BA-5000 Rework

Discussion in 'Exclusively Sansui' started by HDJR808, May 10, 2016.

  1. HDJR808

    HDJR808 Active Member

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    Cautiously optimistic that I will be successful, this is hopefully my first post to chronicle a complete rebuild on one of these beauties.

    Between a non-working example and a pure parts carcass I am hoping that one functioning amp will result. The non-working unit didn't look too bad, but a clipped off power cord was not a good sign. Digging into it unfortunately has been pretty depressing, with soot everywhere, boards that are pretty toasted, butchered wiring, and missing connectors with wires soldered directly to pins (which seems to be amazingly common).

    The external panels aren't bad, but there has been quite a bit of corrosion on the chassis. The donor unit had no panels (except for a top panel that I passed along to member Vigman), missing outputs, cut off input pot shafts (!), an unbelievable amount of dirt and what appeared to be a small rodent skeleton.

    Surprisingly the boards on the parts carcass seem to be in better shape than those in the complete unit, so they will be the ones rebuilt.

    My plan is to refurbish every square inch, so I am starting with possibly the scariest portion- the heatsink and TO-3 sockets. Several emitter resistors had been sloppily replaced and thermal grease slathered everywhere, so out it all came.

    I have acquired the .33 ohm BPR series resistors as noted by Echowars in a posting elsewhere and a supply of Mil-spec Tefzel and tinned copper wire to lace everything back up. These first photos are of the cleaned up heatsink and tediously de-soldered and cleaned TO-3 sockets back in place:

    Heatsink.JPG Heatsink2.JPG Heatsink3.JPG

    This heatsink is a little rough, but unfortunately the sink on the donor unit was even worse (that was the end it appeared to be dropped on).

    More to follow on this long-term project...

    Herb
     
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  2. 4-2-7

    4-2-7 Smart Ass Sponsor Subscriber

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  3. JOMARK911

    JOMARK911 Super Member

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    Will watch with great interest.
     
  4. HDJR808

    HDJR808 Active Member

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    The inside of this amp was a scary sight:
    IMG_0953.JPG IMG_0954.JPG IMG_0955.JPG IMG_0956.JPG

    Aside from being toasted in many areas, it had apparently spent a lot of time in a barn or outside in the elements. The chassis stampings on the parts unit were actually in nicer shape and I used them where I could, although quite a few were bent from the amp presumably being dropped.

    A cobbled together bare chassis:


    IMG_0959.JPG IMG_0960.JPG
     
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  5. JOMARK911

    JOMARK911 Super Member

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  6. HDJR808

    HDJR808 Active Member

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    Some progress with a few items. A previous meddler in this unit had done some creative re-wiring where the leads come off the transformer into the filter caps and rectifiers. Somewhat like what the utility companies refer to as a "mid-line drop," the leads were cut short and tied in to some new jumpers between the big SG-5T diodes:

    IMG_0891.JPG

    This is the behemoth of a transformer opened up to allow me to splice in new leads long enough to reach the original attachment points on the diodes:

    IMG_0996.JPG

    Other than the trimmed blue and yellow leads the rest of the transformer wiring is in okay shape. If there is enough slack when re-installing I may replace the ring terminals on the other leads since they are a little beat up.

    Also being dealt with is the buffer board, which is a good illustration of the pitiful condition of the guts on this thing:

    IMG_0991.JPG

    This buffer board, from a 1975 serial number unit, has the same cut traces, cut diode leg, added resistors and jumpers as discussed here starting in post #15:

    http://audiokarma.org/forums/index.php?threads/ba-5000-for-repair.545595/

    IMG_0988.JPG

    The buffer board from the donor unit is exactly the same, so my plan at this point is to replicate what I suspect is a factory modification of the board.
     
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  7. JOMARK911

    JOMARK911 Super Member

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    Alright keep going. You are doing fine so far.
    :thumbsup:
     
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  8. Overundr1

    Overundr1 AK Subscriber Subscriber

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  9. HDJR808

    HDJR808 Active Member

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    New leads spliced onto the transformer outputs, utilizing the NASA sanctioned "lineman's splice"

    western-union-or-linemans-splice.jpg

    with a double layer of shrink.

    IMG_0997.JPG

    I've picked up quite a bit of mil-spec wire that's sold by the pound at the wonderful Apex Electronics here in LA that I will use for most of the re-wiring that this amp will need. This is the MIL-W-22759 aerospace wire with ETFE insulation (the higher strength version of PTFE) and a 600V 150 degree rating. This is the tinned copper, not silver plated copper like a lot of the mil-spec stuff. A little difficult to strip, but very durable, small diameter per equivalent AWG, and solders very nicely. And if it can be trusted to keep a jet in the air it ought to do quite nicely here.:)
     
  10. JOMARK911

    JOMARK911 Super Member

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    Hmmm , if it holds a Jet in the air , it doesn't necessarily does the job for audio. Being an airman and an audio purist-tech for decades .
     
  11. HDJR808

    HDJR808 Active Member

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    Always eager to gain knowledge, so relevant to this material, what might make 600V 150 degree ETFE insulated tinned copper hookup wire not a good substitute for 600 V 105 degree PVC insulated tinned copper wire? I can see where some of the exotic mil-spec coax cables might be hit or miss for signal applications, but would assume there would be fewer potential pitfalls for hookup wire.

    On another note, these beauties:

    IMG_0998.JPG

    arrived in the mail today from Michael Percy. Very promptly I might add- ordered on Monday, arrived on Friday.

    There were other screw terminal caps I was looking at, but the dimensions on the ones that had comparable specs (and some a little better) seemed to be a little too close for comfort. I just didn't want to take the chance of the terminals being right on top of the chassis.
     
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  12. onwardjames

    onwardjames Hoardimus Maximus Subscriber

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    This level of dedication amazes me.

    Watching with great interest.
     
  13. damacman

    damacman Blown and Injected Subscriber

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    How does such an amp become neglected and serviced by amateurs? Good luck bringing it back to its former glory!
     
  14. Daunia 70

    Daunia 70 Lunatic Member

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    Great work!! It's something I couldn't ever do!
     
  15. JOMARK911

    JOMARK911 Super Member

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    I didn't mean to offend you with my saying. More of a joke was the quote.
    Great caps you have there. I use the same on my restorations.
     
    Last edited: Jun 4, 2016
  16. HDJR808

    HDJR808 Active Member

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    Please, no offense taken. I would hope that a member would point it out if I was doing something ill-advised...
     
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  17. JOMARK911

    JOMARK911 Super Member

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    Sooo any progress there?
     
  18. HDJR808

    HDJR808 Active Member

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    Not so far- in addition to being typically very slow with this stuff, I'm away for a few days of R&R. Buffer board's getting close being done though...

    I have to add for anyone that might have a chance to go there, the Big Sur/Monterey Peninsula area is spectacular.
     
  19. jdwk

    jdwk AK Subscriber Subscriber

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    great thread I will be watching this too
     
  20. HDJR808

    HDJR808 Active Member

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    Buffer board set aside for now, awaiting some 5pf COG ceramics. They slipped through the cracks I guess when I made my first couple of big orders.

    Working on the first of the driver boards now. Since this unit was so trashed, my intent is to replace all semiconductors as well as caps, so even with a desoldering gun it was a couple of hours of work to depopulate this board:

    image.jpeg

    R23 and 26 were encased in the dreaded glue, so they were pulled as well. From all that I've read, there is pretty good consensus on contemporary substitutes for all the transistors except for the 2sc984 bias transistors, and I picked up handful of NOS on the bay.
     

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