Weak Alnico magnets

[Gary L]

I don't know a better way to title this but I have some questions regarding the Alnico magnets.

Is there any way to measure the magnetic power of the speaker?

How does one know if the magnets need recharging?

Can we DIY recharging at home?

I know when I send speakers to GPA for rebuilding he recharges the magnets in the process. Is there some special machine where this recharging is done and what does it take to recharge them?

GaryL

[Earl K]

I don't know a better way to title this but I have some questions regarding the Alnico magnets.

Is there any way to measure the magnetic power of the speaker?

> Yes, one can measure the TS parameters ( & if the magnet needs recharging the Qes parameter will be higher than normal ). Entering the obtained TS parameters into a box tuning program ( such as WinISD pro ) will auto-calculate the BL figure ( which is a measure of magnetic strength per coil length ) .

How does one know if the magnets need recharging?

> BL will be lower than manufacturers spec ( which isn't typically available from Altec ).
- anecdotally, midrange performance will have suffered ( though bass response will typically be fine )

Can we DIY recharging at home?

> NO !

I know when I send speakers to GPA for rebuilding he recharges the magnets in the process. Is there some special machine where this recharging is done and what does it take to recharge them?

> It takes a special recharging machine that uses dangerously high voltage levels ( stored within a massive bank of capacitors ) to zap the magnet ( which sits within an inductive loop ).

GaryL

[more10]

I know when I send speakers to GPA for rebuilding he recharges the magnets in the process. Is there some special machine where this recharging is done and what does it take to recharge them?

GaryL

GPA probably got original Altec charging machines. Huge machines with lots of volts and amperes.

Each driver needs a magnetic impulse of a specified shape (amplitude/duration) in order to recharge properly. GPA knows the proper values for all Altec drivers. Other brands you need some experience to recharge them.

[Gary L]

Thank you both. I just added another one to my bucket list if I ever get out that way. I would love to visit Bill at GPA and have a tour of his shop showing all the equipment he uses to do the repairs and recharging. Maybe a few here have been there and could give a description of his operation. I have no idea if he has just a few people working with him or a lot of staff doing all sorts of speaker manufacturing and repairing all over the shop. Is it a big place with massive machinery or just a small shop? Can we even get a tour if we go there?

GaryL