A 416 dilemma. What to do?

[Panomaniac]

Well at GPA it does not seem to be. From my conversations with them, it did not seem that they do this. They do have the equipment, tho. And for my second recharge they could not do it, at least not without ripping the new cones off.

I also got the impression from Bill that he did not do the first remag, someone else in the shop did. I do believe he did the recone - it's very nice - and maybe he did the second attempt at a remag.

My main question now is - Can the magnets go beyond repair? Even when there is no obvious damage? Bill said no, but at least one other Altec fan I've spoken to has said yes.
Anyone know?

Obviously I'm bummed because I thought that having the woofers reconed and remagnatized would bring them back to spec. That was not the case for mine. So I wonder how many others have had the same bad luck and never known it?

[airboss]

Ok, here we go. Hairbrained idea #xxxxx.

Open the magnets from the back. You may have to take it to somebody with a lathe. remove the magnet, (I haven't the foggiest idea if you can do that. Never seen the insides of one) call up these guys:

Thomas and Skinner

get some new magnets. Drill and tap the body casing and clearance drill the cover that you have had your machinist cut off. Then screw the assembly back together with lots of screws. Sorry, my lathe stops at 6". I'm thinking you'll need a 12" home machinist or a shop that's desperate for work.

What kind of alnico is in there? This of course is resuscitation beyond the call....

[mah]

Thomas and Skinner- Alnico made in the USA, AND exported to China. :CAT:

[Earl K]

Obviously I'm bummed because I thought that having the woofers reconed and remagnatized would bring them back to spec. That was not the case for mine. So I wonder how many others have had the same bad luck and never known it?

- I'm thinking that the new normal ( SOP or Standard Operating Procedure - before reconing ) should now include a "gauss check of the gap" to confirm that proceeding with a recone is indeed worthwhile .

Is magnet strength testing after a recharge but before a re-cone a standard practice?

Well at GPA it does not seem to be. From my conversations with them, it did not seem that they do this. They do have the equipment, tho. And for my second recharge they could not do it, at least not without ripping the new cones off.

- I have no idea if GPA would incorporate this additional step into the remagging / reconing process . Since it adds a bit of time / the service may need to be added to the bill .

My main question now is - Can the magnets go beyond repair? Even when there is no obvious damage? Bill said no, but at least one other Altec fan I've spoken to has said yes.
Anyone know?

- I don't know . The general consensus has always been that under normal circumstances an Alnico magnet can be fully recharged .

- Your 416a magnets provide the challenge to this oft quoted rule and it would be really helpful to understand why they are resisting a full recharge .

<> cheers

[robertbartsch]

Isn't it weird that both cores are impacted in a similar way; and the charge is lost not once but twice and possibly three times?

If these mags won't stay charged up there is a reason why!

Does this indicate that the composition of the Alnico alloy is incorrect? It seems unlikely if this is not a common issue or at least a know risk with other older Altec cores and since these two specific Altec cores suffer the same exact problem.

If I owned these at this stage, and GPA does not want to help you get to the bottom of the problem, I might consider shipping a single unit to a repair shop other than GPA that could do a recharge without ripping out the good "new" re-cone.

...just a thought, I suppose...

[Cal Weldon]

What kind of alnico is in there?

Speakers use alnico 5.

[airboss]

thanks

[RonSSS]

I just have a few comments.

416-A or 416-8A was way before EV arrived, correct?
Unless I missed it, what is your method of measuring the parameters?
I have a procedure, but I'd have to dig through countless piles of paperwork to find it. Ok, here it is online:
Measuring Loudspeaker Driver Parameters
On stock altecs I've measured, they were within +/- 10% of spec, which is probably the norm given production tolerances. The measurement is touchy, especially Fs. I hang the speaker from the ceiling with chains.
Have you measured a stock good working unit to compare?

I'm wondering if GPA knows wether their magnatizer is even working? How does one measure the magnatization when done. Seems to me if it's busted, it could demag!

GPA did the first pair of 411-8A for me, and I measured the TS on the one good working one before sending them in. It was spot on, but the cone was sunk. when I got the reconed ones back, they measured like good 416-8B drivers......the parts used just weren't the same as the originals. Spider and surround were different. Of course, these are ferrite.

Bought GPA parts for a pair of 416-8C, had a local reconer install them, and they measured very close to spec. Another ferrite driver.

I also have GPA parts for a pair of 416-8B that I bought new, I want to recone these myself someday, but the parts are not dead nuts to the originals, so I wonder.....tha magnets should be good, they were never overheated, dropped or abused.

Ron

[sba2]

I recommend the model 8500...

Capacitive Discharge Magnetizers - Magnetic Instrumentation Inc.

[robertbartsch]

I'm reasonably certain that GPA and others who have mag capability do NOT discharge and re-charge cores with ferrite (non-Alnico) motors.

Anyway, this is what Bill told me recently when I asked him about a re-cone for a pair of ferrite cores. Apparently, ferrite cores do not suffer permanent loss in strength when exposed to big current hits like Alnico, so in general, there is no need to do this.

I believe I was also told the magnification (recharge) involves two separate processes; (1) demag the motor to a point where it has zero strength, and (2) recharge the motor to full spec.

I thought GPA recharged all cores with Alnico motors as a standard practice. At least one other repair shop located in California that I know does not recharge cores unless you ask, and there is a separate fee (about $25 each) for this service.