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A-700 Restore

Discussion in 'Yamaha' started by Scottfer55, Mar 6, 2018.

  1. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,898
    Location:
    Fort Dodge, Iowa
    I wouldn't. Keep it as close to original values as possible. Upping the voltage will likely increase the physical size. Some of those phono sections are pretty crowded already.
     
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  2. Scottfer55

    Scottfer55 Member

    Messages:
    93
    Location:
    Martinez, GA
    Ok thanks, that helps.
     
  3. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,898
    Location:
    Fort Dodge, Iowa
    If your ordering from mouser the caps part number will begin with 647-UPW.................. or 647-UHE............
     
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  4. zaibatsu

    zaibatsu Well-Known Member

    Messages:
    596
    I presume you mean the 1000uF KZ for the phono stage?
    You need to use 25V here, the 50V is too big to physically fit.
    On the power amp board the 50V fits fine (matches original :)).

    RE: temperature - I meant choose 105*C rated ones for anything I didn't list. Yes, most I listed are 85*C, it's fine for those. Some of the smaller ones I didn't cover are closer to the heatsinks (further out from center of power amp board) so films or 105*C are good.

    It's up to you on the film caps - I like them because it means I never have to worry about them again for the life of the amp (they don't degrade, at least not like liquid electrolytics), but if you just go up a voltage rating where possible on the remaining electrolytics (do check dimensions if doing this) they'll probably work just as well.

    What avionic said for the PW / HE, (KZ is now UKZ too).
    Best wishes on the rebuild!
     
    Last edited: Apr 24, 2018
  5. Scottfer55

    Scottfer55 Member

    Messages:
    93
    Location:
    Martinez, GA
    Yep the 1000uF is what i meant. Its all cleared up now. Much thanks!
    Decisions decisions... film caps or original...
    Seems like a no brainer though, you guys know what your talkin about.
    Ill check cost and decide preciate it
     
  6. Scottfer55

    Scottfer55 Member

    Messages:
    93
    Location:
    Martinez, GA

     

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  7. zaibatsu

    zaibatsu Well-Known Member

    Messages:
    596
    I believe it's just the packaging, one is on a cut-tape reel.
    You can go for the cheaper one, it won't matter since those will directly fit the factory holes with 5mm lead spacing.

    For some caps the reel is nice since you get longer leads and can bend them to fit strange mounting locations.
     
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  8. Scottfer55

    Scottfer55 Member

    Messages:
    93
    Location:
    Martinez, GA
    Ok I’ll go with the cheaper ones, that’s a big price difference too. I want to have the trim pots on hand in case the existing ones don’t clean up good. Can I use the d5 DeOxit to clean those?
     
  9. zaibatsu

    zaibatsu Well-Known Member

    Messages:
    596
    Yes you can. Just swab off the excess with some alcohol after leaving the deoxit on / cycling.

    If you want a cheaper option, the single turn ones (sealed eg. Bourns/Vishay) work fine, just takes a little longer to hit target adjustment.
    Make sure you get top-adjust versions of whatever you get.
     
  10. Scottfer55

    Scottfer55 Member

    Messages:
    93
    Location:
    Martinez, GA
    Think I’ll go with the multiturns @OMGCat! linked earlier, after cleaning and recapping I’ll see how the voltage holds. If there’s any doubt I’ll pop the new ones in.
    I don’t think I’ll be using the class A option, so Can I just leave that pot alone? Could a problem occur if someone turns it on without it being adjusted properly.
    Is there a mod for the speaker output posts? I don’t particularly like the ones that are on it.
    Thanks again
     
