
    2,182
    Location:
    France
    6550 is american designation
    KT88 is English designation
    6550 is not a KT88 sub
    KT88 is a 6550A sub
    do not use 6550 where there is 6550A in original units

    For MC75 and MC275 I will use KT88 GEC if they still available
     
  3. ofery

    ofery Active Member

    Messages:
    189
    KT88 GEC tubes are too expensive, ~$1,000 for quad !
    What is the cheapest recommend KT88 for MC75 ?
    How about Electro Harmonix or Genalex Gold Lion Reissue ?
     
  4. clinic-audio

    clinic-audio all on YAMAHA untill 1990

    Messages:
    2,182
    Location:
    France
    check first screen current with accurate tube meter
     
  5. Pio1980

    Pio1980 AK Member Subscriber

    Messages:
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    Angel Station, Alabama
    Either should be OK, and much more affordable for matched pairs than vintage GEC GLs.
     
  6. jeanmarie

    jeanmarie AK Subscriber Subscriber

    Messages:
    2,090
    I run a quad of GEC KT 88 tubes in my MC 75s. It is fabulous sounding with a MX 110. I tried the gold lion reissues with good results I would run them if my others go south.
     

     

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  7. Mike Gibson

    Mike Gibson Modulator Staff Member Super Mod Subscriber

    Messages:
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    Over the years I've had many different output tubes in my original 275. You will get a more discernible change in sound by switching the small signal tubes than you ever will changing output tubes IMHO. There are many threads here on tube rolling. So far I've found the tubes I like the most (other than original GEC's) are the Gold Lion reissues and the Tung-Sol 6550 reissues. I still switch the small signal tubes when I want a change of sound or apparent change of sound. :) Even though the 275 doesn't require matched tubes I always buy them that way for peace of mind I guess.
     
    ron-c and chuckworkb like this.
  8. chuckworkb

    chuckworkb AK Subscriber Subscriber

    Messages:
    3,190
    Location:
    CT
    I personally had a lot of issues with Gold Lion reissue KT88's. I have a set of Penta Lab KT88's at the moment that have worked very well. I agree with the previous poster if you want to experiment with sound swap out the small signal tubes for the best result for your ears.
     
    ron-c likes this.
  9. twiiii

    twiiii Addicted Member

    Messages:
    6,226
    Location:
    west Texas
    At Mac clinics that Davie was conducting he would take the time to show Mac owners of MC 60's MC 75's and MC 275's that the KT 88 had lower distortion, with better signal to noise and better linearity and how the amplifier would put out more power above its rating with KT 88. Of course the factory only used hand picked Gold Lions at the time. One of the reasons I switched from 240's to 275's was by the KT 88 having a much larger envelope the amps ran cooler as did the Power transformer easily doubling the life of all the out put tubes and the tubes near buy. The 275 always sounded a little mellower to me though the 240's and the 275's basically measured the same at lower power levels

    For folks who thought 275's were inferior in the bass, we would hook up a C-24 and play a record noted for bass, The issue was not the 275. A C-24 could wipe a C-22's any time any place. It was scary. After I heard a C-28 driving 3500's compared against my C-22 I was immediately sold on SS. The next move was a horizontal one and one of my two regrets I made buying Mcintosh. I traded my 275's for 2100's. I should have bought the 3500's while I had the chance. Even if they were a maintenance night mare at first. But I knew I was going to bi-amp, and having to purchase two more 3500's eventually was almost financially impossible and the amps would soon be discontinued.

    I'm way off subject now:

    The other regret wasn't as severe. I should have bought MC 7200's when they came along. I knew they sounded better, but I didn't. I kept my Crowns fore close to 30 years, before I bought my 207's and 206. . The 207is a great amp. Not as warm as Mac tube amps and SS amps like the 2200 with low damping factor and not as dry as Crown amps. A nice pleasant, easy to listen to amp. But its not laid back either and little noises and distortion are easily revealed. But you don't feel like you have been smacked in the face either, like the Crown amps often would. Back in the day Crown amps could be 20 db quieter than Mac tube amps and 15 to 20 db quieter than Mac ss amps and that was a bunch. That's the difference between buying a Quad balanced amp recently and unbalanced amps like my 207's MC 252 and MC 300. Its something you can hear but not all the time. When you are listening to quiet passages with semi efficient speakers you only have about 50 db below the signal where the noise lies. Thats marginal for sure. 70 db would be better for sure. Thats what quad amps give. Where would I put 8 MC 301's and one 207?. I'll stick with my two 207's.

