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Fisher 400 - Rebuilt but sounding muddy

Discussion in 'Fisher' started by healyc139, May 6, 2018.

  1. healyc139

    healyc139 New Member

    Messages:
    29
    Location:
    Chicago, Illinois
    Hey everybody,

    So I found a decently priced rebuilt Fisher from a reputable seller on eBay, bought it and it sounded incredible. Such amazing sound, I've been very happy with it up until early last week. I had the radio playing and noticed it sounded just a tad bit muddy, kinda 'boomy'. Then I received Dave's Picks Vol. 26 in the mail and played that through my Denon D9 CD player, and that kinda sounded boomy too. I'll be testing out the Phono section tonight and probably playing some albums I'm super familiar with to see how they sound, I'll update after I do that.

    It is also worth mentioning - a couple of days after getting the receiver and having it plugged in, I came home to the tube in V9 being broken. It looked like it popped.. I replaced the tube and it sounded fine again, but that definitely seems odd.

    I've placed a picture of the under side of the receiver here as well in case anybody wants to check it out.
     

    Attached Files:

     

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  2. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
    21,791
    Location:
    Glen Burnie Md.
    I've outlined 3 sections I'm either concerned about or the previous owner or whomever did the work, didn't finish.
    1.) in light green. Insulate the large axials from the small one laying perpendicular to the Large Axials.
    2.) Phono. In YELLOW Replace the two ceramic caps with film caps. The smaller the better. Cornell Dublier DME series work well here.
    3.) Driver to output coupling caps. Light Red or Pink 2 different types. Change one per channel to the same series of cap. Make sure all axials and other components DO NOT TOUCH. The axials should have there bodies heatshrinked as the russian tube have been known to have their bodies "ELECTRIC-fied". Illinois Cap work well here and come in the well regarded.

    Clipboard01.jpg
     
  3. healyc139

    healyc139 New Member

    Messages:
    29
    Location:
    Chicago, Illinois
    Thanks for the input Larry, I'll definitely get the parts to replace each area you mentioned. Do you think that will help with my muddy sound problem, or is that just some concerns that you noticed?
     
  4. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
    21,791
    Location:
    Glen Burnie Md.
    A bit of both. The one in green I'd slip a piece of heatshrink over the smaller cap as it's right up against the other cap, and the russian caps do have a tendency to have "hot" cases. As for the output coupling caps in the pink area, I'd replace the russian caps with some Yellow Illinois Caps. Brreak the chain of Russian caps. That in itself may brighten it up. Use a Cornell Dublier DME series in the phono section to replace the ceramics over the tubes and leave the russkies there.
     
  5. healyc139

    healyc139 New Member

    Messages:
    29
    Location:
    Chicago, Illinois
    Ok, I'll do the updates and see how it goes. It still really sounds great, but the bass is where it gets a tad muddy/boomy. Hopefully that will fix it. Any thoughts on the exploding tube?
     
  6. healyc139

    healyc139 New Member

    Messages:
    29
    Location:
    Chicago, Illinois
    Also if you have recommendations on what values to use for the replacement parts that would be great. Unless its not necessary to change the values, that is.
     

     

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  7. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
    21,791
    Location:
    Glen Burnie Md.
    Not really. Sometimes they do that after cracking along the bottom, or they just let go due to a thin spot in the glass. jostling it heavily while moving it could cause cracking if the tube is bent over while the pins are in the socket.

    Have you got a MONO RECORD? If so put it on, and set the phono to PHONO MONO. Then sit between the speakers and listen to it. You might have a speaker out of phase with the other. With the twin lead that is colored silver and gold, I use gold for ground (black on spkr) or common, and silver for "HOT" (red on spkr). See attachment below. Disregard mention of Rev/Normal switch. The 400 doesn't have one. Just reverse the leads on one spkr if found out of phase. Easier to do it at the spkr.
    Clipboard02.jpg

    Leave values as is on all but the output coupling caps. Check the grid return resistors (the ones that are perpendicular to the caps on the terminal strips between the output tubes and caps) if they are 330K, change them to 220K and change the value on the capacitor to .068uf 600v or 630v. AES should have the Illinois in those values and voltages.

    grid return resistors look to be Dale resistors, but determine value. Two areas in blue.
    Clipboard03.jpg
     
    Last edited: May 6, 2018
  8. fred soop

    fred soop Super Member

    Messages:
    1,975
    Another way to phase speakers, if you can see the woofer cone, is to connect a battery. This can be a 1.5 V or even a 9 V. If the cone moves in, reverse polarity. When the cone moves out, mark the positive lead.
     
