KA-8150 Overhaul

Discussion in 'Kenwood-Trio/Kensonic-Accuphase' started by gort69, Oct 1, 2017.

  1. gort69

    gort69 AK Subscriber Subscriber

    Messages:
    845
    Location:
    Vancouver, WA
    Got this several months back from the bay, an 8150 - the bronze faced version of the KA-8100. Same exact amp with selectable voltage.

    Nothing really groundbreaking here that hasn't been covered in other threads - more of a show and tell really.

    All electrolytic caps were replaced. The new filter caps are 15,000uf 63V (United ChemiCon KMH)- the originals were 10,000uf 56V. Since these are snap-in caps vs the original solder lug caps, new holes for the lugs had to be drilled in the board to accept them. To do the job I made a template of the bottom of the new cap, placed it on the board exactly where I wanted it, marked the spots and drilled with a pin vise and a numbered bit (I forget which size) There is "just" enough space on the solder side to accomplish this - in a couple of spots I had to scrape a little to enlarge the solder pads. The glue was removed with lacquer thinner on a Q-tip (or 10). Lacquer thinner is pretty harsh stuff, but makes quick work of removing the glue. I had no issues with it removing the screening on the board, but try this at your own risk.

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    All that yucky flux on all boards was removed with 91% isopropyl acohol from a spray bottle using chip and tooth brushes.

    I ditched the original filter cap/fuse board brace in favor of a stainless steel wire tie and short spacers. The new caps looked a bit lost in the original brace. I covered this awhile back - http://www.audiokarma.org/forums/index.php?threads/ka-8100-filter-cap-brace.783845/

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    The caps on both the pre-amp and tone boards were all Nichicon UPW 105 degree (I had a bunch left from other projects) with a few exceptions. The exceptions: The two signal path caps on each board got Elna Silmic IIs. All caps originally with an orange jacket got Nichicon UKL, and ALL 1uf caps were replaced with Wima films. Of course I forgot to take photos of the pre-amp board.

    The heat-sinked regulators on the tone board were replaced with On Semi MJE15032/3, and resistors Ri97,98 were upped from 1/4W to 1W (maybe 2W, I forget)

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    The main amp board got mainly Nichicon UFG (had a bunch of those also). The 3 transistors in the protection circuit were replaced. The rectifier diodes were upgraded from 2.5A rated to 5A. A new Omron relay was installed. A previous owner had already replaced the 4 original trimpots with Bourns mult-turns, 'so I had that going for me, which is nice' (Carl Spackler)

    IMG_0306.JPG

    The power switch was disassembled, and the body rotated 180 degrees to utilize the unused contacts and reassembled. The two sides were then bridged together to share the load, and a triac was installed to greatly (drastically) reduce wear on the switch. I drilled a hole in the verical section of the chassis in front of the transformers and mounted it with a Genuine Kenwood Screw.

    P1011178.JPG

    I sent the cover out to be powder coated and they screwed it up (badly) TWICE. So I decided to use the p-coat as a base for Zolatone "Lilith Charcoal" paint. Doesn't sound very manly, but I'm really happy with the way it turned out. This isn't rattle can paint - you need a compressor and a gun to spray it. It's tough stuff - lots of aluminum drift boaters use it, fire departments, etc. It's also used as trunk spatter. Yikes!

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    Thanks to roger2 for his recent KA-8100 restoration thread, and to hopjohn who gave advice via PM.
     
    Last edited: Oct 1, 2017
    dlucy, Karl vd Berg, 8xlaxx and 3 others like this.
  2. hopjohn

    hopjohn Kenwood Krazy Subscriber

    Messages:
    866
    Location:
    Dallas, TX
    Beautiful work on the triac and filter caps. I like the spray coating too. It gives it a rugged vintage look. If you wanna be a badass like rjsalvi and name your amps, you might consider Lilith for this one. Sexy.
     
    rjsalvi likes this.
  3. gort69

    gort69 AK Subscriber Subscriber

    Messages:
    845
    Location:
    Vancouver, WA
    Thanks John. I have a KA-8100 that I'll name Frasier.
     
