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

Fisher X-100 Restoration

Discussion in 'Fisher' started by baconbadge, Oct 12, 2018.

  1. baconbadge

    baconbadge New Member

    Messages:
    39
    Location:
    Queens, NY
    Hi All,

    I recently acquired a stock X-100 that I'll be restoring. There are a bunch of X-100 threads, but sometimes they cause confusion because of the model variations.

    So to clarify, this is a serial# 32xxx with 7189/6BQ5 outputs and GZ34 tube rectification. Obvious initial safety measures are installation of a CL-80 thermistor & replacement of all electrolytics.

    1. Are there any other recommended restorations/upgrades for this model (besides coupling caps & IBAM)?

    2. I know the power transformers on the X-100 are prone to failure. What is the typical cause of PT failure on the X-100, and on which models is it more of a concern?

    3. What is the definitive answer on using 6BQ5 vs 7189s in the output stage? With the schematic showing 380v on the plates, I'm assuming 7189s are the safer bet, but quality NOS are getting scarce.

    I'm using NOS Teles for V1/V6, RCAs for V2/V7, GEs for V3/V8, slightly used Mullard GZ34, and a matched quad of NOS Reflector 7189/6BQ5s. I'd like to keep my unit as stock as possible for now, with possible upgrades in the future after I've lived with her for a while and know how she sounds.

    Thanks!

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]
     
    Last edited: Oct 12, 2018

     

    Please register to disable this ad.

  2. baconbadge

    baconbadge New Member

    Messages:
    39
    Location:
    Queens, NY
    And some closeups...

    [​IMG]

    [​IMG]

    [​IMG]

    [​IMG]
     
  3. Theron D

    Theron D AK Subscriber Subscriber

    Messages:
    55
    Excellent! I have a model very close to yours (38xxxk) and am a newbie so will be following along when the experts chime in! Please note Ill start a thread too with my indivdual restoration so as not to highjack yours! Good luck! Nice looking amp you got there! Hope you dont mind, here’s the one I just purchased...

    2B6B2707-59A7-4C4B-BBD9-3F16F05757B4.jpeg 87346A4F-66AB-49B5-83BD-C2F5061B6B27.jpeg 407974FC-311B-4AA6-BEC2-460DBD557D00.jpeg
     
    Last edited: Oct 12, 2018
    baconbadge likes this.
  4. baconbadge

    baconbadge New Member

    Messages:
    39
    Location:
    Queens, NY
    Lookin good! What tubes you got in there?
     
  5. Dadbar

    Dadbar Super Member

    Messages:
    1,883
    Location:
    Waltham & Gloucester MA
    Since the unit has a tube rectifier, the inrush limiters are probably overkill. If the unit were mine I would still replace or restuff the cans and definitely replace the common bias cap (the large fat paper cap all alone under the chassis.)

    If this were my unit, I would never run 6BQ5 tubes in it....only the toughest stuff I could find (like those military Russian 6P14EB) and I would make sure I used really high quality 12AX7 tubes as well. The reason is that these amps derive DC heater string current by serving as part of the bias resistor for the power tubes. If one of your 12AX7 heaters goes out of whack your power tube bias supply also goes amiss. At the same time, you have to pass a larger quiescent current through the power tubes to ensure sufficient juice to power the 12AX7 heaters. It's a simple system as long as everything works well and the tubes are in good shape....so use a really high quality matched quad of power tubes and a good set of 12AX7 and you will be good.

    As far as an IBAM, if this were my unit and I didn't care about keeping it stock, I would consider adding a small transformer to power the 12AX7 tubes with a dedicated DC power supply and unlink the 12AX7 tubes from the bias circuit prior to considering an IBAM. Then you could run the power tubes at a lower bias current for longer life.
     
    bhamham and baconbadge like this.
  6. baconbadge

    baconbadge New Member

    Messages:
    39
    Location:
    Queens, NY
    Bump for all the Fisher Gurus!
     
    Theron D likes this.

     

    Please register to disable this ad.

  7. bhamham

    bhamham AK Subscriber Subscriber

    Messages:
    2,033
    Location:
    Austin
    That's a good idea with the separate dedicated DC power supply, dadbar. I thought of doing that on an X-100-B.

    The other day I started re-doing an X-100-3, no tube rectifier. Cut the cans off with an oscillating saw and started the stuffing process. Not sure how far I'll take it other than changing our the electrolytics and replacing any bad components plus cleaning it really well. I was thinking of just getting a matched quad of 6P14EBs and not doing an IBAM - getting lazy these days.

    I'll be interested to see how you tackle your X-100 baconbadge. That's a super nice one! All the best with it.
     
    Theron D and baconbadge like this.

Share This Page