  9. healyc139

    healyc139 New Member

    Messages:
    29
    Location:
    Chicago, Illinois
    Following up with some better pictures. I have this on my work bench now to begin work. Going to be following your suggestions Larry. If anybody else notices anything or has any advice on what I might want to check to get rid of the (mild) muddy bass let me know! Continuing research as well.

    Thank you
    Healy
     

    Attached Files:

  10. Dave451

    Dave451 AK Subscriber Subscriber

    Messages:
    1,104
    Location:
    Philly area
    Watching your thread with interest. Just acquired a second 400 that's working and bone stock but needs some rehab. One thought: how are your output and PI/Driver tubes? The old manuals sometimes said to 'replace tubes when they start sounding bad' or such. I've often wondered how they would start to sound when they were failing--muddy bass? Tubes do go bad ultimately and certainly more often than passive components like capacitors.

    Second thought: why put heat shrink on the axial electrolytics? It can't possibly hurt, but modern electrolytic caps have good surface insulation, the positive ends are not highly exposed (I do heat shrink the + leads), and the can end is usually at chassis ground potential and, let's face it, there are already long bare leads with B+ running all over the chassis with the stock wiring. I'm not being critical at all; I'm always looking to upgrade my work technique, so I'm just looking for the rationale for doing this to consider in my own work. It makes great sense on the Russian PIO's which, as Larry mentions, can have a hot metal case.
    Thanks!
    Dave
     
  11. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
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    I think he bought it that way. I thought it was a bit over the top too, but to each his own.
     

     

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  12. healyc139

    healyc139 New Member

    Messages:
    29
    Location:
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    Ya I purchased it that way, not sure if the previous tech thought it was necessary or if he was just being safe? Either way, doesn't hurt. I replaced some of the tubes with reissued Tung Sol's but didn't really get any difference in sound so I think it is something underneath
     
  13. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
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    Healy. Can you take a picture of the guts on the front 1/2 of the unit. (include the pots please)
     
  14. Dave451

    Dave451 AK Subscriber Subscriber

    Messages:
    1,104
    Location:
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    Got it. Going to have to re-cap mine. All but one can are physically leaking or failed the working voltage leakage test. All the tubes are good and the outputs are about 80% and pretty closely matched. Good luck running down the sonic issue! If it's not the output tubes or speaker phasing, I agree with Larry that the output stage couplers are the next focus and that IC yellow MPW's are a good choice--I use them a lot.
     
  15. sberger

    sberger Hard Core Geezer Subscriber

    Have you tried playing with the switches? Make sure that the loudness switch is off? Make sure that the bass control is where it should be, that it didn't get turn forward for some reason. I know that the changing out caps is great advice, but in my dealings with these very old receivers sometimes the simplest solutions can be right in front of us.
     
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  16. gadget73

    gadget73 junk junkie Subscriber

    Messages:
    36,571
    Location:
    Southern NJ
    If nothing seems obvious, maybe the thing to do here is to seperate the power amp and preamp to see where the issue lies. Inject signal direct into the power amp and see if that behaves itself nicely.

    me being me, I'd want a frequency response test just to see if its something easily measured. Last time I had weird muddy sound, the high frequency response fell off a cliff. Long story short, I found a bent tab on one of the tone controls that was shorting and causing the problem.
     
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  17. healyc139

    healyc139 New Member

    Messages:
    29
    Location:
    Chicago, Illinois
    Yes I messed with the switched a bit, turned the loudness on and off as well. It helped a little, but didn't solve the problem completely.

    Gadget, how would one inject signal direct to the power amp on a 400?
     
  18. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    At the Volume pots. inject into the center tap of the volume pot using a signal generator with a sweep control. Set controls to AUX (nothing hooked up to it), Volume zero. all other controls centered.
     
  19. healyc139

    healyc139 New Member

    Messages:
    29
    Location:
    Chicago, Illinois
    Some more underside pictures Larry, including more of the front of the chassis. The grid return resistors are Dale's but I'm not sure what value. They say '8401J' 'RN60D' & '2213F'.
     

    Attached Files:

    Last edited: May 9, 2018
  20. notdigital

    notdigital AK Subscriber Subscriber

    Messages:
    2,237
    Location:
    NYNY
    Try headphones. Boomy bass may be component mismatch, room conditions, speaker placement, etc.
     

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