  11. zaibatsu

    zaibatsu Well-Known Member

    Messages:
    596
    • The multiturns are nice. If I were buying them I'd install them too but it's up to you
    • I haven't had an issue with the stock pots wandering once set
    • Yes you can leave the class A switching pot alone, if you haven't moved it the function will still work fine. I think I still have at least one here where I use the mode and haven't checked the adjustment, no problems. It would only cause some distortion if it was way out of spec (and only after exceeding the 5W range, which is about the tolerable listening limit on most speakers), shouldn't actually damage anything anyway
    • I haven't seen anyone change the binding posts on this exact amp, I'm sure you could do anything you like
    I've found those posts can securely clamp quite thick bare wire, what I do is split the end into two even bunches and twist them up separately (into a Y shape), then with the binding post backed all the way out, press it in (this part can be a bit crude) so that the Y splits around the center. It exits through the cutout as normal - I hold it in place, while pushing stray strands in to get clamped.

    wire.jpg

    By all means change them if you like though!
    Best wishes
     
    Last edited: Apr 26, 2018
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  12. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,898
    Location:
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    Yep..I concur...:biggrin:
     
  13. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,898
    Location:
    Fort Dodge, Iowa
    I find that 12 gauge ,OFC multistrand . Car audio speaker wire does the trick for me.
     
  14. Scottfer55

    Scottfer55 Member

    Messages:
    93
    Location:
    Martinez, GA
    I use banana connectors on the ends of my #12 stranded that I bought from monoprice. I’ll just have to remove them and terminate on the screw type binding post, no big deal. It’s probably a better connection.
    I also bought a pair of kef q100 bookshelf speakers. Quite impressed
     
  15. Scottfer55

    Scottfer55 Member

    Messages:
    93
    Location:
    Martinez, GA
    What was the purpose of the old corrosive adhesive under the caps and should I use an alternative such as silicone?
     
  16. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,898
    Location:
    Fort Dodge, Iowa
    Stabilize components during wave soldering (assembly line) . 99% of the time I don't use any adhesive on caps. If I do use any , its permatex sensor safe black gasket sealant.Give it a good 24 hours to cure. Note: Use sparingly. That stuff is strong once cured.
     

     

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  17. avionic

    avionic " Black Knights " Subscriber

    Messages:
    42,898
    Location:
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    Most silicone sealants(RTV) outgas during the curing and smell like vinegar(acetic acid)<--- not sensor safe..:biggrin:
     
  18. Scottfer55

    Scottfer55 Member

    Messages:
    93
    Location:
    Martinez, GA
    Glad I asked! I’ll skip the silicone :banana:
     
  19. Scottfer55

    Scottfer55 Member

    Messages:
    93
    Location:
    Martinez, GA
    99BA0710-E1F7-415D-A949-06765D290718.jpeg 2BAC156B-B3E7-4D07-9B2F-EB33DCE5C131.jpeg DDB28A48-8BD3-46DC-921B-E83CB186F430.jpeg
    Desoldered all old caps, recorded old vs new values placed new caps in place.
    Some of the new cap esr values were nearly as high as what I took out in particular the nichicon 2.2uf 100v, I used the pw series c227-230. But the majority were much lower esr.
    I don’t begin to act like I know what the esr value does I just read that the lower the better in most cases. They’re in there now so I’ll get to soldering here a little later and hopefully get a relay click. Getting excited about warming this thing up...
     
  20. zaibatsu

    zaibatsu Well-Known Member

    Messages:
    596
    Nice work, yes lower is better for ESR.
    It has some proportionality to ripple current and case sizing, which is why I pushed for bumping up the voltages to match stock case sizing where possible.
    Hopefully it was comparable / lower on all the bigger caps. It's normal for those little 5mm electrolytics to not be so great, hence switching for films when budget allows.

    I snapped some pics of my bias transistor mounting as promised:
    A-700_bias_1.jpg A-700_bias_3.jpg

    I advise changing these along with your caps (if you ordered them), as the legs can be brittle from heat cycling over the years even w/o physical movement. You can mount it in the stock position too, just run a file along that top surface to ensure it's flat (there's a high spot around the threads). Use thermal compound either way, and if you do change them, DBT for first power-up, and check the idle values are normal/low (they will read lower than normal on DBT, ~2-5mV probably) just to make sure no short / orientation error has been made.

    Best wishes
     

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