Replacement filter caps for AU-919

Discussion in 'Exclusively Sansui' started by lbcgav, Jul 24, 2018.

  1. lbcgav

    lbcgav AK Subscriber Subscriber

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    That makes sense, since Australia as a British colony is much younger than the US. I wonder when and why the US dropped the use of the "u" in words like colour, favour, labour, etc.

    I found another guy on eBay willing to make a deal on the remaining two knobs and some screws he had left over from the teardown. I also picked up the recommended screws for the output transistors from my local Home Depot. :thumbsup: I've spent roughly an additional $120 due to the lost knobs and screws so far. I'll need more screws for the mounting the boards, chassis, bottom cover, and filter caps, but it hasn't been as bad as I originally thought it would be.
     

     

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  2. kevzep

    kevzep Its all about the Music Subscriber

    Oh the blasphemy!! New Zealand is its own country, nothing to do with Australia, its like saying Canadians are Americans!! :yikes:........:D

    Good you were able to find all the parts you needed, you stuck gold, fortunately I have not done something like that, I do have a few customers amps in bits, I have a method to my madness so I don't lose everything or at least I hope I don't lose things......like that screw that you drop on the floor and you can never find it until a couple of weeks later....
     
  3. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    I don't know when all this happened, but think they were trying to simplify the spellings, removing letters that were perceived to be redundant. All this did was to give more weight to the widely attributed quote "The United States and Great Britain are two countries separated by a common language", and to place us where we are now discussing who is right. :D

    Sorry, this thread is now way off track. :(
     
    Last edited: Jul 28, 2018
  4. lbcgav

    lbcgav AK Subscriber Subscriber

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    You know, after I wrote that last night I was thinking to myself, "is Kevzep from New Zealand and not Australia?" I was going to go back and check, but when you have little kids, things happen. Sorry about that.

    I've rebuilt about 15 amps now, and this is the first time I've lost anything major. The lost parts at work were definitely thrown out by another employee. The day after the first night I brought it there and had already started to tear it down, I was walking through that particular shop and I noticed that someone had placed one of the bins I used on a cart. It was the bin into which I placed the cup with all the screws and knobs (wrapped up in a shop rag). I asked him why my stereo was out on the cart and he said he thought it was an old power supply that was torn down and was BER (beyond economical repair). He was going to have someone scrap it. I told him it was my stereo and it was a good thing I stopped by. Later that night is when I realized that the cup was missing.
     
  5. kevzep

    kevzep Its all about the Music Subscriber

    You're all good!! No problem, I was just messing with you....:D

    There you go, people messing with your system!! But sounds like you're sorted now so that was a lucky escape...
     
  6. lbcgav

    lbcgav AK Subscriber Subscriber

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    I'm having trouble finding trimmers to replace the four 33k ones on the MC headamp. I can't find multiturns in 30k on mouser. To further complicate matters, in Leestereo's AU-919 thread, the amp he worked on had resistors in place of the trimmers. What is the consensus here on what to replace these with?

    A second question: The SM says if you don't have a distortion analyzer to do the THD minimization procedure, you can set VR01 and VR02 to 2/3 the way. Wouldn't fixed resistors in these spots be better if that's the case? What did others do with these trimmers? Right now, I have on order two 200 ohm multi-turn pots. If going with pots here, I'm wondering if single turn would be better so I can visually see the 2/3 positions of the wiper.

    Any input is greatly appreciated.
     

     

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  7. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    I used 50K trimmers in place of 30K, and in my thread I do mention that no difficulties were encountered. If you look at how they are used in the schematic you can see that the entire track is only in circuit when they are set to maximum resistance. Once you have found the 'set point', by doing the adjustment - even using the old trimmers - you can replace the value measured on the trimmer with a fixed resistor. (best to carefully remove the adjusted trimmer before you measure its resistance).
    Use the trimmers you have ordered, without a distortion analyser, setting them to 2/3 resistance by measuring them with your multimeter before you install them, is all you can do. And once again a fixed resistor could be used here in the same way as for the other (MC Head Amp) trimmers. However, if you are going to be using the MC input, leave the trimmers in and get the amp to someone who does have a distortion analyser and can adjust the trimmers for you.

    Be careful to make sure you select the correct trimmer legs to measure between when finding out the fixed resistor you require to replace them. ;)
     
    Last edited: Aug 2, 2018
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  8. lbcgav

    lbcgav AK Subscriber Subscriber

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    Thank you for all the help. I've placed my Mouser order. For whatever reason on the one I have, they went crazy with the glue--they slathered the stuff on--and it's much more difficult to remove than on the couple AU-717's I've rebuilt. I have to remove and replace all the resistors around the larger caps on main power supply.
     
