Applying a new speaker cloth

Preparing a frame

The steps I used to glue a new speaker cloth to the baffle of an old radio have been described before in the NVHR magazine, “Radio Historisch Tijdschrift”.

The cloth needs to be stretched and straightened to make sure it will glued perfectly straight to the baffle. So my first step was to construct a rectangular frame to fix and stretch the speaker cloth.

I measured the size of the baffle and the newly made piece of fabric. From a few scraps of wood I made a rectangular frame that was about 2 cm smaller than the piece of fabric. The fabric was only 4 cm larger than the baffle so I didn't have much margin and I could afford to lose only 1 cm to glue it to the frame.

Fabric to the frame

The next step was to glue the fabric to the frame. As I said, I only had 1 cm of slack. Using string sticky tape (not as strong and sticky as Duct Tape, as I was afraid to pull strands from the fabric), I attached the fabric to the frame at the short sides. I made sure that the sides of the fabric were parallel to the frame. After that, I squirted white wood glue between the fabric and the frame and left it to dry for a day.

After a day, the fabric was stuck to the short sides of the frame. I could now increase the tension. I did so by unscrewing one of the sides and driving two wedges (halves of cloths pins actually) between the side and the long sides of the frame. When I had a suitable tension, I fixed the board again. After that, I used tape again to straighten the fabric and attach it to the long sides of the frame. When it was straight, I squirted glue again and waited for another day.

Detaching the old fabric

Getting the old fabric off the baffle didn't take too long. I used warm water with a bit of dishwashing detergent and wetted the surface of the fabric. I could pull off the fabric quite easily, except for the spot where a previous owner had used white glue in a repair attempt. Left-over strands and specks of glue could be easily removed using a putty knife.

What adhesive to use

There are several options for the adhesive to use.

• White wood glue (usually PVA suspensions). This is a modern easy alternative. It has a few disadvantags though. First, most white glues cannot be dissolved after curing. Most of them do soften when treated with warm water, so you can take things apart, but you may damage tha fabric. Secondly, glue stains in the fabric are generally impossible to remove.
• White paper glue. Some types of PVA glues can dissolve in water after curing. They are sometimes sold for use by children, as most parents like the idea of stains in clothing being able to be removed in the washing machine. I have used such an adhesive for paper, but I wouldn't trust it to keep a speaker cloth in place for more than 10 years. By the way, not all white glues intended for paper can be dissolved. There are types of super strong white PVA-based wallpaper paste. I once used such stuff to stick heavy wallpaper onto PVC wallpaper. It worked fine, and I don't think that adhesive can be removed. I have used the same paste to fix a corner of the speaker fabric of my Philips 170A radio, because I needed really strong adhesive to keep it stuck to the baffle after stretching the fabric.
• Rubber cement (known as “Bison Kit” in The Netherlands) or transparent contact adhesive. Really a bad idea, though it might work for a while. You will have to apply the rubber cement to both sides to be joined, the fabric and the baffle. It sticks at first contact, so make no errors, it can't be moved if you do. Stains can be removed using thinner. The worst thing is, these types of glue will dry out after 10 years or so. Even the transparent varieties will turn dark brown by the years, making stains uglier.
• Strong wallpaper paste. Some collectors say in wallpaper paste was used in the Philips factories. On my Philips 470U I glued the new fabric using a strong mix of strong wallpaper paste. The result is still fine after 6 years, but looking at old wallpaper in my house coming off here and there, I do have my doubts whether the fabric will still be snugly in place after a few decades.
• Bone glue. A very old type of glue for strong bonds, often used by furniture makers. It can easily be detached by using heat and water. The use of bone glue for speaker fabric was advised by a merchant selling the stuff on one of the NVHR swapmeets. I had my doubts at first. After all, it's a traditional artisanal type of product, not a twentieth century industrial material. But I decided his claim might be plausible, so I tried it.

Of course, one would like to use the same material that was used in the factory, but the information about this is scarce and sometimes contradictory. I decided to try the bone glue.

Before doing the real thing, I warmed up an amount of glue and glued an old T-shirt to a piece of wood. That worked well, though the fabric could be fairly easily be torn loose, except for the spots where the glue was still really fresh when the t-shirt was applied. As you will understand, the glue will cool down quickly after application, becoming less liquid and less adhesive. But it was strong enough, even on places where the fabric could be torn loose.

Glueing the fabric on

I took the frame with the fabric and put it upside down on a pair of supports. I placed a lamp under the frame so I could easily align the baffle to the strands of the fabric.

First I put the jar of glue in a bowl of hot water on an electric heating plate. Stirring the glue with my left hand, I started to warm up the baffle using a hot air gun in my right. This took about 15 minutes. When I thought the baffle had warmed up sufficiently, I took the brush and started to spread the glue over the baffle. When it was all wetted with glue, I picked it up it and put it upside down on the fabric in the frame. The use of the frame is to stretch the fabric so it will have a good tension in the speaker opening. To stretch the fabric a bit more, I put some weights on the baffle after I had lied it down on the fabric. I pressed the fabric against the wood to make it stick better, and waited for the glue to cure.

That didn't take too long, only a few hours. I carefully cut the fabric from the frame and heated the jar of glue again. Then I dabbed the sides of the baffle with glue and folded the fabric around the sides.

Messed it up a bit

The next day, I cut off the excess fabric on the sides and I cut the hole for the tuning indicator in the middle. The fabric was a little bit loose around the hole. I thought I could easily fix that by reactivating the glue.

That was a mistake...

I ironed over the baffle near the tuning indicator, using a damp tea-towel to add extra moist. This worked a bit too well, so that the liquified glue came through the fabric on the places where ironed and some stains became visible. That wasn't funny. After letting the glue cure again, the stains were slightly less visible. But they are still there...

I tried to clean the fabric surface using a brush and warm water with dishwashing detergent. That didn't really help, things seemed a bit worse.

So I gave up and hoped that the stains would eventually be camouflaged by the ornaments on the baffle. I mounted the vertical bars and the window for the tuning indicator. As my wife said: if you don't know it, you don't notice. So I hope.

After this, I mounted the baffle in the cleaned and polished case, and finished the repairs to the B7X63A.

Other speaker cloth experiences

Looking back, I have fixed the speaker cloth of three other radios, besides the B7X63A:

On the Philips 470U I bough a custom fabric made by Corrien Maas, Here, I used the frame method for the first time, but I used a different type of adhesive (wall paper paste).

On the Philips 170A the fabric had come loose on the lower left hand corner. It looked warped and loose. I didn't want to detach it for fear of tearing it, so I reattached the corner using strong white glue. In order to stretch the fabric, I stuck Duct Tape to the side and pulled the fabric straight by the tape. This was a risk, but I was lucky and didn't tear the fabric nor pull out many strands. The result is quite reasonable, but the lines in the fabric aren't perfectly straight.

On the Philips 667A I restored in 2005, I decided to go cheap and use the fabric from a spare BX560A baffle I had. This type of fabric is not identical, but it is good enough. The piece of fabric was only just large enough. Having no margin at all, I couldn't use a frame to stretch the fabric. I used duct tape instead to stretch the fabric and fix it to the baffle as the glue was drying. The result was not bad, although after 4 years, the fabric isn't as tight in the baffle opening as I would have liked.

So there are many ways to vary. Try if you like but at your own risk.