I have a 40-150 slant back and the speaker VC is rubbing. I tried to align, blow it out, clean it...it sounds like one of the wires in there are lose and just scraping. Sounds terrible. As a test, i lifted one of the VC wires from the speaker and connected a 4 ohm smaller fixed magnet speaker to it. It actually sounds amazing..so much better. Was wondering what i would need to do to make this permanent. The original speaker has 36-1483-3 printed on the rear mounted transformer...
So my questions are...
1-Is this a bad idea...i know it is not original but since it improved the sound so much it would be nice
2-The current voice coil measures 4.3 ohms. I assume i can use something in the 4 to 6 range...I have a perfect sized speaker that is 2.3 ohms...would that be too low.
3-I know the speaker has the transformer on the back end of it. I assume that needs to be kept in place. Can i simply leave that speaker, say, screwed to the inside of the cabinet somewhere and lift the 2 VC wires and take that to the new permanent magnet speaker...?
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Thanks for any advice. This radio has had all the caps and bad wiring replaced so this is the last thing to make it sing.
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Hi Peter,
First off, it appears that the transformer is not on the back of the speaker. What you see there is the "field coil". This is the device that provides the magnetic field.
The speaker appears to be in rather good shape. You could attempt to "recenter" the voice coil. There may be a procedure in this Phorum to do this. It usually involves ungluing the speaker cone, which may be tricky. Try this alternative procedure :
Removing any felt cover over the magnet pole and voice coil on the cone.
Loosening the 4 screws that hold the field coil and magnet piece to the speaker frame and the 2 screws that hold the "spider" to the field coil.
Place speaker on table or gently into a vice with cone side up (This will allow clearance to tighten hardware after centering.
Place shims between voice coil and field coil pole. Lift frame and lower several times.
without moving anything (and this is the tricky part) tighten all screws.
If you already tried this and failed, then remove the field coil frame by removing all 6 screws and lifting off. This way, you can inspect the voice coil.
The Phorum experts may know someone who can recone the speaker at a reasonable price.
Speakers are rated in impedance, not resistance, so the resistance reading on a DVM may not be the true impedance.
One could install a PM Speaker in the correct location, remove the field coil frame from the speaker frame, remove the connector, cut the 2 wires going to the voice coil, connect those wires to the new speaker and hide the field coil. No modification needs to be done to the radio, however, this is destructive to this original speaker. save the parts in case you later decide to get this one repaired.If the rest of the radio is in great shape, consider getting this one repaired.
Hope this helps!
Thank you for the very informative reply. I will try the recentering you mentioned. (loosening the screws and see what happens. I have reconned speakers in the past (perm. magnet), even had to recenter the magnets. the odd thing is that when a VC is offset i can usually apply slight pressure to the cone and find a direction where it moves freely..then shift accordingly. On this one I cant see to find a direction that does not scratch.
If i cant get it will do as you said and definately save all the parts
I am about to re-cone (in a couple of weeks) a 6" PM speaker of near identical design of spider...
The spider is a bit unusual as it is also paper and similar construction in that there is a steel frame that is adjustable. That spider has fallen apart into crumbs.
BTW, your F.C. speaker also has a hum bucking coil.. A PM speaker does not have this so if you have not noticed hum it maybe O.K. Mounted in the baffle the hum may become more noticeable. Increasing the condenser MF after the choke will be beneficial in lowering the residual hum.
I would suggest re-cone that speaker as it is fully adjustable, even the field coil can be removed for repairs...
It is a learned skill but beware of shortcuts...
GL
Chas
Thanks...i took a closer look at it and i see the root issue (i think)... the spider is completely separated from the cone/VC. I can see space all around it. The scraping i am hearing, i think is the paper spider rubbing on the voice coil or cone since it is not flexing with it. Any suggestions on what to do about that?
Quote:I can see space all around it. The scraping i am hearing, i think is the paper spider rubbing on the voice coil or cone since it is not flexing with it. Any suggestions on what to do about that?
That spider is not made any more...
Use a molded cloth mesh spider cut off the flange as close a circle as possible, center and glue to both the metal ring and the voice coil assembly. May have to extract the entire cone to do it correctly.. Unless someone has added more modern stickum goop, the OEM cement is collodion, easily softened to the point of release with acetone also Ether, but you don't want to fall asleep on the job... I have to re-cone a similar speaker. So I will have to make a jig to assemble the voice coil/spider on correct axis, pre-coat with G-C cement and left to dry, then assemble, shim into place and clip the surround. Then apply either acetone or Toluene to the joints. The solvent for the G-C cement is Toluene but acetone kinda works. The G-C cement will grab and in 30 minutes bond. In about hour it is done, pull shim, add dust cover and "Rock & Roll" You can touch up with more G-C cement, use a plastic disposable eye dropper, the kind with a long, thin snout. The snout can be pulled with pliers and made even thinner/smaller, gets a bead of the G-C just where it needs to go : )
See:
https://www.ebay.com/usr/speakerguy2002 gives O.K measurements but the inventory cannot be searched by size, very exactly.
Fast service got my parts in 4 days... Regular mail...
Might as well get a cone too, yes, real paper surrounds, watch for the depth and the cone size. But, you know all that
Fresh paper cone is surprisingly tough, worth it... Get a cone with leads, helps, doing ones own lead wires can be messy. For the black goop on V.C. leads use G-C liquid tape, works great too...
You will be forced to buy two, so a spare if one gets hosed...
Chas
wow that ebay seller is a great resource..thanks for that. its nice the the speaker comes apart with just some screws. Will research some more and see what i need. Thanks again.