Refurbishing 7C

wbrokow1
wbrokow1 Posts: 16
in Vintage Speakers
I have a great pair of 7c's purchased in 1986/7 . They sound good but I think they are due for a crossover rebuild. Exactly where can I get all the capacitors etc. for doing the rebuild.
I figure I would start there before changing the tweeters. Any tips or advice is appreciated.
Thanks in advance
Onkyo TX-6000 (2)
Nakamichi 480
Nakamichi Cassette Deck 1
Nakamichi zx-7
Technics sl-1200
Polk Monitor 7c
Mission 700
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  • CH46E
    CH46E Posts: 3,591
    Try Parts Connexion
    Parts Express
    Sonic Caps

    Just to name a few I have used.
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  • F1nut
    F1nut Posts: 50,543
    Sonic Craft who makes and sells Sonicap capacitors.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."

    President of Club Polk

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  • wbrokow1
    wbrokow1 Posts: 16
    thanks
    Onkyo TX-6000 (2)
    Nakamichi 480
    Nakamichi Cassette Deck 1
    Nakamichi zx-7
    Technics sl-1200
    Polk Monitor 7c
    Mission 700
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  • wbrokow1
    wbrokow1 Posts: 16
    Ok I took a look at the capacitors inside the unit and they are original. The capacitance rating is not visible without desoldering and inspecting. Is there a parts list that I could get to buy the caps first before taking it apart or do these values vary from speaker to speaker and I have to pull them out first. Thanks
    Onkyo TX-6000 (2)
    Nakamichi 480
    Nakamichi Cassette Deck 1
    Nakamichi zx-7
    Technics sl-1200
    Polk Monitor 7c
    Mission 700
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  • F1nut
    F1nut Posts: 50,543
    edited July 2019
    The schematics are listed at the top of the page. Replace the resistors as well.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."

    President of Club Polk

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  • DaveHo
    DaveHo Posts: 3,515
    This should be the correct schematic for the 7C with the SL2000 tweeter.

    https://us.v-cdn.net/5021930/uploads/attachments/4/6/7/2/8/18773.pdf
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  • wbrokow1
    wbrokow1 Posts: 16
    None of those sources have a 34 microfarad electrolytic capacitor or a 2.0 ohm 5w resistor. Not even Digi-key. 33 yes , 2.2 or 1.8 ohm yes. Anyone think it will matter if I substitute?
    Onkyo TX-6000 (2)
    Nakamichi 480
    Nakamichi Cassette Deck 1
    Nakamichi zx-7
    Technics sl-1200
    Polk Monitor 7c
    Mission 700
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  • F1nut
    F1nut Posts: 50,543
    Forget electrolytic caps, upgrade to film and foil. Sonic Craft has everything you need.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."

    President of Club Polk

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  • wbrokow1
    wbrokow1 Posts: 16
    ok so I went to sonic craft. filled my cart. Looks good?vjbqljl474np.png
    Onkyo TX-6000 (2)
    Nakamichi 480
    Nakamichi Cassette Deck 1
    Nakamichi zx-7
    Technics sl-1200
    Polk Monitor 7c
    Mission 700
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  • F1nut
    F1nut Posts: 50,543
    It's a good idea to replace the original 5 watt resistors with either the 10 or 12 watt Mills versions. Sorry, I didn't mention that earlier.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."

    President of Club Polk

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  • DaveHo
    DaveHo Posts: 3,515
    Most also remove the polyswitch & replace with a 0.5ohm resistor. Not sure if you can just get a 2.5 ohm resistor & jump the polyswitch spot on the board or if you need and actual resistor in that spot. I'll defer to someone more knowledgeable than me.
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  • F1nut
    F1nut Posts: 50,543
    Good point DaveHo.

    Yes, remove and jump the poly, then use this resistor to replace the original 2 ohm. http://www.soniccraft.com/product_info.php/25-ohm-vishay-mills-mra-12-p-4634
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."

    President of Club Polk

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  • wbrokow1
    wbrokow1 Posts: 16
    thanks
    Onkyo TX-6000 (2)
    Nakamichi 480
    Nakamichi Cassette Deck 1
    Nakamichi zx-7
    Technics sl-1200
    Polk Monitor 7c
    Mission 700
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  • F1nut
    F1nut Posts: 50,543
    You're welcome.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."

