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

Got me a rusty old Marantz model 8 to restore

Discussion in 'Tube Audio' started by cptnCanada, Sep 22, 2016.

  1. cptnCanada

    cptnCanada Active Member

    Messages:
    259
    Location:
    Canada
    s-l1600.jpg s-l1600 (4).jpg s-l1600 (9).jpg s-l1600 (11).jpg Picked up a Marantz Model 8 in absolutely horrible physical condition. Looks like it has been sitting in a unconditioned storage shed for the last 30 years. Lots of surface rust, dented chassis, missing transformer cover, cutoff power cord, missing fuse holder, etc.

    Underneath it looks to have never been touched. All original, wiring all straight, no signs of electrical problems. The game plan is to bring this back to be my daily driver. If all goes to plan, and with lots of luck on my side, this ugly duckling should turn into rusty gold.

    Here is the list of to-do's

    Remove transformers and soak chassis in simple green
    Test transformers
    Straighten chassis
    Replace selenium rectifiers with modern diode equivalents
    Replace electrolytic caps in power supply
    Measure all carbon comp resistors for drifting
    Purchase new tubes

    I would really like to keep all the caps in the signal path original. I believe they are mylar good-all and Sprague bumblebee caps. Any comment on if this is a good idea?

    Also looking for a transformer cover as this one is completely missing.

    I have brought a couple tube amps back to life in the past but I am by no means an expert so you can expect a lot of questions along the way. Will be posting lots of pics as I go so hopefully somebody will be able to use this as a guide in the future as I am finding no decent Marantz 8/8b restore threads anywhere on the internet.
     
    Last edited: Sep 29, 2016
    BobHol, mech986, Pio1980 and 5 others like this.

     

    Please register to disable this ad.

  2. arts

    arts Super Member

    Messages:
    3,625
    Location:
    Qc, Canada
    Wow,that poor thing has seen hard times! I really like the Franken-amp look myself.

    The bumblebee's are notoriously poor survivors,and have caused many problems in old amps.I look at them the same way I regard old electrolytics: not worth the trouble of saving or the risk of using.I'd pull them (but do keep them just for posterity) and replace with whatever flavor of cap you prefer.

    Appearances aside,that is one hell of a good amp!
     
  3. knockbill

    knockbill Addicted Member

    Messages:
    7,702
    Location:
    SE PA
    Cool,,, looks like you found a winter project!
     
  4. ferninando

    ferninando Lunatic Member

    Messages:
    12,467
    Location:
    San Jose Ca.
    the hardest part is going to be restoring all the lettering after striping all the paint from the chassis.
    the rear panel is a mess.
     
    asilker likes this.
  5. 2526

    2526 AK Subscriber Subscriber

    Messages:
    3,496
    Location:
    Pittsburgh, PA
    Rat rod amp.
     
    onwardjames likes this.
  6. gadget73

    gadget73 junk junkie Subscriber

    Messages:
    36,583
    Location:
    Southern NJ
    Personally I've never had any luck with those stripey things. They have usually been leaky, especially if stored in the damp. My Philco TV was loaded with them and a large portion had swelled internally to the point where the plastic shell was cracking off. I restored a National shortwave radio for someone that had them, and they were actually leaking some sort of magic juice. No clue if they ever made those in a PIO version, but they had something coming out of them and they all failed the cap tester.

    If you want to try keeping them, be sure you test them at full rated voltage for leakage. I've got some old mylar caps in service that are perfectly fine. Film caps last just about forever, paper are just garbage.
     
    mech986 and autoanalog like this.

     

    Please register to disable this ad.

  7. sheltie dave

    sheltie dave Addicted Member

    Messages:
    6,876
    Location:
    St. Louis
    Don't soak these transformers in anything, what have they done bad to you? That is pretty much above average condition for a thirty year in the basement amp, and is a stellar find and a legacy for the next fifty years.

    You DO NOT want to soak an amp in a tub of salts, citrates, oils, and alcohol. http://simplegreen.com/downloads/SDS_EN-US_SimpleGreenAllPurposeCleanerFreshScent.pdf

    Crooner's restoration thread is outstanding on AK. Look it up.
    http://audiokarma.org/forums/index.php?threads/marantz-8b-project.149341/
    http://audiokarma.org/forums/index.php?threads/marantz-8b-restoration-saga.19324/
     
    Last edited: Sep 23, 2016
    biscuithead, mech986 and Pio1980 like this.
  8. BuzzK

    BuzzK AK Member Subscriber

    Messages:
    1,766
    There is nothing really magical about the chassis. I think it is beyond repair because of the rust. I would fabricate a new one and have it silk-screened.

    I recently sold a transformer cover that I had purchased (by mistake) and had repainted. I wonder now of the person I sold to has a spare . . .

