Fisher 500B - time for a full-blown restoration

Discussion in 'Fisher' started by Winters, Feb 2, 2019.

  1. Winters

    Winters Active Member

    Messages:
    266
    Location:
    Poland
    I purchased my 500B seven years ago. It was used on a daily basis ever since, never causing me much trouble (apart from one EH 7591 that died on me prematurely). I've never properly restored it, just done the basic stuff (silicon rectifier, 100 ohm screen resistors, 10 ohm cathode to ground resistors, K42 capacitors). It sounded great at first, then the sound quality started to slowly deteriorate to the point I'm no longer enjoying it. I think it sounds rather dull and harsh and struggles to power my 1967 Wharfedale W70Ds.

    So I decided it's time to do something about it!

    I want to:
    - redo some of my previous work with better quality parts (1% metal film resistors and what not)

    - replace all of the electrolytic capacitors AND hide them all inside the chassis - I've seen several folks do that with 500B and it seems the only acceptable route for me. I do not want to hack the old cans up and restuff them + I've done that before on some other pieces of gear and was never fully satisfied with the visual outcome. New cans are out of question as their price coupled with shipping costs to Europe and import duties would kill me. I prefer to spend that amount of money on new 7591 tubes.

    - install the IBAM board

    - replace / install some other, less important stuff: new "death cap", add a thermistor protection etc.

    I've already ordered most parts (Nichicon low ESR caps and terminal strips to install them on etc).

    I have some questions to those who have tucked the new electrolytics in the chassis - what is the best way to connect the negative ends of the caps to the chassis? Solder? If so, where? Add to already existing ground lugs / connections? Or just use solder to the terminal strips terminals which are also grounding terminals (the other end is supposed to be screwed to the chassis)?

    When all of that is done, I'd like to buy a new quad of 7591 tubes. Should I get Tung-Sols? Everyone seems to be very happy about them. I've actually purchased a matched quad of their 7591 and it was a rather unpleasant experience. There were HUGE differences in the glass sizes. One two was about one centimeter smaller than the other three and the store I've purchased them from initially refused to accept my return.

    Best regards,
    Pete
     

     

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  2. Dave451

    Dave451 AK Subscriber Subscriber

    Messages:
    1,302
    Location:
    Philly area
    The 500B is a great receiver. I restored one not too long ago and did many of the things you want to do, including the IBAM (D. C. Gillespie circuit), Tung Sol 7591A's, and some cap work. I offer the link to my thread, not because I am any great shakes at this work, but mainly because of how I had to fiddle with the IBAM board to properly bias the Tung Sol 7591A's.

    http://audiokarma.org/forums/index.php?threads/fisher-500b-re-hab.756462/

    I didn't have to replace most of the caps (I did rigorously test them), but I have for other units using under-chassis axials and would offer the advise I got. That is, the first couple of caps in the B+ string should have their grounds at the place where the original cans were grounded to avoid ground loops. I grounded the new caps on the same can they replaced (after the old can had been removed from the circuit, of course, but still attached electrically to the chassis).

    Further down the string, you can move the new caps to the point in the circuit where they're needed, making sure to pick a good solid local ground point for them.

    Here's the link for the under-chassis replacement work I did (on a Fisher 400) if it helps:

    http://audiokarma.org/forums/index.php?threads/fisher-400-locating-under-chassis-caps.822635/

    Good luck with the work!
    Dave
     
  3. Winters

    Winters Active Member

    Messages:
    266
    Location:
    Poland
    Many thanks for your help, Dave. Very tidy work on that 400.
    I also thought about using axials but since I would like to mount my new caps on new terminal strips (and mount those using bolts/holes that are already in the receiver), I went with regular mount electrolytics (not axials) except for one 47uF 500V cap.
     
  4. audmod01

    audmod01 Super Member

    Messages:
    1,386
    Location:
    Tioga, TX
    Winters;

    I think you will be OK with mounting the replacement electrolytics under the chassis as Dave detailed. Many modern electrolytic caps are physically much smaller than the original ones of decades ago even though they have improved voltage ratings, lower ESR and higher temperature ratings. Watch lead dress and use extra insulating sleeving if needed to help prevent any shorts to other components nearby or to chassis ground. The best sleeving available is the translucent Teflon type. It survives all soldering operations easily.

    If new caps seem to be not adequately physically restrained, you might find other nearby terminal strips or other structures underneath that you could secure them to using nylon plastic zip-ties. Be watchful of any high temperature high wattage resistors that could touch the side of the capacitor and melt through its plastic insulating cover.

    You will find plenty of members here willing to help you along the way. You have a nice unit. The 500-B looks aesthetically pleasing in operation with its tuning eye and the dial lighting on. Have fun!

    Joe
     
  5. Dave451

    Dave451 AK Subscriber Subscriber

    Messages:
    1,302
    Location:
    Philly area
    I used tie strips for mounting as needed and didn't have to drill any holes in either the 400 or the 500B. The 500B is pretty roomy underneath. Radial caps work fine as well and are actually easier to work with in many cases when using tie strips.
     

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