Fisher 400 - help with planning the next phase of restoration

Discussion in 'Fisher' started by Jon Kasper, Dec 4, 2017.

  1. Jon Kasper

    Jon Kasper New Member

    Messages:
    11
    Hi All,

    Hoping you might be able to take a minute and help me out with planning the path/next steps for upgrading my Fisher 400 receiver, later version. I''m a complete rookie when it comes to this and am out of my depth, so any time out of your day and any help/insight you're able to provide will be very greatly appreciated.

    So the history is that I purchased this Fisher 400 receiver 6 months back via ebay... obviously lots of risk involved with doing that. Once it arrived I had a local tech take a quick look, fix a few minor items per some recommendations on this wonderful board, bring it up to speed on a variac and fix any minor issues to get it working.

    I've been told the current status is as follows:
    - a basic recap has been done for all necessary areas to make it operational
    - the selenium bridge rectifier has been replaced with a new bridge rectifier.
    - output tube bias has been changed from 5.6Kohm resistor to a 3.3Kohm.
    - added set of four 10 ohm resistors between the output tube cathodes and ground in the power tube circuitry to act as fuses in the event of one of the 7868 power tubes shorting internally.
    - thermistor has been installed to protect power switch
    - the tech took a look at the tubes, and the output tubes need to be replaced quite badly, thought he other tubes are in ok condition though the tuner tube is near end of its life.

    I did a quick inventory of the tubes installed in the unit, all appear to be original old stock as follows:
    V1 - Sylvania
    V2 – general Electric
    V3 – Silvertone
    V4,V5, V6 – FISHER
    V7 – tuning indicator, couldn’t see
    V8- Toshiba (toyko shibaura electric)
    V9 - Toshiba (toyko shibaura electric)
    V10- Sylvania
    V11 – nothing on tube other than “ASB USA”
    V12- ”made in usa fox PILOT radio”
    V13- ”made in usa fox PILOT radio”
    V14,15,16,17 original FISHER
    V100 – BOGEN
    V101-- ”made in usa fox PILOT radio”
    V102 - Valvo

    So it seems like a complete sorgasboard of tubes... maybe to get the unit running so the seller could move the unit on ebay? I assume this isn't ideal, but I paid for the unit at a bit of a discounted price based on the "as is" status... so to be expected I guess.
    I've uploaded a bunch of pics below to show the details of the unit. Assuming the tech's work/assessment of the above work items completed to date is correct, I'd greatly appreciate your help in identifying the next areas of improvement and the next things to do to get it sounding its best.

    I use this receiver as both a phono circuit as well as amp for my Rega planar 3 - TT into the Fisher, and the Fisher out to a pair of Klipsch Cornwall II. So looking to focus on the phono and amp circuits of the unit. Tuner isn't critical.

    I definitely need to upgrade the output tubes (some leaks), the plan is to obtain a nice quad of the Eh 7868 new production which I am currently working on. Also have a pair of VITAMIN Q 0.1 uf 200V caps earmarked for the phono section.

    On top of that, if anyone can provide:
    - a quick look at the caps installed by both the tech as well as the ebay seller - would there be a decent improvement moving up to different caps throughout?
    - does the above tube selection seem ok? Any glaring tubes to look at replacing?
    - any other improvements you can spot that would make a significant gain to audio fidelity.

    Looking to bring this to the top level it can be - plan is for it to be the workhorse in our home for the foreseeable future, and want to maximize its potential! It just sounds so musical, already so even though still work to be done... it's my baby and just want to make it as great as possible!

    Also, I'm a finance guy, professional accountant, so if anyone has any non-audio financial questions/work totally willing to swap financial expertise for your audio expertise!

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    Cheers,

    Jon
     

     

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  2. mrphilco

    mrphilco AK Subscriber Subscriber

    Messages:
    445
    Location:
    Ferdinand, IN
    :lurk:

    I'm afraid I can't offer any advice other than to say that the recapping work underneath looks good. Although, it appears your tech missed one of the brown "dog turd" caps.

    You will want to add IBAM or IBBA, and I'll leave that to one of the resident gurus (Dave or Larry) to explain.

    I have a 400 which works but needs a complete recap; I'll get to it eventually one I work through a few other items in the queue.

    Good luck with yours!
     
