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Undoing the **WORST** DIY "mod" ever...! UPDATE: Audio Classics to the rescue!!

Discussion in 'Marantz Audio' started by Joel Cairo, Apr 20, 2017.

  1. Joel Cairo

    Joel Cairo Video Doctor Subscriber

    Messages:
    174
    Location:
    Portland, OR
    I generally don't shout like that , but I think the piece I just found has to rate as the champion of poor "upgrade" decisions...

    WARNING - The pics you are about to see are not for the faint of heart!

    After you get over the raw shock of seeing them (and it may take it a bit), please give me your best advice as to how to restore this poor Frankenstein-ed thing back to health.

    Here we go--
    Marantz 7C - Pic 1.jpg Marantz 7C - Pic 2.jpg Marantz 7C - Pic 3.jpg Marantz 7C - Pic 4.jpg

    Yes, someone actually converted a Model 7 to solid state. Boggles the mind, doesn't it?

    So-- now that the initial shock is over, what are the most obvious parts that I'll need to procure to get this little gal back to her original condition...?

    More pics will come later, but I think these will get the conversation started...

    Thanks for any help you can give...!!!

    - Kevin
     
    Last edited: Nov 8, 2018

     

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  2. bryans12v

    bryans12v Marantz Junkie Subscriber

    Messages:
    1,359
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    Hudson Valley, NY
    Unbelievable!

    Hopefully you knew about this before the purchase and paid accordingly.

    It's tough to say without seeing the bottom view. Looks like it may still have a functioning tube circuit. Tone controls have been eliminated and what looks to me a 1/4 input in place of the left channel treble. That board may be a separate attenuating circuit for guitar input?

    Do you have the unit in your possession? Can you take a pic of the bottom and a some close ups?
     
  3. Joel Cairo

    Joel Cairo Video Doctor Subscriber

    Messages:
    174
    Location:
    Portland, OR
    Not yet-- I'm picking it up on Saturday... I plan to get some close ups of the interior (upper & lower).

    And yes--fortunately I got it from a very reputable dealer who gave full disclosure (in fact, I asked permission to use their pictures to start this thread, which they graciously granted).

    Here's their description:

    "Welcome to the strangest Marantz 7 tube preamp [we've] ever owned. Apparently the original owner thought solid state was the 'wave of the future' and installed a separate solid state circuit so this preamp has Tube and Transistor outputs. The phono stage is all tube. Treble, bass and several other functions bypassed."

    As to the price, it was much cheaper than the going market price for a fully original unit, but still was over $1,000.00... it **is** a Model 7 after all! (Well, at least partially...!)

    So I'm hoping at least some of the missing parts can be salvaged from other Marantz units of the period-- I'm thinking of the missing knobs/pots, etc... the missing circuit board may be a lot tougher to come by...

    - Kevin
     
    Last edited: Nov 8, 2018
  4. rBuckner

    rBuckner Luv 2 Restore Subscriber

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    In a word: sickening. Props to you for having the goal of restoration!
     
  5. tranguru

    tranguru Active Member

    Messages:
    201
    Location:
    Brussels
    that hurts....:whip:
     
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  6. airtime

    airtime Super Member

    Messages:
    2,181
    Location:
    Central Arizona
    Just out of curiosity can you guess WHEN these mods were done. Like in the 70's or 80's.
    Because I wonder at what point in history would anyone ever think it was the right move to take a piece of audio history and even consider doing that too it.

    So there was a time when 7C's were "DIY and TWEAK" material.

    I think I'll just go and reinvent my Marantz 9 monoblocks into solid state.
     
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  7. txturbo

    txturbo AK Subscriber Subscriber

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  8. Joel Cairo

    Joel Cairo Video Doctor Subscriber

    Messages:
    174
    Location:
    Portland, OR
    I'm told it actually does work, but I'm just not inclined to turn it on while it's in this state...

    And actually, things may be much better than I thought... I've picked up the unit, and now have some pics from underneath. There appears to be much less missing down there, restoration may not be nearly the issue that I was thinking.

    After doing some research, it turns out the 7T uses the exact same bass/treble knobs/pots as the Model 7... and even though the Marantz part number on the "mode" selector is different, both are 5-position rotary switches, so I'm guessing they're likely to be interchangeable.

    And I initially thought that the large bumblebee caps were mounted on a circuit board, but that doesn't actually appear to be the case. They're sitting atop that black insulating pad, and are probably wired point-to-point underneath.

    So after the hardware is procured, it'll really just be down to replacing the bumblebees with Nichicon QX's, replacing whatever other caps & resistors were removed, and having a judicious amount of re-wiring done to restore the original circuit.

    I will need a source for the two missing channel trim pots on the back, though...

    But overall, it's actually rather encouraging. I'll post more pics later.

    - Kevin
     
    Last edited: Nov 8, 2018
  9. SPEC2man

    SPEC2man Are we there yet? Subscriber

    Messages:
    882
    Location:
    Vancouver Washington
    Ask Kurt about the top 10 oddest things that have ever showed up in the store (I have been a customer for 25 years) ... this doesn't make the top 10. Glad to see it has a chance to make it back from the dark side.
     
