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  • Simms Watt 100w Head

    Hi,

    I last used my Simms Watt 100w Head about 20 years ago. The best is around 48 years old.
    I'm now planning to start it up, and fix it I guess...

    Do you have any advises on how to start it up after so many years out of business?

    I first need to get a mains cable, since I lost it, somewhere in time.

    Here's some pics of the amp.

    https://s3-ap-southeast-1.amazonaws....mswatt/p0.jpeg
    https://s3-ap-southeast-1.amazonaws....mswatt/p1.jpeg
    https://s3-ap-southeast-1.amazonaws....mswatt/p2.jpeg
    https://s3-ap-southeast-1.amazonaws....mswatt/p3.jpeg
    https://s3-ap-southeast-1.amazonaws....mswatt/p4.jpeg
    https://s3-ap-southeast-1.amazonaws....mswatt/p5.jpeg
    https://s3-ap-southeast-1.amazonaws....mswatt/p6.jpeg
    https://s3-ap-southeast-1.amazonaws....mswatt/p7.jpeg
    https://s3-ap-southeast-1.amazonaws....mswatt/p8.jpeg
    https://s3-ap-southeast-1.amazonaws....mswatt/p9.jpeg
    https://s3-ap-southeast-1.amazonaws....swatt/p10.jpeg
    https://s3-ap-southeast-1.amazonaws....swatt/p11.jpeg

    I don't have real electronics experience. I can replace simple components and trace them down on the schematics. Last year I managed to bring back to life my old Marshall Valvestate, I just ended up replacing all the main caps of the amp. I hope this doesn't get much more complex though.

    Any hints or suggestions are welcome.

    Cheers.

  • #2
    You should build a light bulb limiter to plug it into when you first start it up. It will prevent and serious damage in case any components have failed.
    "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

    Comment


    • #3
      Well... What I see is that somewhere along the line someone (probably on more than one occasion) kludged that amp with an odd assortment of filter caps (one of which is axial instead of radial) and added a series resistor to the B+ string after the standby switch putting exposed high voltage nodes within reach of the user from outside of the amp. All I can say is that this is a very bad thing that can result in death if such an accident were to happen. Soooooo...

      I would undo that stuff for certain. On the other hand, if the amp worked for you the last time you used it, you have had no trouble and liked the amp as it was then there is the probability that removing the HV rail resistor will change the response of the amp a little. But at the very least that resistor should be mounted on a terminal strip INSIDE the chassis and that axial lead HV capacitor should be replaced with a radial capacitor.

      But I suspect all the electrolytic caps will need to be replaced due to age and disuse. Twenty idle years will kill most electrolytic caps. As g1 said (and if you're comfortable with the dangers I noted) you can bring the amp up on a limiter for a few hours and the caps may survive. Though they may not perform well and you would experience extra noise, hum and odd harmonic overtones.
      "Take two placebos, works twice as well." Enzo

      "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

      "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

      Comment


      • #4
        G1 and Chuck H. thanks for the quick responses.

        When I worked on the Valvestate I paid extra attention to discharging big caps and so. And this one looks much more scary. I'll definitely check the light bulb limiter stuff.

        Yeah those resistors were mounted by a "professional" many years ago, the amp worked fine after that. But I'll follow your advice and at least move them to the inside. If I knew what was the original setup of those resistors I would try to get them close to those.

        Unfortunately I don't have complete schematics. I guess all I have is this: https://drtube.com/schematics/simms/100w-amp.gif

        Regarding that axial lead HV capacitor. Could you please point out which one you mean, on which pic?

        Yep, I understand the caps aging. Lets see if I can carefully bring it up and see what comes out of the amp.

        Currently I can only try it out with a cabinet that has a single 12" speaker at 8.0 hm. Do you think it would be an issue connecting it to that once I can start it?

        PS: I tried to give thumbs up to both and it didn't work as I expected. But again, thanks a lot for your comments.

        UPDATE: Actually, I've seen now a few more pictures of that amp, and all seem to have the resistor on the outside:
        http://i76.photobucket.com/albums/j1...06/chassis.jpg
        http://www.tdpri.com/proxy.php?image...f0591ef83ff038
        Last edited by josegrad; 09-30-2018, 10:54 AM.

        Comment


        • #5
          picture 9 it's the blue one. The negative lead is sticking up outside of the chassis and a wire goes back into the chassis to connect to ground inside the amp

          Comment


          • #6
            Originally posted by josegrad View Post
            UPDATE: Actually, I've seen now a few more pictures of that amp, and all seem to have the resistor on the outside:
            Well looky there! Ok... Not how I would have done it. A bit dangerous and you sure couldn't design the amp like that today. But I should have looked for myself before critiquing. The grommet sort of hinted that it might be a stock installation, but I thought "No way anyone chose to sell the amp new like that." I was wrong.

