Large tube amp POPS when turned off

Discussion in 'Amp Tech Center' started by ArcticWhite, May 18, 2019.

  1. ArcticWhite

    ArcticWhite Tele-Holic

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    My old Valco makes an extremely LOUD POP when I turn it off. It does not have a standby switch. It has a solid state rectifier.

    None of my other amps do this.
    I realize that I could turn down the volume before switching it off, but that is not the solution I'm looking for.

    I figure there's a good place to run a cap or a resistor to prevent this. Anyone?

    (I've already installed a grounded plug, and removed the death cap)

    20190518_065402.jpg
     
  2. schmee

    schmee Doctor of Teleocity Silver Supporter

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    It's common with Fenders too when they are old. Often it is bad contacts in the switch. But it can be other things too. Yeah if you try the switch and that doesn't do it, then a cap can be used but I forget where. Switch to ground I imagine.
     
  3. BobbyZ

    BobbyZ Doctor of Teleocity

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    Try just unplugging it and see if it pops.
     
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  4. tobyk

    tobyk TDPRI Member

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    I'm having the same issue.
    I'm building a Gibson Falcon clone which is as good as finished.
    It's per schematic except for an extra Gibson GA20T channel, added 470K PI grid stopper, no tone sucking network, no tremolo and an added standby switch.

    Everything works as expected, except for a loud click when switching the amp off, if not switching to standby first.
    Switch to standby first, then turn amp off – no click.
    Loudness of click is sensitive to both Volume and Reverb settings and is relatively quiet click with controls turned down.

    Any ideas anyone?
    (I tried putting a .047 uF cap right before the Standby switch – no improvement)

    Schematic:
    http://www.ampwares.com/schematics/gibson/ga19rvt.pdf
     
  5. ArcticWhite

    ArcticWhite Tele-Holic

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    Did you include the death cap shown in the schematic? Three prong cord, grounded?
     
  6. tobyk

    tobyk TDPRI Member

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    No, the death cap omitted. 3 prong cord..
     
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  7. tobyk

    tobyk TDPRI Member

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    It’s built for british 230V.
    I’m guessing the problem lies in the power section.
     
  8. BobbyZ

    BobbyZ Doctor of Teleocity

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    Reason I said to try just unplugging it, is that should tell you if the switch is wonky.
     
  9. ThermionicScott

    ThermionicScott Poster Extraordinaire

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    Plenty of amps "thump" or make odd sounds when you cut the power. What's the PROBLEM?
     
    Last edited: Aug 4, 2020 at 1:20 PM
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  10. mherrcat

    mherrcat Tele-Holic

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    I have a Peavey Nashville 400 that does the same thing. Granted, it is a solid-state amp, but I found that turning the reverb control all the way down seems to help. Odd.
     
  11. Telecaster88

    Telecaster88 Tele-Holic

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    My Vox AV60 does this. It annoys me, so I've learned to stick an adaptor into the headphone jack before turning it off, and that cuts signal to the speaker... No pop. A slight PITA but better to my ears than the pop.
     
  12. Jlwctn

    Jlwctn Tele-Meister

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    I have a Carvin SX200 SS that is doing the same thing, I sprayed the switch, and it helped.
     
  13. ArcticWhite

    ArcticWhite Tele-Holic

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    I'm the OP and I sold this amp about nine months ago.
    I put in grounded inputs, and cleaned it up, replaced some drifted components etc. Pop went away.
     
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  14. tobyk

    tobyk TDPRI Member

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    For the record, I put a 0.1 uF cap across the power switch, that fixed the problem.
     
  15. TwangToInfinity

    TwangToInfinity Tele-Afflicted

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    i always pull the plug on tube amps, never use the switches, that way theyre unplugged when i am not using them
     
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  16. Jon Snell

    Jon Snell Tele-Meister

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    If you fit two 0.1uF or 100n Class X or Class Y capacitors across each pole of the mains switch, that will quench any interference from the contacts breaking. Screenshot 2020-08-06 at 08.04.05.png
    Place similar across the output of the switch if still there are issues
     
    Last edited: Aug 6, 2020 at 6:26 AM
  17. Jon Snell

    Jon Snell Tele-Meister

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    Like this; Screenshot 2020-08-06 at 11.24.16.png
     
  18. tobyk

    tobyk TDPRI Member

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    Thanks, that's exactly what I ended up doing (see post above)!
     
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