Speaker type 9758-05 (Algemeen)
door Pandu Rajan 
, 04.07.2025, 14:27 (4 dagen geleden)
Dear forum members
The above speaker was used in the radio set BX735A/BX745A. The above speaker was procured new a few years back and was unused. recently I thought of using it and found that the coil centering is not OK.I took the following steps to solve the problem.
1. I am uploading few photos of the same in dismantled condition.
2. Before dismantling I applied super glue to the portions shown in the sketch which I have uploaded so that there is no chance of magnet and the pole pieces getting dislodged from its original position.
3. The three nuts were removed and the magnet system was removed carefully from the frame.
4. Cleaned the air gap thoroughly and reassembled the magnet to the frame. But inspite of the best efforts I am not able to center the coil properly.
5. Earlier also I have done this on many 10" and 8.5" speakers and did not face any problem and with slight adjustments I was able to center the coil properly.
6. But with this speaker it has not been possible to do so.
7. I have noticed in all the speakers the position of the coil under normal conditions is such that the top turn of the coil nearly matches the top surface of the magnet system as shown in the sketch.
8. On further checking I noticed that the the cone + coil + spider assembly has gone down 3 to 4mm into the magnet airgap and may be this could be the reason I am unable to center the coil. I presume that the spider due to age has shrunk inside thereby pulling the cone and the coil.
9. I shall request the experts to kindly advise as to how I can change the spider without causing damage to the cone and the coil.
Beat Regards
P.Rajan
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![[image]](images/uploaded/202507041225216867c831dc31a.jpg)
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Speaker type 9758-05
door Maurice 
, Dordrecht, 04.07.2025, 17:29 (4 dagen geleden) @ Pandu Rajan
I see the coil as well out off center.
That coil has probably been centred using the already off-set of center magnet system.
Now you have centred the center, you have also to center the coil again.
But paper-cone its all glued I think.
or take whole system apart and when your magnet center is O.K.
Follow procedure to re-cone the speaker.
There is a manual at hand.
Be careful to take magnet system apart, mostly it loses its strength and it is not advised
to take it apart.
Though whole magnet from cone structure is OK.
--
"I haven't even turned this on to see if it works because as long as I don't it might"
Speaker type 9758-05
door Pandu Rajan , 06.07.2025, 14:27 (2 dagen geleden) @ Maurice
Dear Mr Maurice.
Thanks your reply. Is it possible to get the copy of the manual? I knew that if the magnet is removed from the system immediately the magnet gets discharged. So when ever I work on such speakers before I dismantle the magnet system from the frame I will put super glue to the magnet and top pole and the magnet and bottom pole piece so that there is no chance of the magnet and the pole piece getting shifted from the original position.
I think I will have to remove the top metal ring to remove the cone with coil and spider. Generally in most of these type of speakers the cone is not glued to the frame but kept in position by two paper rings both at the top and bottom of the cone and then the metal ring is fixed.
How should I remove the spider? Which is the best liquid which can dissolve the adhesive between the spider and the cone so that the old spider could be removed without causing damage to the cone and then I can fix a new spider in position.
Your advise will be very helpful.
Regards
P.rajan