Purchased 800C to restore: currently working perfectly

Discussion in 'Fisher' started by Skibrain, Mar 13, 2017.

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  1. Skibrain

    Skibrain New Member

    Messages:
    11
    Location:
    Rocklin CA
    OK, since I am fairly new here, but have learned enough, due to Larry helping when I put my Furura VI in the wrong location, and hopefully I am in the correct Forum area now. ( Sorry )
    So I'm restarting here with my 800C I just bought. I guess history is in order.
    I first bought a modern Walnut Futura VI in excellent working order also. Working on that gave me the bug and I have now slowed work on that as I just bought a fully functional 800C no cabinet. It was in an audiophile home in Seattle and it looks like the person I bought it from bought the house. ( He left the 4 Sansui speakers it was driving and not sure what he did with the R2R with 8 track and other pieces he mentioned. )
    I fired it up and it sounds amazing. Tested AM and FM both work and shut it down afraid of damaging anything.
    Based on some research. I have ordered a kit from Metalbone for the 800C, but didn't specify the serial number. Should I be concerned? Serial # 44614 P. I saw another kit on eBay that seem to have good knowledge but not sure. Any care to comment? I'll share the link if it is OK, don't want to get in trouble.
    I want to make sure I get all the fixes in.
    I see these so far on the forum, beside the main capacitor upgrades.
    1. Replace the selenium with a new bridge rectifier
    2. Change the output tube bias 5.6Kohm resistor to a 3.3Kohm
    3. Add 10 ohm resistors between the output tube cathodes and ground (in 4 places).
    4. There is a CL-90 in series on the switch- stop in rush current that kills switch?? ( I think Metalbone kit has it??)
    5. Main can caps on top? ( 1 Black and 2 silver Can)
    More?

    My neighbor has a The Fisher Model 101R for $250 All original works? Price. Damn I have the bug.
     
  2. AlTinkster92

    AlTinkster92 AK Subscriber Subscriber

    Messages:
    2,705
    Location:
    NC
    Welcome to AK Ski, The resto Kit from Metalbone is fine. Stay away from kits from the Fisher Doc, have heard his parts are cheap. I would Email Metalbone with the serial number of your new 800C.
    The CL90 on the switch is a good thing, also means someone has been in it, (the 800C). Could be a good thing or bad, pics will help the folks in here with a look see.

    The 800C is a great receiver, hope you enjoy it. :) Al
     
  3. notdigital

    notdigital AK Subscriber Subscriber

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    2,104
    Location:
    NYNY
    The most honest answer I can give is that the M'Bone kit will get you started. To get the 800-c up to modern snuff, there are both mandatory things to do, and optional things to do depending on how far you want to dig into it. The best advice is to READ as many restoration threads as you can without going blind, decide based on that study what changes/modifications/additions you want to make, and supplement the Bone kit as YOU want or find necessary. In my view, the Bone kit is a good, albeit a basic one that addresses most of what has to be done. Pushing the unit to performance excellence will require a bit more. Reading up on the resto threads will determine what's enough for you.


    (PS: I would re-think the CL-90. CL-80 is rated at 3A and CL-90 at 2A. If you check your fuse you'll see that the 80 is a more appropriate device.)
     
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  4. Skibrain

    Skibrain New Member

    Messages:
    11
    Location:
    Rocklin CA
    Thanks to both of you on the responses. I had just read about going to a CL-80 or CL-60 due to the edge of current with the CL-90.
    So much to do.
    1. Cleaned and Lubricated the pots and switches already
    2. Chassis is pretty much clean now also.
    3. Just got the kit from Metalbone- 2 days- Bam it was here. very fast shipping. ( this has the
    4. Going to get the Can kit from Hayseed.
    I'll start with those and hope it all works when I'm done. ( Check the Resistors as I go )
    Not sure if Metal bone kit has the output tube bias 5.6Kohm resistor to a 3.3Kohm? ( i'll read his info tonight.)
    Also if it has the 10 ohm resistors between the output tube cathodes and ground (in 4 places) - Metalbone kit has this in the kit
    I'm going to bring it up with a Variac, I'm hoping to get this week.
    Anyone know what the ramp rate on voltage should be to bring the tubes up with the variac? Also what voltage to hit- 105V initially?

