100W Tube amp Amp Draw, Choke and Resistor Switch Question

Discussion in 'Marshall Amps' started by Michael Inglis, Nov 30, 2021.

  1. Michael Inglis

    Michael Inglis Active Member

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    Just installed a Choke in my DSL100HR, sounds great so far. Low end is certainly tighter than before when the volume is up to gig levels. Pics at bottom for the hell of it.

    But the point of this post is to pose this question. I want to add a switch on the chassis so that i can switch between the 220 ohm resistor and the choke (when the amp is turned off obviously, ill have to take the back off the amp to switch it and if someone else ends up with the amp they would have to also. That should insure its not switched when the amp is on, ill even used a vinyl decal to warn against doing so). Ive seen other guys ask this question and the answer has always been "sure it will work but youll have to find an adequate switch which might be hard"....hmmm, a 100 watt tube amp would roughly draw .83 amps (100watts divided by 120v). And every dpdt switch ive used in my pedal builds has a rating of 2A @ 250V and 5A @ 120. So....what gives? That seemed pretty easy to find to me.

    The mains fuse on my DSL100 says its 4 amps so even if the amp magically was able to draw that much current the fuse would go before the switch would if the rating on the switch is to be trusted, correct? Or am i missing something?

    It should be mentioned i plan on using a slightly better quality switch just in case but the question remains, if those ratings are to be believed wouldn't those little red DPDT switches suffice?
    Marshall DSL100HR Choke Mod 1.jpg
     
    Last edited: Nov 30, 2021
  2. Tatzmann

    Tatzmann Well-Known Member

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    Why the eff you want to make this switchable?
    Why?
     
    neikeel and Jethro Rocker like this.
  3. South Park

    South Park Well-Known Member

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    The only thing in switch gear is amps not voltage . Power adds so you add the amp draw of the plates and that gives you the switch rating . A one amp switch is all you need for this
     
  4. DonP

    DonP Active Member

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    Probably to see if the choke makes a difference or not.
     
  5. neikeel

    neikeel Well-Known Member

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    Personally I would not bother but……..

    The 120v is ac mains - irrelevant

    You are switching in the rectified HT B+ line and your HT fuse is 1 or 1.5A?
    So a 2A switch will suffice, particularly if you only ever switch it when cold.
     
  6. Michael Inglis

    Michael Inglis Active Member

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    I actually remember switching the HT fuse when I first got the 100HR and it was actually some really odd value for a HT fuse like 635 ma. As far as the 120v mains not correlating that makes perfect sense. I knew it was the B+ line that would be actually on the switch. I guess I just thought it was encompassed but the total AC voltage fuse value. But after giving it more thought it's really not an accurate way of finding out what kind of loads a switch in that position would be under.

    As for the "I would not bother", I have to admit I feel that way also. Any difference would be minimal. My reasoning is that I HATE taking away stock functionality with any guitar, pedal or amp mod I do. I ALWAYS go out of my way to keep the stock functionality/circuit available should I want to revert back to it later on. But from what little difference I can hear and feel in the amps low end response after installing the choke I can tell i prefer the amp with the choke anyways.

    Thanks for the reply/info brother!
     

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