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The KA-2000 restoration

Discussion in 'Kenwood-Trio/Kensonic-Accuphase' started by hopjohn, Nov 12, 2018.

  1. hopjohn

    hopjohn Silver Face Subscriber

    Messages:
    1,104
    Location:
    Dallas, TX
    Released in 1968, the KA-2000 is Kenwood's earliest, entry level, all solid state, integrated amplifier. The earliest versions of the KA-2000, as denoted in the brochure below, had two auxiliary inputs, later models have two phono inputs instead.
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    Last edited: Nov 14, 2018
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  2. milo63

    milo63 AK Subscriber Subscriber

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    Everett, WA
    I had a KA-2000 and sold it in a pique of "too much stuff". Adorable little thing and if I find another I'll buy it.

    Looking forward to the lesson.
     
  3. hopjohn

    hopjohn Silver Face Subscriber

    Messages:
    1,104
    Location:
    Dallas, TX
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    Last edited: Nov 18, 2018
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  4. rjsalvi

    rjsalvi Well-Known Member

    Messages:
    581
    Location:
    San Diego, CA
    Reminds me of those Lafayette amps.
     
  5. gort69

    gort69 AK Subscriber Subscriber

    Messages:
    1,118
    Location:
    Vancouver, WA
    Looks like a fun project. Any oddball hard to find stuff in there?
     
  6. Moving Ahead

    Moving Ahead Active Member

    Messages:
    330
    Location:
    Australia
    The Ka 2000..........Known in my neck of the woods as TK150U. (the U being quite important as it has a lovely sticker in the front which was a precursor to this:))

    Although its not a silver face unit hopjohn the khaki gets my thumbs up. BTW that wood grain metal finish is a lost art.
    40W.......Do you think they are over compensating for something? Though the big things come in small packages is probably right.
    Ohh.... I'd like to see the size of their cigar box!......68' won't see any Cubans
    Which reminds me this board was flogged in subsequent models. Maybe the designers were also busy drinkin beer?:beerchug:
    http://www.thevintageknob.org/kenwood-KA-2002.html

    Yeh the alignment @ 6 trimmers. eeny, meeni, miini, moe. (......+1 for phono separation?)

    Looks like the rear chassis next to the fuse holder has a slight wobbly, wobbly.

    Good luck with your resto.
     

     

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  7. hopjohn

    hopjohn Silver Face Subscriber

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    Yes, It's been rumored that the Lafayettes were OEM'd by Kenwood. The see saw switches are rather cool. I like the very definitive click.

    Yes, it took a knock from the heavy-handed USPS as a result of an ebay packing job unfit for a sponge.

    It has six trimpots, two each for the protection circuit, center voltage, and bias adjustment. Phono separation looked to be an unrealized consideration. Components are left off where "seperarion adj." is labeled on the phono amp board.

    The 2SD91 outputs are TO-66 package that are like miniature TO-3 (I'll show them in more detail at some point here) and I doubt there are any drop in replacements. There's probably some other oddball things I'm unaware of, but to this point, anything I'm looking to replace I have a part for.
     
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  8. peteCWA

    peteCWA New Member

    Messages:
    16
    Location:
    NJ
    Trio-Kenwood was the OEM for a number of Lafayette products.
    2SD91 was a common audio output transistor for a number of Lafayette receivers and amplifiers and for a number of other manufacturers. I replaced probably several hundred of these doing Lafayette's service work. They're still available on the open market. I don't remember how many I still have.

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  9. Goldie99

    Goldie99 Well-Known Member

    Messages:
    792
    Location:
    The original Boston, UK
    I've got the Trio badged equivalent (KA-2000) waiting in a pile - you'll find the SM on HFE if you need it - looking forward to watching the rebuild.

    :lurk:
     
  10. hopjohn

    hopjohn Silver Face Subscriber

    Messages:
    1,104
    Location:
    Dallas, TX
    The unit arrived to me in working order. So here are my project goals.

    • Try to maintain the tonal qualities of the amplifier by leaving carbon composition and carbon film resistors in place unless they prove to be out of value.
    • Clean pots and switches for noise free operation
    • Replace all of the electrolytic capacitors
    • Upgrade smaller capacitor values to polyester film where they will fit
    • Replace any of the potentially noisy 2SC458 transistors with KSC1845
    • Replace all of the unreliable carbon trimmers for sealed multi-turn types
    • Adjust the protection circuit, bias, and offset in accordance with the service manual
    • Increase capacitance slightly to supply components and output coupling
    • Upgrade power rectification to handle a bit more current
    • Replace the safety cap with a modern UL approved design

    Tone Amp UA13091A
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    The Tone Amp is not defeatable and as such will always remain in the signal path. Therefore, I opted for using low leakage electrolytic types here, Nichicon KL. The schematic claims that Ci1 to Ci4 are 10uf 16V, but I found that 10uf 25V were what was actually installed. Kenwood used general purpose caps (gray jacketed Elnas of the era) in these positions so this change could potentially make an improvement in the noise floor. All the other capacitors on this board are Mylar (polyester film) so there really isn't much more improvement to be had. I suppose you could use some smaller polypropylene caps, but the stock Mylar caps measure very well and replacing them doesn't seem like a worthy endeavor.

