'78 Champ "death cap" anomoly

Discussion in 'Amp Tech Center' started by ozrict313, Sep 3, 2020.

  1. ozrict313

    ozrict313 TDPRI Member

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    I just bought a silver face Champ, looks like a 1978 (seller told me 1980). Clean sounding and looks like it has some new JJ tubes. I opened it up to change the damaged 3 prong power chord and to take a look at the caps to see what needs to be replaced and noticed that the cap between the transformer and the chassis (the death cap) has a different value than any schematic I have seen. its rated at 125 volts unlike the 600 volts that it should be. Why would someone switch that cap for a lower voltage value rather than just clipping it out like most people recommend. I'm curious to know if anything else looks strange. From what I can see everything looks as it should be. I plan to change the electlytics, cap can, and replace the power cord.
     

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  2. Whatizitman

    Whatizitman Friend of Leo's

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    You sure you're looking at the right one? The death cap is the big blue .047 cap. You can only see it in the first photo.
     
  3. ozrict313

    ozrict313 TDPRI Member

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    I think so, its this guy circled here, its marked .047 uf 125 volts.
     

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  4. Whatizitman

    Whatizitman Friend of Leo's

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    The death cap would put 125VAC to the chassis. But yeah, the schem calls for 600v. If you plan on snipping it out, and replacing all the filter caps and such, I wouldn't worry about it. Chassis looks very clean for its age!!
     
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  5. ozrict313

    ozrict313 TDPRI Member

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    Cool, thanks!
     
  6. King Fan

    King Fan Poster Extraordinaire

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    Side note; if it's me, I'd be inclined to replace the dropping resistors with 3W metal oxide, and the bias resistor with maybe a 5 or 10W wirewound.
     
  7. Lowerleftcoast

    Lowerleftcoast Tele-Afflicted

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    Caps can be rated for VDC and VAC. It wouldn't surprise me to see 125VAC and 600VDC.
     
  8. Wally

    Wally Telefied Ad Free Member

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    Fwiw, for: the factory the serial number from 1977 through 1985 gives the date for the chassis. 1978will read A8xxxxx while a 1980 will read F0xxxxx. A=1980s, F denotes 1980s. The first digit is the second digit of the year.

    Clean amp...congrats.
     
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  9. ozrict313

    ozrict313 TDPRI Member

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    yep, there it is, it says 125 vac
     
  10. Jon Snell

    Jon Snell Tele-Holic

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    I do wonder why there is a capacitor between the neutral and earth (I presume white is neutral) ... doesn't do anything as you have an earth connection to chassis, luckily!
    Take it out as it does nothing and they used to got to the centre pole of a switch enabling Live or Neutral selection, depending on mains polarity and hum, (very dangerous).
     
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  11. ozrict313

    ozrict313 TDPRI Member

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    What's the benefit of switching these resistors?
     
  12. tubegeek

    tubegeek Friend of Leo's

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    More robust/less risk of a failure/longer working life.
     
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  13. Whatizitman

    Whatizitman Friend of Leo's

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    Don't even try to play dumb with us. We know what you do. :lol:

    But for the rest of us with limited amp knowledge, @robrob has a nice explanation of the death cap.

    https://robrobinette.com/Death_Cap_and_Ground_Switch.htm
     
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  14. King Fan

    King Fan Poster Extraordinaire

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    ^^^ thanks, my friend. I've been trying to write shorter posts (heh) but forgot I still want to include a reason or citation for a suggestion. :D
     
    Last edited: Sep 4, 2020
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  15. tubegeek

    tubegeek Friend of Leo's

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    I gotcha back! And you got mine!
     
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