Death caps?

Discussion in 'Amps/Cabs Tech Corner: Amplifier, Cab & Speakers' started by sniffin, Jun 11, 2019.

  1. sniffin

    sniffin Member

    Messages:
    385
    Joined:
    Aug 3, 2006
    Location:
    Italy
    I've currently got this vintage italian made bass head on the bench. It has a 3 way power switch (2 ons and central off position) and 2 10000? 1000v caps attached to it that go to ground on the pcb. The amp has a 3 wire power cable with the earth wire screwed to the chassis.
    My question is would they be death caps or what are they?
     
  2. pdf64

    pdf64 Member

    Messages:
    5,652
    Joined:
    Aug 9, 2008
    Location:
    Staffordshire, UK.
    Given the scenario of mains wall outlets with no safety ground and unpolarised mains plugs, death caps were used to reduce hum / buzz by referencing an ungrounded amp chassis to the mains neutral, which is itself grounded. A significant issue being the caps used were not designed to fail safe, and if they shorted there would be a 50% likelihood that when the amp was plugged into the wall outlet the amp chassis (and hence potentially the instrument and musician) would then be directly connected to mains hot.
    As your amp's chassis is grounded by design they can't be death caps.
    They are probably intended to suppress mains borne noise.
    It would be best to either remove them or replace with modern caps class Y caps that are fail safe, themselves designed for that application.
     
    HotBluePlates likes this.
  3. BluntForceTrauma

    BluntForceTrauma Member

    Messages:
    2,998
    Joined:
    Jun 6, 2014
    Location:
    Tucson, AZ
    Those caps are probably to lessen any pops from the operation of the switch.
     
  4. HotBluePlates

    HotBluePlates Member

    Messages:
    5,572
    Joined:
    Mar 27, 2017
    The pair of "On" positions is the tip-off that the caps are there to function the same as a "death cap." That is, it's a single switch that performs both power switch & ground switch functions. Usually, flip one way & one of the two power cord wires connects to ground through a cap, flip the other way and the other power cord wire is grounded through the other cap.
     
  5. BluntForceTrauma

    BluntForceTrauma Member

    Messages:
    2,998
    Joined:
    Jun 6, 2014
    Location:
    Tucson, AZ
    Yes but if the amp has a properly installed 3 prong plug as the poster says then those caps are useless.
     
  6. Tron Pesto

    Tron Pesto Member

    Messages:
    661
    Joined:
    Feb 18, 2016
    Location:
    Mahwah, NJ
    Those are two independent things. An amp can have a three-prong cord installed that is chassis grounded, and otherwise "correct" (in the broad sense), and also have death cap(s) (and/or switch poppers) and a polarity function switch. And they wouldn't be useless, they would function as they were intended to function.
     
  7. pdf64

    pdf64 Member

    Messages:
    5,652
    Joined:
    Aug 9, 2008
    Location:
    Staffordshire, UK.
    I think that some european standards are grounded but unpolarised, ie hot and neutral can be flipped according to which way around the plug is.
     
  8. BluntForceTrauma

    BluntForceTrauma Member

    Messages:
    2,998
    Joined:
    Jun 6, 2014
    Location:
    Tucson, AZ
    I stand corrected.
     

Share This Page

  1. This site uses cookies to help personalise content, tailor your experience and to keep you logged in if you register.
    By continuing to use this site, you are consenting to our use of cookies.
    Dismiss Notice