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  • #46
    Finally got to look at this in the light of day this morning--with an alert mind, the answer is obvious--you are absolutely correct. A bridge is not going to work. So, you will have to do a cost tradeoff on whether to just order another identical bridge and only use half of each one, or whether is is better to go with individual diodes--since you have those great heat sinks, either way should be pretty easy.

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    • #47
      Here are the power rectifiers that look like they would do the job. Almost cost half of what the whole welder was worth. Click image for larger version

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      • #48
        Yep, four of them add up. But that machine is worth it. At least their shipping is reasonable.

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        • #49
          The main power rectifiers finally arrived in the mail. Here they are being mounted on the heat sink that I intend to use. The studs are screwed directly into the aluminum of the heat sinks, which are electrically isolated from each other and will be isolated from the frame. That means the heatsinks themselves will be two of the terminals. My machine seems to be one of the oldest here, and the schematic of the power rectifiers is a little different from the more recent machines. Click image for larger version

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          • #50
            Lookin' good!

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            • #51
              This is a great hobby, its better than sitting at the bar. As a going concern regarding the welding machines I am not tearing mine apart unless it craps out. Its working and not going to invest in what if,,, what could go wrong, all that to an obsolete machine. Its not a bad thing,,,, do all that crap and could get a new one runs on half the wire, runs from common 50A.

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              • #52
                Yep, four of them add up. But that machine is worth it
                Not really. Similar, I got a car, at first glance it looks ok, engine shates and I get a lot of advice about it but I am not putting 5K engine plus a lot more work in a car I can buy running for 1500$. This guy has a running machine, might even be a different cause if it was broke but can buy these regular for well under 1K look and run like new. Hobby user could never wear it out and if it does crap it cost less to replace than upgrade,,, that is an IF it craps.
                Great machine to learn on, great to use, nothing wrong with it if a guy has 100A service for it. But I aint shoving one full of new parts to entertain myself.

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                • #53
                  Whatever floats your boat, I suppose. The possibility of the old selenium rectifiers self destructing, ruining a good machine, stinking up the whole garage with very toxic fumes is something that should be avoided. I will have less the 200 invested in getting rid of these dinosaurs, plus labor which is very cheap when doing it yourself. Retirement is a great thing for doing what you want to do, not because it makes economic sense but because it is an interesting project and keeps a retro machine out of the landfill.
                  Cheers, Alfred

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                  • #54
                    There is a lot of assumption that something bad will happen to it. Speculation really. I have used a whole garage full of them and never even seen one hiccup. But,,, I did elude to this being a hobby, then its a different case but doesnt change the real value of it.

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                    • #55
                      A bunch of us also work with older Kohler generators that have selenium bridges in the control box. The first thing done to these is replace them with a dirt cheap, much more reliable silicon bridge, because if and when that selenium unit bites the dust, it will take the compounding transformer with it, and these are made of unobtainium.

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                      • #56
                        The know how and the expertise in this thread is priceless.

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                        • #57
                          Originally posted by 07wingnut View Post
                          A bunch of us also work with older Kohler generators that have selenium bridges in the control box. The first thing done to these is replace them with a dirt cheap, much more reliable silicon bridge, because if and when that selenium unit bites the dust, it will take the compounding transformer with it, and these are made of unobtainium.
                          Right on. I cannot think of a single reason to have a selenium rectifier in any piece of equipment I own or repair. Far too cheap and easy to get rid of them, as opposed to the unrecoverable damage they can do when (not if) they fail.

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                          • #58
                            I own a lot of stuff. Never had a selenium rectifier fail. Never had to service e one.

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                            • #59
                              Every car engine will fail if its driven enough. It's not the only thing that breaks on them.

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                              • #60
                                I have a 300 synch. I suppose it's got them. Tossing more at it than the 200$ I have in to it would defeat the point of getting it cheap 20 years ago. Why hasn't it blown up yet if it's a sure thing? When might it happen and if it blows up likely to part it out considering all the compulsive junk savers we have access to today. But,,,, almost bet that 99% of them owned today will outlive the people that own them.

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