    Check this out too. It may or may not be a dead end.

    http://www.oocities.org/mnowlen/marantz8b.htm
     
  9. crooner

    crooner Tube Marantzed

    Messages:
    4,117
    Location:
    San Diego, CA
    Congrats on the purchase. I almost pulled the trigger on that one, but declined due to the multitude of projects I have right now, including my turbocharged Model 7 preamp.
    My plan was to build brand new monoblocks with the output iron and associated parts. Like a smaller version of the Model 9 with a nice brushed aluminum front panel and meter on the front. Built in tests including the signal to balance the driver tubes. Power transformers could be brand new, perhaps using a full wave circuit instead of the doubler....

    I would recap it with the new Arizona "Cactus" caps, they are PIO combined with Mylar. Best of both worlds. So far they sound fantastic on my souped up Model 7!
     
    mech986 likes this.
  10. Pio1980

    Pio1980 AK Member Subscriber

    Messages:
    26,161
    Location:
    Angel Station, Alabama
    The older ones were afaik oily paper, but I've had one member insist otherwise.
    The stripers in this amp are in the front end LF rumble filter network and normally have no DC bias to "leak". Normal recommended operation of this amp bypasses them with the "test" input, so replacement is essentially optional imo if the filtered input option is never implemented and they are intact.
     
    Last edited: Sep 23, 2016
    crooner likes this.
  11. cptnCanada

    cptnCanada Active Member

    Messages:
    259
    Location:
    Canada
    Thanks for the speedy replies folks! Sounds like most are for getting rid of all the couplers in there and replacing with something new. I have used the Russian PIO caps in the past and have enjoyed the resulting sound. Those Cactus caps are also a possibility, gotta look into them a bit more.

    Sheltie Dave, I have removed the transformers and bias gauge before dunking the chassis in simple green/ water mix. I have been using this mix for years on all sorts of projects and have never had any residual corrosion problems. It really helps clean all the tobacco gunk from the solder joints which I find makes them a lot easier to work.

    As for the chassis, My parents have a neighbour who fixes autobody dents for a living. His work is magic, all by working the metal with small hand tools. I figure if he can take a dent out of a curved fender he should have no problem straightening up this rectangle. I am leaning on not stripping the paint and leaving it kind of a rat rod look. I actually think it will look kind of cool that way. Once stripped, lettering will be long gone, and by that point could you even still call it a model 8?
     
    Pio1980 likes this.

     

    Please register to disable this ad.

  12. Pio1980

    Pio1980 AK Member Subscriber

    Messages:
    26,161
    Location:
    Angel Station, Alabama
    Mine still has the Goodall caps. Afaik, they are similar to the Sprague 160 polyester caps in McIntosh amps.
     
  13. cptnCanada

    cptnCanada Active Member

    Messages:
    259
    Location:
    Canada
    A couple pics after transformer separation and simple green bath.

    Appears to be manufactured in 1960 by PT date code and potentiometer date codes

    image.jpeg image.jpeg image.jpeg
     
    Pio1980 and asilker like this.
  14. asilker

    asilker Bible Reader Subscriber

    Messages:
    2,691
    Location:
    Chicago IL
    Can't wait to see the finished project. props, my friend
     
  15. Pio1980

    Pio1980 AK Member Subscriber

    Messages:
    26,161
    Location:
    Angel Station, Alabama
    Mine still has the Goodall caps. Afaik, they are similar to the Sprague 160 polyester caps in McIntosh amps.
     
  16. onemug

    onemug AK Subscriber Subscriber

    Messages:
    2,926
    Location:
    Southern California
    It needs your love. Good luck.
     

     

    Please register to disable this ad.

  17. crooner

    crooner Tube Marantzed

    Messages:
    4,117
    Location:
    San Diego, CA
    Yep. I think this is going to turn out really sweet. The 8 is a sleeper in my opinion.
     
    Pio1980 likes this.
  18. Pio1980

    Pio1980 AK Member Subscriber

    Messages:
    26,161
    Location:
    Angel Station, Alabama
    I like the idea of working with as much of the original amp as possible. Imo, the transformer cover is unnecessary.
     
  19. nj pheonix

    nj pheonix AK Subscriber Subscriber

    Messages:
    9,839
    Location:
    New Jersey
    I'm late to the thread. Honestly I thought based on the description in the the first post it would look way worse than the pics that followed. Good luck with the project!:lurk:
     
  20. crooner

    crooner Tube Marantzed

    Messages:
    4,117
    Location:
    San Diego, CA
    And also, the majority of Model 8's I've seen have unpotted power transformers with end bells. That's the way they came from the factory. The later 8B, of course, had all potted transformers.
     
    Pio1980 likes this.

Share This Page