SPEAKER DUST CAP REPAIR
(referencing Hartke aluminum cones)
I had practically stolen a 1991 Gallien-Krueger 800RB with 1991 Hartke Transient Attack 410 and 115 cabs from the original owner. The deal was so good, I didn't even ask for a demo - I just assumed the worst and met him in a parking lot just after sundown. The "worst" only turned out to be two speakers producing that buzz/fart sound, which was an easy fix. Lucky day.
I narrowed the problem speakers down by removing the metal mesh speaker cover and placing my hand on each speaker to see if I could reduce the buzzing while playing a note. The bottom left 10" was to blame along with the 15", which had been repaired at one point with something brittle, most likely superglue. I removed the problem speakers from the cabs to examine them closer. Unfortunately, it took a really keen eye a few times to finally notice the exact issue of the 10" - I had placed the speaker on a Lazy Susan and meticulously inspected the edge with an LED penlight. In some spots, pressing on the cone allowed me to see an extremely slight separation where the paper dust cap met the aluminum cone. The 15 was much easier - I could here the stiff superglue, stuck to the dust cap, scraping along the cone as it slid less than a millimeter.
With the dust caps still in place, I lightly cleaned the years of dust and grime from the cones using Wenol (a fine-abrasive polish) and a soft-bristle toothbrush, avoiding staining the paper areas. Be careful, the aluminum is very thin and delicate and will show scratches or indentations easier than paper. I removed the polish residue with rubbing alcohol on a cotton ball. To completely separate the dust caps, I chose something much more delicate than the standard knife option: a piece of paper. I wedged a corner of the paper under the dust cap. Working it around, it was enough to break the cement, though I had to "saw" through some tougher areas. It took awhile on the 10", but left the cone totally unscathed. The super glue on the 15" was so stiff that the dust cap nearly popped off the cone. Lesson here is to never use superglue, no matter what the hacks might say. Once everything was cleaned-up, I vacuumed near the voice coil to pull up any dust that may have fallen in.
The 10" dust cover looked like it was reusable since it did not have a lip - I removed the old glue by carefully trimming the glue remnants off and then using sandpaper to smooth the edge back to perfection. The 15" dust cover was going to need replaced since the underside of the lip was hardened and covered in superglue. The cone on the 15" still had excessive superglue stuck to it that I could not get off for fear of damaging the delicate aluminum. None of the solvents I had on hand would remove it. I decided to get a slightly smaller dust cap so I would have a perfect contact surface for the repair. I ordered a 5" diameter dust cover, but this was too small and the underside of the dust cap was making contact with the voice coil leads attached to the cone. I ordered a 135mm dust cap that cleared the leads and was a diameter slightly smaller than the superglue residue on the cone. I purchased an adhesive that was recommended for aluminum cones (Simply Speakers MI-3035) ...it looks and smells a lot like Testors model glue.
REPAIRING THE 10"
I placed the speaker on the center of the Lazy Susan. This allowed me to work steadily with the right hand while spinning the speaker with my left. I started by cleaning the contact area with rubbing alcohol on a cotton ball, followed by a q-tip dipped in acetone. I centered the dust cap and placed a large wrench socket on the cap so it caused the edge to make solid contact the entire circumference. I practiced a few glue beads on some waste paper to get a feel for the flow rate. With the glue held in my right hand like a pencil, I started a bead where the two surfaces met and rotated the Lazy Susan. I went slowly, squeezing gently, and laid down a perfect bead around the entire edge that leveled out smoothly. The key here is to not overdo it, but rotate back a little to add more if the flow didn't happen to add enough in a spot or a bubble forms - it is much easier to add than to take away. If a string of glue lays across the cone when you pull away, use a toothpick and a q-tip to carefully get it up without disturbing the bead. I let that sit overnight with the weight in place - 24hours, actually.
REPAIRING THE 15"
The 15 was a different animal since this dust cap has a lip on it - glue must be added to the underside of the dust cap, then placed onto the cone. I chose to replace the original dust cap since the glue had also made the lip completely non-pliable - I knew this would inhibit the new glue from bonding to the paper dust cap and thus increase the chances of the repair separating later. The old ring of excess superglue left on the cone would be a guide when placing/centering the new dust cap. I attached a piece of painters tape on the dome of the dust cap as a handle for placement, then set the new dust cap on the Lazy Susan, upside-down and added a small weight to keep it in place. Using the same application technique as the 10", I made sure to cover the underside of the lip with a moderate, consistent film of glue (not too much that it would ooze out like the previous repair). With the dust cap centered on the cone, I placed a plastic container on it that was large enough to deliver the weight near the outer edge and added a large wrench socket on top. I then used a clean q-tip to tamp down the perimeter of the lip, being mindful not to spread glue anywhere. I let it sit for 24hours.
With it all back together, I was rattling the house and annoying the neighbors with 400w of pristine awesome.