Monitor 7 / Model 7 Factory 2nd's ??

LilPolker
LilPolker Posts: 40
edited March 2023 in Vintage Speakers
PIC's to follow, oh and also band new to Polks and to this site.

I picked up some 7's yesterday, without knowing about the 10" PR. Long story short, I got the pair for $100. Cabs are good / very good with a few edge battle scars, all in all the drivers looked clean and I was happy to get them onto my test receiver (120W Technics SA 800). I noticed that the MW appeared to do the heavy lifting, and the W was just along for the ride. So after some of more re-reading the specs (I missed the detail of the PR) it started to make sense. I was pretty surprised that I missed that detail, but anyway ....I digress.

Overview:
* 7's with Peerless with hole mod
* Grilles (w/ emblems) cover entire speaker
* Polk Audio embossed on plastic escutcheon below posts, single fuse.
* Both Cabs have mis-drilled MW hole (upper left) where the screw does not fasten
* No serial or P/N's anywhere
* One MW driver pulled to see if magnet shifted
* MW wiring is soldered to tabs on speaker terminals
* MW driver dated 12 26 79 - Magnet is totally secured to top and bottom plate
* OD of MW driver magnet is not centered (way off) to top plate and bottom pole plate.
Off center by where magnet overhang (past the plate) approx .214" and .074" at the
max/min, where it should be ~ .15" all around (difficult to measure w metal caliper)
* Top and bottom plate appear to be centered to basket
* MW does not rub with one slight exception, but in general is clear of the pole when
pressed in squarely.

Have not looked at both MW's but the unseen one is working , and to my ear is ok.

Is it possible, being there are no serial or p/n's, and the other anomalies, that these speakers could have been sold as factory seconds? I know that there were compromises to get product out the door, but is that a possibility? Serial and P/N stickers could have fallen off, but were there supposed to be P/N stickers on the back of the cabs for this year (per the MW date code)?





Post edited by LilPolker on
«134

Comments

  • F1nut
    F1nut Posts: 49,781
    Part numbers? There were never any part numbers on the cabinets.

    The serial number was a paper label stuck on the binding post plate, easily lost over the years.
    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

  • xschop
    xschop Posts: 4,682
    edited March 2023
    Are these silver-basket MWs?
    Whether silver or black baskets, the offset magnets from factory should be remedied. The suspensions will get worse over time and the coils will rub.
    Don't take experimental gene therapies from known eugenicists.
  • LilPolker
    LilPolker Posts: 40
    F1nut wrote: »
    Part numbers? There were never any part numbers on the cabinets.

    The serial number was a paper label stuck on the binding post plate, easily lost over the years.

    I saw p/n's on Monitor Series 2 (M7 +s/n) so I assumed that was the convention
  • LilPolker
    LilPolker Posts: 40
    xschop wrote: »
    Are these silver-basket MWs?
    Whether silver or black baskets, the offset magnets from factory should be remedied. The suspensions will get worse over time and the coils will rub.

    Silver baskets. Is it easier to just replace as I saw a poster who made a fixture for alignment. Not sure how to best proceed. Any advice is appreciated...btw, the one speaker I'm testing does sound pretty awesome. Thanks in advance...
  • mhardy6647
    mhardy6647 Posts: 33,020
    edited March 2023
    As @F1nut has noted (repeatedly!) in the past (including the very recent past :p ), Polk in the early-mid 1970s wasn't exactly operating in an "ISO 900x" mode! ;) There was considerable... umm... malleability on the factory floor. B)
    It's part of the charm of a small business.

    There's also the hard-to-factor impact of the passage of four or five (!) decades of lifetime of any given speaker (or pair) -- what's been done to it to keep it chuggin' along.
  • LilPolker
    LilPolker Posts: 40
    mhardy6647 wrote: »
    As @F1nut has noted (repeatedly!) in the past (including the very recent past :p ), Polk in the early-mid 1970s wasn't exactly operating in an "ISO 900x" mode! ;) There was considerable... umm... malleability on the factory floor. B)
    It's part of the charm of a small business.