  9. lbcgav

    lbcgav AK Subscriber Subscriber

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    I got done reading another great AU-919 rebuild thread by @Hyperion where I saw that he changed R39 and R40 in the MC head amp. Now, I use a Denon DL-301 II with an output impedance of 33 Ohms. Per Denon's literature, a load impedance of 100 ohms is recommended, and I know that ten times the source impedance is the rule of thumb for most MC cartridges. What would most recommend here as replacements for R39 and R40 given this info? Should I go with 10 times the Denon DL-301's impedance (~330 ohms) or go with 100 ohms per Denon's recommendations.
     
  10. Soundphile

    Soundphile Active Member

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    Nice thread. Somehow, the 919 rebuild is cleverly buried within the English lesson.
    This is learning plus entertainment.
    Have fun ... I mean, with the rebuild !
     
  11. lbcgav

    lbcgav AK Subscriber Subscriber

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    Ok, now I'm a bit confused. I thought the 33 Ohm R39 and R40 resistors on the MC Head Amp corresponded directly with the load impedance. I now see that the load impedance of the MC head amp is 10 ohms, not the 33 ohms I assumed after I read John's thread about increasing R39 and R40 to 10X the source impedance of the MC cartridge. If R39-40 are 33 ohms, and the input impedance is only 10 ohms, what would I put in R39 and R40 to create 10X of 33 ohms (330 ohms)? The math (or maths for those outside the US;)) is beyond my grasp.
     

     

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  12. lbcgav

    lbcgav AK Subscriber Subscriber

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    Flat amp is done. This is going to be a slow restoration:
    20180807_171338.jpg
     
  13. lbcgav

    lbcgav AK Subscriber Subscriber

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    BTW, I think I'm going to go with 330 ohms for R39 and R40 in the MC head amp. I still don't know how those resistors relate to the calculation of the load impedance.
     
  14. lbcgav

    lbcgav AK Subscriber Subscriber

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  15. ghamilton

    ghamilton Super Member

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  16. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    Just a reasonable guess that they would be largely responsible for the overall input impedance, I had seen it done elsewhere, and I asked around (via PM) in this particular instance, and the consensus was to give it a go, it worked satisfactorily well in the example I tried.

    Q. Regarding the regulated PSU - did you spot the 'gotcha' regarding the incorrect silk screening markings on the board for C7 & C8 - you need to install the replacements the same as the ones that came out - and not as per the silk screening on the board.

    Edit update
    A. Yes you did, yours are correctly orientated. :thumbsup:

    PS: Flat Amp and PSU looking good. :thumbsup:
     
    Last edited: Aug 10, 2018 at 3:43 AM

     

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  17. lbcgav

    lbcgav AK Subscriber Subscriber

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    Thanks John. Your input is always appreciated.

    Regarding R39 and R40 in the MC head amp, I've decided on 330 ohms because that is the max I'd like to go to match the DL 301 II. If the resultant impedance is lower than 330, I'll be fine with that as well. One thing I know for sure, 33 ohms is too low for the DL301 II, and ten ohms, which is what the spec sheet says about the impedance of the AU-919's head amp, is way too low.

    PS, I've finished the main power supply board, but I'm not happy with my selection of the 680uF, 63V caps that Leestereo recommends. The ones I ordered have too large of a diameter and don't fit right on the board. I've got new ones coming from Mouser.
     
  18. Hyperion

    Hyperion Roobarb & Custard Subscriber

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    That's an important consideration, you are right to be concerned about this and putting it right. However, it is extremely unusual for Leestereo to be wrong regarding component selection, I suspect he is even more meticulous than me! - and that's saying something. :D
    Providing you are happy now that's fine - but as always you can run a component selection by me and I'll give my considered opinion if you need it. ;)
     
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  19. lbcgav

    lbcgav AK Subscriber Subscriber

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    Sorry, I wasn't precise with my wording, when I mentioned " the caps that Leestereo recommends." He stated values (630uF, 63V, low ESR) in his thread, not the exact part he used. I believe he uses Nichicon PW and United Chemi-Con KYB. I wasn't diligent enough to check that the diameters were correct when I ordered the ones I did, I only checked lead spacing. Thank you for the offer to run the component selection by you in the future.
     
  20. Leestereo

    Leestereo Super Member

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