1. Time for some upgrades in server hardware and software to enhance security and take AK to the next level. Please contribute what you can to sales@audiokarma.org at PayPal.com - Thanks from the AK Team
    Dismiss Notice

Help Saving 400-CX SA-100 and 100-R Tuner

Discussion in 'Fisher' started by moondogtn, Oct 10, 2017.

  1. moondogtn

    moondogtn AK Subscriber Subscriber

    Messages:
    461
    Location:
    Pleasanton, TX
    I have been trying to get a break to get back to this. I have put a parts list together for the EFB but had a few questions. For resistors, will metal film be good? What about power ratings for those not specified? 1/4 watt or 1/2 watt? Here is the current list....I have included extras just because and I know PDF isn't the greatest way to share this. BTW, there are some metal oxide resistors that I am ordering for something else, disregard those. If there is a better way to do this, let me know or I can try to list parts links individually. Thanks

    Bill
     

    Attached Files:

     

    Please register to disable this ad.

  2. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

    Messages:
    9,673
    Location:
    Ball Ground, GA
    Moon -- Unless otherwise marked on the EFB™ schematic, .5W resistors are fine, as are the use of MF pieces. The 1M 1W resistor should be a close tolerance piece.

    Dave
     
  3. moondogtn

    moondogtn AK Subscriber Subscriber

    Messages:
    461
    Location:
    Pleasanton, TX
    Dave, thank you. I ordered parts plus extras. I hope to get this done next week providing I don't drop a tube or burn something up. I will need to reread the various threads on the EFB install but IIRC, I simply install(or replace) according to schematic and then redo adjustments in same order?

    Bill
     
  4. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

    Messages:
    9,673
    Location:
    Ball Ground, GA
    Yep -- but also be sure you have installed individual cathode resistors and Screen Stability resistors in the process if not already done.

    Dave
     
  5. moondogtn

    moondogtn AK Subscriber Subscriber

    Messages:
    461
    Location:
    Pleasanton, TX
    I haven’t and didn’t know I needed them, must have missed that step? I will have to place another order once I figure out what I need.

    Edited...I can’t believe I didn’t catch that. I will still need to determine what it all means so will likely need some guidance.

    2. Remove the damping control circuits. This is an antiquated feature, and its removal will allow two terminals on each output strip to be used as individual output tube current measurement points, as the original design only allowed for measurement of the total current draw of each channel.

    3. Install individual 10 ohm cathode resistors to allow for current measurements of each output tube at the new terminals created above.

    4. Install individual 100 ohm screen stability resistors. This will allow for the use of a screen supply source of much lower impedance without any concerns of output tube arcing.

    5. Remove the old screen bleeder-regulator circuits.

    6. Install the screen voltage control portion of EFB II

    7. Install the bias supply regulator portion of EFB II.

    I may have some of these values available. This seems pretty complicated to a newbie on tubes since I don’t know what most of this means. Time to do some research. Lol

    Bill
     
    Last edited: Oct 11, 2018 at 1:57 PM
  6. notdigital

    notdigital AK Subscriber Subscriber

    Messages:
    2,237
    Location:
    NYNY
    Moon: If it'll help, I've attached a pic that shows most of the EFB and other mods mentioned above. DSCN0329.JPG
     

     

    Please register to disable this ad.

  7. moondogtn

    moondogtn AK Subscriber Subscriber

    Messages:
    461
    Location:
    Pleasanton, TX
    Notdigital, I appreciate the pic. I just need to dig into a bit as the terminology has me thrown off. I did look at yours and Dave’s threads. I see what was meant by some of the items. Let me get some better questions together to clarify. Thanks again.

    Bill
     
  8. notdigital

    notdigital AK Subscriber Subscriber

    Messages:
    2,237
    Location:
    NYNY
    No worries. Just a little while back reading latin was easier than reading some of these tech related posts. After pouring over and studying many related restoration posts, my brain developed a library of terms that was sufficient to get me through. Nothing deep but just enough of the basics to address the task at hand. You'll be happy when it all starts to click.

    Just so you know, the pic above is virtually a snapshot of the work Dave did in his thread. Referencing your post #125, what you do not see in the pic is #2 &3. Unabashedly, I copied heyraz' way of providing for cathode current test points which I thought was a slick way of providing for the modification.
     
  9. moondogtn

    moondogtn AK Subscriber Subscriber

    Messages:
    461
    Location:
    Pleasanton, TX
    I read some more. It’s starting to make sense. I will use some pics with markup to ensure I get it correct prior to applying power.
    Just to make sure I get the correct parts. These two values (10 and 100) should be 1/4 watt? Thanks again.

    Bill
     
    Last edited: Oct 14, 2018 at 9:21 AM
  10. notdigital

    notdigital AK Subscriber Subscriber

    Messages:
    2,237
    Location:
    NYNY
    I use 1/4 watt metal film devices for the cathode or "test point" resistors. Same for the screen stability resistors. I want either or both to let go if an over-current situation develops.

    For sure the cathode resistors should be 1%, very closely matched components.
     
  11. moondogtn

    moondogtn AK Subscriber Subscriber

    Messages:
    461
    Location:
    Pleasanton, TX
    Not, from what I read, that was reason to use 1/4 watt but I wanted to make sure. Also, I plan to use metal film 1% but can also match them too with my meter. Thank you for clarification.

    Bill
     

     

    Please register to disable this ad.

Share This Page