  3. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
    21,694
    Location:
    Glen Burnie Md.
    400 mods.JPG

    Looks like a few items were missed, by either the previous owner or the tech. Circled in RED, Yellow or another color.
    1.) 1uf 350v electrolytic along side the MPX board. You can't see it in this picture. (C-210)
    2.) the 8uf 50V Gold colored FRAKO Electrolytic. (C-41)
    3.) The Brown "Dog Turd" and possibly it's mate on V10. (C-78, C-79)
    4.) Power supply Diodes (Singles) (CR2 & CR3) (use 1n5404)

    Now for the Add on's
    A.) Replace the 1200ohm 7W with a 10W unit (long tan resistor above the output tubes) (R-41)
    B.) Replace the 2 330ohm 3w resistors(twin tan resistors next to the single Can cap in the back) with 5W units. (R42 & R43)
    C.)Rebuild the phono section as you see fit.
    D.) Add Screen Stability Resistors (100ohm 1/2W) to each of the output tubes.
    E.) Build and install an IBAM or IBBA board and revise the bias/output section. This will allow bias valuations to be in the 70% to 80% range of dissipation which will extend tube life greatly while keeping the distortion to a minimum.

    There are some tweaks and tricks for later that will help with "shaky eye tube", and other problems.

    The following links are in the FISHER FORUM STICKIES and all pertain to the 400 and different parts of it during overhaul or general maintainance. Print them out(the list) and keep with your Service Manual.

    Reference TECHNICAL THREADS.

    http://audiokarma.org/forums/index.php?threads/reference-technical-threads.774760/

    Most Common Parts needed for FISHERS...Sticky needed
    .
    http://audiokarma.org/forums/index.php?threads/most-common-parts-needed-for-fishers.327561/

    Alternate BIAS Adjustment Modification
    http://audiokarma.org/forums/index....dividual-bias-adjustment-modification.601583/

    Getting the Most from FISHER FM Stereo mpx Tuners and Receivers
    http://audiokarma.org/forums/index....er-fm-stereo-mpx-tuners-and-receivers.708033/

    Improving the Fisher 400 Receiver
    http://audiokarma.org/forums/index.php?threads/improving-the-fisher-400.511867/

    400 eyetube adjustment procedure wrong!!
    http://audiokarma.org/forums/index.php?threads/400-eyetube-adjustment-procedure-wrong.687346/

    Fisher 400 owners please read....Important. concerning opt's and NFB network.
    http://audiokarma.org/forums/index.php?threads/fisher-400-owners-please-read-important.682273/

    FISHER 400 Service Bulletin
    http://audiokarma.org/forums/index.php?threads/fisher-400-service-bulletin.671281/

    The pdf is the printed list.
     

    Attached Files:

  4. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
    21,694
    Location:
    Glen Burnie Md.
    As for tubes. By the time the late 400 version came out, tube gear production had all but halted, on the FISHER production lines. Transistorization was the rage but FISHER held on to a few of the flagship units and tubes. But as their demand was less now than even a few years prior, European tubes were more expensive and they needed an inexpensive tube set that still sounded good. Sylvania had been supplying small signal tubes to Fisher for years and they fit the bill.

    So the Late 400 and later models of the 800c/1800 got either all tele's, a mix of Tele's and Sylvania's, or all Sylvania's. When a tube went bad on an owner, they got what was available in the repairmans box, or what was available at the corner store's tube tester. Hence one possibility for your mix of tubes. Another is what you brought up earlier.

    In my 400's (I have an early version and a late version) while being pretty much identical underneath, the tube pkg is different.
    The Early model has all Telefunkens in the 12ax7's,
    The LATE Model has Sylvania tubes(12ax7) in all positions except for the output's.
    The Outputs are EH's in both units.
    The RF/IF STRIP tubes in both are GE's.
    Both unit's have IBBA or IBAM boards, and the output's are set to provide 75% of maximum plate dissipation.

    Running them both thru a pair of NLA's. With the controls all set to center and the volume set to about 10:00 on phono, and listened to Take 5 by Brubeck, thru a Technic's SL-1200 (1st version with the Servo motor) with a Shure V15-III with a brand new VN35E. Both exhibited classic FISHER sound. Lush, FULL Bodied, High's sparkly, and tubby bass that was controlled somewhat with the Bass control. In the Late version with the Sylvies there was a hint of graininess in the high's during passages that I didn't hear with the Early and Tele's. So I swapped tubes (just the 12ax7's). The graininess moved with the tubes. It's a minor point and it was something I wasn't listening for but I heard it and thought it weird, so I swapped tubes and found the culprits. The graininess between the tubes is like the difference between 400grit and 401 grit. It's so minor as to not really define it. I doubt that 99.999999&4/10's of the people would be able to discern it.

    I like GE RF/IF TUBES in all my gear. They have been extremely relliable, last decades, and basically it's very hard to kill them (unless you use a hammer):D. I do use GE tubes in both the 400's in the RF/IF strip. They are a better tube than just about everything else out there for RF/IF strips. In my '51 Coronet I have original GE Tubes from 1950-1951 in all the RF/IF Strips. And all test way above minimums for gm and emissions.

