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Finally rebuilding my Sansui G-8000, I’ll post all my questions here.

Discussion in 'Exclusively Sansui' started by saabracer23, Sep 6, 2018.

  1. saabracer23

    saabracer23 AK Subscriber Subscriber

    Messages:
    1,049
    Location:
    Salem, Oregon
    Hey all, so I came across this mint G-8000 that I’m starting a rebuild on. One channel has zero output and so I’m working on finding those issues. I’m doing a full recap etc. First question: on the power supply board there is a large resistor and the manual calls for a 3.9 ohm 15w resistor. The one in there now definitely does not look factory and measures at 16.2 ohms, made is a 10w and 5w in parallel. Now I know that there can be discrepancies in Sansui manuls. I have a 4 ohm 25w, a 3.9 ohm which I believe is 17w???, and a pair of mills 12w 8 ohm that I can wire in parallel for 4 ohm 24w.

    Thoughts? Anyone with a G-8000 that can confirm what value goes there?

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    Dan
     

     

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  2. kevzep

    kevzep Its all about the Music Subscriber

    It is the soft start by-pass resistor, 4Ω is close enough so put your 25 watt 4Ω in there.

    It would be a good idea to test the output transistors on the dead channel and also the drivers on the corresponding driver board.

    Then measure all the emitter resistors and also all the low value resistors around the driver transistors on the driver board too.
    There are a lot of resistors which go hiZ when there is a failure in the output section.

    Let us know how you get on...
     
  3. saabracer23

    saabracer23 AK Subscriber Subscriber

    Messages:
    1,049
    Location:
    Salem, Oregon
    Also I noticed there is a large 220v sticker on the back, but a 220v/110v switch on the inside. Will this have any change to the materials in the amp and service manual?

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    Dan
     
  4. saabracer23

    saabracer23 AK Subscriber Subscriber

    Messages:
    1,049
    Location:
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    Thank you so much, I intend to measure all of the outputs and the drivers. When I get to that step I’ll definitely share!

    Dan
     
  5. saabracer23

    saabracer23 AK Subscriber Subscriber

    Messages:
    1,049
    Location:
    Salem, Oregon
    Alrighty, replaced the soft start by-pass resistor.

    162FDA4B-808A-4FB8-85CF-ABF5869D0BF3.jpeg

    Also, does anyone know where you can purchase or use for the SS-5R/SS-5 rectifiers? Whenever I do a full restoration I like to replace the bridge rectifiers.

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    Dan
     
  6. kevzep

    kevzep Its all about the Music Subscriber

    No need to replace those, I have never ever had any issues with those. They are well rated for the job at hand.
    I have never seen one fail and I have worked on literally hundreds of amps that have those rectifiers.
     

     

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  7. saabracer23

    saabracer23 AK Subscriber Subscriber

    Messages:
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    Great thanks. I’ve rebuilt several amps that use them as well such as the Kenwood KA-8006 and have never seen one dead. I thought since I run into them so often maybe I should look at finding a replacement. No need, thanks!!!

    Dan
     
  8. mattsd

    mattsd AK Subscriber Subscriber

    Messages:
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    Just a FYI for anyone looking, these are a perfect replacement to the G-8000/9000 soft start resistors. I used one recently for a G-9000 that had been to 3 different shops and they all couldn't fix the problem. Just needed the soft start relay replaced due to badly burnt contacts along with the resistor.

    20180722_145946.jpg
     
  9. kevzep

    kevzep Its all about the Music Subscriber

    Always a good standard operating procedure to replace the relay if the soft start resistor is toast.

    I might grab a few of those to keep in stock, thanks Matt...

    Its amazing what I've found when guys bring me units that have been to "three other places that couldn't fix it"
     
  10. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    And I bet they all said "The mains transformer is blown" :D
     
  11. kevzep

    kevzep Its all about the Music Subscriber

    I bet they did too John....
     

     

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  12. saabracer23

    saabracer23 AK Subscriber Subscriber

    Messages:
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    So I’m rebuilding the mic amp circuit board and there are two .068 uF caps that I’m replacing and the closest I have on hand are some Wima .1 uF caps. Anyone know if they’ll have any ill effect in the circuit by going with that value? C03 and C05.

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    Thank you,
    Dan
     
  13. kevzep

    kevzep Its all about the Music Subscriber

    Are you sure they aren't 0.68µf? Are they electrolytics?
     
  14. lbcgav

    lbcgav AK Subscriber Subscriber

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    Mattsd used Panasonic ECQs (polyester) in those spots. According to his cap list, they were originally tantalums.
     
  15. saabracer23

    saabracer23 AK Subscriber Subscriber

    Messages:
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    They are tantalum, I want to get all of the tantalum out.

    Dan
     
  16. kevzep

    kevzep Its all about the Music Subscriber

    Tantalum in this particular application is absolutely fine. They are just in the audio path, and they are a far better dielectric for the job they are doing than any film cap or electro.
    If you wanted to, you could just buy new tantalums to fit...

    Tantalums are also used in Tuners for their excellent ESR and accuracy, these need to be left as well.

    Tantalums in some power supply applications are where its better to get rid of them, as they are prone to failure (and spectacularly) when they spend 100% of their working life under stress as they would be in a power supply.
    In power supplies we like reliability.
     

     

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  17. saabracer23

    saabracer23 AK Subscriber Subscriber

    Messages:
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    Oh, okay I’ve always read that it’s a good idea to remove all tantalums from the unit. So I’ve always removed them. I’ve read that they should be replaced with film (I use polypropylene) as they have a lower ESR than the electrolytics. I can put the tantalums back in, just feels weird to do something different, though it’s in a part of the amp that will likely never be used.

    So tantalums produced in the 70s will have a lower ESR than films currently made?

    Dan
     
  18. saabracer23

    saabracer23 AK Subscriber Subscriber

    Messages:
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    Location:
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    So I measured the original tantalum and they show an ESR of 30.9 ohms and the .1 uF films measure an ESR of 5.39 ohms. Should I still put the tantalums back in even though they have a much higher ESR?

    Dan
     
  19. kevzep

    kevzep Its all about the Music Subscriber

    I remember now with my G9000, I just left those tantalums in that mic preamp circuit, both those ESR readings seem high to me though....
    It does seem a waste of some nice Film caps to put them in something you'll never use.
    The Tants aren't going to cause an issue there, no danger of them randomly exploding, so I would leave them.
    But its up to you of course, we all do things differently..
     
  20. saabracer23

    saabracer23 AK Subscriber Subscriber

    Messages:
    1,049
    Location:
    Salem, Oregon

    Yeah I’m not entirely sure how accurate the meter is. My other meter which is very nice quality will only measure down to 1 uF. Even if it’s off it seems the tantalum has a higher resistance. Thanks for your assistance, I’ll likely put them back in.

    Dan
     

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