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  • Replace Death Cap with Safety Cap?

    I read that a lot of technicians will remove the RF interference capacitor "death cap" in old amps when they install a grounded 3 wire power cord. Why not just replace the RFI capactior with an Safety Cap that is Y2 rated?

  • #2
    Originally posted by Axtman View Post
    IWhy not just replace the RFI capactior with an Safety Cap that is Y2 rated?

    Probably safer to have a grounded mains wire (where you have a 3 wire mains system). At least that way you are reasonably certain the chassis is always gonna be at ground potential
    Building a better world (one tube amp at a time)

    "I have never had to invoke a formula to fight oscillation in a guitar amp."- Enzo

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    • #3
      You can. Peavey, for example, uses X/Y caps on a lot of their domestic amps' AC lines. Not on the exports, though.

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      • #4
        No, you upgrade to a proper, grounded AC cord and throw the Death Cap in the trash!
        John R. Frondelli
        dBm Pro Audio Services, New York, NY

        "Mediocre is the new 'Good' "

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        • #5
          And where did the idea come from that the death cap was for RF suppression? The idea was it linked the chassis to ground through the power line. Since there was no grounded outlet in the early days, the switch allowed you to select which side of the mains your chassis was coupled to. the result was lower HUM and fewer shocks.

          A three wire power cord leaves the cap redundant and pointless, not to mention potentially dangerous. Just get rid of it.
          Education is what you're left with after you have forgotten what you have learned.

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          • #6
            PT's with copper bands around them handle the RFI problems.
            Now Trending: China has found a way to turn stupidity into money!

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            • #7
              Any comment on why Peavey uses X/Y caps in equipment with a grounding AC cordset? For example, the 5150 (domestic version) has one on the polarity switch and another across the line. If they were redundant, pointless, and dangerous, why would they use them? It adds to the cost, so there must be a reason.

              Just wondering.

              BTW, we're not talking "death" caps; these are properly-rated "safety" caps.

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              • #8
                Well now, I guess we are wandering down the path of pedantry. When I hear "death cap" to ME it means one thing only - a cap to chassis from one side or the other of the mains. WHich side is switchable. I don;t care what type cap it is, safety rating or no. It is a "death cap" by nature of its function, not its ratings. (Just as identical electrolytic caps could be either filter caps or bypass caps depending on their function.) These are the caps installed in old amps made before three-wire power plugs were common. That is the sort of amp the original poster referred to.

                Now I may be the only one who looks at death caps that way, and if so, sorry for any confusion.

                SO in response to the original post, that cap is what I refer to. A three-wire cord makes it irrelevant. It is an older amp, it has an older cap. By leaving it in after a three-wire conversion, it offers little benefit, and potentially can fail, meaning a danger.

                A 5150 is not an old amp, and is not an amp of the two-wire era. it is however a gain monster, and PV engineers had to be more concerned over power line noise getting into the system. Not generally an issue on a 5E3. Note that those caps are not present on the 240v model.
                Education is what you're left with after you have forgotten what you have learned.

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                • #9
                  I just restored a modded BF Bandmaster head that was converted to 3-wire and the tech (a prominent NY amp builder, no less) left the Death Cap/Ground Switch in. Seriously, there are some people that have no clue.

                  It IS true that the copper bands (Faraday shielding) are around some transformers for RFI purposes.
                  John R. Frondelli
                  dBm Pro Audio Services, New York, NY

                  "Mediocre is the new 'Good' "

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                  • #10
                    Yes, but not the death caps.
                    Education is what you're left with after you have forgotten what you have learned.

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                    • #11
                      I have an older Peavey head (Rock Master) that has the three-conductor plug, but also the cap and a three-way switch. According to the manual, the switch is intended to stay in the middle position UNLESS the amp is being used in places that don't have grounded-outlets.... The manual says that in those cases, use a lift-adapter and the switch...also has the associated warnings.

                      Personally, I'd just avoid places like that....

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                      • #12
                        At the risk of being even more pedantic: The copper band is not for RFI. It helps stop stray flux leaking out of the tranny and making your pickups buzz.

                        What does help with RFI is a Faraday shield: a piece of copper foil buried in the windings between the primaries and secondaries, and connected to a "screen" terminal that you're supposed to ground to the chassis.
                        "Enzo, I see that you replied parasitic oscillations. Is that a hypothesis? Or is that your amazing metal band I should check out?"

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                        • #13
                          ABC's of Safety (Interference Suppression) Capacitors for Tube Radios

                          decent discussion of X and Y caps (no death mentioned!)

                          aren't the X and Y caps for RFI, symmetric and asymmetric respectively? Evox Rifa says so...
                          http://www.evoxrifa.fi/technote_pdf/rfi_fact.pdf

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                          • #14
                            So, if it's THAT "essential" that the A.C. grounding cap. (which everyone here wants to call a "death" cap.) be removed after a grounded cord has been installed, then why did so many companies [such as Fender] continue to have A.C. polarity switches on there amps, for many years, even after grounded power cords became mandatory?
                            I've always left them in when I install a grounded cord, with the premise that at some point a ground lift adapter may be needed such as in the aforementioned case of a non-grounded outlet (which, granted is rare these days, but can still occasionally occur), or in the case where you may have a gig at some old/dive bar [for instance], where the outlets may or may not have grounding facilities, but the outlet has been incorrectly polarized by some "do-it-yourself" electrician that didn't know what he was doing. I've run into these conditions in a few occasions.
                            Mac/Amps
                            "preserving the classics"
                            Chicago, Il., USA
                            (773) 283-1217
                            (cell) (847) 772-2979
                            Now back on Chicago's NW side in Jefferson Park!
                            www.mac4amps.com

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                            • #15
                              Don't leave the old ones in. If you want to keep it in circuit, swap it with the correct part.

                              This is what (eventually) happened when Ampeg started installing 3-wire cords and left the polarity switch/death cap in circuit:
                              http://music-electronics-forum.com/t14550/

                              Non-rated caps are why they're referred to as death caps. X/Y rated caps are designed to fail in a safe manner, if they do. The '51 Zenith (2-wire AC) console I just had in got 4 new "safety"/suppression caps to replace the standard old film caps they used back then.
                              Last edited by Dave Curtis, dB AudioTech; 08-24-2009, 09:44 PM.

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