I would think that as along as the pole piece and the top plate near the gap aren't too deeply pitted it would be fine once cleaned up. Even if pitted it may sound fine. There's no way to tell without actually cleaning it up. The camera can exaggerate the way it looks at the moment, and it's tough to know even looking directly.
Audio_by_Goodwill
Michigan, USA
I will try the cleaning solution and see how that works. Luckily, I have 2 other 802-8G's sitting on the shelve so I can get the system up and running.
I'll put some effort forth to see what I might be able to do. I'm curious to what extent I might be able to potentially get it working - although very concerned that the internals are rusted extensively also.
Learned my lesson - always open up and inspect both diaphragms.
One of the things Altecs are famous for are their very tight manufacturing tolerances. One of those tolerances is width of the magnetic gap. I see no possible way that enough corrosion could occur to tightly lock the voice coil in place without a loss of material that will put the gap dimensions out of spec, and cause significant deviation from proper/expected parameters. We're talking just a couple thousandths here.I would think that as along as the pole piece and the top plate near the gap aren't too deeply pitted it would be fine once cleaned up. Even if pitted it may sound fine. There's no way to tell without actually cleaning it up. The camera can exaggerate the way it looks at the moment, and it's tough to know even looking directly.
Another problem area that we cannot see without dis-assembly is the surface where the front plate meets the magnetic return pot. This surface as well as the mating surface of the return pot need to be a smooth even finish in order to provide an even/consistent magnetic circuit. The same conditions also apply to the surface where the polepiece meets the magnet slug. To resurface that part of the front plate would probably take it below the minimum thickness spec by the time any pitting is cleaned up.
IMO&E, salvaging that driver beyond an exercise in determining the exact extent of damage would be an exercise in futility given the availability and value/cost of replacements. I think it's best use is as a conversation piece, or door stop.
Certainly it could be salvaged, even to the extent that the return pot, front plate, and throat/polepiece were all replaced with GPA modern production, using only the original alnico slug and 11 slit tangerine.
But, i don't think it could be done for the ~75 bucks or less that a replacement assembly can be sourced for.
It'd be interesting(but probably not practical) to actually clean this one up and try to return what's there to a "working" condition. My curiosity would be to see how obvious any audible differences would be as well as the degree of measurable variation beyond what i think is quite predictable from a simple visual inspection. I think you'd immediately notice reduced sensitivity and quite possibly rolled off HF.
Just my .02...........................
Whether it's salvageable or not, I want to see it disassembled and cleaned up just for forensics sake. I have cleaned up rusty water pumps and such by just submersing crap in pure Muratic/ pre-diluted hydrochloric acid. Find out what the magnetic gap is, and cut/ grind down a feeler gauge to form a slim pick to clean out the crud. A stainless steel cup rotary drill wire brush should work great.
It'll make a dandy door stop. : /
An acid will remove some good metal, Though. It would be better to use something like Evapo-rust. It's more expensive than acid, but safer for the driver, and safer to handle.Originally Posted by VolvoHeretic
Audio_by_Goodwill
Michigan, USA
With some good cleaning and some work with a wire brush, I actually got it working!
I used some WD 40 extensively, and a thin razor blade to clean out the gap. I then used some paper speaker shims and compressed air to clean it out even more. I then used a wire brush to clean the rust off of the plate. Here are some before and after pictures:
http://i976.photobucket.com/albums/a...e/P1070132.jpg
http://i976.photobucket.com/albums/a...e/P1070134.jpg
I installed a diaphragm and hooked it up and got good sound out of it. I had another standalone 802-8G and hooked it up (both outside of the speaker box) and they sounded about the same. Definitely not a final test but getting closer to potentially saving this driver.
Question: do you think that I should still use the Evapo-rust?
If the gap is rust free you can probably skip it.
Did you clean all the WD40 off, and out of the gap? I'd probably clean it with soap and water and then blow it out with air....... or maybe alcohol (the 90+% stuff) in the gap, and then blow that out with air.
Disclaimer...... I've never worked on a HF driver, I'm just tell you how I would approach it, given my experience in cleaning other things.
Audio_by_Goodwill
Michigan, USA
WOW! Great work!
I am impressed. I think you may have salvaged it after all, at least good enough for a working spare. That looks a LOT better than i would have expected, especially in the gap. I was really afraid the oxidation would have eaten away some of the edge of the crown on the polepiece.
That said, i still couldn't sleep at night knowing it was bolted to one of my horns. It'd have to find a new home.
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