    One more question. If the front glass is stuck on any special way to get it to come off? I have the 4 screws out and the little clips off but no go. Help am I missing something?

    Thanks
    Ken
     
  5. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

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    18,153
    Location:
    Glen Burnie Md.
    With regards to the Front glass sticking, get an X-Acto blade kit and handle. Use the scalpel blade (#11) and slip it between the glass and rubber block behind the glass. Cut down between them staying on the glass all the way down from the top. This will break it loose from the rubber. (Put the clips back on loose to keep the glass from dropping out).Lube the blade with dishwashing liquid before slicing, it helps keep the rubber from sticking anymore.

    Forget about the 5.6k to 3.3kohm resistor. 1.) what are your output tubes? 2.) a.)are you planning on a single bias arrangement or b.)an individual bias adjustment setup, or c.) Dave's Bias.Balance setup (Best) 2.b and 2.c are the best way to bias these. The single bias arrangement(2.a) is marginal even with absolutely matched tubes.

    Right now you don't need the variac. You'll need it for bringing it up AFTER you've replaced the can caps and done all the other work. Do you have a DBT (Dim bulb Tester)? If not google it and build one.

    CL-80 is the correct limiter.
    Reliability and Safety add on's. Will allow use of both ORIGINAL TYPE(OLD STOCK) and Russian reissues ( NEW STOCK) interchangeably.

    New Silicon Bridge Rectumfrier. Maintains reliable -DC Voltage to Bias supply and DC Tube Filaments.
    10 ohm 1/4 watt cathode resistors (4 to ground from Pin 5) METAL FILM RESISTOR
    100 ohm 1/4 watt Screen stability resistors (these we'll get into install later) METAL FILM RESISTOR.
    220K ohm 1/4 watt grid return resistors (replace the 330K 1/4 grid returns)
    0.082 to .1uf output coupling caps. (replace the 0.047uf couplers) Your choice on value. If they are in the Metalbone kit they'll most likely be 0.1uf.
    Upgrade the power supply diodes to 1Kv 3a (1n5408 or UF 5408).
    C110 gets a X1-Y2 rated Safety cap. 0.01uf 300-350VAC(Note the AC Volts rating) This fails OPEN rather than failing short which puts line voltage on the chassis (you will not like the results when you touch the chassis if it fails!!!!!!)

    These are all simple to implement, and inexpensive (under $20.00 total for ALL). They will allow the original tubes to operate safely at todays higher voltages, but adjusting the bias to between 70%-80% of Maximum Tube dissipation of 19watts. Even if you did run the tubes wide open they would still operate in a safer part of the Operating envelope compared to the original setup.

    They were pushed actually past the tubes limits and general concensus has it that tubes were dead cheap back then (I checked) 7591's averaged $4.95 in 1964 which is roughly equivalent to $38.54 today. Actually 7591's today are less expensive. But that's neither here or there. They were highly and readily available. You could walk down to the neighborhood Drug store and you could almost guarantee there would be a quad of 7591's there. Whether they were matched or not was no concern then. As long as it played for the masses. Today you are asking the tubes to work under conditions the designers never considered. Increase in voltage from 105 to 120 as designed to 120 to 130v today. Depending on your house voltage, you either use a variac to drop the voltage down, or a bucking transformer. It's no spring chicken any more. More like a nagging old tough stringy hen. The Make over will take 25 years off it, and get you another couple decades. If you document all the changes in the manual, then when your grandkids get into it in 30-40 years they'll have a general idea what will need replacing again when it starts showing it's age again.

