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Sansui 1000A Repair

Discussion in 'Exclusively Sansui' started by Agorax, Nov 23, 2018.

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  1. Agorax

    Agorax New Member

    Messages:
    5
    Hello there, I recently inherited a 1000A tube receiver, I have replaced all the Elna and Suzuki oil caps, and have extensively cleaned all the controls.

    The recap / Deoxit restored proper function to a lot of the tone controls, inputs, balance, and other functions.

    However I have a weak right channel, it sounds a bit staticy and seems to be about 20% sound strength, compared to the left channel.

    I have not messed with any tubes yet, any info on tubes and possibly what certain tubes on the unit actually do would be greatly appreciated. I have never worked with tubes, I mainly have owned 70s Marantz 2xxx 4xxx units.

    All functions and inputs seem to be working, however my right channel is consistently weak. The stereo reverse function seems to work, I feel like that may be telling us the sound is processing correctly, just that the receiver can't deliver proper sound output to whatever channel is assigned to the right speaker.
     

     

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  2. blhagstrom

    blhagstrom Mad Scientist, fixer. Subscriber

    Messages:
    12,857
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    Duvall, Washington
    Hopefully it’s a weak tube and not a bad output transformer.

    You can swap tubes side to side to check to see if the problem follows a tube.

    The best thing is to have a tube tester.
    It’s near required to own and maintain and repair tube gear.
     
  3. Agorax

    Agorax New Member

    Messages:
    5
    The transformers look original so I hope they're okay too. Im currently looking for information about the different tubes in the 1000A and what jobs they do.
     

    Attached Files:

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  4. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    The Service Manual has both the Schematic and a top layout diagram. Fairly easy to discern what tube does what from them. The most likely suspects are the 6AN8's right in front of the OUTPUT Tubes. Swap them left to right. If the lower level follows the tube, get a pair of them. The other pairing are the 12ax7's in the Front of the unit. These are the pre-drivers. Again, swap them L & R.
     
  5. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    sansui 1000a tube layout.jpg

    V1,2,3 are your RF AMP, Mixer and Oscillator for FM.
    V4,5,6,7,10 are the IF Tubes and Discriminator for AM/FM
    V8, V9 are the AM RF Tubes.
    V11,12, 13 are the FM Multiplex Tubes.
    V14, V18 are Predrivers (Audio Amp).
    V15, V19 are Driver/Phase inverter
    V16, 17, 20, 21 are the output tubes.
     
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  6. Agorax

    Agorax New Member

    Messages:
    5
    Wow Larryderouin, that is extremely helpful, thanks for taking the time to share that info. Next I am going to thoroughly clean and Deoxit all the tube contacts.

    When I initially powered the unit on (fresh out of the attic without any checking or cleaning) after a few minutes V20 started red plating (I assume this is the term used when most of the tube glows bright red). After a cleaning and partial recap this has never happened since, and I've had the unit powered on for a few hours at a time.

    Now that I know a bit more about the tubes I will look into things further and share what I find.
     
    Last edited: Nov 27, 2018

     

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  7. slimecity

    slimecity Super Member

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    I recently had a hum on one channel of a little tube amp and what fixed it was me going thru all the valve pins with mini bottle cleaner brush soaked in contact cleaner. After that, I then prised the sockets closed with a tiny screwdriver - effectively making them tighter.
     
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  8. Agorax

    Agorax New Member

    Messages:
    5
    Swapping those two pairs L+R didn't change operation at all, the right channel is still consistently weak. Im hoping it's output tube related, and not a transformer.

    Cosmetically, the output tubes look very cloudy and tired compared to the rest of the crystal clear smaller tubes. (And like I said above, one has red plated in the past) I'm sure they've seen a LOT of heat as well.

    Removal looks like simply undoing the 7mm ish nuts for the clamps and pulling them out.

    Should I swap the output tube pairs left to right?
     

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  9. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    DO NOT LOOSEN the Spring Clamps. Push down on the clamp with the TUBE COLD, It will release from the tube and you can use your free hand to lift tube out. You can try the output tube swap, If you haven't installed them, install 10 ohm cathode resistors, and 100 ohm screen grid resistors. You can measure ma draw for each tube across the cathode resistors to help determine bias settings, and to balance out the output's.

    I'd bet on the toshiba's being Extremely tired.
     
  10. Agorax

    Agorax New Member

    Messages:
    5
    I see, glad I waited for input before trying. After pushing the spring clamps down they come right out, I'm cleaning the contacts and swapping them now. Thanks again for the information.

    Edit : After switching output pairs L+R, my right channel is still weaker than the left, however the left has developed some static, especially before it warmed up, almost constant static sounds.

    Also the bass response on my previously good left channel has degraded, not coming in as well and a bit scratchy.

    The bass response on the right channel, despite the channel being weak, has changed to very tight and rocks the house now like my previous left channel once did.

    Extra Edit : I have not replaced the 4 large can capacitors on top. All four are Elna, two of the can capacitors are easy to read, 200uf 350v, however the two metal finished caps read :

    Cap.20-20-20MFD 500v, 550 surge Cap.20-20-20-20MFD 350v These styles of cap markings I have not come across before.

    Last Edit : I just learned these are called multi section capacitors and may not be as simple as replacing standard two terminal caps.

    Once I figure out how many capacitors I need for the multi section caps, I think I plan to install modern capacitors underneath the chassis leaving the originals in place up top.
     
    Last edited: Dec 2, 2018
  11. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    No Room for separates. It's crowded like any store 4A.M on Black Friday in there now. www.tubesandmore.com (AES) has a 4 section CE BRANDED 22uf 450V drop in, also for the 3 section.(See links below.) The 2 Singles, bump up to 470uf @ 450V. You can use Nichicon Radials and stuff the cans for the singles. These take a lot of abuse.

    4 Section https://www.tubesandmore.com/products/capacitor-ce-mfg-475v-20202020-f-electrolytic

    3 section https://www.tubesandmore.com/products/capacitor-ce-mfg-525v-202020-f

    Larry
     
    Last edited: Dec 3, 2018

     

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  12. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    Try swapping V15 and V19 (6AN8's). One usually goes weak before the other. Don't just replace the one. Get a pair of Matched tubes from a reputable supplier. Jim McShane is one of the best out there. And his prices are in line with others who don't test tubes as well or at all.
     

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