    My first job out of school was a manufacturing facility, so I kinda know the drill, was just wondering if this was excessive. I didn't know per xschop that the factory let the drivers out with misaligned. Seems pretty ironic as there is a singed off QA sticker. It was the day after Christmas 1979, so maybe a little bit too much eggnog was a factor...lol
  • LilPolker
    LilPolker Posts: 40
    Wondering how big the hole is in the magnet which allowed / is allowing the driver to not rub. Anyone know what the hole size is?
  • pitdogg2
    pitdogg2 Posts: 24,549
    LilPolker wrote: »
    Pic of MW l663rd1htndo.jpg

    MW6500 part number. Looks as if it was early enough to have a mortite gasket. i.e. window rope putty. That stuff is nasty if it is.
  • Gardenstater
    Gardenstater Posts: 4,180
    LilPolker wrote: »
    Wondering how big the hole is in the magnet which allowed / is allowing the driver to not rub. Anyone know what the hole size is?

    Hole in magnet is around 1.27" and the O.D. of the voice coil is around 1.05" with about 0.0065" radial clearance to the pole piece inside and the top plate hole outside.

    So you can have the magnet around 0.11" off center before the magnet actually rubs the voice coil.
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Crown D150 amp
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
  • LilPolker
    LilPolker Posts: 40
    pitdogg2 wrote: »
    LilPolker wrote: »
    Pic of MW l663rd1htndo.jpg

    MW6500 part number. Looks as if it was early enough to have a mortite gasket. i.e. window rope putty. That stuff is nasty if it is.

    Gasket is white foam and very well sealed. I use a mechanics pic tool to pull speakers out, which sometimes can be precarious.
  • LilPolker
    LilPolker Posts: 40
    LilPolker wrote: »
    Wondering how big the hole is in the magnet which allowed / is allowing the driver to not rub. Anyone know what the hole size is?

    Hole in magnet is around 1.27" and the O.D. of the voice coil is around 1.05" with about 0.0065" radial clearance to the pole piece inside and the top plate hole outside.

    So you can have the magnet around 0.11" off center before the magnet actually rubs the voice coil.

    Thanks for that George... Is is possible that the magnet hole was not concentric, and the factory just made it work?
  • Gardenstater
    Gardenstater Posts: 4,180
    edited March 2023
    LilPolker wrote: »
    LilPolker wrote: »
    Wondering how big the hole is in the magnet which allowed / is allowing the driver to not rub. Anyone know what the hole size is?

    Hole in magnet is around 1.27" and the O.D. of the voice coil is around 1.05" with about 0.0065" radial clearance to the pole piece inside and the top plate hole outside.

    So you can have the magnet around 0.11" off center before the magnet actually rubs the voice coil.

    Thanks for that George... Is is possible that the magnet hole was not concentric, and the factory just made it work?

    One would hope they had that excuse, but no I do not believe so 🤣

    The ferrite magnets are sintered in a mold and then they are blanchard machine ground to the desired height and flatness. The holes and outer diameters are not perfectly round and concentricity isn't perfect but they aren't off by very much.

    Also, they are not magnetized until they are glued up and aligned on the driver so I do not believe it was an attempt to adjust for some sort of magnetic center, but who knows for sure?
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Crown D150 amp
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
  • LilPolker
    LilPolker Posts: 40

    The ferrite magnets are sintered in a mold and then they are blanchard machine ground to the desired height and flatness. The holes and outer diameters are not perfectly round and concentricity isn't perfect but they aren't off by very much.

    Also, they are not magnetized until they are glued up and aligned on the driver so I do not believe it was an attempt to adjust for some sort of magnetic center, but who knows for sure?