    Larry
     
  6. Skibrain

    Skibrain New Member

    Messages:
    11
    Location:
    Rocklin CA
    Thanks Larry,

    Output tubes are GE 7591's
    Now I am planning on Dave's bias balance setup tubes.
    Off to the Dim Bulb building supply. ( a little like the HP Original Audio oscillator using a light bulb as a variable resistor.( I think ))??
    Good test unit for a few buck. Hardest part these days is finding a real incandescent light bulb.
    I'll add what is in the Metalbone kit so everyone will know.
    I may have time to start soldering tonight.
    I have to order the Hayseed can kit, but I better sell some of my other stuff first my wife is gettign irritated as 200 here and 200 there disappear from my account. But I can't leave these Tubes to others.
    I really want to hear this again soon, so thanks for the help.
    I know there is a lot more for me to learn after I get all the parts in.
     
  7. Skibrain

    Skibrain New Member

    Messages:
    11
    Location:
    Rocklin CA
    Hi Larry,
    Great info on the Variac run up and the Dim Bulb tester. I found this from you in the "Fisher 800C project for 2014" thread.
    I'll go through this again as it has many of the questions I will be asking and hopefully I'll just need some clarification.
    But I did want to add this to my thread as it will be good info for anyone who reads this and wants to learn how to bring up old equipment that hasn't been run in a while.

    "Bring it up slowly on a VARIAC with a 150W bulb dbt on it. Start at 30V for an hour and bring it up 10V an hour until 90V. If anywhere in there the light goes bright and stays that way, shut it down. If by the time you get to 90V or so and the bulb is dim and the can's are cool, go ahead and jump to 110 and let it sit for a while. Check the temps on the can's and the transformers. If any are getting hot, shut it down.

    Keep an keen eye on the DBT and the temps while bringing up. You may even take an occasional voltage reading on the B+ of the output tubes to make sure they are all drawing plate, grid, cathode voltages fairly evenly.

    Any glitches, shut it down and rebuild the power supply and coupling caps 1st.

    Make sure Cheap speakers connected."
    Reposted for this thread, Complements of Larry, thanks!

    Wish I would have found this before I started playing my Futura VI or even this 800C. We live and learn, but nothing blewup . Lucky me

    Ken
     
  8. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

    Messages:
    18,153
    Location:
    Glen Burnie Md.
    Note: As you go up in voltage, the DBT lamp will increase slightly in brightness. This IS NORMAL!
     
  9. Skibrain

    Skibrain New Member

    Messages:
    11
    Location:
    Rocklin CA
    Thanks, Just built the DBT and bought a Variac 1.4kw, tested with the bulb and DBT. Working perfectly.
    Actually tested with my Mazzer coffee grinder 900W and worked good for RPM control.Hooked up to a Solid State Receiver, after a couple of clicks it cam on with dim Bulb. ( Cool test unit) I have to travel a few days and rebuild my son's computer- So probably Saturday and soldering begins.
    Hope I don't let out the smoke gods! Should I do a section at a time? ( Best practice, but I would hate to put the tubes in and out that many times.)
    Thoughts.
    I'm starting with the Metalbone kit, after that works I'l; do the Hayseed Caps or maybe rebuild them?? I think Hayseed at this point. What is an extra $100 when I could blow something up!! I'll rebuild the can caps on my Futura VI to save money.
    Tell me to stop if I'm going into shark infested waters with my plan.
    Hope everyone on the East Coast survived without incident with the weather.
    Thanks,
    Ken
     
  10. larryderouin

    larryderouin Do I get Food, Med's, or more gear this Month? Subscriber

    Messages:
    18,153
    Location:
    Glen Burnie Md.
    Leave the tubes in, The trnsformers should be tall enough to keep the tubes from the bench. If not then remove the output's only. Do a section at a time. Start with Power supply and make sure all voltages are up to snuff. Then everything else should fall right into place with the P.S. done 1st.
     

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