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Kenwood KA-3500 recap

Discussion in 'Kenwood-Trio/Kensonic-Accuphase' started by Dingman, Apr 14, 2017.

  1. Dingman

    Dingman Do you know where your towel is? Subscriber

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    Hiyas guys~ this is my first time in the Kenwood section.

    You fools, you left the door open. :)

    I have a KA-3500 that I'll be re-capping. Originally came to me as having right channel not working properly. Owner had identified that bias couldn't be set properly on Rch.

    I replaced Qe15,17 and got bias correctly set on both channels.
    EDIT: this repair is suspect. I can't explain why bias is OK now. Original transistors test fine on two diff cheapo testers.

    Nevertheless, this is a 1977 vintage unit. Since I already had to remove the boards (a little tricky) for the bias issue, now is the time to replace electrolytics. 40 years old is good enough, thank you.
    Unit is opened, boards half-way out. I removed both the pins conneting main board to black wires (neutral) of the transformer. This allowed me to get the main (and thus other) boards out for work. The bottom of this unit does not come off, you have to remove all the boards.
    Kenwood KA-3500 recap 01.jpg

    I'll update as needed! I hope to have this all done in a week or two. Or three.
     
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  2. SoundOfSound

    SoundOfSound Super Member

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  3. hopjohn

    hopjohn Silver Face Subscriber

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    Welcome to the Kenwood forums. The KA-3500 doesn't get much play here it being pretty much BOTL. Any photos, troubleshooting, or information you provide is greatly welcomed and your trail to blaze.

    I like the lazy susan BTW.

    Cheers.
     
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  4. gort69

    gort69 AK Subscriber Subscriber

    Messages:
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    I recapped one last year- unfortunately this is the only picture I took. Lots-o-disassembly! The spring clamp was just to hold it somewhat upright. Surprisingly powerful and nice sounding amp - worth the effort.

    [​IMG]
     
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  5. hopjohn

    hopjohn Silver Face Subscriber

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    You aint kiddin' Where's the chassis? Haha :D
     
  6. Dingman

    Dingman Do you know where your towel is? Subscriber

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    Actually, I do have a question. The rectifier looks to be fairly robust (and easily replaced), so what's the opinion on upping the final filters from 6800\42 to 10K\50?
    I'm thinking this will be just fine and in fact should be a nice upgrade.
    Kenwood KA-3500 Filter10k.jpg
     

     

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  7. Dingman

    Dingman Do you know where your towel is? Subscriber

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    Got some work done on the main board - kinda going overboard on caps, but I have them on hand, so in they go. Some of this is signal path (I think), so not wasted caps. The black caps are general purpose, they are in the power supply side (pretty sure). LOL, I'm not great at understanding the schematics.
    I thought about removing completely from the chassis and I still might. But working like this on the main board for now.
    Kenwood KA-3500 recap 02.jpg Kenwood KA-3500 recap 03.jpg Kenwood KA-3500 recap 04.jpg
     
    Last edited: Apr 16, 2017
  8. Dingman

    Dingman Do you know where your towel is? Subscriber

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    This is baffling - I've never seen this before. The main filter caps, 6800uf, both tested out at around 2400uf. Now, I am wondering if I should put 10kuf back in. The owner liked the sound before and going from 2400 to 10K is a large jump. But of course, the spec is 6800uf. Hmmm.
    And a few other small caps testing bad as well. (in each pair of lines, top is old cap, bottom is new cap).
    Kenwood KA-3500 recap values 01.jpg Kenwood KA-3500 recap values 02.jpg Kenwood KA-3500 recap values 03.jpg
     
  9. DrumminDaddy

    DrumminDaddy Hit it, Baby !!

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    Lost in musing circumstances
    Wasn't me...:rolleyes:

    Whatcha got going on with that black unit on the back of the bench? Can't quite make it out.
     
