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Input grid stoppers: on tube socket vs on input jacks

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  • Input grid stoppers: on tube socket vs on input jacks

    Any problem is putting the 68K resistors right on the input jacks? It's not a high-gainer by any means. The guy I'm making it for wants the Hi/Lo input scheme so it'd be easier to put them right at the input.

  • #2
    Can you mount a little terminal strip along side the socket?
    I don't like the idea of two wires and two resistors hanging on and stressing the cheap little metal lug on the tube socket.
    Bruce

    Mission Amps
    Denver, CO. 80022
    www.missionamps.com
    303-955-2412

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    • #3
      Originally posted by Hardtailed View Post
      Any problem is putting the 68K resistors right on the input jacks? It's not a high-gainer by any means. The guy I'm making it for wants the Hi/Lo input scheme so it'd be easier to put them right at the input.
      Should be fine. Actually I think most people mount their stoppers on the input jacks, unless there is some serious distance between the jack and the input tube, which is unlikely.

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      • #4
        I usually put the 68k 'grid resistors' (and the 1M to ground) at the input jacks, and shield the cable(s) from there to the V1 grid(s) with the cable shield grounded at the input jack grounds
        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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        • #5
          Hi,
          though theory says that grid stoppers are maximally effective when wired directly to the tube sockets, countless builders and manufacturers around the world mount them at the input jacks with no apparent problems, all the more so if the amp is a low/medium gain one like yours is, so +1 on what our "fellow fume breathers" just said.

          Cheers

          Bob
          Hoc unum scio: me nihil scire.

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          • #6
            If the 68ks aren't very close to the tube then they aren't really functioning as grid stoppers (as I understand it), but rather just input mixers.
            I always mount them on the tube socket terminal, leave the other end hanging and heatshrink insulated on to the 2 wires from the input sockets, then the 68ks function as mixers and grid stoppers.
            Using that method, I've built and modded fairly high gain amps without using screen cable or low pass snubber caps.
            The switching arrangements on the input sockets work don't care where the resistors are mounted (for the standard fender/marshall thing) - just need to run 2 wires to the grid terminal.
            Bruce has a point that solder joints solid core wire (like the resistor leads) are less vibration resistant than joints made with stranded wire.
            But with good lead dress it shouldn't be a problem (run the wires so that they press into the chassis corner, which will act to partially screen them and will give some measure of support).
            Obviously the regular arrangement of putting the mixer resistors onto the sockets works fine generally, but if you're building it from scratch, you might as well follow best practice to minimise the liklihood of parasetics.
            My band:- http://www.youtube.com/user/RedwingBand

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