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-100-3 Refresh

Discussion in 'Fisher' started by bhamham, Oct 14, 2018.

  1. bhamham

    bhamham AK Subscriber Subscriber

    Messages:
    2,013
    Location:
    Austin
    Hey guys, I'm a bit rusty not having done any Fisher tube work in a couple of years, but I found this very nice X-100-3 on ebay and thought I'd like to try it out. The 7189 is probably my favorite output tube. It's in pretty good shape, there's some letter loss on the back of the chasis, but the face is very clean and overall the chassis is in decent shape.

    I cut off the cans with an oscillating saw - pretty easy to do as there's a lot of maneuvering room on top. Then removed the guts from the cans and cleaned them up. Air hosed everything and gave it a good bath. Now ready to stuff the cans and mount them.

    Not sure what I'm doing with this guy other than changing out all the electrolytics, checking the components and cleaning/lubing all the switches, sockets and jacks. Not sure about an IBAM just yet; thought I'd just get a matched quad to make a little easier on me.

    [​IMG]


    [​IMG]


    [​IMG]


    [​IMG]
     

     

    Please register to disable this ad.

  2. Patrice B

    Patrice B AK Subscriber Subscriber

    Messages:
    2,230
    Location:
    Montréal, Canada
    IBAM possible for a cathode biased amp? This one rely on the string of 12v tubes for bias IIRC.
     
    bhamham likes this.
  3. bhamham

    bhamham AK Subscriber Subscriber

    Messages:
    2,013
    Location:
    Austin
    You could revise the bias system and use a separate DC supply for the 12AX7 heaters. Using a small transformer and a voltage doubler rectifier followed by a filter. A bit of work but it would probably benefit in performance.
     
    baconbadge and Patrice B like this.
  4. Patrice B

    Patrice B AK Subscriber Subscriber

    Messages:
    2,230
    Location:
    Montréal, Canada
    Ah, I see. Interesting...
     
    bhamham likes this.
  5. Dave451

    Dave451 AK Subscriber Subscriber

    Messages:
    1,131
    Location:
    Philly area
    Do you want to think about replacing the coupling caps or will you check those in hopes of preserving the originals (ero fols)?
     
    bhamham likes this.
  6. bhamham

    bhamham AK Subscriber Subscriber

    Messages:
    2,013
    Location:
    Austin
    I plan on keeping the two original ero fols providing they test ok and replacing the old, black mylars with some ero fols I have on hand. I think the ero fols are a pretty hardy cap and help to preserve the original sound.
     
    baconbadge likes this.

     

    Please register to disable this ad.

  7. baconbadge

    baconbadge New Member

    Messages:
    38
    Location:
    Queens, NY
    I have heard firsthand the differences between the original ERO FOLs & the new yellow Carli mylar caps that most people use in the output coupling stage of my 500c. If they test fine, keep em! But don't want to derail this into a cap thread!
     
    bhamham likes this.
  8. rufleruf

    rufleruf AK Subscriber Subscriber

    Messages:
    1,116
    I like these amps - my 6 year old son used one for a while- he left it on for a few hours once and it smelled like old electronics in his room so I moved it out.

    Bruce - I'm curious to hear how you reattach the can tops after cutting. I cut a few and never came up with a satisfactory remount scheme.
     
    bhamham likes this.
  9. Tim D

    Tim D AK Subscriber Subscriber

    Messages:
    1,337
    Location:
    Melbourne, FL
    I used JB Weld.
     
    bhamham likes this.
  10. bhamham

    bhamham AK Subscriber Subscriber

    Messages:
    2,013
    Location:
    Austin
    Matt, I use Shoe Goo and put a big, liberal bead around the inside of the rim of the can where it connects to the base. Never had a problem with mounting them and they were firmly in place after the adhesion set up.

    Use to use JB Weld, Tim, but got tired of mixing it and found Shoe Goo as effective. The RC airplane guys like to use shoe goo mounting all their gear in their planes.

    Hope to get to those cans on the X-100-3 in the next day or two. For the unintiated to stuffing cans here's a few pics of a stuff job I did on a 400 a few years back. I like to glue the bottom of the new, discreet caps to the top of the cans so they're hanging upside down. The leads go through a big hole I drilled in the base and then soldered to the old tabs. I did use JB Weld to mount these cans.


    [​IMG]



    [​IMG]



    [​IMG]


    [​IMG]
     
    baconbadge likes this.
  11. bhamham

    bhamham AK Subscriber Subscriber

    Messages:
    2,013
    Location:
    Austin
    Finished stuffing the cans and mounting them today. Noticed on the Fisher schematic for the X-100-3 the values are wrong for the can caps. The parts list has it right; that it correlates with what's printed on the cans.


    Put the leads on the new caps and glued their bottoms to the inside top of the cans.


    [​IMG]


    [​IMG]


    Big, liberal dose of Shoe Goo on the inside rim where it rests on the can bottom. When it sets it's on there. But... if you need to you can take it apart with a little force. I had to 'need to' a couple of times before.


