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dampening tube sockets with silicone gasket.

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  • #31
    I'm resurrecting this thread to post an update on a couple of observations on the overall performance of the construction experiment.
    First, due to circumstances surrounding the covid-19 pandemic, I've really very little access to the shop I use for personal projects, until fairly recently.
    This particular amp build, was one of several projects I've been getting back into. So, putting the amp up on the bench again brought, I decided it was a good time to finally change something which had been bothering me for a while.

    When I decided to install Belton noval sockets to replace the earlier 9-pin sockets, I (for some reason) replaced all the preamp sockets, but used ceramic sockets for the output tubes. (see below).

    Click image for larger version

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    The quality of the Belton sockets was so much better that these ceramic sockets in nearly every way, with the exception that thermoplastic can melt. The ceramic sockets would not secure the EL84s to any acceptable degree. The EL84s could be moved or dislodged without much torque at all, and it became clear pretty quickly that these output sockets needed to go to.

    Retrofitting and rewiring the sockets was a bit of work, but I probably shaved a 1/3rd of the time off the project since there was no longer any need to drill out and machine my own base plates. I just needed to source M20 machine washers, and drill out the mounting holes. For the preamp tubes (photographed in earlier posts), I used Zinc plated steel for the mounting bases because they were readily available, and easy to machine. But they were already beginning to show quite a bit of oxidization.

    Click image for larger version

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    Because the silicone gasket provided galvanic isolation between the aluminum chassis and mounting plate material, I decided to use A2(18-8) stainless steel for the output tubes. So, I called Boltdepot, to see if they had M20 size washers. They only carried up to M16 (I believe), but referred me to another supplier in MA called Belmetric (https://www.belmetric.com). Belmetric carried several types of M20 washers, and the price was right for 18-8 at $0.39 a piece.

    The interesting thing I learned about
    Austenitic stainless steel, is that it cannot be hardened by heat/tempering, but it can be work hardened. With types 304 & 316, the process of drilling alone will harden the steel significantly along the cutting edge and tip of the drill. So, care must be taken in setting the speed of the cutter, or you can wear them out quickly.

    After drilling out the bases, I cut small grommets in halves to add some further isolation for the machine screws during the install.

    Click image for larger version

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    Unfortunately, it was a pretty big improvement over the first attempt on the preamp sockets. So, I couldn't help myself from redoing the rest of the sockets. The fact that the zinc plated washers were showing corrosion already was a big factor as well. You can see the difference below.

    Click image for larger version

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    here are the finished sockets.

    Click image for larger version

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    If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.

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    • #32
      Did you read the paragraph on Vibration aborption in the link of your post #27? High elasticity does not mean good absorption. But I'm sure your solution will provide at least some shock mitigation.
      Last edited by Helmholtz; 09-02-2020, 07:01 PM.
      - Own Opinions Only -

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      • #33
        Originally posted by Helmholtz View Post
        Did you read the paragraph on Vibration absorption in the link of your post #27? High elasticity does not mean good absorption. But I'm sure your solution will provide at least some shock mitigation.
        Well, I just re-read it .
        But, I fully admit that the silicone sheet I used for this project isn't ideal. It was a cheap general purpose/high temp silicone used for cooking as far as I can tell. There are better rubber materials for shock absorption. But if I could get my hands on some KE-5560 phenyl base silicone rubber, it's tough to find a better material over a wide temperature range than that – particularly at room & higher temperatures.
        Some of the issues I was dealing with were that the amp was particularly sensitive to microphonic noise, particularly in V2. This makes some sense, because it is a recovery stage after a fairly lossy fender style tone stack. This was compounded by the way the aluminum chassis is constructed. The sides are folded but not welded in the corners which make it more likely to vibrate.
        The added mass and weight (and perhaps shock absorption of the gaskets), seem to mitigate a some of this.
        As far as the V2 noise, I paralleled the input stage, which should drop the noise at the input by -3dB. But it also allows me to drive half the input impedance of the tone stack. So I shifted the RC values to lower the resistor/potentiometer values by half, thereby decreasing the resistor's thermal noise by -3dB as well (If I understand it correctly)...
        It's a team effort.

        ps. It's kind of a cool look, though. Isn't it?
        If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.

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        • #34
          Now you can measure the clang-to-noise ratio and see if there is an improvement

          https://www.dalmura.com.au/static/Mi...n%20valves.pdf

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          • #35
            I wish I had 10% of you guys skill!
            The only good solid state amp is a dead solid state amp. Unless it sounds really good, then its OK.

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            • #36
              Has anyone tried this stuff? No idea if its suitable for areas with heat like tube sockets.

              https://www.isolateit.com/vibration-...s-pads-49.html
              The only good solid state amp is a dead solid state amp. Unless it sounds really good, then its OK.

              Comment


              • #37
                Originally posted by mikepukmel View Post
                Has anyone tried this stuff? No idea if its suitable for areas with heat like tube sockets.

                https://www.isolateit.com/vibration-...s-pads-49.html
                I have not. I looks very cost prohibitive for me.
                If I have a 50% chance of guessing the right answer, I guess wrong 80% of the time.

                Comment


                • #38
                  That sorbothane would likely be good for chassis isolation where the chassis is heavy and can compress the sheet a bit, but I doubt it could keep the self resonance frequency enough below a kHz if the suspended mass was just a tube socket and tube.

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