    Yeah if it's coming from a mold then I guess trying to give them the benefit of the doubt was probably not just.
  • xschop
    xschop Posts: 4,682
    LilPolker wrote: »
    xschop wrote: »
    Are these silver-basket MWs?
    Whether silver or black baskets, the offset magnets from factory should be remedied. The suspensions will get worse over time and the coils will rub.

    Silver baskets. Is it easier to just replace as I saw a poster who made a fixture for alignment. Not sure how to best proceed. Any advice is appreciated...btw, the one speaker I'm testing does sound pretty awesome. Thanks in advance...

    If you hear one starting to rub, just flip it upside-down and see if that helps. If not, then you have to disassemble and clearance the base plate ID as the suspension is too worn.

    Polk's QA/QC dept. had the munchies.
    Don't take experimental gene therapies from known eugenicists.
  • LilPolker
    LilPolker Posts: 40
    xschop wrote: »
    LilPolker wrote: »
    xschop wrote: »
    Are these silver-basket MWs?
    Whether silver or black baskets, the offset magnets from factory should be remedied. The suspensions will get worse over time and the coils will rub.

    Silver baskets. Is it easier to just replace as I saw a poster who made a fixture for alignment. Not sure how to best proceed. Any advice is appreciated...btw, the one speaker I'm testing does sound pretty awesome. Thanks in advance...

    If you hear one starting to rub, just flip it upside-down and see if that helps. If not, then you have to disassemble and clearance the base plate ID as the suspension is too worn.

    Polk's QA/QC dept. had the munchies.

    The drivers are not rubbing, and per Gardenstater's comment on the clearance specs, the magnet that is most offset is about .070" offset and will clear. Although this is probably not ideal, it is working. What is the best procedure to align? I am a bit afraid that if I attempted an alignment I could damage/crush the VC as the magnetism of the assembly will be fighting the centering. I am assuming that people have done this without removing the cone? And I bet the munchies had something to do with it..lol
  • LilPolker
    LilPolker Posts: 40
    Peerless Tweeter PIC...assuming USA made? With what I have shown thus far , are these speakers 7b's?hfgtaq53tph7.jpg
  • Gardenstater
    Gardenstater Posts: 4,180
    Yes they are most definitely 7Bs. Those Peerless may have been made in USA but we really don't know how to tell for certain unless there is a "Made in USA" sticker on them. They were making them in the US even in the very early 70s and I have seen 7514s with a "Made in USA" sticker.
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Crown D150 amp
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
  • LilPolker
    LilPolker Posts: 40
    Yes they are most definitely 7Bs. Those Peerless may have been made in USA but we really don't know how to tell for certain unless there is a "Made in USA" sticker on them. They were making them in the US even in the very early 70s and I have seen 7514s with a "Made in USA" sticker.

    ok, thanks again George...What would you do with that one driver that has the big magnet offset? replace or repair?, and do you have any advice on either approach?
  • xschop
    xschop Posts: 4,682
    Just run 'em until you hear rubbing, then call me for rebuild/clearancing unless you can get ahold of member Kryten for the loaner MW jig.
    Don't take experimental gene therapies from known eugenicists.
  • LilPolker
    LilPolker Posts: 40
    edited March 2023
    Here are the holes or maybe should be called missed holes. I recall seeing something about a better way to fastengdk8yrmhvqws.png
  • ken brydson
    ken brydson Posts: 8,647
    LilPolker wrote: »
    I recall seeing something about a better way to fastengdk8yrmhvqws.png

    Hurricane nuts or rings if you can find them

  • LilPolker
    LilPolker Posts: 40
    In Gardenstaters sig, it says 7b's with Std Mods, what are the std mods fo the 7b's?
  • Gardenstater
    Gardenstater Posts: 4,180
    edited March 2023
    The standard mods would probably be (can substitute other materials of similar performance):

    1) Dynamat Xtreme on the outside of baskets of MW and Passive Radiator
    2) Square of Blackhole 5 behind the MW
    3) Upgraded capacitors and resistors in the crossover.
    4) Upgraded binding posts
    5) Upgraded internal wiring; driver supply and returns and wires from binding posts to PCB.
    6) Some sort of stiffening of the baffle and I chose xschop's semi-rings behind the MWs, glued in place.

