Snagged a Fisher 400 - resto time!

Discussion in 'Fisher' started by Thumper, Jun 27, 2017.

  1. larryderouin

    larryderouin You can be sure if it's Westinghouse??????? Subscriber

    Messages:
    20,127
    Location:
    Glen Burnie Md.
    The 330K resistors are the Grid return resistors. R-117-118-119-120. Change them to 220K or 200K and then change the coupling caps to whatever the metalbone kits sent you. Probably .1uf.
    The screen resistors(100ohm) are an add on to alleviate or at worst minimize arcing of the tubes. It's more prevalent on the Russian tubes BUT it's a good idea on all tubes. Go into the Stickies Subforum and find the Thread "Common FISHER PARTS". There is a post on the 3rd or 4th page IIRC with pics on how to add them on 7591 sockets and also the 7868 sockets.
     
  2. Thumper

    Thumper Active Member

    Messages:
    209
    Location:
    Laurel, MD
    Thanks Larry, you got me sorted now...

    A funny aside - the wife came downstairs last night while I was playing it quietly after I just finished putting my new knob brights on. I don't think she had even seen it powered up yet. She says, "I saw what it looked like when you brought it home but I didn't know it was going to look like THAT!" Fisher 400 = wife approved.
     
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  3. larryderouin

    larryderouin You can be sure if it's Westinghouse??????? Subscriber

    Messages:
    20,127
    Location:
    Glen Burnie Md.
    Funny how they see a piece of junk in their mind when you 1st bring it in the house, then when they see it cleaned up they are all over it like White on Rice. Mine like's my FISHER's better than my Sansui's or Pioneer's....and that's including the S.S. Stuff. But she' won't touch any of it, except her '65 Custom Electra, and the 71 Magnavox she got from her brother's estate.
     
  4. Thumper

    Thumper Active Member

    Messages:
    209
    Location:
    Laurel, MD
    I finished installing the rest of the metalbone kit last night (except for 3 film caps in the MPX circuit - is the MPX section not part of the schematic?) and hooked up an antenna for the first time. I was almost shocked to see that the tuning eye actually works! It doesn't seem to pull in stations very well and the eye kind of 'dances' with the music (is it supposed to do that?). Plus the indicator is about 1/8" to the left of where it should be when tuned in to a station.
    I've read on here that the MPX pot on the side tends to get messed with and should be at it's center of rotation - it wasn't, so I played around with it without much improvement. I haven't tested ANY of the small tubes on my tester so I guess that's next on the list - after I unbox and test out my new scope which shows up today. My old all tube Heathkit deal finally kicked the bucket about a week ago after limping along for the last 10 years or so.

    [​IMG]2017-07-20_10-37-12 by rickenbacker_man, on Flickr
     
  5. IraGress

    IraGress Active Member

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    147
    Location:
    Detroit/ Houston
    Wondering what sort of mental syndrome might lead to such an impeccably clean and organized workbench...
     
  6. Thumper

    Thumper Active Member

    Messages:
    209
    Location:
    Laurel, MD
    Ha! It actually comes from years of being extremely disorganized - one winter I realized I spent more time looking for stuff than working on stuff and so I decided to get organized. Everything has a place, everything in its place.

    [​IMG]
     
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  7. RS Steve

    RS Steve Tube Junkie Subscriber

    Messages:
    7,337
    Location:
    Jupiter, Florida
    The eye tube will slide some in its bracket to center up the two bars, get the IF tubes, and MPX tubes checked for strength, and there is a resistor that can be added to minimize the dancing bars. There is also a thread about the dancing bars that explains the fix, your 400 has come a long way, congrats on all your progress!
     
  8. IraGress

    IraGress Active Member

    Messages:
    147
    Location:
    Detroit/ Houston
    Wow.
    You are so grown up.
    I'm beginning to think that may never happen to me.
    Hey, that's a pretty sexy receiver, by the way.
     
  9. Thumper

    Thumper Active Member

    Messages:
    209
    Location:
    Laurel, MD
    Thanks Steve, the eye tube is actually pretty centered, the pic just makes it look offset. I will test the IF and MPX tubes tonight. I found your thread where Dave talks about the dancing bars fix, reading it now.

    Work performed thus far:
    -recapped with Hayseed cans and Metalbones kit
    -one good used GE 7868 from the auction site installed
    -10 ohm cathode resistors installed for bias measurement
    -deoxited all pots and switches
    -LEDs installed
    -front panel and glass cleaned up and new knob caps installed

    I still need to install the thermistor and a new power cord, and build Dave's bias/balance (IBBA) board (with 220k grid resistors onboard). I may or may not do some or all of his 400 mods too - still have lots of reading up to do on those. Oh, I will need a new volume control, too - it's really unbalanced at lower levels.
     
  10. RS Steve

    RS Steve Tube Junkie Subscriber

    Messages:
    7,337
    Location:
    Jupiter, Florida
    I thought you meant the bars were not centered, my bad. I guess you mean the dial needle. I have been able to slide the needle over on the string on units I have restored, but only after I determined that the tuner was working properly. There is some glue on the needle where it has the string going through it, it usually pops of if you poke at it with a small flat blade screw driver. I then work the string over each ear on the ends, then the needle slides easily. I mark the string after powering the unit up and tuning in the station perfectly, then pop the string back over the ears and double check. Your 400 will be like a new one, but better when finished.
     
