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Death Cap?

Discussion in 'Amp Central Station' started by TimboMc, Jul 22, 2006.

  1. TimboMc

    TimboMc Tele-Meister

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    Death Capacitor?

    What is this death capacitor in fender amps that I hear about? Where is it?

    Thanks
    Timbomc
     
    Last edited: Jul 22, 2006
  2. El Capitan

    El Capitan Tele-Holic

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    It's on two prong power corded amps.
    comes of the polarity switch.
    .50 cap I believe
    if the cap fails, I believe the chassis is HOT in one position.
     
  3. Bill Ashton

    Bill Ashton Tele-Afflicted

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    Ah, the death cap...

    The "Ground" switch on tweed amps switches a .047 mfd capacitor between legs of the two-wire power lead, allowing you to get rid of buzz or hum; however component failure could result in the hot side of the power lead making the chassis...and probably your guitar...hot as well.

    Not a good thing.

    Proper modification entails removing the ground switch and cap, placing the fuse in the hot side of the line before the power switch, attaching the neutral side (white) of the line direct to a transformer lead and attaching the third (green) ground wire from the new cord to the chassis.

    I know I have seen an "Uncle Spot" diagram put up here before; same one as in Dave Funk's book. Does anyone have it to put up???
     
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  5. crawdad

    crawdad Tele-Afflicted

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  6. Bill Ashton

    Bill Ashton Tele-Afflicted

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  7. TimboMc

    TimboMc Tele-Meister

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    Thanks for the replies. The same applies to a champ without the ground switch I assume. I have a Big Blue .047 Cap on the side of the fuse that goes to ground. I should remove this and complete the uncle spot mod?
    Thanks
    Tim
     
  8. -CB-

    -CB- Tele-Meister

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    It only applies to amps with a ground switch, particularly 2wire amps.

    A three wire power cord amp with ground switch will blow the outlet's fuse/breaker (hopefully) if you go hot to chassis/ground, but with building wiring as it is, thats not guaranteed. Neither is it guaranteed if you defeat the 3wire with an adapter and dont ground the pigtail wire.

    HOWEVER - the chances of shorting that cap are pretty damn small. I mean really small. Can it happen? Well probably. Has it happened, can't say that I've never heard of one documented case, only anecdotal stories.

    I mean consider this - if your preamps 12AX7 shorts plate to grid, your guitar is gonna have +200vDC on it. And let me tell you folks, tubes short WAY more often than capacitors (which usually go open). Do you hear about that problem happening? No. Also capacitors will almost never go short all at once. And, capacitors pass AC (which your wall has) and block DC, so in a way you're getting that chassis potentially revved up a bit anyway even when its working fine, and people are just not dropping dead all over the place from it.

    Don't lose sleep over the "death cap". Its an issue folks have picked up on that is really not a big deal. If you want to though, put a 630v Orange Drop in there, and you can think on it lasting another 30 years with no issues.
     
    Last edited: Jul 22, 2006
  9. JohnnyCrash

    JohnnyCrash Doctor of Teleocity

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    Check your PM's Tim.

    Since I put a 3 prong power cord on there, the death cap can be removed.

    What's the "Uncle Spot mod"?
     
  10. TimboMc

    TimboMc Tele-Meister

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  11. JohnnyCrash

    JohnnyCrash Doctor of Teleocity

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  12. JohnnyCrash

    JohnnyCrash Doctor of Teleocity

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    The Champ didn't have a ground switch normally.

    From my understanding the ground switch was also for the old 2 prong outlets. I thought it was supposed to reverse Live and Neutral in case you plugged the 2 prong cord in "reversed" on the old sockets (if you did, there'd be a hum, so the switch was needed to reduce that hum).
     
  13. -CB-

    -CB- Tele-Meister

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    JohnnyCrash - cap or no.... bad stage power OR bad equpment can turn yer lip into a fuse.

    I'll take a moment to remind everyone that stage power MUST, and I mean M.U.S.T come from one and only one source. No matter if the stage is a pro stage, some club, impromptu backyard jam... ONE SOURCE for power.

    Taken in the literal - a backyard jam. Moe plugs his PA into the outlet over by the pool pump, and Joe plugs his amp into the outlet on the other side of the house by the AC unit, with an extension cord. Electricians never saw it coming in days of yore.* Both sources are 230v, and the electrical folks wired one outlet off one phase to give accessory 115v, and the AC man wired an accessory outlet off the other phase. If one amp has a fault, you get 115 on your lip. If both go... you get to boogie like a cockroach in the sun.

    A small voltmeter isn't a bad thing to have in your bag of trix.
     
  14. Glen W

    Glen W Tele-Afflicted

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    Very true, CB. But, this scenario exists everywhere - residential & commercial buildings can & do have outlets fed from either leg possibly in the same room. It's even possible (although rare) to have a 3-wire feed from 2 adjacent breakers to one duplex outlet. With the receptacle's hot-side link broken off, you get two separate circuits - one up & one down, sharing the same neutral, and have the 230V potential mentioned in your post above. An outlet like this can LOOK like it's the same source...

    It's not a problem unless there's a problem!
     
  15. crawdad

    crawdad Tele-Afflicted

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    Amen to that CB! I can't even count the number of times I made the mistake of not following this advice, but I finally learned. Its the only way, short of the VOM to be sure that all equipment shares the same polarity.
     
  16. -CB-

    -CB- Tele-Meister

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    I totally agree anythings possible.

    In the same room, it is, and has been for a long time, illegal for electricians to wire from opposite phases. Not to say it doesn't happen, but... its supposed to be guarded against. New construction since the early 70's has had GFI's in certain areas, but they're getting more common all the time.

    I'm not sure what you're saying on the 3wire with the hot broken off... that scenario seems to be digging a bit deeper than even the death cap on - but yes it IS possible.

    And "things" are possible too, don't get me wrong! I've been hit by lightning 3 times, injured twice! Just carry a meter, set it to an AC range, and read from geetar to micofone. Oughta be like kissin' yer sister - NUTHIN!
     
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