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Old Oahu amp issue . wont power on

Discussion in 'Amp Tech Center' started by mkster, Oct 12, 2017.

  1. mkster

    mkster Tele-Afflicted

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    I know , i bought it anyway... 12 bucks ... i dont see the date .
     
  2. mkster

    mkster Tele-Afflicted

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  3. Wally

    Wally Telefied Ad Free Member

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    I have never seen an electrolytic without a date code in some form. $12 is the clue......I have never paid so little for a multisection. can.
     
  4. mkster

    mkster Tele-Afflicted

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    Its probably UPT111145 ...

    Looking at the bill 14.99 , the last time i went the i bought two 6973 for 70$ bucks. They sure look like my old marconi's. The guys is old , bad tempered and stuck with much more stuff then he will ever sell.
     

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  5. Wally

    Wally Telefied Ad Free Member

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    Well,I don’t see any date code that jumps out at me there. No biggie....it is simply that the box we saw on page 1 has been in stock for many, many years. I have handled too many NOS tube boxes to miss the telltale signs of old cardboard boxes. I would not trust that cap, and I am one of those old curmudgeons that has more stuff than will ever get sold. I threw out maybe 500 old, unwanted tubes back in April....more to go soon....along with undesirable/worthless speakers and speaker frames, etc.
     
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  6. ThermionicScott

    ThermionicScott Poster Extraordinaire

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    If you do use those black paper capacitors, I'd check for leakage once the amp is powered up.
     
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  7. mkster

    mkster Tele-Afflicted

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    My tough exactly , but also if they do leak i will use them in guitars anyway...
     
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  8. mkster

    mkster Tele-Afflicted

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    I think i have found the problem , i have looked at the coils resistance and they match the new part , then i looked if the was a short and the red (sec) has a short with green one (heater) i get 300 ohms ... I don't think that is normal ...
     
  9. mkster

    mkster Tele-Afflicted

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    I have question about the ceramic caps they don't show a voltage value , since i am going to the store ( i am planing building a clone ) so i will get the kit , since the cap are not form the power section and are tone shaping is the voltage less , anyway what voltage should i get.

    Thanks
     
  10. mkster

    mkster Tele-Afflicted

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    I made a better copy of the Supro schematics , might as all well share it. Untitled.png
     
    Last edited: Dec 1, 2020
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  11. ThermionicScott

    ThermionicScott Poster Extraordinaire

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    On Fender amps, any caps not marked with a voltage rating were often assumed to be 400V. But for some of those spots where the cap is bypassing a grid-leak resistor or blocking DC from the input jack, it doesn't have to be a high-voltage part. :)
     
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  12. mkster

    mkster Tele-Afflicted

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    I have found the old radio a while back it should make a great little supro clone , i hope the PT is good .

    https://www.radiomuseum.org/r/olympic_6_617.html

    Mine is a little less clean and the cover is missing . It will make a nice head !
     

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    Last edited: Dec 2, 2020
  13. mkster

    mkster Tele-Afflicted

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    Alright i got most part , i am not sure what to do .

    But , i will replace the power cord , caps (except the big cap Since they are not known to fail . According to Brad ) , and the PT since its most likely bad since of the shorted coils .

    The power switch maybe ..

    Any suggestion welcomed , or approval of my plans ..

    Thanks
     
  14. mkster

    mkster Tele-Afflicted

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    Someone played in this amp before me , i suspect he removed the shield from the tubes , because they are gone and since we are there the 12ax7 are cheap sovtec's the RCA's i imagine have diapered at the same time ...

    Also 2 capacitor were changed one with the wrong value.Probably because usually phase inverters have matching cap .

    I started recapping ...
     

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    Last edited: Dec 3, 2020
  15. Wally

    Wally Telefied Ad Free Member

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    You might want to rewired that AC supply in the best and safest manner.
     
  16. mkster

    mkster Tele-Afflicted

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    What do you mean ? Do you mean the power cord in series with the fuse on the black wire ?

    I am preceding slowly it is still my first amp repair , i admit there are details i am not so familiar with .


    Or is it the green wire , that is bugging you ?
     
  17. Wally

    Wally Telefied Ad Free Member

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    Well, it is a mess around there, and I may have spoken too soon. If that white wire contacting the fuse holder is the neutral of a three wire AC power cable, then I have problems with the wiring. The neutral should go directly to one end of the PT primary winding. The black HOT wire of the AC cable should go to the END of that fuse holder. A connecting wire from the contact where the white wire is at this t8me should go from there to the switch, and the switch would feed the other end of the PT primary. Green goes to ground. atnot time should an incoming power supply contact the fuse holder anywhere except the end of the fuse holder.
     
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  18. mkster

    mkster Tele-Afflicted

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    Green to ground . White to PT lead . Black to the fuse end and a a wire from the other side of the fuse to switch . Its confusing if the drawing is proper i will follow it.
     

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    Last edited: Dec 3, 2020
  19. Wally

    Wally Telefied Ad Free Member

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    Mkster, that is better, but best would be to have the fuse before the switch.
     
  20. mkster

    mkster Tele-Afflicted

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    IS this it ?

    Thank you very very much for your help !

    Its really appreciated !

    Marc
     

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