Celestion vintage speaker repair - Advice needed.

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HoofHoof Frets: 491
Hi, I've been considering selling my 70s Orange 4x12 cab so thought I'd give it a test, open it up and inspect etc. Whilst play testing it I noticed that one speaker had a raspy quality to it. No other differences, sonically speaking but there was a definite raspy overtone. 

I took the speaker out and discovered that the centre dustcap had partially detatched and it seems to be the cause.

What glue do I need to repair this? The speakers are Celestion G12H 30w 75hz Blackbacks from 1975 so I'd rather not just try any old stuff and bugger them up.
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Comments

  • Bygone_TonesBygone_Tones Frets: 1527
    I normally use evostick.  It is best to remove the whole thing and reglue it back on rather than trying to fill the gap. It will look a mess if you try to do that.

    To glue it back on just add a thin bead of glue all around the lip. Then get a piece of masking tape and roll it sticky side outwards. Stick it to the outside center of the dustcap and use it as a 'handle' whilst you lower the cap back into place.

    Then once it is in place I normally place a cardboard tube from a toilet roll on top of it, and a small piece of wood over the top of that, just to apply a bit of pressure on it whilst the glue sets.
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  • HoofHoof Frets: 491
  • Bygone_TonesBygone_Tones Frets: 1527
    contact adhesive, but dont use it like it says on the instructions. just apply it wet to one surface (the dustcap) put it in place and let it set over time. I usually allow 48hrs.

    either the red stuff or the blue (timebond). timebond is probably better as it sets slower.
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  • Stuff i got from speaker repair company looks like PVA.
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  • HoofHoof Frets: 491
    edited April 2017
    An update: I glued the cap back on and was generally pretty pleased with the job until I remounted it in the cab and play-tested it and found that it sounded far weaker than any of the other drivers. 

    I tested it with a multimeter, no problems there. The resistance matched the other speakers. Then I tested it by putting a battery across the points. It worked but was clicky rather than the nice thuddy sound from the others. I took it out of the cab and manipulated the cone and while it moved quite freely it was rubbing on the coil and sounded as if some debris had gotten into the gap. The spider had also detached from the chassis at a few points. Not good, and I feared that this might be fit for the bin or at least have to be reconed which was not a pleasant option as this has the 1777 cones (Pulsonic?) and I was keen to keep this nice old cab fully original.

    I found a local guy: http://www.amp-repairs-leicester.com/ who was keen to have a look at it and after an hour on his work bench it's as good as new! The fault was caused by corrosion of the pole which had begun to rub against the voice coil former. After some careful attention with fine sandpaper, shims, glue, airlines and sine wave testing the old Blackback lives again!
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  • John_AJohn_A Frets: 3775
    edited April 2017
    He's just down the road from me. Added to the useful addresses list
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  • Hoof said:
    An update: I glued the cap back on and was generally pretty pleased with the job until I remounted it in the cab and play-tested it and found that it sounded far weaker than any of the other drivers. 

    I tested it with a multimeter, no problems there. The resistance matched the other speakers. Then I tested it by putting a battery across the points. It worked but was clicky rather than the nice thuddy sound from the others. I took it out of the cab and manipulated the cone and while it moved quite freely it was rubbing on the coil and sounded as if some debris had gotten into the gap. The spider had also detached from the chassis at a few points. Not good, and I feared that this might be fit for the bin or at least have to be reconed which was not a pleasant option as this has the 1777 cones (Pulsonic?) and I was keen to keep this nice old cab fully original.

    I found a local guy: http://www.amp-repairs-leicester.com/ who was keen to have a look at it and after an hour on his work bench it's as good as new! The fault was caused by corrosion of the pole which had begun to rub against the voice coil former. After some careful attention with fine sandpaper, shims, glue, airlines and sine wave testing the old Blackback lives again!

    That's brilliant! 
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  • clarkefanclarkefan Frets: 808
    Hoof said:
    After some careful attention with fine sandpaper, shims, glue, airlines and sine wave testing the old Blackback lives again!
    Airlines?

    Congrats, and yes I'm noting down the guy too, thank you :)
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  • CarpeDiemCarpeDiem Frets: 275
    Great result - I'm pleased you got it fixed.
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  • HoofHoof Frets: 491
    clarkefan said:
    Hoof said:
    After some careful attention with fine sandpaper, shims, glue, airlines and sine wave testing the old Blackback lives again!
    Airlines?

    Congrats, and yes I'm noting down the guy too, thank you :)
    Yeah, well after you've rubbed down the corrosion or any other causes of rubbing/foreighn objects, you get dust inside the magnet which will cause further problems. So the only hope you have of getting it out without removing the cone is the blow it out with a high pressure airline. Another technique he used was varying the sine wave frequency all the way across the speaker's range while holding it face down. You could literally hear the voice coil cleaning out as the rattle/rasp turns into a nice smooth tone.

    It was pretty interesting to watch him work.

    His next job is to cure my JCM 900 SL-X of it's gremlins.
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  • clarkefanclarkefan Frets: 808
    Thanks, congrats and good luck :)
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  • Bygone_TonesBygone_Tones Frets: 1527
    Hoof said:
    An update: I glued the cap back on and was generally pretty pleased with the job until I remounted it in the cab and play-tested it and found that it sounded far weaker than any of the other drivers. 

    I tested it with a multimeter, no problems there. The resistance matched the other speakers. Then I tested it by putting a battery across the points. It worked but was clicky rather than the nice thuddy sound from the others. I took it out of the cab and manipulated the cone and while it moved quite freely it was rubbing on the coil and sounded as if some debris had gotten into the gap. The spider had also detached from the chassis at a few points. Not good, and I feared that this might be fit for the bin or at least have to be reconed which was not a pleasant option as this has the 1777 cones (Pulsonic?) and I was keen to keep this nice old cab fully original.

    I found a local guy: http://www.amp-repairs-leicester.com/ who was keen to have a look at it and after an hour on his work bench it's as good as new! The fault was caused by corrosion of the pole which had begun to rub against the voice coil former. After some careful attention with fine sandpaper, shims, glue, airlines and sine wave testing the old Blackback lives again!

    Sounds like he knows what he is doing. Out of interest how did he remove the cap after you had already glued it back on? evostick is strong stuff, or did you use a different glue?

    Not sure if those cones are pulsonic without seeing pics. If they are from early 75 and have the larger 'ribs' on the cone then they could be some of the last pulsonics yes. But if they are late 75, they are more likely to be Kurt Muellers.

    I'd be checking the other 3 speakers in that quad too. If one has a spider coming loose then there is a good chance the others have that same problem too, definitely worth checking.
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  • HoofHoof Frets: 491
    I managed to get the dust cover back off before the glue had fully cured. It was still quite rubbery at that point so just very gently peeling it up whilst running a razor blade very carefully in the gap to help it separate.

    The date code on the speakers is 16th September 1975 so possibly a bit late for Pulsonics then. 

    There's no audible rub in the other 3 but yes, I will be checking these.
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  • Bygone_TonesBygone_Tones Frets: 1527
    If you upload some photos showing date stamp, cone code, and front of the cone, I can tell you exactly what you have. You can PM me if you dont want to upload them here. 1777 cones in Sept 75 is a bit unusual, the first mueller cones tend to be blank or handwritten but stranger things have happened. There was a guy selling some late 75 speakers with '3' cones (usually found in 73) on ebay a couple of years ago.
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