    The Tone Amp used the notorious 2SC458 transistors which are widely known in the AK community for going noisy. A preemptive approach to replacing these is the way to go here. I found that the KSC1845P will provide a good match to the original specs while maintaining a similar gain figure.

    Tone Amp UA13091A

    Ci1-Ci4 10uf 16V (25V actual) GP > 10uf 63V Nichicon KL
    Qi1/Qi2 2SC458 > KSC1845P
     
    Last edited: Nov 29, 2018
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  11. hopjohn

    hopjohn Silver Face Subscriber

    Messages:
    1,104
    Location:
    Dallas, TX

    Pre Amp UA13064
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    Pre Amp UA13064

    Cd1 100uf 6.3V (10V actual) 10mm > Local Filter Low ESR > 220uf 25V PM 10mm
    Cd2/Cd3 3.3uf 16V LL 8mm (sky blue cap stripe is + ) > Input > 3.3uf MKS2
    Cd4/Cd6 10uf 16 (25V actual) 5mm > 10uf 50V RFS 8mm
    Cd5/Cd7 33uf 16V 8mm > Audio > 33uf 25V Elna RFS 8mm
    Cd10/Cd11 47uf 25V 10mm > Filter Low ESR > 100uf 35V PX 10mm
    Cd22/Cd26 10uf 16V (25V actual) > 10uf 50V Elna RFS 8mm
    Qd1-Qd4 2SC458 > 2SC1845P
     
    Last edited: Nov 29, 2018
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  12. Goldie99

    Goldie99 Well-Known Member

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    @hopjohn - very good photo's & schematics, and nice to see someone listing part selection criteria, thanks.

    Q. Have you already cleaned the boards ? or did you just get lucky ? mine are filthy....
    Q. There are also a few components mounted on the back of the Pre-Amp board - are they part of the schematic, or later additions ?

    Alan
     
  13. Moving Ahead

    Moving Ahead Active Member

    Messages:
    330
    Location:
    Australia
    Out of interest where did you find the 'P' classified transistors 4 sale?

    I've found electronic foam cleaner does a good job quickly: even removes kitchen grease.
     
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  14. hopjohn

    hopjohn Silver Face Subscriber

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    This particular unit was pretty clean, all it required was good dusting (used a chip brush).

    The components mounted on the back of the phono board I have here are on the schematic: Rd27/28 27K Carbon film and Cd30/31 560p Ceramic

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    I guess they've become obsolete since I bought them. You can use the KSC1815Y and try to find some at the high end of its hFE range.
     
    Last edited: Nov 29, 2018
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  15. hopjohn

    hopjohn Silver Face Subscriber

    Messages:
    1,104
    Location:
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    In progress...

    Main Amp 8215
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    In progress...
    Main Amp 8215
    Ce1/Ce7 10uf 25V 5mm
    Ce2/Ce8 1uf 50V 4mm
    Ce3/Ce9 1uf 50V 4mm
    Ce5/Ce11 47uf 25V 10mm
    Ce13/Ce14 100uf 3.15V (3V actual) 8mm
    Ce15 47uf 25V 10mm
    Ce16/Ce17 100uf 10V 10mm (ID & polarity unmarked. Negative to the outside edge of board)
    Ce20/Ce21 47uf 6.3V (10V actual) 8mm (ID & polarity unmarked. Negative toward board edge)
    VRe1/VRe2 30K (B) > Vertical inline top adjust >
    VRe3/VRe4 10K (B) > Vertical inline top adjust > 858-67WR10KLFTB Protection
    VRe5/VRe6 500 Ohm (B) > Vertical inline top adjust > 858-67WR500LFTB Bias
     
    Last edited: Dec 6, 2018 at 2:07 PM
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  16. Moving Ahead

    Moving Ahead Active Member

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    Location:
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    Yay, more c458.
    My unit uses canned TO-1 transistors, so it looks like the early units dodged this bullet.

    How are you finding component removal? Wasn't easy in my experience.
     

     

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  17. hopjohn

    hopjohn Silver Face Subscriber

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    When there is multiple components per solder pad it can make removal a little more challenging, but nothing I'd call difficult. Taking a plethora of photos is well recommended to ensure everything goes back where it came.
     
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  18. Moving Ahead

    Moving Ahead Active Member

    Messages:
    330
    Location:
    Australia
    I was referring to the 'Fish Hooks' the gals on the assembly line took pleasure in bending.
    They'll come out alright but it all takes a bit more persuading.
     
  19. Goldie99

    Goldie99 Well-Known Member

    Messages:
    792
    Location:
    The original Boston, UK
    Mine (Trio KA-2000) has the metal cans on the main amp board as well, although it does have C458's on the pre-amp board.
     
  20. hopjohn

    hopjohn Silver Face Subscriber

    Messages:
    1,104
    Location:
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    My advice for that: Once I've removed enough old solder to expose the lead I use the solder tip (3mm wedge type tip is my go to) to heat, push, and rotate the lead over in combination with lightly wiggling the component with the opposite hand. It has to be done gently which comes with experience. Everybody has their own method, but that's what works for me.
     

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