Advice on Eico 1140 Rebuild

Discussion in 'Amp Tech Center' started by andrewRneumann, Sep 2, 2020.

  1. andrewRneumann

    andrewRneumann Tele-Holic

    Posts:
    591
    Joined:
    Mar 22, 2020
    Location:
    Cincinnati, OH, USA
    Hello All,

    I got an EICO 1140 substitution box off of eBay. I tested it out and I’d say about half of the resistors have drifted more than I’d want and some of the caps are bad. I really want to just replace all the resistors and caps, but it’s a lot of work just finding all the values. What would you suggest I do? Anyone else rebuilt one of these?
    86D89195-DC5A-4D37-AB58-7F062E54E244.jpeg
     
  2. tubegeek

    tubegeek Friend of Leo's

    Age:
    60
    Posts:
    3,770
    Joined:
    Jan 31, 2020
    Location:
    Brooklyn, NY
    R's drifted high? Add parallel. C's drifted low? Add parallel.

    Opposite problems? Replace.
     
    rangercaster likes this.
  3. Jon Snell

    Jon Snell Tele-Holic

    Posts:
    540
    Joined:
    Aug 31, 2015
    Location:
    Jurassic Coast. UK.
    Looks like the resistors are carbon composition, as we always called them 'carbon drifters'.
    Prepare three rings of tinned copper wire, the same diameter as already there. Cut the components off at the ring end, then replace the resistors with equality types at 1 or 2%. MFR50SFTE52 have a good range. https://uk.rs-online.com/web/c/passive-components/fixed-resistors/
    https://www.mouser.co.uk/Search/Refine?N=254363&Keyword=MFR

    Capacitors will probably be the same.
    Mouser, RS, Farnell etc, sell resistors in 10s some in singles and most capacitors in singles.
    Don't forget to clean up the old tag on the wafer and fit the new component using a mechanically sound joint, before soldering it in.
    Hope that helps.
     
  4. mrriggs

    mrriggs TDPRI Member

    Age:
    40
    Posts:
    80
    Joined:
    May 24, 2020
    Location:
    Vancouver, WA
    I've got a couple of these units and, yeah, some of the values have drifted a bit. Considered rebuilding at least one of them with precision components but it never floated to the top of the priority list.

    For what these are used for [at least what I use them for] precision doesn't really matter. Clip it into a circuit and switch from low to high values to see the effect in real time. It's the difference between switch positions that I'm looking for. Kind of like one of those eye-doctor things, "Better one, or better two..."

    When getting down to the nitty-gritty precision measurements I'll clip in a more precise component to do testing and analysis of the circuit. All the stray capacitance/inductance of the substitution box would likely lead to erroneous results anyway.
     
    rangercaster likes this.
  5. andrewRneumann

    andrewRneumann Tele-Holic

    Posts:
    591
    Joined:
    Mar 22, 2020
    Location:
    Cincinnati, OH, USA
    I was wondering if it would make any sense to put it in a metal, grounded chassis.
     
  6. mrriggs

    mrriggs TDPRI Member

    Age:
    40
    Posts:
    80
    Joined:
    May 24, 2020
    Location:
    Vancouver, WA
    Seems like that would just add to the stray capacitance.

    Are you concerned about noise or shock hazard?

    Again, like the concern about precision, in the context of a quick-and-dirty A-B tester it's only the differences between switch positions that you are listening for. You can simply ignore any noise that may be picked up by the box.

    As for safety... Only touch the Bakelite case and knobs when hooked to an energized circuit.
     
IMPORTANT: Treat everyone here with respect, no matter how difficult!
No sex, drug, political, religion or hate discussion permitted here.