Cleaning old knobs

Old radio knobs often come with many year's worth of dirt and grime that can be very difficult to remove, particularly from grooved or textured surfaces.

I've found that the easiest and most effective cleaning method is to put the knobs in a solution of biological washing detergent and warm water, and leave to soak for a few hours.

After this treatment most of the muck can just be rinsed off, and a little effort with an old toothbrush will usually shift anything that remains.

This works because much of the dirt will be organic in origin (mainly oils and debris left by fingers). The biological additives in the detergent digest these, leaving the plastics unharmed.

I've used this method many times. So far I've not had any problems, even with knobs with bright metal inserts.

I've just done the knobs for my Bush VHF81. This set is looking really good now, and I'll be putting some pictures in a blog soon.

Keep listening!

Bush VHF81 Chassis restoration

The electronic restoration of the VHF81 chassis was pretty straightforward. With the chassis removed from the cabinet everything is easy to get to.

Everything looked original, with just five wax paper and two Hunts capacitors to be replaced, including one connected directly across the switched AC input. This was replaced with a X2 type rated at 275V AC. Any other faulty components will be found when the set is powered up again.

The original power cable was replaced with a piece of modern white two core flex. I would usually have used black, but in this case white will fit in nicely with my planned colour scheme. As this is an AC/DC radio, I did a quick check with a DVM to confirm that the neutral was connected to the chassis, and not the live!

The mechanical problems were a bit more difficult. Replacing the broken dial cord took a while. Fitting the cord was reasonably straightforward, although the diagram on the 'Trader' service sheet helped a lot. Getting the tension right was much more difficult, especially when on the third or fourth attempt the tension spring flew off and disappeared somewhere under the bench! Fortunately I had something similar in my junk box, and after a cup of coffee it all came together OK.

The sub-chassis carrying the VHF tuner is attached to the main chassis via anti-vibration mounts; basically rubber grommets with brass bushes through the middle.  The old crumbling rubber bits were replaced with modern plastic grommets. Putting these in boiling water for a few seconds made them just pliable enough to be squeezed, with some difficulty, into the holes in the chassis.

Keep listening!

VHF81 Speaker baffle repair

With the chassis ready for testing I turned my attention back to the cabinet. The original grille cloth was badly damaged and had to go. It came off easily enough, but left behind hard patches of 50+ year old glue which might have shown through the new, thinner cloth. 

The plywood had also started to de-laminate, and trying to scrape the glue off just made it worse. It did eventually come off with help from a hot air gun, but I had to use automotive cellulose filler to fill the damaged areas of the wood afterwards.

24 hours later I used an electric sander and 320 grit abrasive paper to remove the excess filler, followed by a generous coat of black paint.  It's now ready to receive the new black grille fabric.

I also used some filler on the cabinet, as some scratches were still visible even after several coats of undercoat with light sanding in between them. The first coat of  paint looks good, although I did have momentary doubts over the colour... all will be revealed soon.

Keep listening!