KA-5700 -- The Green Machine :-)

Discussion in 'Kenwood-Trio/Kensonic-Accuphase' started by rjsalvi, Sep 9, 2018.

  1. rjsalvi

    rjsalvi Well-Known Member

    Messages:
    517
    Location:
    San Diego, CA
    Just a baby Kenwood KA-5700 with the following work done:

    **Green Hammer finish powdercoated case
    **ALL electrolytic capacitors were replaced (FC in PS -- film, UFG and UKZ in audio)
    **ALL diodes were updated except the germanium ones for the meters
    **ALL resistors 1/2W and up were updated with same value metal film
    **ALL 1/4W 5% carbon film resistors were updated to 1% tolerance metal film ones
    **ALL transistors updated except for outputs and phono stage JFETs
    **New lamp and fuses
    **Potentiometers and switches received the prerequisite Deoxit treatment (speaker and input selector pulled apart and contacts cleaned)
    **Main filter caps bypassed with film caps and upped from 6800uF, to 10,000uF

    I restore a lot of 5700s because they're not only easy, but because they provide great bang for the buck and when I sell them. Being at the low end of the price range for properly restored gear...they sell relatively fast. They're kind of like the VW Beetle of Kenwood amplifiers...inexpensive, but reliable as hell...and they sound really good! :)
     

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    Last edited: Sep 11, 2018
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  2. slimecity

    slimecity Super Member

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    Thats really nice work with all the metal film replacements!

    Nice lid colour too!
     
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  3. ferninando

    ferninando Lunatic Member

    Messages:
    12,467
    Location:
    San Jose Ca.
    I too have a 5700. All Ive done is new PS caps.
    It sounds very good IMO. Really glad I got it.
    Its a keeper.
    Also have a 7100. Another great sounding KW amp.
     
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  4. rjsalvi

    rjsalvi Well-Known Member

    Messages:
    517
    Location:
    San Diego, CA
    Thanks! The 5700 is a sweet little amp in its own right because of the passive preamp section. When one changes out all the components with modern low noise ones, it really cleans things up! It's ton of work, but well worth it, imho.
     
  5. Milesc2

    Milesc2 New Member

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    23
    Nice work!
     
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  6. rjsalvi

    rjsalvi Well-Known Member

    Messages:
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    Location:
    San Diego, CA

     

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  7. slowpat

    slowpat Slowly but surely.... Subscriber

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    Does changing from carbon film caps to metal film caps change the sound? Or are the carbon composite the ones that keep the vintage sound?
     
  8. rjsalvi

    rjsalvi Well-Known Member

    Messages:
    517
    Location:
    San Diego, CA
    They're metal film resistors, not caps and as a system-wide change, yes, the sound changes too. From here:

    "Metal film resistors have good characteristics for tolerance, stability and TCR. Furthermore, the resistors feature low noise properties and a high linearity because of a low voltage coefficient. Therefore, in circuits where tight tolerance, low temperature coefficient and low noise properties are important, often metal film resistors are used."

    "TCR", as mentioned above, is the variation in resistance due to temperature changes. You'll usually see the TCR spec represented as PPM. Lower PPM >>> less change in resistance with temperature. Changing from 5% tolerance carbon film resistors to 1% tolerance metal film resistors -- especially in the signal path -- usually manifests itself as cleaner, more pronounced high frequencies and overall lower noise. One of the added benefits of utilizing tighter tolerance parts, is better channel balance (L/R)...and of course, they tend to last longer.

    Why change all the resistors? For me, it's purely philosophical in that I'm after sonic purity -- not a "vintage sound" -- and also because these units are 40 y/o. At 40, what's the next weak link to go? If I restore a piece of gear and I'm asking someone to pull out their wallet and pay top dollar, the last thing I want is for that customer to call me in six months and say "something's wrong". (chuckling) I'm also OCD, so restoring units it to the nines is just how I roll.
     
  9. slowpat

    slowpat Slowly but surely.... Subscriber

    Messages:
    3,882
    Location:
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    Thanks for the explanation. Yes, I meant "resistors" as I typed capacitors..LOL

    Yes, I can see the benefits you mentioned. It's just a lot of work to change all of them, but you are delivering a high quality restoration after all....
     
  10. rjsalvi

    rjsalvi Well-Known Member

    Messages:
    517
    Location:
    San Diego, CA
    Yes, it's a s**tload of work to change them all, especially in a receiver which has multiple boards for the tuner as well! :eek: Having said that, when the voltages are dialed in and it's time to run an audio signal through it, that's when the magic happens! :thumbsup:
     
  11. SicMan

    SicMan Fire up those speakers Subscriber

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    I just had to post this ... :rflmao:

    burning_amp.jpg
     

     

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  12. rjsalvi

    rjsalvi Well-Known Member

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    LOL!!! I'm glad you did!
     

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