  4. rjsalvi

    rjsalvi Active Member

    Messages:
    340
    Location:
    San Diego, CA
    You guys are killin' me... :crazy:
     
  5. hopjohn

    hopjohn Kenwood Krazy Subscriber

    Messages:
    866
    Location:
    Dallas, TX
    [​IMG]
     
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  6. SicMan

    SicMan Fire up those speakers Subscriber

    Messages:
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    Location:
    Wolcott - CT. USA
    I like the speckled coating on that one. Looks good.
    Keep it up.

    John
     
  7. ferninando

    ferninando AK Subscriber Subscriber

    Messages:
    12,465
    Location:
    San Jose Ca.
    frazer and his X. right?. the one who makes the winnd blow cold. cant think of her name. Help me. got it , Lilith.
     
  8. Karl vd Berg

    Karl vd Berg Super Member

    Messages:
    1,867
    Nice work. :thumbsup:

    Which 5A rectifiers did you use here?
     
  9. gort69

    gort69 AK Subscriber Subscriber

    Messages:
    845
    Location:
    Vancouver, WA
  10. mcfl

    mcfl Active Member

    Messages:
    102
    Do you mind sharing the part numbers for the replacement of resistors Ri97,98. Also the part numbers for the 3 transistors in the protection circuit area.

    Thanks
     
  11. Oldbutgood

    Oldbutgood New Member

    Messages:
    2
    Looks good man I'm actually about to buy a la 3500 off Craigslist but guy wants $120 and I'm kinda questioning the price
     
  12. Oldbutgood

    Oldbutgood New Member

    Messages:
    2
    KA*
     
  13. gort69

    gort69 AK Subscriber Subscriber

    Messages:
    845
    Location:
    Vancouver, WA
  14. mcfl

    mcfl Active Member

    Messages:
    102
    Thanks for the fast response, really appreciated
     
  15. mcfl

    mcfl Active Member

    Messages:
    102

    Thanks a lot for the great info, I am also restoring a ka-8100 and this is a tremendous help. Can you please tell me how did you match the On Semi MJE15032/3 to the originals. Like the MJE15032 to what original part number and the MJE15033 to what original part number since they are different
     
  16. gort69

    gort69 AK Subscriber Subscriber

    Messages:
    845
    Location:
    Vancouver, WA
    I'll explain how I do it, since I don't have many of these memorized.

    First off, you must replace a PNP with a PNP, and an NPN with an NPN.

    After working on several, I figured out that Japanese transistors that start with "2sa" are PNP, and those that start with "2sc" are NPN. Fairchild followed suit, except their prefixes "ksa (PNP)" and "ksc"(NPN). (There are Japanese and Fairchild transistors that don't have any of those prefixes)

    When I'm not sure - which is most of the time - I google the datasheet. For a random example 2sa620 datasheet: https://alltransistors.com/transistor.php?transistor=8636. For replacements I usually search the part# at Mouser, then click their link to the datasheet.

    This should be enough info for you to do a little research and learn.

    I don't remember off hand which regulators Kenwood used on this amp, but 2sa755/2sc1419 were very common for them. From memory, this is a bit of an oddball setup in that both regulators share one rather small heatsink. One of them is insulated from the heatsink with a mica insulator and a special insulating bushing for the screw, while the other is screwed directly to the heatsink. Pay attention when you remove the originals and duplicate what the factory did when installing the replacements. And be sure and use fresh thermal compound.
     
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  17. hopjohn

    hopjohn Kenwood Krazy Subscriber

    Messages:
    866
    Location:
    Dallas, TX
    This is correct. I can confirm that the regulators are Qi13 2SC1419 NPN and Qi14 2SA755 PNP and are located on the control board. The replacements MJE15032 is NPN, and MJE15033 is PNP.
     
  18. mcfl

    mcfl Active Member

    Messages:
    102
    Thanks a lot for the help
     
  19. mcfl

    mcfl Active Member

    Messages:
    102
    Do you all recommend to change the 3 transistors from the protection circuit even if they look ok ?
    Thanks
     
  20. mcfl

    mcfl Active Member

    Messages:
    102

    Do you recommend to change the 3 transistors from the protection circuit even if they look OK ?
    Thanks
     

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