  10. Fredrik 1977

    Fredrik 1977 Super Member

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    stick those 10000uf in, it will be just fine!
     
  11. Dingman

    Dingman Do you know where your towel is? Subscriber

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    It's my home made connection panel. I got tired of re-arranging connection cables, depending on if I was working on amps, pre-amps, speakers, ect. So, I got a backpanel from some generous AK'er and used the terminations on the back to keep things cleaned up. A little, I guess it's still a little ugly, but it does work and is fast for changing configuration. Wired that up to an impedance matching speaker selector.
    Test Bench connection panel.jpg
     
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  12. Dingman

    Dingman Do you know where your towel is? Subscriber

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    Kenwood KA-3500 recap values 04.jpg
    Yes, I think so too. And the ones I already have will save owner money (I just checked, replacements will be another $12) and they fit perfectly. I suspect there may be a significant low freq boost going from 2400uf to 10kuf? Is that right?
    For entertainment~ picture of me tracing signal - I've already put a few nice caps where they weren't needed. Doh. I got ahead of myself.

    NOTE that C1 and C2 both have a 1uf\50v installed, NOT a 0.47 as the schematic and parts list show. Not a huge deal, but I stuck with 1uf
     
    Last edited: Apr 16, 2017
  13. Fredrik 1977

    Fredrik 1977 Super Member

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    yes it will be one hell of a boost in performance.

    if those 1ufs are signal coupling, i´d consider using mkt filmcaps in those positions.

    and i like your homemade patch-bay:)
    i use a crappy technichs amp where i have mounted the speakerposts and aux-in, pre-out and mainamp in. on the front :D that way it can handle most of what i need to test. it works but i think its starting to act up on me! i´ll make something more serious later on.
     
    Last edited: Apr 16, 2017
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  14. Dingman

    Dingman Do you know where your towel is? Subscriber

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    they are coupling, and I put WIMA's in there. I have some mkt type 1uf's and do use them sometimes, the WIMA are pretty sterile. I think the mkt's aren't so... cold? All subjective.
     
  15. Fredrik 1977

    Fredrik 1977 Super Member

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    YEY! very good!

    well now i saw you list some posts up. :oops:
     
    Last edited: Apr 16, 2017
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  16. Dingman

    Dingman Do you know where your towel is? Subscriber

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    I don't always succeed but I try to bend the leads over to get a mechanical connection and not just rely on the solder to make the connection.
    Kenwood KA-3500 recap 06.jpg
     
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  17. Fredrik 1977

    Fredrik 1977 Super Member

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    well i dont think the wima is especially good, but its the only brand that makes em in the perfect size for this application. and they are way way way better than any electro cap.
    i would like ROE mkt caps in the sizes fitting preamps.
    but i use wima all the time in amps. because of the size. they are perfect for replacing those pesky electros/tantalums in the signal-path. atleast up to 10uf.

    i did try some different caps in a cdp (output coupling) long ago. and i did like roe mkt/mkc best, wima came pretty low on my list :)
    mkp caps were pretty nice too...but they are even bigger
     
    Last edited: Apr 16, 2017
  18. Dingman

    Dingman Do you know where your towel is? Subscriber

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    Ya, space was tight, wima small enough to fit. My mkt's are pretty large.
     
  19. Dingman

    Dingman Do you know where your towel is? Subscriber

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    I see good things about this amp. And bad things.
    Bad things: Crappy solder joints.
    LOL, tested camera with a magnifying lens to see if I could get SUPER close. Nope, looks like camera auto-focuses to... whatever. 2nd pic is just came, no stupid lens. Turned on "flower" mode or some funny girlie name like that and it got way close! Nice!
    Kenwood KA-3500 solder joint 01.jpg
    Kenwood KA-3500 solder joint 02.jpg
     
  20. Dingman

    Dingman Do you know where your towel is? Subscriber

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    Good golly, the glue.
    Kenwood KA-3500 recap 07.jpg
     

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