Hah! Recharging the old JBL magnets!

[mixsit]

So I was considering putting a couple of old D-120's back into guitar amp service and just found out,, or relearned perhaps that these (70's) JBL's could have lost maybe half of the magnet strengths by now!
So I Googoo'd it..

Speaker Magnet Recharging Done Easy

 

[muttley600]

Thats all done keyhole style now with special nano sprinkles...

n00b...

 

[notCardio]

Yeah, they probably sound like crap by now, but being the generous type, I'll take 'em off your hands so that they aren't cluttering up your place. Hell, I'll even pay for shipping. 'Cause that's just the kind of guy I am.

You're welcome.

 

[mixsit]

Well, I just got done doing some more poking around, and it may well be I was given some poor info from a repair co regarding there 'losing magnetism over time.
The way I read it it is high drive current that does it, and even if recharged', a similar exposure would just knock it back down anyway.
The Great Alnico / Ferrite Debate

What brought this on is I was looking at reusing these D120f's that came with a 70's Twin again to gain more level out of a LoneStar Special. The rough comparison with a sound level meter which surprised me was it seemed to indicate Mesa's c90 is just as efficient (or more slightly so perhaps!) than these d120's.
Another factor though, I may have had these reconed with non JBL parts.

 

[muttley600]

A lot of times the degaussing that happens is desirable. Some of my favorite speakers are plus 25 years now with lots of abuse...

 

[JCH]

I've wondered about this too. AlNiCo magnets usually have pretty good retention. Some grades better than others. I'm in San Diego this weekend hanging out with my Dad, but when get back home I'll measure a new Jensen P12R, and compare it to one that's from the 50's. I have a few other vintage speakers that I could measure for comparison also.

Some old pickups I have show no significant loss, and I measured many others when I've had the opportunity with the same results. I think it's the exception rather than the rule when magnets break down.

 

[ecc83]

Mixit's link tells me what I have always thought to be the case, "modern" magnets, be they ferrite or Alnico, do not lose energy over time unless exposed to a large current pulse or (not mentioned?) mechanical shock and that last is unlikely in a cabbed driver since the cab would be destroyed before the "G" was high enough to de-mag the unit even slightly.

I have read an article (by Celestion, will try to find it) re the "ferrite/Alnico" sound debate and there IS it seems a difference but it is small and comes down the fact that Alnico is an electrical conductor and ferrite is not.

I doubt any VALVE amp you could lift onto the van could put enough current thru a 16 Ohm coil to cause magnetic compression and in any case that would be insignificant compared to the THERMAL compression that must accompany such a high drive.

Bottom line: I doubt ANY speakers ever need their magnets "re-charging"!

Dave.

 

[mixsit]

Mixit's link tells me what I have always thought to be the case, "modern" magnets, be they ferrite or Alnico, do not lose energy over time unless exposed to a large current pulse or (not mentioned?) mechanical shock and that last is unlikely in a cabbed driver since the cab would be destroyed before the "G" was high enough to de-mag the unit even slightly.

I have read an article (by Celestion, will try to find it) re the "ferrite/Alnico" sound debate and there IS it seems a difference but it is small and comes down the fact that Alnico is an electrical conductor and ferrite is not.

I doubt any VALVE amp you could lift onto the van could put enough current thru a 16 Ohm coil to cause magnetic compression and in any case that would be insignificant compared to the THERMAL compression that must accompany such a high drive.

Bottom line: I doubt ANY speakers ever need their magnets "re-charging"!

Dave.

Yeah. I've been poking around in music and equipment all this time and now just stumbled into all of this. I'm going to give 'edgewoud's shop a call (Home
The cones look to be in real good shape. I can't see reconing -if that gets back to higher efficiency parts and so far I've been told it's apt to be wort just a few db, don't know.
If I can't pick up a sizable boost in the efficiency end another angle is add a slave amp into this extra cab' idea. Ick, trying to keep it simple

 

[kyubikai]

Seriously, though and thank you all for your responses. It does indeed sound like a gimmick.

 

[muttley600]

Seriously, though and thank you all for your responses. It does indeed sound like a gimmick.

 

[Lt. Bob]

I have 4 old D110s from a Fender Super that need reconing but it's so freakin' expensive to recone old JBLs that I'm not sure if it'd be worth it.