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 Post subject: Speaker cone & voice coil replacement
PostPosted: Jan Thu 13, 2011 12:28 am 
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Location: Dawson Creek BC, Canada
Does anyone know where i can get a replacement cone and voice coil for the speaker in my RCA R-7.The company i usually buy speaker parts from said that they can't get parts for something from 1931.I would prefere repairing and using the original speaker over a modern one as the feild coil is good and i do not want to have to replace it with a resistor or choke.I would also like to repair the speaker myself rather than having someone else do it as you can only learn by doing.

Nick

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 Post subject:
PostPosted: Jan Sat 15, 2011 12:11 am 
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Location: Powell River BC Canada
What is wrong with the cone/coil .
Could you get enough measurements
to make a new one?

A tinsmith knows exactly how to make
a funnel of any shape,likely in 2 steps.
If you can glue, and used his technique
you could make a new one.

How cool would it be to recone speakers,
and even make your own .

Image

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 Post subject:
PostPosted: Jan Sat 15, 2011 7:58 am 
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The cone is ripped into about 10 peices but if i glue it back together really carfully i would have a complete cone.It just wouldn't sound good.When the cone was shredded the voice coil was jammed into the magnet which has caused it to partially un-wind but the coil form itself is not damaged.I imagin that if push came to shove i could re-wind the voice coil.I just need to find the correct wire.

Nick

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 Post subject:
PostPosted: Jan Mon 17, 2011 3:32 pm 
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Location: Powell River BC Canada
If magnet wire of a small size is a problem, let me know. I
bought up all the stock and the coil winding machinery when
the mill I worked for decided to not continue winding. I could send
a few feet of the guage, if I have it easily in a letter envelope.

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 Post subject:
PostPosted: Jan Mon 17, 2011 7:28 pm 
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Can i cut about 1 foot of wire out of the voice coil or will that affect it's resistance too much?It is right at the beginning where the old lead wires soldered on.If i can cut it off without affecting perfomance i can reuse the old voice coil.
Also,what can i use to glue the wire down so that it dose not un-wind again?I had been thinking about using super glue but i don't know if that will damage the enamel on the wire or not.

Nick

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 Post subject:
PostPosted: Jan Tue 18, 2011 4:34 am 
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Location: Powell River BC Canada
No, absolutely not. When you do this, you need carefull data,
photos will help too. From an identified terminal, follow the tinsel
lead down to the coil. Does it attach to the start of the winding?
which way is it wound, keft or right with respect to cone end or
other end of bobbin. The winding is likey coated with a substance like Glyptal that is then baked to harden it, without warping the coilform.

If you can see the voice coil look at it,count the turns, see
what the resistance is , (accurately, then calculate the length
and, based on copper wire tables, see what guage it is.

You might dissect a few other trashed, blown or othewise useless
speakers to work up some feel for the task.

And also, they now make magnet wire with a sticky coating
on the surface of the enamelling to hold it in place when winding
certain shapes of pi-wound coils but I dont have any of that.

If you took a few turns off a voice coil which represented about
10 percent of the coils active length you probably would not
notice too much difference in the way it worked, but it would be
a trick to keep the coil from unwravelling.

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Last edited by radiotechnician on Jan Tue 18, 2011 8:47 am, edited 1 time in total.

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 Post subject:
PostPosted: Jan Tue 18, 2011 6:24 am 
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Location: Aurora Colorado
I heard that a guy here on the forum named Ken, and he does re-coning. There is also Hank Brazeal?

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 Post subject:
PostPosted: Jan Tue 18, 2011 8:50 am 
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Location: Powell River BC Canada
glasdave wrote:
I heard that a guy here on the forum named Ken, and he does re-coning. There is also Hank Brazeal?


True, lots of excellent speaker rebuilders, but it would be nice
to do it up here in the cold North where shipping is just the
cost of buss freight between cities.

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 Post subject:
PostPosted: Jan Tue 18, 2011 7:07 pm 
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The peice of wire that i was wondering if i could cut off is right at the start of the coil.
The resistance of the coil is 3.4 ohms.
The wire is wound 2 layers deep.

