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Old 21st Nov 2020, 5:31 pm   #1
MurphyNut
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Default Faulty Celestion speaker, is it repairable?

I have a Celestion speaker (pictured) that has developed a fault. It actually comes from a Bush record player but I've encountered this same speaker in Bush radios of similar age.
It intermittently buzzes badly with anything with some bass. On removal it looks perfect, the spider has not become detached, the cone is perfect and moves freely. I then discovered if I tap the magnet I can feel something vibrating inside.
There's a screw on the back of the magnet, I thought at first this might just be lose but it's absolutely solid and trying to loosen or tighten it just starts to bur up the head.
Is the speaker a "write off" or is there a way to fix it that I haven't yet discovered?
A shame to bin it!
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Old 21st Nov 2020, 7:09 pm   #2
Leon Crampin
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Default Re: Faulty Celestion speaker, is it reparable?

Clive, a standard fault with Celestion 'speakers of this vintage is a failure of the glued joint at the corrugated centreing device on the outside of the cone, near the magnet, where it joins the frame.

My fix is to apply dc, such that the cone moves outwards, opening the broken joint. Apply PVA glue with a cocktail stick, remove the power and check that the cone is centred by applying light, evenly distributed pressure. Then reverse the dc power supply to preload the joint whilst the glue sets.

If the cone is not centred, it can be shifted very slightly by using small croc clips to hold the glued joint closed, after applying some radial pressure to centre the cone. Check your results with the croc clips in position, but (obviously) before the glue sets.

Never shift the screw on the back of the magnet. This holds the pole piece which, if loosened will shift radially to the opposite pole, trapping the voice coil. You can't easily put it back...

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Old 21st Nov 2020, 8:22 pm   #3
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Default Re: Faulty Celestion speaker, is it reparable?

Thanks for your reply Leon, perhaps I wasn't clear, but this aspect of the speaker is in fact fine, the "corrugated centreing," I referred to this as the "Spider" is firmly attached to the frame. I know exactly what you mean as I've fixed a few of these on Dac 90a sets in this respect.
The problem I'm encountering is something else, a vibration when I tap the magnet, this a strange one! Speakers aren't particularly complicated but I really cant workout what is causing this noise.
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Old 21st Nov 2020, 8:32 pm   #4
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Default Re: Faulty Celestion speaker, is it repairable?

Possibly the voice coil has come partly 'unglued' from the cone or even possibly a couple of turns of the coil have become loose and are catching between the gap of the magnet and the pole-piece. Up to you how you try to tackle it but it could be an awkward one.
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Old 21st Nov 2020, 10:55 pm   #5
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Default Re: Faulty Celestion speaker, is it repairable?

Hi Clive, I've got a 6in x 4in Celestion but yours looks bigger - worth asking though in case mine would fit? Jerry
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Old 22nd Nov 2020, 8:39 am   #6
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Default Re: Faulty Celestion speaker, is it repairable?

Quote:
Originally Posted by cathoderay57 View Post
Hi Clive, I've got a 6in x 4in Celestion but yours looks bigger - worth asking though in case mine would fit? Jerry
Thank you very much Jerry, but I found a replacement from a Bush VHF90a I have for spares. Interestingly that speaker is a 6in x 4in Celestion but has a larger magnet but still fits perfectly. So I'm enjoying the record player without the buzzing.
I'm going to connect the faulty speaker up to extension speaker socket of a radio and perhaps see what's going on with it outside of a cabinet.
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Old 22nd Nov 2020, 11:35 am   #7
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Default Re: Faulty Celestion speaker, is it repairable?

If, as you say, you can hear a rattle when tapping the magnet, the loose object inside the magnet enclosure will not be ferrous material, as the magnet would hold it fast. It just might be a small blob of hardened ancient glue from the production process which has got in there and was not spotted before te speaker was assembled at the factory. This may be moving about, and occasionally coming into contact with the bottom end of the voice coil, thus causing the effect you are observing.
Just a thought. Tony.
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Old 22nd Nov 2020, 7:24 pm   #8
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Default Re: Faulty Celestion speaker, is it repairable?

Tony, I think that must be it, the speaker is almost unusable, I connected it up and it sounds horrible. I'm contemplating taking it apart just to satisfy my curiosity, I haven't got anything to lose!
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Old 23rd Nov 2020, 11:27 am   #9
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Default Re: Faulty Celestion speaker, is it repairable?

Clive - You could try operating the speaker using a continuous low frequency tone ( ? 30- 40 Hz ) moving it at various angles to see if gravity had any effect on the resulting sound quality.
This may help to prove or disprove my theory without dismantling first. Tony.
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Old 23rd Nov 2020, 11:40 am   #10
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Default Re: Faulty Celestion speaker, is it repairable?

If only to serve as an experiment, if you're going to cut it up, try to do it in a such way that afterwards it may be possible to glue the cone back together again using existing speaker cone repair techniques. You may be able to remove the offending foreign body and fix the speaker afterwards.
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Old 23rd Nov 2020, 11:43 am   #11
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Default Re: Faulty Celestion speaker, is it repairable?

Steve's advice is good.

I would be tempted to start by removing the front dustcap (with a scalpel) just in case the foreign body is under there.
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Old 11th Jan 2021, 1:25 pm   #12
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Default Re: Faulty Celestion speaker, is it repairable?

I've spent a bit of time on the speaker and sorted out the problem.
With the unit out of a cabinet I connected it to a external speaker socket from a well preforming set and tuned into a strong station with plenty of bass (an Asian one on MW.)
I reduced the treble and gave the speaker plenty of volume to get the diaphragm really moving.
With good light I was able to examine and listen to it properly and I spotted the problem pretty fast. On the underside of the cone were the wires come from and connect to the voice coil I could see one of them bent down and coming into contact with the cone when there was any bass. I simply bent the wire away from the cone and the buzzing ceased. The speaker now performs perfectly, rather pleased.
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