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Safe grounding? (pics)

Discussion in 'Shock Brother's DIY Amps' started by calvin006, Aug 24, 2010.

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  1. calvin006

    calvin006 TDPRI Member

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    I'm doing some maintenance on a Rickenbacker M-8E (single-ended from '57) and I want to make sure that I'm safely grounding things. Is there way to test with a multimeter? For instance, I've grounded the three prong plug as Gerald Weber suggested in one of his videos, by soldering to a lug secured to the chassis by one of the PT screws:
    [​IMG]
    [​IMG]

    In this next picture, I've removed one of the old bypass caps and soldered the new one to a little piece of the old one that connects to ground. I knew I wouldn't be able to solder directly to the chassis, so I thought this was just as good. The joint seems strong, but is there a way I can test it? Also in this picture are the two new filter caps which I soldered to a lug connected to the OT. I realized later that the lug is not touching the chassis, so I need to fix that, but in general is this a method that could work? Again, can I test for good grounding before actually plugging in the amp?
    [​IMG]
     
  2. rainedave

    rainedave Tele-Holic

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    Since all of those wires are going to ground, it might not be a huge issue in this case, but I would still put heat shrink tubing on any wires that could potentially touch each other. These wires are pretty close to touching.
     

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    Last edited: Aug 24, 2010
  3. Crawfish

    Crawfish Tele-Afflicted Silver Supporter

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    You can use a multimeter to check your grounds...you should have no resistance. A VTVM is probably best, but a modern DMM will work just as well.

    Those grounds look ok to me. If you're using a lug or other contact to an old chassis, you might want to clean up the area it contacts a bit...I usually do since there is probably oxidation and you want a nice shiny surface. But what you have in the pictures should work fine.

    On the lug going to the xformer, it does contact the chassis - through the transformer lug and also the bolt you have going through it. If you feel better putting the lug under the xformer, go for it. Unless there is rust there, it will work either way.

    You could also run the negative side of that bypass cap to the same lug.

    I agree with Dave about the insulation - you might want something on the positive lead of that cap in case it touches the negative lead of the filter cap. If you buy a couple strands of shrink tubing you'll just get in the habit of doing it all the time.

    Cool amp...I dig Ric stuff and would love to have one of their old amps.

    -Kevin
     
  4. Wally

    Wally Telefied Ad Free Member

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    That is also a high dollar cap, relatively speaking, to use for that 'death cap'. Most of us would probably just eliminate that 'death cap'. Some don't.
    I have a problem with that blue AC leg connection. IF you haven't made that safe, that need to be done. THat bare cnnection must be insulated!
     
  5. limbe

    limbe Tele-Afflicted

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    I would be very grateful if you removed the "death cap".It´s not for nothing it has earned it´s nickname.Or have you done it already?Next time you install a grounded cord make the green-yellow wire a bit longer than the other two.The idea here is that if you pull at the cord with a lot of force the groundwire should be the last one to come loose.
     
  6. calvin006

    calvin006 TDPRI Member

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    Thanks for the tips. I was also concerned about those exposed wires... I have some shrink tube so I will definitely wrap them up in the spots where they might touch.

    @Wally and limbe, that death cap is no longer connected to anything. Originally it was wired to the fuse, but I removed it while installing the three prong chord. I didn't want to completely remove it because it shares that ground with two other wires from the PT. Is it OK to leave it wired to ground with the other end hanging free?

    @Crawfish, I have a DMM (no VTVM) but I'm fairly new to using them. How exactly do I connect the leads to test for no resistance? Sorry for the newbie question. And yes, it's a great little amp. I'm hoping to cut down on some buzzing and noise with this maintenance.
     
  7. limbe

    limbe Tele-Afflicted

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    You shouldn´t have any exposed wire hanging free.The best thing to do is to clip off the capacitors wire as close to the solder as possible without harming the other two wires that are soldered to the ground,if you don´t want resolder the two wires which could be tricky.
    Don´t apologize for asking questions!Only a 3-year old thinks he knows everything.
    1 Set your VTVM on the lowest resistance range.(Could be 200 ohm for example)
    2 Put your testprobes together and check that your meter shows zero ohm.
    3 Attach one of the probes to a good ground on the chassie of the amp.
    4 Now take the other probe and touch everything that should be grounded.
    5 Look on your meter while doing this to confirm that the meter shows zero ohm
    on all those points.When one probe touches the chassie and the other probe touches something that should be grounded the VTVM should show 0 ohm.
    Please ask me again if I am unclear about anything and thank you very much for removing the "death cap"
    Limbe
     
  8. calvin006

    calvin006 TDPRI Member

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    Thanks for the info, limbe. I went through this weekend and improved things: sanded the chassis where my ground lugs touch it, shifted the green ground wire to get some more slack, clipped the death cap, and added shrink tubing to my filter caps.

    I tested my grounds as advised. My DMM, when set to 200 Ohm, reads 00.5 when I touch the leads together. It also reads the same for all my grounds, so I think I'm all set.

    I'm planning on running current through it for several hours to get the caps ready, another suggestion of Gerlad Weber. He uses a variac and slowly increases the voltage. I don't have a variac, so I have to start at full line voltage. But once that's done, we'll see how she sounds. Thanks for all the help. This is my go to forum for learning about amps because I know people are credible.
     
  9. the fatch

    the fatch TDPRI Member

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    Agreed on the AC leg connection. I would put locknuts on the grounding bolts.
     
  10. clintj

    clintj Friend of Leo's

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    Seeing as the OP hasn't posted anything since 2014, and this thread is from 2010, I wouldn't worry about it too much.
     
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  11. Joe M

    Joe M Super Moderator Staff Member

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    Agreed, closed.
     
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