Altec 604E Super Duplex conundrum

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Lads...in a bit of a pickle here...

Had a set of Altec 604E Super Duplex units w/N1500 x/overs foisted on me today.

While one unit is tickety-boo the other unit :eek::eek::eek:has suffered the insult and injury of having some boob apply polyurethane to the backside of the surround:mad: ( I imagine in some misguided attempt to compensate for some form of voice coil rub).

Although the LF/MF unit coil tests ok for continuity the resistance reading of about 5 ohms is definitely off. The other non-handicapped 604E LF/MF coil measures at 11.5 ohms.

A play-test with a very low output signal applied to the LF/MF unit confirms almost zero cone excursion, but there is undistorted sound (I didn't dare subject the unit to anymore output as I didn't want to burn out the coil).

It's obvious this horrendous hack job must be remedied...so my question is how?

I am contemplating using acetone or some other agent to soften that gawd-awful foam, but am concerned that in doing so, I may likely damage the surround and/or the cone material.

Suggestions, insights?
 

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Gentlemen......GPA, of course, is the go-to source for Altec repairs if money was not an obstacle...but I am inclined by nature to investigate this a little further.

So my question remains...what agent could I use to soften and remove the polyurethane foam without damaging the original surround material and cone material?

Thanks, Leo
 
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I'm saying that - if Rdc is erring more than 10% in any direction (from regular value ) , you can call that voice coil Dodo

so - as I understood - that one measuring 5 something is way off , so there is no point thinking about it's cone/surround condition - it needs complete recone

so Dave mention GPA

if other cone is in very good shape - leave it as is ; if it's in so-so shape - recone it , too

those spks are well worth your trouble

I think that boyz at GPA will check AlNiCos routinely

if all that is too much for ya , just send them to me , for proper disposal , free of charge ;)
 
Methylene chloride is a solvent that would dissolve or loosed the urethane but you will have to be careful as it would also dissolve the glue line between the cone and surround. It sounds to me that you have a burned voicecoil but I can't be certain of that. The two voicecoils are separate so I don't see how they could be paralleled internally by any method. You could always contact a company that sells a recone kit, there are a few that have the parts to rebuild that cone section.
 
snip....if other cone is in very good shape - leave it as is ; if it's in so-so shape - recone it , too

those spks are well worth your trouble

I think that boyz at GPA will check AlNiCos routinely

if all that is too much for ya , just send them to me , for proper disposal , free of charge ;)


I think the cone is salvageable Zen Mod, it's the coil and surround that are distressed...my understanding is that where at all possible one wants to retain the original cones on these 604s...
 
OK...like I said before I'm a curious monkey...so I took a cheap surplus no name $5.00 woofer with DCR of 8 ohms and applied some downward pressure to prevent the cone from any excursion at all and measured the DCR in that state and found it dropped to around 3 ohms...when I returned it to its natural state the DCR returned to 8 ohms which leads me back to pondering the plight of my polyurethane foam-fouled 604E cone...

If I were to free it up from its polyurethane web might I expect the DCR on it to rise as well?

I can't help thinking that this 604E may be salvageable with a little DIY patience and a lot of care...
 
If the voicecoil has been forced so that it is partially out of the gap then that could affect the impedance, but that should be more than a slight offset to cause that. The blocked dcr rating should not by itself change the impedance very much though, holding the cone still under just the dvm readings.
 
Inductance and therefore upper range impedance is effected by cone position, but DCR will not change. I don't know why your sample woofer seemed to show that but it just doesn't change with placement unless movement is causing something to partially short. You do need to freeze motion as they work as a generator with any movement (including sound) that makes the DCR hard to measure.

Were these a pair? I don't remember if the 604 came in 8 and 16 ohm versions? 5 ohms might be the DCR of an 8 ohm version (very high efficiency would pull up the midrange Z a little bit).

A partially shorted coil will give very high back EMF and make the cone feel "draggy" when you excercise it up and down by hand. Is that the case? You can also tap a 1 1/2 volt battery across the good one and the suspect one and they would sound very different if one is shorted.

If the coil is bad it will have to be rebuilt.

Were these mounted in a wall? Looks like someone went crazy with the insulating foam. I would pick it off with an Xacto knife.

David S.
 
If the voicecoil has been forced so that it is partially out of the gap then that could affect the impedance, but that should be more than a slight offset to cause that. The blocked dcr rating should not by itself change the impedance very much though, holding the cone still under just the dvm readings.

Thanks Steve...I think I'll simply put these up for sale and/or trade and let an Altec fan sort this out and spend the time and money to send the mucked-up one to GPA..

My tastes in ldspkrs are a little more understated and I wouldn't have the room to do these bad boys any sonic justice..
 
Inductance and therefore upper range impedance is effected by cone position, but DCR will not change. I don't know why your sample woofer seemed to show that but it just doesn't change with placement unless movement is causing something to partially short. You do need to freeze motion as they work as a generator with any movement (including sound) that makes the DCR hard to measure.

Were these a pair? I don't remember if the 604 came in 8 and 16 ohm versions? 5 ohms might be the DCR of an 8 ohm version (very high efficiency would pull up the midrange Z a little bit).

A partially shorted coil will give very high back EMF and make the cone feel "draggy" when you excercise it up and down by hand. Is that the case? You can also tap a 1 1/2 volt battery across the good one and the suspect one and they would sound very different if one is shorted.

If the coil is bad it will have to be rebuilt.

Were these mounted in a wall? Looks like someone went crazy with the insulating foam. I would pick it off with an Xacto knife.

David S.

Thanks David...tried to repeat the results of my experiment with several other test drivers and you are right, the DCR readings did not change.

No, the 604s are both 16 ohm versions...the 604E only came in 16 ohms according to information at Lansing Heritage....

Oh, the cone is draggy alright! it is essentially welded to the backside of the face of the frame at three points by the urethane-foam...so hand manipulation of the cone is impossible...

I posited the question regarding the effect of restricted cone excursion on the DCR impedance of the LF/MF driver coil thinking that if I were able to remove all the polyurethane foam the 604E LF/MF driver might return closer to spec.

Wishful thinking, no doubt...but worth the query....

I may try cutting out the middle portions of the foam to judge that effect upon cone excursion and DCR readings on the coil...just for my own interest, of course.

My fears are that I may damage the cone beyond salvage using some kind of acetone or agent to soften/remove what remains after I get in there with an exacto knife..

I think the cone is salvageable even if the coil and surround need retrofitting.

Regards. Leo
 
Well,
If one has half the impedance than the other you can be fairly certain that the voicecoil has a short from either being burned or touching the steel of the motor and then that would point to no insulation on the wire. Either way the voicecoil is toast. Someone could potentially save the cone but would have to be very careful. Paper cones that old are usually rather soft after that many years of use. You could use something like acetone to remove the surround from the cone as even if it softened the cone while removing the surround if you just let the solvent evaporate it should go back to its previous condition. It would be a bit different at the voicecoil junction as that would most likely be a rigid cement connection. Still it could be done.
 
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