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Caps in my 1963 Gibson ga 8t Discover

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by raildog, Feb 28, 2009.

  1. Feb 28, 2009 #1
    raildog

    raildog Member

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    I have 4 electrolytic caps in my amp 3 mallory 20 mfd 450 vdc and 1 500vdc, are these the correct caps for this amp, the 500 is connected to the volume, thanks as always,Scott
     
    raildog, Feb 28, 2009
    raildog, Feb 28, 2009
    #1
  2. Feb 28, 2009 #2
    SatelliteAmps

    SatelliteAmps Member

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    Could be. Probably are. Pictures would help make a definite answer.
     
    SatelliteAmps, Feb 28, 2009
    SatelliteAmps, Feb 28, 2009
    #2
  3. Feb 28, 2009 #3
    raildog

    raildog Member

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    [​IMG]
     
    raildog, Feb 28, 2009
    raildog, Feb 28, 2009
    #3
  4. Feb 28, 2009 #4
    WaltC

    WaltC Member

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    They *look* OK, but looks can be deceiving. Is the amp quiet? Do you get a loud 60hz hum? If the amp is quiet and no low level 60hz hum then these electrolytics are probably fine. FWIW the cap "attached to the volume pot" isn't *really* attached to the pot for any volume-related reason, it's just attached there as a convenient place to solder the ground (-) side of the electrolytic to chassis ground.

    Again, FWIW, your Discoverer looks pretty good inside compared to the ones I've worked on (15 or so GA-8T EL-84 Discoverer's at this point).
     
    WaltC, Feb 28, 2009
    WaltC, Feb 28, 2009
    #4
  5. Feb 28, 2009 #5
    raildog

    raildog Member

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    Walt, Thanks for the info, i may just do the power cord and see how she sounds, it didn't have any noise but for the 15 watts i thought it would have been louder, maybe the ot needs changing.Scott
     
    raildog, Feb 28, 2009
    raildog, Feb 28, 2009
    #5
  6. Feb 28, 2009 #6
    GuitarsFromMars

    GuitarsFromMars Member

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    I see a 'bee,and a Black Beauty...
     
    GuitarsFromMars, Feb 28, 2009
    GuitarsFromMars, Feb 28, 2009
    #6
  7. Feb 28, 2009 #7
    skeeterbuck

    skeeterbuck Member

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    This pic is a perfect example of point to point wiring. NO BOARD in the layout.
    So many think that any handwired amp is PTP which just isn't so.
     
    skeeterbuck, Feb 28, 2009
    skeeterbuck, Feb 28, 2009
    #7
  8. Feb 28, 2009 #8
    capnjuan

    capnjuan Member

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    Hi Scott; yes ... the cap that's 'connected to the volume' is only grounded on the body of the control; it has nothing to do with volume; the cap is the preamp cathode bypass cap around the 1.5K cathode resistor. If you replace the primary filter caps, replace that bypass cap too. John
     
    capnjuan, Feb 28, 2009
    capnjuan, Feb 28, 2009
    #8
  9. Feb 28, 2009 #9
    raildog

    raildog Member

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    I was trying to check how much electricity was in my caps and not really sure how to, I placed my multi meter on dcv and the 500 setting touched the black lead to the chassis and the red probe to the positive end of the cap, no reading, what am i doing in correct? thanks,Scott
     
    raildog, Feb 28, 2009
    raildog, Feb 28, 2009
    #9
  10. Mar 2, 2009 #10
    slider313

    slider313 Silver Supporting Member

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    If that was my amp I would replace all the electrolytics. These amps seem to "bloom" after 7 on the volume knob. That's when they thicken up and you get some volume out of them. They can sound thin with low output under 7. Even dimed they aren't overly loud but between 7-10 is where I used to keep mine, and I used it at blues jams and it cut through the mix.
     
    slider313, Mar 2, 2009
    slider313, Mar 2, 2009
    #10
  11. Mar 2, 2009 #11
    Trout

    Trout Member

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    If it were mine, I would swap out the 4 Metal caps with FT Brand simply because they are similar in physical size, the have nice long leads, and having used hundreds of them, very reliable.

    I would also replace the little black electrolytic bypass cap near the center of the chassis.

    I would also get a 3 prong power cord on there.
     
    Trout, Mar 2, 2009
    Trout, Mar 2, 2009
    #11
  12. Mar 2, 2009 #12
    TNO

    TNO Member

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    The filter caps were originallly 20-10-10 uF. Three 20s will work fine but The preamp sound more "open" with the 10s. I like Nichicons for their smaller size. The very cheap filters from WeberVST work fine and are very compact.
     
    TNO, Mar 2, 2009
    TNO, Mar 2, 2009
    #12

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