    There are other mods that are without doubt up for debate and in my opinion they can take the speakers to a higher level still.
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Crown D150 amp
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
  • xschop
    xschop Posts: 4,682
    LilPolker wrote: »
    Here are the holes or maybe should be called missed holes. I recall seeing something about a better way to fastengdk8yrmhvqws.png

    Hangover Monday
    Don't take experimental gene therapies from known eugenicists.
  • LilPolker
    LilPolker Posts: 40
    The standard mods would probably be (can substitute other materials of similar performance):

    1) Dynamat Xtreme on the outside of baskets of MW and Passive Radiator
    2) Square of Blackhole 5 behind the MW
    3) Upgraded capacitors and resistors in the crossover.
    4) Upgraded binding posts
    5) Upgraded internal wiring; driver supply and returns and wires from binding posts to PCB.
    6) Some sort of stiffening of the baffle and I chose xschop's semi-rings behind the MWs, glued in place.

    There are other mods that are without doubt up for debate and in my opinion they can take the speakers to a higher level still.

    Thanks George, I did searches for the items in your list...that helped a lot...
    Curious about the Dynamat on thePR, did you removed it? I'm asking as I tried one attempt to remove my PR and it is in there solid, I mean solid to where I don't know how I'd even know how to get the leverage needed to remove it... and then how to reseal. Actually just checked see if it's even feasible to "not" removing the PR to Dynamat it, but maybe not enough room to get it applied.
  • Gardenstater
    Gardenstater Posts: 4,180
    I know what you mean. That gasket material is really almost bonded when it hasn't ever been removed for decades. But if you use a putty knife that has a thick blade with a bevel on it, you can carefully work around the perimeter and pry upwards in various diametrically opposed places and you can break the seal and you can do it without damaging the gasket because you don't have to penetrate that far.

    I use one of those painter's 5 in 1 tools, I believe they call it. Very thick blade with a bevel. You can even give it delicate little taps with a small brad hammer.
    George / NJ

    Polk 7B main speakers, std. mods+ (1979, orig owner)
    Martin Logan Dynamo sub w/6ft 14awg Power Cord
    Crown D150 amp
    Logitech Squeezebox Touch Streamer w/EDO applet
    iFi nano iDSD DAC
    iPurifier3
    iDefender w/ iPower PS
    Custom Steve Wilson 1m UPOCC Interconnect
    iFi Mercury 0.5m OFHC continuous cast copper USB cable
    Custom Ribbon Speaker Cables, 5ft long, 4N Copper, 14awg, ultra low inductance
    Custom Vibration Isolation Speaker Stands and Sub Platform
  • F1nut
    F1nut Posts: 49,781
    LilPolker wrote: »
    F1nut wrote: »
    Part numbers? There were never any part numbers on the cabinets.

    The serial number was a paper label stuck on the binding post plate, easily lost over the years.

    I saw p/n's on Monitor Series 2 (M7 +s/n) so I assumed that was the convention

    That is a model number, not a part number.

    To remove the PR, remove the binding post plate and use a wooden dowel or other long object to push the PR out. You may have to tap the dowel with a hammer...lightly though. Have someone in front to catch the PR.

    All this magnet stuff...much ado about nothing. If the drivers sound ok while playing there is no problem. Some like to nit pick/over complicate matters.

    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

  • LilPolker
    LilPolker Posts: 40
    edited March 2023
    xschop wrote: »
    LilPolker wrote: »
    Here are the holes or maybe should be called missed holes. I recall seeing something about a better way to fastengdk8yrmhvqws.png

    Hangover Monday

    MW date codes says it all, Dec 26 1979 and Jan 2 1980 ...LOL

    And I didn't check yet to see if the entire bolt circle is hosed... I may have to plug up, some / all of the holes and re-drill.