            NBD on mounting the axial cap with the ground lead sticking out of the chassis. There's no HV on that lead. I've done sort of the opposite mounting radial caps on boards made for axial caps. The amp doesn't know the difference

            Good luck with the light bulb limiter. I've done exactly the same thing. I knew a guy that had two NOS amps still in the factory cardboard box (25 years old). I warned him about the filter caps and their age but he wasn't sure I knew what I was talking about because, you know, these are brand new and never used! So he plugged one in and it smoked and burped electrolyte all over the innards in about five minutes. So we brought the other up with a light bulb limiter for about four hours in idle with the standby in play mode. That amp did "work". But it was noisy and had the odd harmonic overtones I mentioned. I ended up replacing the electrolytic caps in both amps before it was over.
            "Take two placebos, works twice as well." Enzo

            "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

            "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

            Comment


            • #7
              Hi there,

              I have a question about the schematic I'm following.
              I think I should have almost everything with the top part of this:

              Click image for larger version

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              And this:

              Click image for larger version

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              But I'm not sure which part is that area on the left that says "3x1AT". Where is that located?

              ----

              On the other hand I just got a Bulgin connector from the UK.

              In the attached image you can see how the power connector is connected inside the amp. With a Red, Green and Black cable.
              Then there's the cable I'll use with Blue, Brown and Yellow/Green.

              If I'm not mistaken the cables should end up like in the table below.
              I'll appreciate any corrections obviously.

              AMP NEW CABLE FUNCTION
              Red Brown Live wire
              Green Yellow/Green Grounding
              Black Blue Neutral
              Click image for larger version

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              After that I'll start building the light bulb limiter and see what happens when I turn it on.

              I know this is not an electricians course, but any comments on my connection plans will we appreciated. Just in case.

              Thanks in advance.

              Comment


              • #8
                Originally posted by josegrad View Post
                But I'm not sure which part is that area on the left that says "3x1AT". Where is that located?
                It looks like a mod to add three 1A T fuses to the standby switch area. I think the fuse marked with an 'X' is to go in series with the bias winding where it's marked with a second 'X'

                The wire colour table is correct.

                Comment


                • #9
                  Thanks Dave.

                  Connection done.

                  I'm now investigating how big of a bulb I need to use for the light bulb limiter with this amp.
                  I guess I'll need pretty big bulb. Now sure if I can still get big enough to buy.

                  Cheers.

                  Comment


                  • #10
                    You can probably still get 200W or 250W incandescent outdoor spots at any hardware store.?. It doesn't need to be "light bulb" shaped.
                    "Take two placebos, works twice as well." Enzo

                    "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

                    "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

                    Comment


                    • #11
                      Too big of a bulb defeats the purpose. It will limit too late.
                      I've seen people use a rough rule of thumb that the bulb should be the same wattage as the amps output power. That being said, I don't think you need to use less than a 100W bulb for low power amps.
                      The bulb is only used when getting the idle conditions correct. Then you get off the bulb to do any signal or power output testing.
                      "Everything is better with a tube. I have a customer with an all-tube pacemaker. His heartbeat is steady, reassuring and dependable, not like a modern heartbeat. And if it goes wrong he can fix it himself. You can't do that with SMD." - Mick Bailey

                      Comment


                      • #12
                        I don't know why, but when I read that Jose thought the limiter had to be matched to THIS amp I saw the title "Simms 200W head" in my mind.

                        The typical 100W bulb would be fine.

                        You can still get incandescent hundys in specialty bulbs. You may need to order them on line. I still have a couple of plain ol "light bulbs" in my stash. But I'm sure I'd come up with something if I didn't.
                        "Take two placebos, works twice as well." Enzo

                        "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

                        "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

                        Comment


                        • #13
                          Ha,

                          Did I mention I'm in Finland? I can find trees and lakes of any size.

                          And also these bulbs I can get easily:

                          Click image for larger version

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                          But 100W old style bulbs are harder to get. Hmm, I bet the Russians have

                          Cheers.

                          Comment


                          • #14
                            Originally posted by josegrad View Post
                            Ha,

                            Did I mention I'm in Finland? I can find trees and lakes of any size.

                            And also these bulbs I can get easily:

                            [ATTACH=CONFIG]50727[/ATTACH]

                            But 100W old style bulbs are harder to get. Hmm, I bet the Russians have

                            Cheers.
                            Nothing wrong with halogen bulbs, as shown in your picture. They are incandescent lamps and work just as fine as the old ones as limiters.
                            - Own Opinions Only -

                            Comment


                            • #15
                              Originally posted by Helmholtz View Post
                              Nothing wrong with halogen bulbs, as shown in your picture. They are incandescent lamps and work just as fine as the old ones as limiters.
                              And typically last longer AND make a nicer spectrum of light If it mattered.
                              "Take two placebos, works twice as well." Enzo

                              "Now get off my lawn with your silicooties and boom-chucka speakers and computers masquerading as amplifiers" Justin Thomas

                              "Being born on third base and thinking that you must have hit a triple is pure delusion!" Steve A

                              Comment

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