I think that i am starting to get a feel for making the cone as i made a temp. one out of printer paper and taped it to the voice coil and i did get sound out of it although it was badly distorted.I am planning on making the proper one out of black construction paper.I still need to find a way to attach the cone to the edge of the speaker frame.

Nick

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 Post subject:
PostPosted: Jan Tue 18, 2011 8:18 pm 
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Joined: Sep Thu 23, 2010 6:37 am
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Location: Powell River BC Canada
Yes, the surround is critical. Use common sense for now, Lots
of folks have experimented with that because the surrond retro kits
for the old hifi classics are a bit pricey.

As guitar guy, ( I assume) think of a speaker cone as a drum.
tap it gently with your finger. Listen. Then short the terminals
and do it again. Let your brain figure out what the thing is
telling you.

There are some tricks to measure the mass of the cone and
the compliance of the surround/spider and come up with grams
and dynes/cM. Handy in comparing speakers.
All you need is an audio oscillator, some modelling clay, a
resistor and an amplifier and an audio VTVM. I posted an old
step by step calculator routine for the TI52 that I used in the
lab of the old Pro-Linear speaker factory on Alberta Street
in Vancouver in the 70's. The factory made the boxes. We made
the Xovers in Mexico with our design. Drivers were made in
Ontario, RSC or Marsland, and in Paduka Ky. CtS. We tald
them what cone, they rooted around, found a cone , made
10 samples and sent them for testing.

I seemed to understand that few new original cones were
never made, just coppiesd from thousanda of existing, which
when used and modified, became part of the pile of designs.
Also , we could tell the saleman that we would like a cone
similar to one Bose or someother big firm was using, and they found a way.

I think you have to plan the coil attachment of the coil to the
cone when you make the cone with a square cut exactly parallel
to the top plane. Remember too, the dust cap replaces the
spider of old.

When you get the guage of the wire, let me know and I'll see
if I have some.

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VE7ASO VE7ZSO
Amateur Radio Literacy Club. May we help you read better.
Steve Dow
ve7aso@rac.ca


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 Post subject:
PostPosted: Jan Thu 20, 2011 9:30 pm 
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I couldn't find anything that tells me what guage the wire is so i measured it with my digital caliper.It said that it was 0.007''.The resistance of the coil is 3.4 ohms.I hope that this is not completely useless info.

Nick

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I am not accountable for any damage this causes


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 Post subject:
PostPosted: Jan Fri 21, 2011 11:28 pm 
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Would it work to make the cone out of heavy poster board or should i use a lighter paper?

Nick

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Life without music would be a mistake-Nietzsche
I am not accountable for any damage this causes


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 Post subject:
PostPosted: Jan Sat 22, 2011 12:25 am 
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Joined: Sep Thu 23, 2010 6:37 am
Posts: 12437
Location: Powell River BC Canada
7 mils is about what #33 copper is. It is 4.8 ohms per foot
so 3.5 ohms is about 17 feet. If it is a 1 inch diameter coil
it would be 64 turns. 2 layers about 32 turns/layer.

Plug in your actual numbers.


I have #33 Formex 0.0071. let me know if you need some.


The cone mass and the 'springyness of the surround and the spider
determine the bass free air resonance. The coil mass is added to
the cone mass.

density: ?? I could suggest Braille paper would feel something like a 40's cone. Btw. Do you have a papermaker close like
this? http://www.pioneerthinking.com/makingpaper.html

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VE7ASO VE7ZSO
Amateur Radio Literacy Club. May we help you read better.
Steve Dow
ve7aso@rac.ca


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 Post subject:
PostPosted: Jan Sun 23, 2011 1:34 am 
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Location: Dawson Creek BC, Canada
Here are the actual numbers from the coil.
The wire is .007in in diameter and the coil has a resistance of 3.4 ohms.

The voice coil has a outside diameter of 1 11/32 in.

As far as i could tell the coil should have 52 turns.26 per layer.It may be slightly more or less as the damage to the coil makes it impossable to tell the exact number.

Thanks for all the help.

Nick

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Life without music would be a mistake-Nietzsche
I am not accountable for any damage this causes


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