    President of Club Polk

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  • wbrokow1
    wbrokow1 Posts: 16
    So your saying remove the fuse and jump it?c6peyf5j2c67.jpg
    Onkyo TX-6000 (2)
    Nakamichi 480
    Nakamichi Cassette Deck 1
    Nakamichi zx-7
    Technics sl-1200
    Polk Monitor 7c
    Mission 700
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  • DaveHo
    DaveHo Posts: 3,515
    Odd, I didn't think the 7c had fuses. Can you post a pic of the drivers, front and back, to make sure we're on the same page?
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  • wbrokow1
    wbrokow1 Posts: 16
    Ok here
    Onkyo TX-6000 (2)
    Nakamichi 480
    Nakamichi Cassette Deck 1
    Nakamichi zx-7
    Technics sl-1200
    Polk Monitor 7c
    Mission 700
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  • wbrokow1
    wbrokow1 Posts: 16
    y8uw411sxol9.jpg
    6y380bzxmtoq.jpg
    q3txjh9tgfs1.jpg
    Onkyo TX-6000 (2)
    Nakamichi 480
    Nakamichi Cassette Deck 1
    Nakamichi zx-7
    Technics sl-1200
    Polk Monitor 7c
    Mission 700
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  • wbrokow1
    wbrokow1 Posts: 16
    The manufacturing date stamped on the crossover is 5/18/84
    Onkyo TX-6000 (2)
    Nakamichi 480
    Nakamichi Cassette Deck 1
    Nakamichi zx-7
    Technics sl-1200
    Polk Monitor 7c
    Mission 700
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  • F1nut
    F1nut Posts: 50,543
    edited July 2019
    Those are not 7C's. You should pull a crossover to check the component values before ordering anything.

    This is a 7C.

    o40qncjnot00.jpg
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."

    President of Club Polk

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  • wbrokow1
    wbrokow1 Posts: 16
    Yes they are. I purchased them from The listening Room in scarsdale NY brand new in box. ~7 hundred dollars. I personally opened the factory sealed polk audio box myself.
    Onkyo TX-6000 (2)
    Nakamichi 480
    Nakamichi Cassette Deck 1
    Nakamichi zx-7
    Technics sl-1200
    Polk Monitor 7c
    Mission 700
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  • wbrokow1
    wbrokow1 Posts: 16
    I just checked the drawing for the original 7c and all values for components match exactly.
    Onkyo TX-6000 (2)
    Nakamichi 480
    Nakamichi Cassette Deck 1
    Nakamichi zx-7
    Technics sl-1200
    Polk Monitor 7c
    Mission 700
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  • F1nut
    F1nut Posts: 50,543
    I can read the model 7C on the binding post plate, but I'm telling you those are not what are considered to be 7C's.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."

    President of Club Polk

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  • wbrokow1
    wbrokow1 Posts: 16
    Look closely at the original drawing. The original 7c had a fuse and was removed. The resistor was changed from 2.7 ohms to 2 ohms. capacitor values match exactly. So mine is probably a very short run of orignial 7c's . You're probably used to seeing the other revisions. So yeah it is a 7c.
    Onkyo TX-6000 (2)
    Nakamichi 480
    Nakamichi Cassette Deck 1
    Nakamichi zx-7
    Technics sl-1200
    Polk Monitor 7c
    Mission 700
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  • F1nut
    F1nut Posts: 50,543
    I'll give you that yours is likely a transitional model, but note the schematic is dated 6 months after your production date.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."

    President of Club Polk

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  • wbrokow1
    wbrokow1 Posts: 16
    Yes I see that. Basically they started with my version and then as the revision block on the drawing says changes were made on 7/1 to the resistors and fuses. Then the engineering drawing was released on 11/26/84 for the next production run. So mine is and official 7c and all that followed are revised ones. The facts are on the drawing.
    So I win LOL. It's to bad you guys don't have an original haha.
    Onkyo TX-6000 (2)
    Nakamichi 480
    Nakamichi Cassette Deck 1
    Nakamichi zx-7
    Technics sl-1200
    Polk Monitor 7c
    Mission 700
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  • txcoastal1
    txcoastal1 Posts: 13,281
    So what did you win...I want to see the prize
    2-channel: Modwright KWI-200 Integrated, Dynaudio C1-II Signatures
    Desktop rig: LSi7, Polk 110sub, Dayens Ampino amp, W4S DAC/pre, Sonos, JRiver
    Gear on standby: Melody 101 tube pre, Unison Research Simply Italy Integrated
    Gone to new homes: (Matt Polk's)Threshold Stasis SA12e monoblocks, Pass XA30.5 amp, Usher MD2 speakers, Dynaudio C4 platinum speakers, Modwright LS100 (voltz), Simaudio 780D DAC

    erat interfectorem cesar et **** dictatorem dicere a
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  • wbrokow1
    wbrokow1 Posts: 16
    Nothing just goofing around. Thanks for your help , F1nut, really. Back to my original question. So my capacitor and resistor choice are good?
    Thanks for any input.
    Onkyo TX-6000 (2)
    Nakamichi 480
    Nakamichi Cassette Deck 1
    Nakamichi zx-7
    Technics sl-1200
    Polk Monitor 7c
    Mission 700
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  • F1nut
    F1nut Posts: 50,543
    You should check what the component values are on your crossover first.
    Political Correctness'.........defined

    "A doctrine fostered by a delusional, illogical minority and rabidly promoted by an unscrupulous mainstream media, which holds forth the proposition that it is entirely possible to pick up a t-u-r-d by the clean end."

    President of Club Polk

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  • wbrokow1
    wbrokow1 Posts: 16
    Ok thanks
    Onkyo TX-6000 (2)
    Nakamichi 480
    Nakamichi Cassette Deck 1
    Nakamichi zx-7
    Technics sl-1200
    Polk Monitor 7c
    Mission 700
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