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Marantz 8B Questions

Discussion in 'Marantz Audio' started by Leilei787, Nov 3, 2018.

  1. Leilei787

    Leilei787 New Member

    Messages:
    10
    Hi friends ,last week i bought a Marantz 8 on Ebay. it seems that this unit has been serviced at some points. But i just do not know what has been changed since i do not have any records. Could anyone let me know

    1) what kind of service has this unit been done?
    2) the seller claim that A1 tube bias can only adjusted half way otherwise, it will be getting very hot..how to fix this?
    3) any other services that need to be done?

    thank you for helping!! sorry for all silly questions.

    [​IMG] [​IMG] [​IMG] [​IMG] [​IMG]
    [​IMG]
     

     

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  2. Chrisxo55441

    Chrisxo55441 AK Subscriber Subscriber

    Messages:
    2,489
    Location:
    Twin Cities Minnesota
    This is a pic of an original 8B, there has been a quite a few caps replaced on yours and i would assume the 2 large can caps on top were bypassed and new ones were under mounted that is what i had done on mine but it doesnt look quite like yours. im not a tech so cant tell you much more.

    [​IMG]

    mine after restoration my Dave Olsen at HI-FI Sound

    20160510_130143 (800x450).jpg
     
  3. Leilei787

    Leilei787 New Member

    Messages:
    10
    Interesting. Yours look a lot cleaner. Thank you. Is Dave still fixing vintage audio? Thank you all
     
  4. Chrisxo55441

    Chrisxo55441 AK Subscriber Subscriber

    Messages:
    2,489
    Location:
    Twin Cities Minnesota
    Yes Dave is top notch and was still there a couple months ago, he only works a couple days a week and will probably be retiring sometime in the near future i would think. those straps holding the caps on yours are interesting, never seen like that.
     
  5. Leilei787

    Leilei787 New Member

    Messages:
    10
    Still curious what kind of service this unit has done. Does it look right? Thanks
     
  6. bktheking

    bktheking Gitter Done! Subscriber

    Messages:
    12,857
    Location:
    Ottawa Ontario
    All your power supply caps have been replaced, some resistors and your coupling caps. Have you checked the bias circuit to see if it's in spec? It appears the selenium rectifier may have been removed and replaced with a solid state one, additional resistors are needed to compensate between selenium and SS for voltage drop - if i were your friend i'd take it to a reputable shop to go over it and fix whatever mistake was made in the bias circuit. These are $3000+ amps and deserve to be looked at by someone who knows what they are doing, honestly whoever rebuild this thing was a hack- it's not a clean rebuild by any stretch.
     
    UncleBingo likes this.

     

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  7. Leilei787

    Leilei787 New Member

    Messages:
    10
    thank you! do you know how much it usually costs to fully restore piece like this? i got this one around $1800, feel right about the price.
     
    Pio1980 likes this.
  8. bktheking

    bktheking Gitter Done! Subscriber

    Messages:
    12,857
    Location:
    Ottawa Ontario
    One would have to sit down and do a parts list then factor in labour, prices vary- it’s a tough question to answer.
     
  9. Pio1980

    Pio1980 AK Member Subscriber

    Messages:
    26,456
    Location:
    Angel Station, Alabama
    If I bought it for listening, I'd have the bias issue checked and the amp bench checked for proper performance and otherwise leave it as is as the most cost effective approach.
     
    Eric n Kc likes this.
  10. Chrisxo55441

    Chrisxo55441 AK Subscriber Subscriber

    Messages:
    2,489
    Location:
    Twin Cities Minnesota
    im sure prices vary but i paid $600 for my restore a few years ago. i was offered a choice of some pricey russian i think oil filled caps which would have raised it up but i decided on solen's
     
  11. Pio1980

    Pio1980 AK Member Subscriber

    Messages:
    26,456
    Location:
    Angel Station, Alabama
    I'm not convinced that replicating the original cap sound is the only way to go for an amp rebuilt for listening, rather than as a museum resto.
    I do wonder how much sq difference polyprops or Teflon caps would make compared to the oem Goodalls in my 8.
     

     

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  12. Leilei787

    Leilei787 New Member

    Messages:
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    random question, how do 8 and 8b compare? does 8 go for more than 8b?
     
