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  1. #1

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    Default The journey of a million mods begins with a single sheet of Dynamat Extreme

    Thought I'd document some really rudimentary stuff here in case it helps other beginning modders, and maybe provide a little general entertainment value.

    I've got lots of plans for the Polks I've long owned or recently acquired but first needed to start getting experience working with some of the materials used in basic modding. Let's just say there's a reason I don't try to make a living working with my hands. I hit on a good little project this weekend, entry-level and low-risk, and have had an overall positive outcome while learning a lot.

    No Polks were at any risk of harm in this production.

    A couple months ago my son picked up a small guitar amp that had been left out on the street for the taking or trash, very beat up - cone torn, tweed front gone, etc. Apparently I suck at taking "before" photos but honestly I can't say it was insane that it nearly ended up in a landfill. Here it is after some dissection:



    Turns out the thing is a circa 1966 Teisco Checkmate 14, solid state with what is labeled as a 21-watt amp although the limited info available on the Internet indicates it should be 14 watts. I've learned that tube Teiscos are collectable and there'd likely be some barely non-zero dollar value in this SS piece if it were in good shape, but it's far from that. So it's a great platform for me to work on - certainly vintage (I now know what nearly 50-year-old particle board is like to work with ...) and while if there were a Club Teisco forum bad karma undoubtedly would be flying my way for me saying it, it wouldn't really be the end of the world if I were to accidentally visit fatal misfortune upon this amp.

    Anyway, a week or two after my son got the amp I was rummaging in the attic and happened upon the 8" 2-way Panasonic car speakers from my car 30 years ago. A few days later I realized that was the same size as the amp driver, and when I checked it out with my son it dropped in perfectly, four screws and that's that. Not sure what the impedance of the old driver was and the replacement is 4 ohm but at least in initial testing, nothing spontaneously combusted - we have a functional amp, even if some things need work. And it's not designed to be an airtight cabinet nor are we talking hi-fi here so even if the replacement speaker specs are all wrong, for a practice amp I don't much care.

    So this weekend I did the following:


    - removed the Panasonic speaker and applied Dynamat Extreme to the frame (liberally, figuring there's reportedly no potential harm from overkill other than maybe a few pennies and minutes wasted).




    - I also applied Armaflex even though the cabinet is not sealed and thus I'm thinking a gasket probably doesn't buy me anything - just wanted to work with Armaflex a little (which was good as frankly I didn't do a terribly neat job with it in this first try).




    - Loctite and JB Weld or equivalent are still on my shopping list so no practice with those steps at this stage


    - sanded the front of the front panel to try to remove as much of the grill cloth glue and other crap as possible, then cleaned the panel front and back (brush, then vacuum, then a swipe with a tack cloth). Decided to reverse the sides as what had been the back doesn't have glue remnants on it.


    - sprayed polyurethane on (what now will be) the back of the front panel, with multiple coats around the speaker opening and screw holes. For future reference I am thinking brushed-on poly might be better - is that right?


    - when the poly dried I turned the panel over and spray-painted the (new) front flat black. Here it is drying:




    HEY WAIT! Those are CRS+ frames in that photo - but I said no Polks could be harmed! -- Don't worry, I didn't plug in the soldering gun ...




    I'm just replacing the CRS+ grill cloths, the originals of which unfortunately were not fit for presentation in my family room. The speakers themselves stayed safely in my family room (where, btw, I recently hooked them up to my newly repaired common-ground receiver, thereby officially joining the SDA club - me likey ...)


    Anyway, back to the amp front panel, I attached the Armaflexed speaker using hurricane nuts. Very valuable experience here. I tightened the socket cap screw to pull in the nut and despite my polyurethaning efforts they quickly spun anyway ... will redo this at some point with a dab of glue to get them to hold.






    - screwed front panel to (solid wood) cabinet frame. Did not bother with hurricane nuts for that. Here's the basic look (yes as a matter of fact I did crop rough edges out of this photo ...):






    - as that tweeter frame extrudes a bit, I didn't want to simply glue grill cloth to the front panel as was originally done; there would be a bulge. So I built a frame out of some old wood I had lying around, spray-painted that black, then cut acoustic architectural grill cloth (from the eBay seller westmassguy recommends) and attached it using spray adhesive (which is fairly not fun to work with). I do not yet have this installed on the amp though as I need to get velcro or something to mount it.