    [​IMG]


    Mounted. The black cardboard cap just slides over the base - I like those a lot, pretty easy. Thought about trying to find some cardboard tubing that would work where you could cut to length and fashion some kind of cap, then paint them silver or black. But thought it would look pretty ugly.

    I'll let them set overnight. Then I can hook them up later.

    [​IMG]
     

     

    Please register to disable this ad.

  12. baconbadge

    baconbadge New Member

    Messages:
    38
    Location:
    Queens, NY
    Nice!
     
    bhamham likes this.
  13. bhamham

    bhamham AK Subscriber Subscriber

    Messages:
    2,013
    Location:
    Austin
    Thanks baconbadge!

    Wired the cans today. Replaced the death cap with a safety cap and added a CL-80 thermistor. Decided on doing a cathode buss with 4 - 10 ohm, 1/4 watt, 1% resistors so I know the bias of each output tube. Got a matched quad of Sovtek EL84Ms from Mr McShane, although, I have a quad of old school 7189s. I'll see how well matched they are.

    I replaced the two black mylar output coupling caps with a couple of ERO-FOLs that I had on hand. Cleaned all the sockets, switches, pots and jacks.

    [​IMG]


    [​IMG]
     
  14. bhamham

    bhamham AK Subscriber Subscriber

    Messages:
    2,013
    Location:
    Austin
    Powered the X-100-3 with a variac to around 90v and started checking bias on a group of Russian 6N14N-EPs that I have. Got nine of them but really couldn't get a quad to match like I want. So, I went with the Sovteks EL84Ms that Jim McShane sent. Emailed him on a Friday afternoon and had them on Monday - what great service. My cathode buss had 29.2 vdc (s/b 30) at 117v measured just after the thermistor. The tubes biased at 32.8, 33.4, 32.5 and 32.9mA less than 3% variance from lowest to highest. I'd say that's pretty good!

    I put in a CD to see what's what... well, no R channel totally silent. Checked the speakers, the CD connections, started turning pots, wiggling tubes; you know, all that stuff that you hope is a quick fix. Well, didn't work so started poking with my chop stick and found a short with, I suspect, the PEC attached to the Treble control or it could be the control, maybe even the High Filter switch. I resoldered all the connections to these components but it's still not right. I'd tweak some wires around the PEC and the R channel would come on, then quit. I'd get it playing and then touch the balance or volume control and lose it again. It was really annoying :) The latest, it played a couple of hours w/o loss of the R channel after I fiddled with that PEC for the 100th time. It seems if it's cocked just right everything is great. And, when both channels are playing this little guy sounds very, very nice!

    Anyone have an idea how I can troubleshoot this better? Or, how I can change out the PECs with normal caps/resistors. Maybe even take out the tone control circuit. I'm mulling over my options.
     
  15. rufleruf

    rufleruf AK Subscriber Subscriber

    Messages:
    1,116
    The manual has the PEC's broken out. This is from the X-100-2 / X-100-A (never seen a -2).

    pecs.JPG
     
    bhamham likes this.
  16. bhamham

    bhamham AK Subscriber Subscriber

    Messages:
    2,013
    Location:
    Austin
    Thanks Matt!

    I had a look at the X-100-3 schematic and sure enough the PECs are broken out there too. A bit different values than the ones for the X-100-2/X-100-A (above). I think I'll try to fix the short first, then make a decision about restructuring the PECs.
     

     

    Please register to disable this ad.

  17. bhamham

    bhamham AK Subscriber Subscriber

    Messages:
    2,013
    Location:
    Austin
    Well, I guess I'm done; at least for a while. The short has gone away for the time being - we all know what that means! It's been playing several days for about 8 hrs/day and hasn't missed a beat. It sounds really nice and I plan to make it my phono playing amp. When the short shows itself again, I'll probably change out the PECs for discreet components. I'll do some searching to see if there's some phono specific mods I could do too.

    I have a case for it. The grill was so encrusted with nicotine that nothing would take it off. I tried simple green and mineral spirits and it didn't make a dent. Then I sprayed it with about 10% ammonia and the brown crud just flowed off. It really looks nice now. The case itself was nothing special but I sanded and restained it, then went over with Howards restore a finish. Then a couple of coats of Howard's beeswax. I even gave the faceplate a beeswax coat. Put on new knob caps too, I think it's very presentable now.

    [​IMG]



    [​IMG]
     
    lopezluna, baconbadge and Man in Cave like this.
  18. notdigital

    notdigital AK Subscriber Subscriber

    Messages:
    2,245
    Location:
    NYNY
    Nice work as usual Bruce: ENJOY!!
     
    bhamham likes this.
  19. bhamham

    bhamham AK Subscriber Subscriber

    Messages:
    2,013
    Location:
    Austin
    Thanks a lot, George. I really like these little amps and maybe this one a bit more than my X-200. It's all about preference but my ears seem to really enjoy the 7189/EL84 sound over the 7868/7591. There's a sweet spot that I really find captivating.
     
  20. rufleruf

    rufleruf AK Subscriber Subscriber

    Messages:
    1,116
    Came out great and this short thread makes it look easy! I agree on the 7189 sweet spot - I'm about due for a downstairs daily driver swap out - may go for a 500-S for this reason.
     

Share This Page