    In the V-12 and V-13 (phase inverter) use only Domestic or European (Tele, Mullard, Brimar, Phillips) in these positions. DO NOT USE RUSSIAN Tubes here. Dave explains why in the Phase inverter threads in the stickies.

    There should be numeric codes on the tubes 274 would be RCA, 337 is Westinghouse, GE would be 188, etc. The codes are usually 6 digits long. The 1st 3 are the manufacturer's code. The 2nd 3 are the year and week of manufacture. so for example a 274937 would be a RCA tube made in the 37th week of 1959 (1939-49-or 69 could be a possibility depending on the tube.) Note that the listing of the numbers on the tubes could be one straight line or broken down into 3 digit groups and stacked.

    Here's a PARTIAL LIST of Tube Manufacturers. NOTE that this is not complete as it doesn't have Japanese tube manufacturers listed.

    Tubes and CRT's EIA code
    Amperex (USA) 111
    Bendix 125
    DuMont 158
    Eimac (Eitel-McCullough, Inc) 162
    Electronic Tube Corp 169
    General Electric Co (USA) 188
    Hytron (CBS-Hytron) 210
    Machlett 231
    RCA (Radio Corp of America) 274
    Raytheon 280
    Superior Tube Co 310
    Sylvania (Hygrade Sylvania Corp) 312
    Tung-Sol 322
    United Electronics 323
    Western Electric 336
    Westinghouse 337
    Zenith Radio Corp (CRT's) 343
    Nortn American Philips Corp 423
    Taylor (aka Cetron-Taylor) 713
    Lewis & Kaufman 738
    National Electronics (also Cetron) 749
    Penta Laboratories 771
    Vacuum Tube Products 781
    Varian Associates 809
    Litton Industries 879
    Electrons, Inc 935
     
  5. thornev

    thornev Active Member

    Messages:
    415
    Location:
    Mid Hudson Valley, NY
    Is it OK just to cut the wires that connect each power tube to each other via pins 4 and 8 without adding in the 100 ohm 1/4watt resistors between pins 1 and 4? Or is this procedure not needed if pin 5 of each power tube has the 10 ohm resistor connected to ground? My understanding is that both procedures protect the power tubes.
     
  6. Catmanboo

    Catmanboo AK Subscriber Subscriber

    Messages:
    446
    Location:
    Atwater, ohio
    That's protection for 2 different grids. 100 ohm resistors go between the bias line & grid 2 (screen), which is connected at both ends at pins 4 & 8 on 7591's. Drops the mojo a bit, enabling tubes to be pulled back from running at red line, so to speak & they run a bit cooler, last a lot longer
    & theory is that they go poof in event of thermal runaway, aka red-plating, which puts that expensive, rare tube at risk of shorting, which may let out smoke &/or shrapnel from them expensive cans up top. Failed resistor, a $.20 part sacrificed to save a $$$ tube &more (maybe).See 500c stickies, even though this thread's on the 400's. 2 different tubes (7591's in 500c & others), 7868's in 400's. Both tubes have identical operational parameters but different pinouts, as well as different types of bases. 500c's have a bias bus (straight-through feed wire) right through all 4 outputs at pins 4 & 8 for increased assembly efficiency, since it just happens that they all line up, thus they all get same bias voltage. Cut the bus between tubes, & only v8, where bias feed comes in, gets bias voltage, the other 3 get nothing, & they dont conduct. Remember, pins 4 & 8 connect to same grid. With the mod, each tube is biased through its dedicated 100 ohm resistor. Pin 1 is not used in 7591's, so it's a convenient connection point for bias feed through the new resistor to screen grid (#2 on tube diagram). On 7868"s, pin 8 not used.
    Internally, cathode (which emits the electron beam when heated & makes the tunes flow) & grid 3, suppressor, are connected to pin 5, which is grounded. Any internal short to either cathode or grid can put high voltages (375-430v or more)direct to ground, causing havoc throughout the high voltage supply & possibly back into low-voltage bias supply , causing even more havoc. Read time & $$$$$ to fix. Putting the 10 ohm 1/4watt resistor in place of ground jumper provides a fuse, if you will, to pop in case this condition occurs. Resistor goes bang, opens the path to ground, shutting it all down before further damage occurs. Once again, cheaper by far to sacrifice a 10 cent resistor than a bunch of caps, tubes, opt's, etc.
    Here's my sketches to keep my brain on track through the screen stabilization mod next to completed mod for clarity. Orange wire(s) that I installed to match bias supply are bias voltage in. There's an easier, quicker way to do this using a floating bus above everything, but this looks better, like the factory would've done (tnx, Dave, your idea!) I haven't gotten to the 10 ohm from pin 5 to ground yet.
    Here's tube data on both tubes, courtesy of RCA tube manual, 1968 version.
    Larry & Dave, correct anything I screwed up, please! :deal::)
     

    Attached Files:

    thornev likes this.

