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Recommendations on MG 15 Rebuild

Discussion in 'classic' started by louisjames, Sep 9, 2017.

  1. louisjames

    louisjames Member

    A while back I posted about an issue with my GRF's and that one speaker was lower in volume (87dB on a SPL meter versus 92dB for the other) than that other and also sounded muffled. After having the crossovers, switches, wiring, terminals and speaker plugs checked out it was determined that the driver is the issue and most probably the tweeter. I have found a service center who will do the job but they have said while there is a tweeter available, it is a modern unit and will probably sound different from the original, and certainly different from the other speaker that is not broken. I have sent a note to Lockwood Audio to see if they have an original replacement, but if not, would like recommendations on how best to move forward:

    1) change just the one tweeter and try and adjust for any difference

    2) change the tweeter in both units so they sound similar to each other

    3) have both the tweeter and woofer changed out / refurbished in both speakers so I'm starting fresh -- even though this will probably alter the overall sound I'm used to (any ideas how different this would be?)

    4) try and find an original tweeter unit -- if this is even possible?

    Since the one speaker definitely needs repair I will have to go with one of the routes above but before doing anything would love to get input from the forum as you folks have been so helpful and have much more experience with the older Tannoy's than anyone I've spoken here in the US.

    Thanks so much
    lj
     
  2. Tony L

    Tony L Administrator

    Change both. The current replacement just has a plastic and is in one piece rather than the metal back two piece construction of the original. It was introduced with the HPD and is backwards compatible with the Gold and Red, and possibly Silver. The negative is it is a little easier/harder to align depending on ones perspective as it is more 'plug and play' so if at the end they still sound a bit different (and being Tannoys they will!) there is less you can do to nudge them in. The other negative is the plastic back is rather thicker so the gold plastic magnet covers don't fit as well. In reality it is your only option as the chances of finding a pair of NOS original metal back ones are somewhere around zero. You will unquestionably improve them substantially, but don't be too surprised if they are still a couple of db of each other. It is just what they do, and I suspect why they have level and roll-off controls! I've owned three very clean, tidy and non-abused pairs of 15" Golds so far, much nicer looking pairs than 95% of what goes through eBay, and none were matched the way one would expect a modern pair of speakers to be.

    Here's a couple of pictures to show what the originals look like:

    [​IMG]

    Front.

    [​IMG]

    Back with metal/felt rear cover removed but in shot. The new ones are plastic and glued on.

    PS If you decide to do this yourself be *very* careful as it would be so easy to damage the fragile compression driver. To be honest I'd either do it yourself if you are very good with fragile mechanical things (I am) or send it to a proper Tannoy specialist e.g. Lockwood. Be really careful getting the good working one out as it will have a eBay second hand value that may pay a fair bit of the replacements cost!
     
  3. louisjames

    louisjames Member

    Thank you Tony. Tannoy had suggested "The Speaker Exchange" in Florida, but as that's cross country for me, and they seemed a big vague when I spoke to them, I opted to go with the head tech from Orange County Speaker who opened his own shop after OC closed down. He has experience with MG's so I'm going to have him do the job. Agree that having it done right is the utmost importance and if it comes down to it I'll send it overseas to a specialist like Lockwood or back to Tannoy, who said they could do the job as well. And yes, there always was a slight difference between the two speakers even when new, but not like it is now. Thank you again for your help. Right now I'm using a pair of IMF 50s and while they are pretty nice, have the "British" sound I like and very good bass for their size, I'm missing my old friends. On an somewhat related note - - it turns out that some Tannoy with MG's used the earlier metal crossover cases (as I posted in the other thread) that were used with the Red's instead of the more typical plastic case.
     
  4. Tony L

    Tony L Administrator

    I didn't realise you were in the USA, it sounds like you have it in hand. I'd stress to whoever does it that you want the still good compression driver removed intact and returned to you, my guess is you could easy get $150+ for it. There is of course a chance both are still good and the issue is one of alignment or a particularly dirty magnet gap. When they fail they tend to fail completely due to the fragile alloy wires breaking. They certainly drift in alignment with time.
     
  5. louisjames

    louisjames Member

    If it comes down to it I'd rather take the expense and risk of shipping it to Lockwood. The fellow who was at Orange County seems very confident but you never know. I'll certainly call out all of the points you mentioned in addition to having the good driver removed carefully and returned to me. One thing I did notice is the woofer paper is a lot lighter / washed out looking on the "bad" speaker and the cabinet insulation is also somewhat "corroded" (chunks falling off) in comparison to the good speaker which is still very dark in color and the insulation is still fully intact. I wonder if it was subjected to heat / excessive light at some point which might have caused some issues. I'll let you know how things progress.
     
  6. Tony L

    Tony L Administrator

    Golds fade badly in daylight, even through grilles, so most pairs have substantial fading, and one is often lighter than the other due to room position The back of the driver reflects the original colour, a very dark charcoal! If there is actual damage to the cones or the surrounds have dried out too much they can be reconed.

    Not quite sure what you mean by 'cabinet insulation', though any corrosion on the drivers should ring alarm bells for sure. Damp is not good for any speaker.
     
