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Akai M-8 SEP amps (tracker-x mods)

Discussion in 'Tube Audio' started by BmWr75, Apr 2, 2011.

  1. BmWr75

    BmWr75 Addicted Member

    Messages:
    5,266
    Location:
    Northeast MS
    Here are some pictures of my new to me Akai M-8 SEP amps. Bought these in a Akai "suitcase" RtR (see unmolested pics here) a few months ago. Read about AKer tracker-x's mods and the cabinets AKer Raul has AKer JohnW make for him.

    A month or so later.....here are the results (see pics).

    I only had one problem after completing the mods. One of the amps had a loud hum and I could only faintly hear the music playing. Ended up it was the amp that has the two piece slide-bar on top that must be pushed to the left to make these amps work as standalone amps. The short piece of the slide bar moves independently and I had not pushed it to the left. As soon as that was remedied, hum problem was solved.

    I'd like to thank:

    1. JohnW for making these white oak cabinets with the ammonia fume finish.

    2. Raul for posting the pictures of his M-8 amps. http://www.audiokarma.org/forums/showthread.php?t=345501

    3. Tracker-x for posting his M-8 amp mods. http://www.audiokarma.org/forums/showpost.php?p=1100906&postcount=9

    An easier to read version of the tracker-x mods is posted here: http://www.audiokarma.org/forums/attachment.php?attachmentid=309141&stc=1&d=1320615983

    I'm still running the stock NEC tubes in all positions and these amps sound sweet. :music:

    Update 1: These amps should probably not be stacked as I've shown them in the pictures. They put out some heat.

    Update 2: List of capacitors purchased for the refurbishment (I ordered a few extra of some of the less expensive.......just in case):
    Tube Depot
    Quantity 9 - Sprague Atom 25 uF 25V
    5 - Sprague Atom 20 uF 500V
    2 - multi-cap cans 20 uF x 20 uF 600V
    6 - Orange Drop .022 uF 600V
    8 - Orange Drop .010 uF 600V
    2 - Orange Drop .0047 uF 600V

    Digikey
    2 - 3.3 uF 350V electrolytic radial
    3 - 1 uF 350V electrolytic radial
    2 - 360 pF 500V mica radial (kind of pea shaped actually)
    2 - 15 pF 500V mica radial

    There is a great possibility I already had some of the required caps lying around which are not reflected in the above orders. They would have been Orange Drops though, probably the .022 uF size.

    Update 3: Added pictures of the bottom of the amps after all the umbilical cords have been stripped out. Pics show the locations of many of the caps there were replaced.
     
    Last edited: Jun 16, 2015

     

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  2. Keessie

    Keessie Super Member

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    Those amps are really nice.
    Congrats
     
  3. diamondsouled

    diamondsouled Recycle belly button lint! Subscriber

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    Wow! I wonder if the same can be done with the Roberts version, the 770X and the 770?

    Cheers

    Lar
     
  4. BmWr75

    BmWr75 Addicted Member

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    There is a Roberts equivalent to these Akai amps. I do not know the model number.
     
  5. diamondsouled

    diamondsouled Recycle belly button lint! Subscriber

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    I believe it is the 770X (first pic). Thing with the 770 (second pic) is the face plate is one piece making it more difficult/involved to make two separates. Not sure if there was a comparable Akai version with an integrated face plate, any one know?

    Cheers

    Lar
     

    Attached Files:

  6. 2010 AR D79A

    2010 AR D79A Active Member

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    Last edited: Apr 3, 2011

     

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  7. JohnMac

    JohnMac Addicted Member

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    I looked but can't find tracker-xs mods. can you help me with a link?

    Thanks,
    John
     
  8. BmWr75

    BmWr75 Addicted Member

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  9. JohnMac

    JohnMac Addicted Member

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    Thanks. I looked everywhere but there.
     
  10. FoolForARadio

    FoolForARadio Super Member

    Messages:
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    Location:
    Goldsboro NC USA
    Good job! I like the cases. AK'er Sloober and I did these mods on an M-8 and and a Roberts at the same time, he kept the Roberts and I kept the M-8. I've got a hum in one of mine that I need to track down.
     
  11. BrokenHill

    BrokenHill Well-Known Member

    Messages:
    761
    Location:
    Newhall Pass CA.
    I came across a pair of the Roberts 770x amps about 15 months ago and did
    the tracker-x mods exactly as described.
    I was very impressed with the results of the mods, so yes the Roberts 770x
    units will respond to the tracker-x Akai M-8 mods, I think the circuits are
    the same or very close.
    I also am using the stock NEC tubes and they sound good in these mono amps.
     

     

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  12. Raul

    Raul Active Member

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    BmWr75-
    you are welcome. Great work! Did JohnW made the cases for you or did you built them?
    A question: how much gain/volume have your modded M-8 amps? Mine, with a standard CD player as input, have a rather low volume and I must turn up the knobs at maximum to have a rather good listening volume. I connected these to a pair of Dynaco A-25 that surely aren't the most sensitive speakers around, but I was able to drive them with other small EL84 SE amps, like the ones removed from Magnavox consoles.
     
    Last edited: Apr 3, 2011
  13. Tubeage

    Tubeage Analog Ready

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    Connecticut
    Now THAT, my friend, is TOTALLY AWESOME!

    -Alan
     
  14. diamondsouled

    diamondsouled Recycle belly button lint! Subscriber

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    Try the Mic inputs, but turn the volume down first :yes:

    Cheers

    Lar
     
  15. BmWr75

    BmWr75 Addicted Member

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    Raul,

    I've not tried them with speakers yet, just headphones and there is plenty of gain for headphones.

    Yes, JohnW made the cabinets for me.

    As the prior poster said, the MIC inputs are high gain. Plug your CD player into them and give it a try. Be sure and have the volume turned all the way down on the amps first though.

    Scott
     
  16. bhamham

    bhamham AK Subscriber Subscriber

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    Well done, indeed. Very nice!
     

     

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  17. jaymanaa

    jaymanaa RIP 1961-2018 Subscriber

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    Some folks do away with that first tube (EF86), but heck, that's my favorite low noise pentode. Also be aware that there is no RIAA equalization on the phono input, so you need to run a phono pre of some sort if you want to play rekkids.
     
  18. goldear

    goldear Certifiable Audio Junkie

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    I've never seen a set of those made too look so great before! I absolutely love those cabinets!
     
  19. diamondsouled

    diamondsouled Recycle belly button lint! Subscriber

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    The tube you can do away with is the 6AR5 isn't it? Sumpin to do with erase head oscillator?

    +1 on the cabinets, lovely wood work there. I've been thinking that since my Roberts 770 has an integrated face plate that it would be interesting to fabricate a clear poly face plate for each individual amp. You'd be able to see the tubes then. :thmbsp:
     
  20. BmWr75

    BmWr75 Addicted Member

    Messages:
    5,266
    Location:
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    Yes, the 6AR5 can be removed. I did. Everything is working as it should without it.

    I left the phono tubes in the amps. Will try it with a TT eventually.

    Note: I added the list of replacement caps to the OP.
     

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