  10. MouseMaster

    MouseMaster Active Member

    Messages:
    330
    Location:
    Monroe Twp, NJ
    Looks like they used a tag board for the bumblebees. You can make your own tag board easily. I'm getting set to build a Fender Champ from scratch, and I'm making the tag board for that. Already have the materials. You can do it easy.
     
  11. restorer-john

    restorer-john Addicted Member

    Messages:
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    Location:
    Australia
    It looks like a classic 70s prototype board and round pack opamps. Why not give it a listen first- you might like it...

    Anyway, I've seen a lot worse than that. It was after all, an ancient preamplifier that someone (perhaps a hobbyist or student) did a quite reasonable job of making into something 'better' they thought.

    The bones are still there- you'll bring it back to its former glory no doubt. :)
     

     

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  12. Djcoolray

    Djcoolray Addicted Member

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    A rocks throw from JBLM !!!!
    That's easy, as far as the timeline for when it could be thought as the best thing to do. It was the seventies when all the silver faced equipment was the rage. Tube equipment was old hat, not where it's at. There was no history yet, only liked and discarded. It's a throw away world except for enthusiasts.... Just like now with so many people getting interested in vinyl, what do you think they are going to do when they loose interest or trash some vital peice of historical equipment??
     
  13. Joel Cairo

    Joel Cairo Video Doctor Subscriber

    Messages:
    174
    Location:
    Portland, OR
    So, folks have been curious about an update--

    I've removed about 4 pounds of extra components (actually true...!) from the unit, and stripped it out to this:

    Marantz 7c - empty SMALL.jpg

    And I've obtained a "donor" 7T which has yielded amazing replacement parts... but I have a question about the caps and resistors that wrap around the treble control. I've figured out the replacements that I need to order for every position but one-- it's position 8 on the 7T control, circled on the wiring diagram below:

    Marantz 7T - treble control components circled SMALL.jpg

    As you can see, this actually does exist on the 7T version, as pictured and circled below:

    Marantz 7T treble control circled SMALL.jpg

    My question is-- does this wiring exist on the original 7C treble control? I think the cap is supposed to be a 1,000 pf ceramic capacitor (500 V)... but if so, what are the values for the two resistors (which I assume are 1/2 Watt, 10% carbon comps)?

    Can anyone with the proper knowledge take a look, and let me know?

    Thanks!

    - Kevin
     
  14. Joel Cairo

    Joel Cairo Video Doctor Subscriber

    Messages:
    174
    Location:
    Portland, OR
    Update - October 2018:

    Well, I knew I was in **way** over my abilities-- and the folks I talked to about taking on the job simply felt they couldn't put the time in to do the restoration work properly, so things looked pretty bleak for this little lady...

    Until I talked with Ryan at Audio Classics-- it seems they have a gentlemen there named George, who a) can accomplish magical things with old tube equipment and b) loves classic Marantz components. Put the two together, and it appears that this little girl will actually get to sing again.

    ***************************************************

    Update - November 6, 2018:


    Just received an e-mail this morning from Ryan, at Audio Classics:

    "OK, I just spoke to my tech on your unit. Boy, that unit was truly stripped!

    We can get it back to original specs."

    And then he gave an eminently reasonable quote for the restoration. Think I should approve it...? Too late, I already did!

    I wish I could adequately express the satisfaction that I'm feeling...

    **Yowzah, yowzah, yowzah!!** :banana:

    I'm very glad to see this happening-- this little lady deserves a far better fate than being pieced out for spare parts!

    - Kevin
     
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  15. Bert 1100

    Bert 1100 Super Member

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    :thumbsup: fingers crossed :)
     
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  16. onemug

    onemug AK Subscriber Subscriber

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    I know George's work, you are very fortunate to have it in his hands. I think you're going to be very happy with it.
     
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  17. John James

    John James "Bob's your uncle" (Stolen) Subscriber

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    Cheers for Audio Classics!
     
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  18. airtime

    airtime Super Member

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    2,181
    Location:
    Central Arizona
    I second that for Audio Classics.

    I've been dealing with them for over two decades and NEVER had a bad experience. Always professional and knowledgeable.
     
  19. Joel Cairo

    Joel Cairo Video Doctor Subscriber

    Messages:
    174
    Location:
    Portland, OR
    Well, I'm just thrilled it's being worked on by someone that knows what the Model 7 should look & sound like, and can effectively bring it properly back to life... I'm guessing George also probably has access to some original units that he can use for a quick & easy reference.

    I've left most of the component choices up to him-- and I mentioned that the real goal at this point is just to bring it back to a stock Model 7 state... there's no hot-rodding or boutique capacitors necessary, right now.

    Hell, just re-wrapping the caps & resistors on those bass & treble controls and getting it to **stock** condition is kind of miraculous, considering where we started from.

    - Kevin
     
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  20. Jonstigator

    Jonstigator AK Subscriber Subscriber

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    No more flux capacitor?
     

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