  13. Pio1980

    Pio1980 AK Member Subscriber

    Messages:
    26,456
    Location:
    Angel Station, Alabama
    Condition, condition, condition.
    The 8B is perceived an advancement over the 8, and that may influence choice and desirability, all else equal. Collectors may insist on as much of the original parts and appearance being present.
    Sonically, tube and replacement signal path capacitor choices may swamp actual audible differences between the versions. Two otherwise identical examples, one of each version with the same components, and tubeset shared between them may give a better idea of the character of each version, someone that has done that would have to say.
    Afaik somewhat more 8Bs were produced, a total of almost 20,000 examples of the 8/8B were built.
     
  14. bktheking

    bktheking Gitter Done! Subscriber

    Messages:
    12,857
    Location:
    Ottawa Ontario
    8b had 5 watts more power output than the 8 and they eliminated the octal plug from the unit in later runs. Otherwise they are pretty much the same amp. Early 8's had different bias meters as well, unless they were swaps from other amps- not sure.
     
    Last edited: Nov 6, 2018
  15. vendo81

    vendo81 AK Subscriber Subscriber

    Messages:
    1,838
    Location:
    California
    I'd probably fix the bias problem and use the amplifier as is. Swap the A1 and A2 EL34's and see if it follows the tube or socket. A variac is really needed for this testing as you don't want to damage the amplifier. A bit crowded in there with how it was rebuilt. Looks like maybe a balanced type input jack was added on the rear? Not sure what that's about as I never noticed that on mine. Maybe it's an early 8b and they replaced the octal socket.

    I swapped both my 8 and 8b in and out of the same system over a couple years. Both are completely stock and I wanted to make sure both got use. Some may disagree, but I couldn't tell any difference sound wise. I've been wanting to rebuild one, mostly for safety sake and to see how they compare. Even after sitting unused for over two years they are both working well, so for now they will stay original. If I used one daily I would rebuild it.
     
  16. Leilei787

    Leilei787 New Member

    Messages:
    10
    another question, is JBL 4312 a good speaker for the 8b?
     

     

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  17. vendo81

    vendo81 AK Subscriber Subscriber

    Messages:
    1,838
    Location:
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    I've never heard the 4312's and have only done extensive listening with L300's and 4345's. I checked and the 4312's are rated at 93db sensitivity so they should be OK with your Marantz. I listened to many tube amplifiers that had power levels comparable with an 8b with the 4345's. If I remember right the 4345's were 93db and played plenty loud and had a rich, full sound. They were different sounding than the many Altec speakers that I like, but in a very good way. If you like the JBL sound the 4312's may be a good choice. I've listened to a couple of friends smaller studio monitors made by JBL that really stood out nicely with tube amplifiers but I don't recall what models they were.
     
  18. Leilei787

    Leilei787 New Member

    Messages:
    10
    thank you. Actually i do have a pair of 4344. i left my L300 in beijing. someday i will have to ship them back to the US. I did not realize 8b can drive 4345..
     
  19. vendo81

    vendo81 AK Subscriber Subscriber

    Messages:
    1,838
    Location:
    California
    If your not using the 4344's in another system they would work great with your Marantz. Many of the JBL's from that era seem to be pretty efficient.
     
  20. USMC Spike

    USMC Spike Active Member

    Messages:
    186
    Location:
    Tejas, North Central
    Here is what a clean original Marantz 8b should look like inside.
    I made one change and one replacement (resistor).
    Can you spot the change?
    The replacement?

    Enjoy

    Beside the that, I also have the Paoli's list of his recommended mods to the amp.

    One major issue with these amps is the Sprague bumblebee caps that leak.
    The issue as I understand it is these are all paper caps. That wouldn't
    necessarily be a problem except they are American made.

    Why would that cause a problem? What about European paper caps?
    Are they different than American caps?
    If so, what? If not, then what?

    When I remember to come back here I'll check up and if anyone
    has answered all the questions and identified the two changes
    I've made to the amp I'll send you a Twix candy bar--you'll have
    to PM me your address. Note: at this time of year that shouldn't
    be a problem unless you live in the wild fire areas in CA, where
    it might melt. It would taste the same, but the pretty chocolate
    ripples on the top of the bar would me flat and smooth.
     

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