Corrosion in 1,5" driver, game over?

[sebackman]

Hi,

I found some 2450 drivers that seem to be in good shape. However when the back cap is removed it looks like there have been water or probably moist in them and there is some light corrosion (orange/brown) under and on the side of the diaphragm on the pole piece.

Can potential corrosion/rust be scrubbed away or is it likely that there will be corrosion in the phase plug that cannot be reached/cleaned?

I guess the gap and pole piece can be brushed with a brass brush and cleaned the normal way unless there is real rust and not on decoloration on the surface.

If too much of a risk I will just let them go.

All input appreciated.

Kind regards
//RoB

[Earl K]

Hi Rob,

I once had ( back in the 90's ) some 2426H drivers that got soaking wet ( while in transit going across Canada in a leaky transport truck ).

The drivers gaps filled with water & by the time I discovered this situation ( a couple of months later ) significant rust had set into the metal that forms the top-plate.

I removed the diaphragms ( which I think were toast ), filled the gap with a water displacing oil called WD40 and then let it sit upright for a day or two .

I then, drained the oil and lightly sanded the gap with a wet/dry ( emery-type ) sand-paper to remove the worst of the rust .

Those drivers performed ( as new ) once new diaphragms were fitted .

Now-a-days, I'd probably first treat the gaps with one of the many auto-motive rust converters ( before putting the WD40 into the gap to "soak & seal the rather porous metal" ).

One ( Canadian made ) rust converter that I like a lot is this ( brush-on type ) ;





- See the MSDS Sheet for the active ingredients ( Tannic Acid & Phosphoric Acid )
- This formulation ( for rust conversion ) is rather old-school ( & there are many ) but this is known to be effective .

I'm sure that if you look around, you can find a locally produced rust converter ( to stop & then convert the existing rust within those drivers ).

Typically, acid based converters will need to be washed off ( so as to neutralize the acids ) . I use WD40 for this job .

[bubbleboy76]

What is the rust converted into?

[Earl K]

Here's a 2014 study worth reading ( from the US, National Park Service ).

[Earl K]

What is the rust converted into?

Okay then ( it is a reasonable question );

Here are the first two paragraphs from the National Parks Service, Mission Statement for their 2010 Rust Study

For conservators working with iron, rust is always a consideration. In museum collections or in our homes, we easily encounter rusty fences, grates, car parts, artwork and collectibles. Iron oxide (commonly called rust) results from the natural oxidation of iron by oxygen. Some metals, like bronze, can form a protective layer of corrosion products called a “patina.” However, iron corrosion will continue to negatively affect an object until treated. Rust is destructive, not protective.

To combat this destruction, conservators utilize a few different methods. For artifacts not containing heavy chlorine-induced corrosion (objects not heavy in salts or near salt water), rust conversion is a reliable avenue for protection. Rust converters, most often containing tannic acid or phosphoric acid, react with the iron oxides to form a stable layer on the exterior of the treated object. There are many commercially available rust converters that are accessible to both the professional conservator and concerned homeowner. However all rust converters do not function equally well, especially over a long period of time.

A rust converter is a chemical treatment that turns iron oxide into a more stable form such as iron tannate.

[sebackman]

I bought the drivers. Two was fine and two have been exposed to water.

I tried several methods but finally settled for the crude way and put a polish round (like a round Scotch Brite) on the drill and just cleaned it down.

Did run a sanding paper in the voice coil gap. Took a while but looked pretty good when finished.

Then cleaning with white spirit, compressed air and finally masking tape. Now clean in the gap, phasing plug and good to go.

kind regards
//RoB

[Earl K]

Some people here in North America might recognize White Spirit as being called Varsol .


Glad this all worked out for you .

[sebackman]

As per above I got some pretty corroded 2450SL drivers a while back and thought I would post some pictures here after cleaning.







They are now operational and one of them do measure within spec. I used some old diaphragms and I think one is out of spec (old PA dia's). Fortunately I have a spare and will try that when I get some free time

Kind regards
//RoB

[ivica]

As per above I got some pretty corroded 2450SL drivers a while back and thought I would post some pictures here after cleaning.







They are now operational and one of them do measure within spec. I used some old diaphragms and I think one is out of spec (old PA dia's). Fortunately I have a spare and will try that when I get some free time

Kind regards
//RoB

Hi RoB,
I only wonder how such mechanicaly removed corosion woul behave after severa years of us, as top plate is not corosion protective layer....
Regards
Ivica

[gibber]

Hi RoB,
I only wonder how such mechanicaly removed corosion woul behave after severa years of us, as top plate is not corosion protective layer....
Regards
Ivica

I think RoB has done a great job as per the pictures. Not sure the result would revert in most "non-extreme" environmental use cases as you perhaps fear...
Unusual case perhaps to have this with so young a purchase as a 2450, but worthwhile the thread for all the Altec / JBL stuff out there from the 50's to 70's, i've had quite a bit of older drivers looking like these for sure.

Appreciated highly, RoB
br,
Ralph

[sebackman]

Thank you for input.

i have measured 4 pairs of drivers and of the two worst one seem to be ok and the other is a bit off spec. Both of these received used diaphragms so I don't know what is causing the difference. However, I do have a spare 8ohm dia and will put that in and see if it is the core or the dia.

The top plate is cleaned and the gap & phase plug is also cleaned mechanically. There is probably still corrosion under the top plate an potentially some thin layer in the phase plug where it is difficult to reach. But it "looks" clean to the naked eye.

Kind rgards
//RoB