  7. louisjames

    louisjames Member

    Drivers are in good shape. Back of both gold speaker covers are excellent. By insulation, I mean the padding in the top section of the cabinet where the speaker is mounted. It's a fairly thick material somewhat like what memory foam looks like.
     
  8. Tony L

    Tony L Administrator

    Ah, that's no issue and can be replaced with modern acoustic foam or whatever. Just make sure both cabs are the same. There are many here who know a lot more about cabinets than me and who should be able to advise what stuff to buy.
     
  9. louisjames

    louisjames Member

    That's what I figured but thought I would mention. I'm actually thinking of having a pal build a better pair of GRF cabinets at some point as mine have taken some hits over the years. But that's a project for another time. Thanks again!
     
  10. cooky1257

    cooky1257 pfm Member

    The correct Tannoy part number is 7900 0205. I'd definitely get both done. An exOC tech is more than up to the job!
     
  11. louisjames

    louisjames Member

    thank you cooky - that's both helpful and reassuring. I've had many guitar amp speakers repaired by OC back in the day when I was gigging and they always did a fine job. Many folks were upset when they closed shop, but it was heartening to learn their head guy for the past 15 years opened up his own. if I were in the UK Lockwood would be the first choice but given that I'm just hours away from the new shop (http://www.speakerrepairpros.com/) it seems like a good choice, and without the risk of shipping either cross country or across the ocean. :)
     
  12. louisjames

    louisjames Member

    cooky - do you know what the difference is between part number 7900 0205 and 7900 0105? The latter was given to me by Tannoy but I can't determine what, if anything, is the difference between the two. I did note that on one site the "0205" is rated at 16 ohms. My GRF's are labeled at 8 ohms, but is that because both the tweeter and woofer are rated at 16 ohms and wired in parallel?
     
  13. cooky1257

    cooky1257 pfm Member

    It isn't an impedance issue more of a mechanical/physical difference.

    The 105 is for the K series and later drivers, they don't 'need' the paper washers for fine tuning.
    [​IMG]
    205;
    [​IMG]
     
  14. louisjames

    louisjames Member

    Thank you. Now it makes sense why the Tannoy rep was referring to the "black backs" on the tweeter. :)
     
  15. louisjames

    louisjames Member

    Note from The Speaker Exchange for reference:

    Both diaphragms can be used for the Monitor Gold 15” speaker. The 7900 0205 is the diaphragm used for speakers produced pre 1979 and costs $225.00. We have them in stock. http://reconingspeakers.com/product/tannoy-diaphragm-7900-0205-hpd295-hpd315-hpd385/
    7900 0105 has an integral card shim (which alters the spacing and interface) and is harder to center because it has a larger aluminum ring than the 0205. It is used for those speakers produced from 79-90. We also have that in stock, $255.00 http://reconingspeakers.com/product/tannoy-diaphragm-7900-0105/
    You can use either one but there will be some performance changes if you substitute one for the other.
     
  16. cooky1257

    cooky1257 pfm Member

    No. I think someone is getting their part numbers/descriptions confused.
    The 7900 0205/monitor gold diaphragm is the one with the integral card shim.
     
  17. Tony L

    Tony L Administrator

    In their on-site description they agree, the one with the card shim is listed as Gold, Red etc compatible, whereas the other isn't.
     
  18. cooky1257

    cooky1257 pfm Member

    Indeed, if they are going to offer a quote for reference you'd think they'd get them the right way round.
    IIRC didn't you have a nightmare trying to fit some replacement dias a while ago ?
     
  19. Tony L

    Tony L Administrator

    I went down this route with my very first pair. It was before I had measurement ability but one was maybe 4db down on the other around 4-8kHz so the image wouldn't centre properly. I tried everything including replacing both compression drivers, but ended up putting the originals back as they were impossible to centre properly. I've gone through three near-mint looking pairs of Golds now and come to the conclusion the pair matching is just shite. A fantastic speaker design, one if the best ever, but built by British Leyland. My current pair are the best I've had, but even so I'm currently running one with a click back on the roll-off and just a nudge of amp balance control back up to compensate for the loss, this gets them within 2db right through the mid and treble and I can live with this. The Decca ribbons help a bit too.

    PS It needs to be pointed out I am just unbelievably picky here, I'm a total hot-seat image freak and OCD about system setup to the extent it is almost an illness - the things that bug the living crap out of me most so called audiophiles wouldn't even hear! This is exasperated to some degree by the fact that my ears are not longer perfect and I do have a slight notch on the right side, so in some respects I can actually benefit from very slightly mismatched speakers!
     
  20. mjkelshaw

    mjkelshaw pfm Member

    I think that is unfair - if Leyland had been allowed to ditch 90% of the British Motor Corporations 'duplicate' models I think that the company could have survived. Leyland Standard Triumph made some excellent products some of which are still well regarded today.
    A fairer comparison would I think be Triumph Motorcycles, not bad products but certainly spoilt by inconsistent assembly and benighted by poor management. Similarly to this now 'disunited kingdom'.

    Regards

    Mike Kelshaw
     

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