Fisher 500-B Restoration Process for The New Guy

Discussion in 'Fisher' started by Josey Wales, Nov 7, 2018.

  1. Josey Wales

    Josey Wales AK Subscriber Subscriber

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    Ok. I've been doing some research on capacitors and i've learned that it's important to determine the outside foil end of each cap and be sure to connect it to ground. Has anyone done this? Also, is there a good, reliable way to do this without having to build my own outside foil end testing box? it seems like a daunting task to build a box to do this or maybe it's not important to do it at all? Thanks in advance.
     

     

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  2. thornev

    thornev Well-Known Member

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    deleted post - misunderstood question.
     
    Last edited: Nov 20, 2018
  3. 1rebmem

    1rebmem AK Subscriber Subscriber

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    I believe he's talking about non electrolytic foil type caps like a Mallory 150.
    The belief is by having the outer foil of the cap to ground, or at least to the lowest impedance point, then you reduce noise in the unit overall.
    http://audiokarma.org/forums/index....uter-foil-of-caps-w-o-an-oscilloscope.792762/
    The black stripe does NOT necessarily indicate the ground side anymore. You can determine the outer foil lead of the cap with an O-scope.
    Jef
     
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  4. 1rebmem

    1rebmem AK Subscriber Subscriber

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    I have built guitar amps and took the time to identify the outer foil end of each cap and installed them appropriately.
    And I have built amps without regard on the cap orientation. Could never tell a difference in the noise floor level.
    But if it doesn't cost anything but time, why not right?
    I rarely take the time..........
    Jef
     
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  5. Josey Wales

    Josey Wales AK Subscriber Subscriber

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    Hello, Yes. What i mean is the non-electrolytic type as 1rebmem describes. There has been some discussion surrounding this and some say that you must do this and others say it's not necessary. Some older capacitors seem to have been marked with the outside foil end written on the cap as "outside foil end" marking. Just curious.
     
  6. Josey Wales

    Josey Wales AK Subscriber Subscriber

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    Thank you 1rebmem!
     

     

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  7. 1rebmem

    1rebmem AK Subscriber Subscriber

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    Josey,
    Since I'm watching your 500B progress, I'm interested in hearing the direction you are going to take.
    What your game plan is?
    A to-do list sort of thing?

    Thanks,
    Jef
     
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  8. gadget73

    gadget73 junk junkie Subscriber

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    I test and mark the outside foil because its easy. I'm not convinced it makes any massive difference, but for something that is so low effort, why not? I use my scope to do it but you can use an old crappy RCA cable and an amplifier. Cut the cable and put clip leads on it. Plug it into the amp and turn it on. Hold the cap and listen to the hum. Reverse the leads. The outer foil end will hum louder when you have the center wire of the RCA cable connected to that end. Same principal on the scope but you're looking at squiggle height, which is a very technical thing to look for.

    I use a marker to color the outer foil end.
     
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  9. rufleruf

    rufleruf Poor Impulse Control Subscriber

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    gadg - that sounds like what a tech did a long time ago to troubleshoot a transistor organ from the 60's. He used a 1/4" jack and basically hovered right over the caps and if there was no hum, he said the cap was bad. He picked out a cap that didn't hum, replaced it, and the silent note suddenly made noise.
     
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  10. Josey Wales

    Josey Wales AK Subscriber Subscriber

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    I ended up purchasing a kit from the auction site. It comes with an IBAM that's mounted underneath. I'm hoping to find an alternate place to mount the IBAM on the top side or somewhere more convenient. I plan to begin the process soon. It comes with "some" helpful instructions and schematics, photos etc. I now have all of the tools etc. and plan to begin this weekend. I've been off for a while gathering everything and now I'm ready to proceed! I will begin posting some photos in order of the steps I took. I plan to take my time and learn as much as I can as I go.
     
  11. sgmlaw

    sgmlaw Well-Known Member

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    Regarding orientation of non-polarized coupling caps, some people prefer to install them cathodes out, to mitigate in-chassis rfi pickup. That requires the cap to be polarity marked.

    Where they are polarity marked, you would connect the cathode end to the input side (HV) on these receivers. The later Ero-Fols used on the C series were marked, and popular replacements such as the Soviet K40s are as well. But most of the GI-made ‘turds’ that Fisher used in the earlier models, and most modern film series, are not. You can speculate based on the direction of any values imprint, but unless the manufacturer specifically states a labeling practice, consider them unmarked.

    Practically speaking, if they are non-polarized caps, you can install them any way you like, and it should make little difference unless there is a problem in circuit layout or operation values.
     
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  12. Josey Wales

    Josey Wales AK Subscriber Subscriber

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    Thank you for the information. They appear to be non-polarized.I will check them again to be sure.
     
  13. thornev

    thornev Well-Known Member

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    Josey - I mounted my IBAM board on top behind the reverb inserts and the wires through the holes in front of the reverb inserts. I didn't secure the board. I used thick enough and insulated wire that their stiffness holds the board in place. To protect the bottom of the board from shorting against the chassis, I covered the bottom of the board with electrical tape. It's not pretty, but there is a picture in some thread somewhere. Thorne
     
  14. Josey Wales

    Josey Wales AK Subscriber Subscriber

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    Thank you Thorne!
     
  15. thornev

    thornev Well-Known Member

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    Josey - I found a pic of my IBAM mounted. Not pretty but easy access was a priority. Thorne
     

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  16. Josey Wales

    Josey Wales AK Subscriber Subscriber

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    Thanks, Thorn! That's just about where i had considered placing it. I'm just about ready to begin the process. I have everything i need now. Work has been crushing me lately so Now that I have a few days off, I might begin tonight. I'm learning to take my time on this one. I want to do it right. Still learning a ton beforehand. Thanks again. It looks great by the way.
     

     

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  17. thornev

    thornev Well-Known Member

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    Good luck, Josey (you and my cat have the same name), and do take your time. We're all here to help. Remember that there is a lot of high voltage in there that can kill you. Be sure to drain the electrolytic capacitors of their voltage before you touch anything. Make sure they measure under 1 volt and remember that there are chemicals inside them that can ramp up a little voltage after you drain them. Unplug the unit.
     
  18. Josey Wales

    Josey Wales AK Subscriber Subscriber

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    Thank you. Yes, i've been learning about how tube amplifiers are loaded with very high voltage. Thats funny about the cat. I took the name form the movie "The outlaw Josey Wales". Ha! I'll begin posting photos soon. Thanks again!
     
  19. Josey Wales

    Josey Wales AK Subscriber Subscriber

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    Thank you! That's the answer I was hoping to find!
     
  20. Josey Wales

    Josey Wales AK Subscriber Subscriber

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    I will try this as i have a guitar amp sitting next to me and I didn't realize it. Lol. Will get back soon with this method.
     

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