  11. Thumper

    Thumper Active Member

    Messages:
    209
    Location:
    Laurel, MD
    Thanks Steve, yeah I meant the needle. I was unclear on that.
     
  12. Thumper

    Thumper Active Member

    Messages:
    209
    Location:
    Laurel, MD
    Some progress pics showing new cans and coupling caps:

    [​IMG]2017-07-25_01-28-59 by rickenbacker_man, on Flickr

    [​IMG]2017-07-25_01-27-09 by rickenbacker_man, on Flickr

    Line cord replaced, XY safety caps and thermistor installed:
    [​IMG]2017-07-25_01-28-08 by rickenbacker_man, on Flickr

    Lastly, Mr. IBBA makes an appearance. The red and black wires are soldered in here because I wanted to test the board out with a 9V battery before installing it. It appears to work perfectly! Oh and 220k grid return resistors are onboard as well.
    [​IMG]2017-07-25_01-25-57 by rickenbacker_man, on Flickr

    Next up will be getting the board installed. I really need to find a replacement volume pot, too. The low volume channel imbalance is driving me nuts. I don't even need the switch - I can add a switch in the headphone jack like I did with my Scott LK-48b. Anybody got any suggestions? I guess it needs a long shaft and I'd prefer it to have loudness taps as well.
     
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  13. RS Steve

    RS Steve Tube Junkie Subscriber

    Messages:
    7,337
    Location:
    Jupiter, Florida
    Looking good! :thumbsup:
     
  14. larryderouin

    larryderouin You can be sure if it's Westinghouse??????? Subscriber

    Messages:
    20,127
    Location:
    Glen Burnie Md.
    Check with Mark Oppat at oldradioparts.net. Tell him exactly what you need including the FISHER Part # on the manual, as it won't be the correct one on the actual pot. It'll probably run between $50-$100 for him to make one from NOS parts, but he'll match the carbon tracks to minimize imbalance. Plus it'll have the loudness taps, and you can wire it all up as original.
     
  15. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

    Messages:
    8,985
    Location:
    Ball Ground, GA
    That is some really great work! Since you elected to mount the output tube grid return resistors on the IBBA board, be careful of the routing the bias wires back to the output tubes they serve. They will now be at grid impedance and signal levels, meaning that they can easily pick up hum or noise along the way if routed through the power supply area. Keeping the grid return resistors over at the output tubes they work with creates a problem in needing a terminal to tie them two. The original two terminals can be used, but you need two more. The up side of doing it that way however, is that then the bias wires leading to the resistors are at AC ground level due to the caps on the IBBA board, and therefore cannot pick up any noise regardless of how they are routed. Just something to be aware of.

    Great job!

    Dave
     
  16. Thumper

    Thumper Active Member

    Messages:
    209
    Location:
    Laurel, MD
    Thanks Larry - I emailed Mark yesterday, waiting to hear back...

    Thanks Dave - how's this look?

    [​IMG]2017-07-26_12-14-29 by rickenbacker_man, on Flickr

    I did it this way because I can then use the old grid resistor terminals for mounting the 100 ohm screen resistors that I haven't yet installed... Hopefully the routing is clean enough to be nice and quiet. I just finished the above work last night and didn't get to test it, so more tweaking and testing is in order tonight...
     
  17. audmod01

    audmod01 AK Subscriber Subscriber

    Messages:
    987
    Location:
    Tioga, TX
    Thumper;

    Great unit to work on. Yours is one of the later models with four FM IF stages. When you get to the RF and IF Dave will be able to help you evaluate as well as Larry. There is lots of good potential in these models. Many people like the eye tube tuning indicators better than the level and center of channel tuning meters. You did a great job on cleaning up and modifying the unit. If hum issues develop on the IBAM board connections to the grids of the output tubes I am sure you will be able to find a better position for the elements of the circuit with Larry and Dave's suggestions.

    Joe
     
  18. dcgillespie

    dcgillespie Fisher SA-100 Clone Subscriber

    Messages:
    8,985
    Location:
    Ball Ground, GA
    The installation looks great! Very neat and nicely done! I would think it will work just fine -- but if you have the capability, it wouldn't hurt to run each channel up to full power at 1 kHz to make sure that there are no parasitic oscillations present. If you do however, watch the screen grids of the output tubes as you near/reach full power to make sure they don't reach critical mass in the process.

    Great job!

    Dave
     
  19. larryderouin

    larryderouin You can be sure if it's Westinghouse??????? Subscriber

    Messages:
    20,127
    Location:
    Glen Burnie Md.
    If it works, then go for it. But watch for the parasitic oscillations as Dave mentioned. I normally mount mine so it's over the grid resistors on the 1st and 2nd tubes, and replace the 1 terminal strips with dual terminal strips then I have separate terminals for the grid's. Then the leads from the boards are quite short, with the ground going to the closest chassis ground point and the power lead to the bias caps.

    I'll watch for the mushroom cloud in Laurel from the bomb shelter in my back yard..:biggrin::biggrin:
     
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  20. Thumper

    Thumper Active Member

    Messages:
    209
    Location:
    Laurel, MD
    No smoke here!

    Got my screen resistors installed last night and had to do a bit of tube jockeying to get the outputs reasonably balanced - here are my readings:

    V17 - .307
    V16 - .319
    V15 - .322
    V14 - .323

    And that's with one bias pot maxed and the other at the min! Dave, either my tubes are WAY OUT or the IBBA board could use some changes to have a bit more range?

    The things sounds great though - it seems like every little tweak I do makes it sound better!
     

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