     

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  7. Catmanboo

    Catmanboo AK Subscriber Subscriber

    Messages:
    446
    Location:
    Atwater, ohio
    Well, that shot of the tube data sux, but the pic in my phone is crystal clear. Go figure! :mad:
     
  8. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
    21,694
    Location:
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    Lo-Res Lo pixel sized pics from phones will be smaller. I have to turn down the pixels down on my Kodak so you guys don't spend 2 hours loading 1 pic.
     
  9. thornev

    thornev Active Member

    Messages:
    415
    Location:
    Mid Hudson Valley, NY
    I took another plunge. I removed the 4 power tubes, labeling each so I know to put them back in the same locations. I disconnected the bare wires that connect the 500-C power tube sockets together via pins 4 and 8. Then I inserted on each tube socket a 100 ohm 1/4 watt 5% resistor between pins 1 and 4. And this mod is known as the "screen protector" so that if one tube goes red line, it doesn't take out the other 3 tubes. Instead it pops the 100 ohm resistor, no other damage.

    I also built myself an electrolytic ("lytic") capacitor discharge tool (though it seems each lytic has its own discharge resistor because every time I would measure the voltage going through the lytics, they always registered zero volts). I forget where I read it, on a forum I'm sure, but it's a 20K ohm resistor taped to a wood dowel, one end bare, the other end soldered to an insulated 12-gauge wire which is soldered to a copper alligator clip. The alligator clip is attached to chassis ground and I touch the bare resistor end to both sides of the lytic, or touch both sides of the tool to each side of the lytic.

    Thorne
     
  10. thornev

    thornev Active Member

    Messages:
    415
    Location:
    Mid Hudson Valley, NY
    I made a mistake somewhere with the above task. I followed the diagram in post 6 above that shows for each power tube connections between pins 1 and 4 with a resistor and pins 4 and 8 with a bare wire. Did I misinterpret? When I turn on the receiver, all I get is a hum, no radio. I thought I followed the steps correctly. This is my first screw up so it will also be my first debugging. Here I go ! Thorne

    Oh crap... I didn't connect anything to pin 1of each power tube. I missed that in the text from where I made notes about the procedure. I'll go search, but if someone reads this post before I find my error, I'd appreciate it if someone could tell me from where pin 1 is supposed to get the bias supply. THANKS ! By the way I used metal oxide resistors for the pin 1 to 4 connections.
     
    Last edited: Feb 14, 2018
  11. Catmanboo

    Catmanboo AK Subscriber Subscriber

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    Location:
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    Thorne, you got that sorted, right? Just now found your post on this. Jerry da catman
     

     

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  12. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

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    Thorne; It's not BIAS Supply (that is on pin 5), it's the SCREEN supply.
    This is from an X-101-B but it's the same as the 500c as far as hook up. The 500c hookups are against the rear bulkhead.
    Cut the jumper between the tubes (short red lines). DO NOT Cut the jumper inside the tube sockets.
    Install the resistors between pin 4 and 1. Solder Pin 4. (Short Green Lines)
    Install Daisy Chain wire between pin 1 to pin 1 on each tube (curved red lines)
    Move the Screen B+ line from pin 4 or 8 on the 1st tube (closest to middle of chassis)
    Solder all pin 1's.
    Make sure the Screen B+ is connected to the proper Section of the can cap. (it should not have been disconnected)Orange lead.

    X-101B Screen Stab Resistor install..JPG
     
  13. thornev

    thornev Active Member

    Messages:
    415
    Location:
    Mid Hudson Valley, NY
    Yes, Jerry, I'm good, thanks. I had to move the C91D orange wire from pin 8 to pin 1 and connect all pin 1's on all 4 tubes.

    Thanks, Larry, for the detailed response and picture. Catman (Jerry) straightened me out too. The orange lead runs from C91D and was to pin 8 but now is to pin 1 which is daisy-chained to all pin 1's on all 4 tubes. I got it done and the 500-C is running beautifully. I am so enjoying the sound hooked up to my recently-acquired AR-2Ax speakers (which is my next restoration project - a woofer was blown and the mid and tweeter adjustment pots are corroded badly).
     
    Last edited: Feb 16, 2018
  14. larryderouin

    larryderouin Turn it UP, POP? PLLUUEEEZZZZZEE Subscriber

    Messages:
    21,694
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    See?!?!? Repeated blows to the head:confused::eek: with a BAT does work...LOL!:bigok:
     
  15. thornev

    thornev Active Member

    Messages:
    415
    Location:
    Mid Hudson Valley, NY
    Oh hey... I don't mind hearing concurrence repeated (or is "repeat concurrence" like saying "may I borrow a dime or 10 cents"?). :D
     

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