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Yamaha C-70 Project

Discussion in 'Yamaha' started by sonavor, Dec 16, 2016.

  1. sonavor

    sonavor AK Subscriber Subscriber

    Messages:
    268
    Location:
    Texas
    I think I see but it is 3 AM and my brain is starting to shut down.
     

     

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  2. stereofanboy

    stereofanboy Addicted Member

    Messages:
    6,161
    Location:
    Pensacola
    Sleep well and dream of preamps that don't burn your hand.
     
  3. sonavor

    sonavor AK Subscriber Subscriber

    Messages:
    268
    Location:
    Texas
    I looked at the service manual adjustment for Step 6 and think I see how the test is supposed to be run.
    When I apply a 150 mVAC, 1K Hz signal to one of the inputs like AUX1 and monitor the PRE-OUT (Normal), I get zero volts of course a minimum volume and 1.5 VAC, 1K Hz at maximum volume. Any adjustment of that gain is by manually selecting and inserting a different resistor for R349 (Left channel) and R350 (Right channel). My settings measured within the limits so I am keeping them as they are.
    yamaha_c70_gain_adjustment_step_6.jpg
     
  4. sonavor

    sonavor AK Subscriber Subscriber

    Messages:
    268
    Location:
    Texas
    That should conclude this Yamaha C-70 restoration. All that is left now is to start using it and monitor its performance. I will keep tabs on the temperature of the case and see if it runs any cooler.
    Here is the finished result.
    yamaha_c70_restoration_complete.jpg
     
  5. Half Life

    Half Life New Member

    Messages:
    33
    Location:
    Virginia
    Nicely done! Thanks for sharing your restoration.
     
  6. zaibatsu

    zaibatsu Well-Known Member

    Messages:
    597
    Very cool thread, appreciate the sharing.

    I enjoy seeing all the adjustments in the older amps too.

    Have you already restored the matching M-70 / any plans for doing that also?
     

     

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  7. sonavor

    sonavor AK Subscriber Subscriber

    Messages:
    268
    Location:
    Texas
    Yes, I have the original M-70 I bought with this C-70 that I need to restore. I'm not sure when I am going to do that. It was a good performing amp when it was my main amplifier back in the eighties.
    When I do restore the M-70 I will replace its power on lamp with an LED that matches the one I changed in the C-70. I checked the schematic of the M-70 and it powers its 14V, 80mA lamp (same type the C-70 had) differently. It uses a 12VDC supply to run its lamps so it doesn't have the same lamp heater problem the C-70 had. Howevere, as I remember, the M-70 did get quite warm when it was running. I used to keep a cooling fan on it as well as the C-70.
    yamaha_m70_lamps.jpg
     
  8. JoeMt

    JoeMt New Member

    Messages:
    35
    I'm surprised no one creates a parts list with p/ns and where to buy....would be so helpful for those without all the capacitor knowledge. Still an excellent post.
     
  9. Nashou66

    Nashou66 AK Subscriber Subscriber

    Messages:
    1,616
    Location:
    West Seneca NY

    One thing you can do here and maybe on the two large heat sinks is add some more surface area
    to dissipate the heat. I did this on my A-960 with the chimney stack type heat sinks they also use.
    The T-220 heat sinks I had laying around do come in taller versions and with longer fingers/fins.

    Here is a pic using the ones i had laying around. I got about a 7 Celsius drop with those added.
    I was going to add two more to each by taping a thread to them , one on top of the transistor and one each on the sides .

    Might help with the large heat sinks as well.

    [​IMG]


    Athanasios
     
  10. sonavor

    sonavor AK Subscriber Subscriber

    Messages:
    268
    Location:
    Texas
    Good idea Athanasios. I am happy to report that my C-70 I restored in this thread is performing great and is running much cooler than it was before. You still wouldn't want to put it in an enclosed cabinet or stack components that sit over the rear vent. However, before the back of the case would get almost too hot to hold a finger to. Now it is warm but not terribly hot. If I could drop it another 7 Celsius that would be great. I have another C-70 in my backlog I can try it on but I won't be able to get to that for quite some time.
     
    Nashou66 likes this.
  11. sonavor

    sonavor AK Subscriber Subscriber

    Messages:
    268
    Location:
    Texas
    I understand what you are saying but with restorations like this there are a number of options regarding what specific capacitors to used to replace originals with. I have my way of doing it and others may differ some in the way they do it (or which specific electrolytic capacitors they choose). There have been many heated discussions on audio forums regarding what capacitors to use or not use so I am reluctant to post specific part numbers for those type of things. Plus I don't necessarily use the exact same capacitor part each time. Sometimes I do create a spreadsheet of the parts I want to order but for this C-70 project I just made a list on paper because I went through the capacitors I already had in stock and determined what I needed to order. When buying parts, I check Mouser, Digikey and Newark most of the time. I look for the best price on the order and try to get everything at one place if I can in order to get the most bang for my buck on shipping cost. I don't buy capacitor parts from Ebay or NOS capacitor parts.
     

     

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  12. pdm4606

    pdm4606 Super Member

    Messages:
    2,948
    Location:
    Las Cruces, NM
    Are there any differences from the C-50 to the C-70? My C-50 is working fine except for a right channel drop out from time to time. I assume it is from dust as I built a plywood top cover with a 4" fan for cooling. All else is open.
    The C-50 transformer is open due to an inside fuse on the main in blown years ago. I dug into the potting and found the windings after the blown fuse and has been working fine since. I mounted the open side up so the plywood cover has a giant hole to clear for wires.
     
  13. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,656
    Location:
    Fort Dodge, Iowa
    Big difference.
    Intermittent relay most likely.Dirty switch or cold solder connections can't be ruled out.
     
  14. pdm4606

    pdm4606 Super Member

    Messages:
    2,948
    Location:
    Las Cruces, NM
    I did the bad solder connection thing once. Around 40 bad or loose connections re-soldered. Better but still interm.
    I really love the voice of this preamp. It is clean and detailed. I am sure modern pre's. will sound not much better.
     
  15. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,656
    Location:
    Fort Dodge, Iowa
    There are around 5 little orange/yellow relays in there.Find RY401 . The relay contacts may have issues.Tap on that relay and see if you can duplicate your malfunction.
     
    Last edited: Jan 19, 2017
  16. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,656
    Location:
    Fort Dodge, Iowa
    The relay RY401 is on the same board as the pre-out jacks. About 1/2 way down on the inner edge of the board.
     

     

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  17. comish4

    comish4 comish4

    Messages:
    677
    Location:
    Sandusky Ohio
    I have a Yammie to work on one side is suffering from very low output on one side unless the direct button is selected. Just been putting it off. Great work!
     
  18. pdm4606

    pdm4606 Super Member

    Messages:
    2,948
    Location:
    Las Cruces, NM
    I have new relays for the pre but they are sitting now. I plan to install new gold contact relays to replace the old intermittent ones I have now.
    I also have another C-50( number 2) that I have removed the relays on. My plan is to do the number 2 C-50 first then replace the number 1 C-50 (the c-50 I am using now).
     
  19. avionic

    avionic " Black Knights " Subscriber

    Messages:
    43,656
    Location:
    Fort Dodge, Iowa
    What part number are these ? Start a new thread or your piece.
     
    Last edited: Jan 20, 2017
  20. Slickrambler

    Slickrambler Active Member

    Messages:
    185
    Location:
    Southern Indiana
    Great post !
     

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