    - cut and attached grill cloth to the CRS+ frames, installed polkaudio badges and attached the grills to the speakers. My craftsmanship was far from perfect on the backs but installed I have to say they look sharp. I think I even may have scored a few WAF points but I'm not sure. Here's one next to a Monitor 7 with original cloth:




    - hooked up the amp speaker, plugged in a guitar, turned it on and ... it still worked! And it looked OK too - better than it started out, anyway (I know, not exactly a high bar ...).


    - it looks a tad worse for the wear today after I had to remove the front panel to remove the electronics, mainly to DeOxit the pots (this worked like a charm) and have a look/take pics.




    But it works pretty well, has a decent tone to it. Tremolo does not work but that's not a show-stopper here. At tone settings that emphasize higher end there is a fairly faint but noticeable hissing/crackling sort of sound, which according to my internet research may indicate a bum resistor. To be continued some other time ....
    Main HT: Polk Monitor 7 (1987-original owner) (L/R) / CSi40 (C) / RTi38 (SL/SR) / SVS 20-39PC (sub), Outlaw 975 pre/pro / Outlaw 7075 amp, Oppo BDP-93 Blu-ray, LG 42LM5800 teevee
    2ch: CRS+ (1987), Outlaw 1050 AVR, Denon DCM-420 CD
    Kitchen satellite 2ch: Polk M3II, Onkyo A-8037 integrated amp fed from Oppo, Yamaha TX-480 tuner
    Awaiting assignment: Model 5 (1978-Danish Peerless), Monitor 5JR (1988), Model 4 (1983-US Peerless), PSW202 (NIB), etc

  2. #2

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    All right, so now that I've looked into this a little more I want to build a new baffle for this thing, and find a reasonably suitable (preferably vintage) actual guitar amp speaker and apply amp grill cloth for closer to the original appearance.
    Main HT: Polk Monitor 7 (1987-original owner) (L/R) / CSi40 (C) / RTi38 (SL/SR) / SVS 20-39PC (sub), Outlaw 975 pre/pro / Outlaw 7075 amp, Oppo BDP-93 Blu-ray, LG 42LM5800 teevee
    2ch: CRS+ (1987), Outlaw 1050 AVR, Denon DCM-420 CD
    Kitchen satellite 2ch: Polk M3II, Onkyo A-8037 integrated amp fed from Oppo, Yamaha TX-480 tuner
    Awaiting assignment: Model 5 (1978-Danish Peerless), Monitor 5JR (1988), Model 4 (1983-US Peerless), PSW202 (NIB), etc

  3. #3

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    Nice little project MM, a good one to practice modding techniques. Gotta think that car stereo speaker ain't long for this world once you start playing an electric guitar through it.

    That soldering iron is a classic wooden handle and cloth insulation!
    "Science is suppose to explain observations not dismiss them as impossible" - Norm on AA; 2.3TL's w/sonicaps/mills, polyswitches removed, Lg Solen inductors, RD-0198's, MW's dynamatted, Armaflex speaker gaskets, H-nuts, brass spikes, Cardas CCGR BP's, upgraded IC Cable, Black Hole Damping Sheet strips installed on back wall behind MW's & Tweeters, interior of cabinets sealed, AI-1 interface with 1000VA A-L transformer

  4. #4

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    Quote Originally Posted by drumminman View Post
    Nice little project MM, a good one to practice modding techniques. Gotta think that car stereo speaker ain't long for this world once you start playing an electric guitar through it.
    FWIW it didn't blow up when I tested it, including with the volume all the way up (it isn't exactly concert-level sound). But I'm already tired of how it looks and the grill frame workaround. I'm not going to try to be all purist about restoring this but now that I've read up on vintage Teisco amps, I have a soft spot in my heart for them - I do want to get this one a little closer to its original state rather than having it be an all-out Frankenamp. Also:

    - if I'm reading my multimeter correctly the original speaker was 8 ohms and the car speaker is 4 so there's that

    - and if I'm reading the label on the original speaker and this Google hit correctly, it is the Oxford 8ES-9 Alnico magnet (the 8 would suggest 8 ohm nominal impedance) and was manufactured in July 1965. So now I'm researching suitable and not overly expensive replacements.