    May I make a suggestion ' a fully balanced MC 2507 or a MC 307. That's a challenge . How do you combine the quad sections without an auto former, Accuphase does. Who had Quad balanced first Mac or Accuphase?
     
    Last edited: Oct 1, 2018
    chuckworkb likes this.
  10. ofery

    ofery Active Member

    Messages:
    189
    It seems that KT88 EH are install at McIntosh 275 amps (the reissue version).
    Is that correct ?
    If this is true then they probably a very good choice & better than Gold Lion.
     
    Last edited: Oct 1, 2018
  11. ofery

    ofery Active Member

    Messages:
    189
    Last edited: Oct 2, 2018

     

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  12. Pio1980

    Pio1980 AK Member Subscriber

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    I be interested in an explanation of how that would alter the physics of their operation. Otherwise, I wouldn't be concerned and use tubes from reputable vendors.
     
  13. leftside

    leftside AK Member Subscriber

    Messages:
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    Location:
    Vancouver, Canada
    Agreed. I have 3 different quads of the GEC KT88's. I very slightly prefer the earlier single top getter version.
     
  14. arts

    arts Super Member

    Messages:
    3,732
    Location:
    Qc, Canada
    I received my MC-275 (1965) with what were likely the original (and still testing perfectly!) Genelec KT88s. I put those away for safekeeping and tried various NOS 6550s. The Tung-Sol and GE types sounded fine,but I found the Sylvania version sounded the best (at least to my ears) and produced,by a wide margin, the best figures on the test bench.Damned near impossible to find these days,as all of the savvy Audio Research guys have snapped them up.Just ignore the ugly spotwelding:rolleyes:
     
  15. nj pheonix

    nj pheonix AK Subscriber Subscriber

    Messages:
    9,921
    Location:
    New Jersey
    I've had very good luck with Reissue Gold Lions in MC60s. IIRC Jim Mcshane thought the reissue gold lines were the best of the new tubes . I've heard told you can run KT120s. The PTs can carry the extra current (those amps were designed to power preamps.
    I briefly toyed with a used set. I preferred the gold lions YMMV.
    Also agreed. Tough to justify a grand for a quad of tubes.
    We've had several discussions on the cryo treated tubes.
    The prevailing consensus is its snake oil.
     
  16. GD vinyl

    GD vinyl AK Subscriber Subscriber

    Messages:
    139
    Location:
    Boise, ID
    Let me start by saying I'm a total novice to tube gear and was lucky to be given a pile of mac gear. I run MC60s and a C20 to a pair of Martin Logan Aeon I speakers. One of the 60s has 1 gold lion KT-88 and the other an unknown KT-88. the other has a Sylvania 6550 and an unknown 6550. The system sounds fantastic as is and if I toggle between left and right channels I might barely be able to tell a difference with a minor preference to the KT-88s. Another AK member hooked me up with 4 KT-88 Sovteks for the price of shipping (thank you if you're reading this) which I need to try all together. Some knock the Russian stuff some say good bang for the buck. What would you do with this collection of 8 tubes if you had to use just what's listed here? Thanks!
     

     

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  17. nj pheonix

    nj pheonix AK Subscriber Subscriber

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    Fortunately for you, matched tubes in the unity coupled design aren't required.
    Electrically for all intents and purposes a 6550 and a kt88 are the same tube.
    In other amp designs matched tubes (At least within a channel would give you better performance
     
  18. Pio1980

    Pio1980 AK Member Subscriber

    Messages:
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    Location:
    Angel Station, Alabama
    While not necessary, I'd want them matched pairs for balanced full power capability.
     
  19. nj pheonix

    nj pheonix AK Subscriber Subscriber

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    Location:
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    I haven't heard the Sovteks.
    By and large the current Russian production tubes have been pretty well received .
    The more popular opinion, NOS as a rule tend to be better made but for most applications (At least in output tubes) there's not a ton of sonic difference. Especially in Macs.
    Generally the smaller tubes in the driver circuit tend to influence the presentation more than the outputs.
    (That effect varies by gear design and some gear changes significantly with tube rolling while other gear changes hardly at all
     
  20. GD vinyl

    GD vinyl AK Subscriber Subscriber

    Messages:
    139
    Location:
    Boise, ID
    Thanks for the reply! I’m going to try some different configurations. I don’t have many extra tubes to try unless I buy some.
     

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