Marantz 8B Electrolytic Caps

Discussion in 'The Projects Forum' started by Rwsteiner62, Jan 26, 2013.

  1. Rwsteiner62

    Thread Starter New Member

    Jan 26, 2013
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    Hi. Ireplaced the selenium rect. with a 1n4007 diode and about to replace the 2 section 20uf @ 150vdc cap. I;m using 2 Illinois 22uf@ 500vdc caps . Want to make sure I'm reading schematic correctly..The first cap . Positive side after diode before 1k res. neg side to Blue transformer wire. Cap 2 ,Pos side after 1k resistor which is also ground. neg side tied to cap 1 neg on blue trans wire. the part that confuses me is cap 2 pos to ground. Thanks ...Rob
     
  2. crutschow

    Expert

    Mar 14, 2008
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    Post a schematic of what you are doing.
     
  3. Rwsteiner62

    Thread Starter New Member

    Jan 26, 2013
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    Marantz 8b schematic
     
  4. Kermit2

    AAC Fanatic!

    Feb 5, 2010
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    One reason a polarized cap is placed with it's 'positive' lead to ground is for filtering of a NEGATIVE voltage output. Sounds as if your amp has a positive and a negative rail.

    Edit: after logging in I can see the schematic you posted and yes, it is a dual rail power supply
     
  5. Rwsteiner62

    Thread Starter New Member

    Jan 26, 2013
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    Thank You Kermit2
     
  6. BReeves

    Member

    Nov 24, 2012
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    This brings back memories.. I worked as a tech rep for Superscope in the early 70's and we were still suporting all the early Marantz componets. Good stuff and proud you are keeping it working.
     
  7. Rwsteiner62

    Thread Starter New Member

    Jan 26, 2013
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    What diode would I use to replace these in the 8b H.V. rect. circuit? Thanks ..Rob
     
  8. BReeves

    Member

    Nov 24, 2012
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    Something rated at 600 volts and 1 amp will work fine.
     
  9. Rwsteiner62

    Thread Starter New Member

    Jan 26, 2013
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    I have 1n4007 's . with the original diodes , which direction does the current flow? to the flat side or the long cylindrical side?
     
  10. Rwsteiner62

    Thread Starter New Member

    Jan 26, 2013
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    Found A photo of those diodes online and found that the flat end is the cathode or banded side. Once again, I am thankful for everyones help . The 8b is a bit complicated than the dynaco mkllls which was my first tube project......Regards
     
  11. Audioguru

    New Member

    Dec 20, 2007
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    Yikes! It has old fashioned vaccum tubies. I had an amplifier with them about 49 years ago.
     
  12. bountyhunter

    Well-Known Member

    Sep 7, 2009
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    I had a Bell "Stereophonic 30-30" tube pre amp/amp that I used for probably 20 years and then sold for a price that seemed silly to me.... but some people really want tube amps.

    The thing was probably circa early 60's, i got it in 1968. It had input selections for both RIAA and EUR equalization modes for the phono input. Didn't sound bad, just had some hum.

    HOLY SNAP!

    HERE IT IS!

    http://www.wingspreadrecords.com/Bell.htm
     
  13. Rwsteiner62

    Thread Starter New Member

    Jan 26, 2013
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    Hello Again. While recapping and changing resistors ,I noticed that the left channel R29 4.7k res. was missing. Clearly cut out. was there a reason for this or should I put one back in? Also, Can anyone explain what the C12 170-780 pf trimmer is for? Thanks ...Rob
     
  14. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Does the receiver/amplifier function as it is with the existing components?
     
  15. Rwsteiner62

    Thread Starter New Member

    Jan 26, 2013
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    don't know yet. Got the amp from my father inlaw .it was in a closet for 20 years. wanted to replace the electrolytics before turning on
     
  16. Rwsteiner62

    Thread Starter New Member

    Jan 26, 2013
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    Polyester or polypropylene? That is the question
     
  17. thatoneguy

    AAC Fanatic!

    Feb 19, 2009
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    Non-Electrolytic caps don't tend to fail from non-use the way electrolytics do.

    If you've replaced the electrolytic caps and selenium rectifiers, I'd suggest bringing the power up on a variac if you have access to one to see if it works before putting more money into it.
     
  18. Rwsteiner62

    Thread Starter New Member

    Jan 26, 2013
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    Finally got it running. All voltages are spot on, bias is stable Sounds amazing right from the start. was on for six hours Transformers running cool. Testing with larry carlton cds, marantz7c preamp and polk outdoor speakers. can't wait till I hook it up to my Altec Lansing 604C's. Once again, Thank you for all of your help.....Regards. Rob
     
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