    That soldering iron is a classic wooden handle and cloth insulation!
    Yeah, my dad left me a lot of great stuff, not all of which I may be brave enough to plug in :-)

    I'm also learning about work processes. Some of what I initially did was admittedly a little rushed as I tried to do as many different things as possible in the available time this weekend. I'd certainly slow it down and take much more of a perfectionist approach, quadruple-checking everything, when working on my Polks.
    Main HT: Polk Monitor 7 (1987-original owner) (L/R) / CSi40 (C) / RTi38 (SL/SR) / SVS 20-39PC (sub), Outlaw 975 pre/pro / Outlaw 7075 amp, Oppo BDP-93 Blu-ray, LG 42LM5800 teevee
    2ch: CRS+ (1987), Outlaw 1050 AVR, Denon DCM-420 CD
    Kitchen satellite 2ch: Polk M3II, Onkyo A-8037 integrated amp fed from Oppo, Yamaha TX-480 tuner
    Awaiting assignment: Model 5 (1978-Danish Peerless), Monitor 5JR (1988), Model 4 (1983-US Peerless), PSW202 (NIB), etc

  5. #5

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    It's fun resurrecting something and getting it working again. Must be part of the reason I love doing speaker mods. You may be already aware of them, but Part Express usually has a wide ranging inventory for this type of thing.
    "Science is suppose to explain observations not dismiss them as impossible" - Norm on AA; 2.3TL's w/sonicaps/mills, polyswitches removed, Lg Solen inductors, RD-0198's, MW's dynamatted, Armaflex speaker gaskets, H-nuts, brass spikes, Cardas CCGR BP's, upgraded IC Cable, Black Hole Damping Sheet strips installed on back wall behind MW's & Tweeters, interior of cabinets sealed, AI-1 interface with 1000VA A-L transformer

  6. #6

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    Yup, I'm already a PE customer. And I see they supposedly can recone that old alnico magnet speaker for the amp, for $65 ... keeping an eye out on ebay for other alternatives, but restoring the original speaker has its appeal.

    From what I've read, the first solid state instrument amps only started being mass-produced in 1962 so this is a pretty early example of the breed.
    Main HT: Polk Monitor 7 (1987-original owner) (L/R) / CSi40 (C) / RTi38 (SL/SR) / SVS 20-39PC (sub), Outlaw 975 pre/pro / Outlaw 7075 amp, Oppo BDP-93 Blu-ray, LG 42LM5800 teevee
    2ch: CRS+ (1987), Outlaw 1050 AVR, Denon DCM-420 CD
    Kitchen satellite 2ch: Polk M3II, Onkyo A-8037 integrated amp fed from Oppo, Yamaha TX-480 tuner
    Awaiting assignment: Model 5 (1978-Danish Peerless), Monitor 5JR (1988), Model 4 (1983-US Peerless), PSW202 (NIB), etc

  7. #7

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    Nice job w/ the Dynamat. What's not widely known is that Dynamat is used primarily by car audio installers and guys like us modding different electronics. When I picked up my pieces (for free) the car guys said they do trunks and inside doors to deaden any resonance. This we know but I thought it was used through out the car restoration industry and it is not.
    2chl- Adcom 555- NAD 1020a pre- JVC-QL-A200 tt- Denon 1940 ci cdp- Samson - 9 outlet- Niles - 6 zone spkr selector- DCM TF 350s- ADC 303ax- KLH 331- Polk Audio '87 SDA 2Bs w/ ic cable (Dynamat extreme, black hole-5- Mills 0.5 resistor, liquid nails, RDO- 194 tweeters, Larry's rings, Armaflex gaskets, stained walnut tops )

    H/T- Toshiba au40" flat- Yamaha RX- V665 avr- YSD-11 Dock- I-Pod- Klipsch #500HD Speaker set- Sony ce 375 5 disc carosel cdp-

    Nikko 6065 receiver- JBL J2060

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