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Unlike an EHT block, or other parts of the speaker, it doesn't take too much diagnostic skill or an involved process to see if the dust covers have damage. They will show splits and tears, plastic 'sticky' tape mends and so on. If they feel a little brittle, as if the next cockroach that walks over them would split them wide open, then it is probably time to replace them. Hey, if you disassembled the speaker the first time (Disassembly Section) without making a split or a hole in a dust cover, then I am awed, to say the least. You need either a heat shrink film of 12 mm (or less) gauge, or some 12 mm (or less) gauge Mylar®. Quad originally used a 6 mm Mylar® for the Treble Panel and a 12 m m Saran® film for the bass panel covers. It is possible to get P.E.T. in gauges down to 0.9 mm, but it is doubtful that it would be robust enough in this application. It is also can be fiendishly expensive! You can also use the tensilised P.E.T. from Area 51 to make a treble panel dust cover identical to the original.
In general, the material of choice for many folks is 12 mm Mylar®, but I use 12 mm heat shrink film that was designed for light duty packaging in the computer industry. I have heard of some people using sandwich wrap, OK, it's a Saran® wrap of a light gauge. The width of the film needs to be about 400mm, and this will cover both Treble (easily) and Bass Panels, leaving enough around the edges to work with easily.
To replace a dust cover, do the following:
- Remove the panel(s) from the speaker - See the Disassembly Section.
- Get out the vacuum cleaner, if you haven't already, this will get messy.
- Once the panel is out, you will see a five layer 'sandwich' of bits and pieces, held together with a (very old) P.V.C. tape. The outer "layers" of the sandwich are light wooden frames, holding the dust cover plastic.
- Using a hobby knife (Stanley® knife) or other razor sharp knife, slit the tape around the perimeter. Be very careful that you don't cut into the panel, as it's only plastic, or the light wood frame. Both of these unnecessary disasters can happen if you're a little too eager with the knife. In the process a lot of old dried up glue dust, wood dust, oxides, and sundry light particles will be released. Be warned if you are an asthmatic! Vacuum as you go - Nature may abhor a
vacuum, but Quads don't.
- Strip the tape, the plastic film, and that gungy brown adhesive detritus from the frame. How you do this is up to you. It will probably flake off. Methylated spirit is a help in dissolving the old adhesive. Very fine (600 grit) sand paper can be useful on the wooden frame, too. You just want the frame to be clean, smooth and in one piece when you're finished.
- Cut a piece of your chosen dust cover plastic equal to the length of the panel, plus about 75 mm (3 inches) over each end. If you're using 400 mm wide material off the roll then you'll have enough to play with at the sides automatically.
- Lay this flat on a smooth laminex surface, or similar. Gently smooth out the major wrinkles and tape the film at the corners of the rectangular piece and the mid-points. No real tension needs be applied.
- Apply your glue of choice to the wooden frame. I use a fast-drying, pressure sensitive spray-on glue that's available in every five and dime. It doesn't dry 'hard' and costs about $AUD5-00 for a 350g spray can. This will do a lot of dust covers. I would estimate a couple of dozen per can.
- Immediately centre the frame glue-side down on the plastic.
- Wrap any excess plastic film at the edges around the frame, away from the glued side. Weight it, if necessary until the glue dries. I find that I can have the frame covered in about 5 minutes from the time I cut out the film to the time I put the frame aside for later use.
- Trim any excess film around the edges with a very sharp (razor) knife.
- Do NOT heat shrink the film at this time! It is far better to wait until the frame is taped back onto the panel during final assembly. These frames do not resist tension at the mid-point at all well, and you will pull them out of shape with heat shrinking at this stage.
- When it does come time to heat shrink, I use a hair dryer, since the film I use is a specialised film designed to shrink at moderate heat levels. If you use Mylar® then you will need to use a heat gun, as Mylar® will not heat shrink well with a hair dryer - doesn't put out enough heat.
- Put your re-covered dust covers in a safe place for later use.
- N.B. Heat shrinking is most critical with the Treble Panel Dust Covers and you must not leave even small "ripples" in the finished cover. This is because the high frequencies it operates at will cause the dust cover to "rattle" or "buzz" if there are even small imperfections. The Treble Panel Dust Covers even have small bolts and felt washers to damp any buzzes and rattles in the dust covers at high frequencies. The Bass Panel Dust Covers are not so critical and even a few wrinkles generally cause no major problems.