Retronics

Restoring, remodeling and creating electronic devices

Plastic fantastic

In the early 60’s, before radios became a standard feature in all cars, Radionette made a portable radio called Transauto, which came with an optional mounting frame for car installation. This frame contained a set of connectors from which the radio was supplied with power from the car battery and signals from an outside antenna, in addition to connectivity for a separate loudspeaker.

In this period, radio manufacturers made use of new plastic materials, streamlining mass production. Some types of plastic like ABS turned out to be strong and durable, while others deteriorated more quickly. The plastic used in Transauto is very brittle, and many of the remaining radios are characterized by broken plastic.

The one I got was in poor condition, with some pieces of plastic broken off, some cracked, all yellowed, and everything extremely dirty.

On the inside, battery acid leakage had caused corrosion.

This would normally be regarded as junk, but I decided to give it a chance.

Trying to fix the disintegrated plastic seemed hopeless, and the best option was to make new parts. I designed new parts in Fusion 360, a great modeling software which is available as a free version for personal use.

The shape of this speaker grille is more complex than it may look at first glance, and comprehensive to 3D model for a newbie like me.

Printing this part took about 10 hours on my Prusa. The material used is Prusament ASA in the color “Natural” which resembles ivory (not bright white, which probably would look unnatural) 😉

Though this printer is known to be one of the best alternatives available within a hobbyist budget, one can easily see that the object is 3D printed (not casted). Therefore, some surface finishing processes are necessary.

I used sanding paper; P120, 400 and 800, and got a reasonably smooth but matte surface.
Next step was to use acetone vapor to make the surface shiny. This process works with materials ABS and ASA, and it’s quite easy: Put the object in a transparent storage box, and leave it there for a while together with paper towels soaked in acetone. Some fans help distributing the acetone vapor, and speeds up the process. In this case, 20 minutes was appropriate.

After taking the object out of the box, I let it dry for a few hours. Now the surface is smooth and shiny, with no evidence of being 3D printed.

Same process for other plastic parts.
Some of the knobs and buttons were also cracked, and all of them yellowed, so I decided to replace them all.
For smoothing the knobs, I used a bench drill and Abralon abrasive pads, before just 2 minutes of acetone treatment.
Old vs new knob. The old brass caps are reused; they just needed a good cleaning and polishing, using abrasive pads up to P3000, and then Autosol metal polish.
New vs. old push buttons. This took some manual sanding before acetone treatment.
The old vinyl cover was also damaged, both from wear and tear, and battery acid, so I stripped it off.

Unable to find new vinyl matching the original blueish gray color, I went with something different: tolex in color “royal blue”, ordered from tube-town.net.

Spray glue worked well. A heat gun was used to stretch the tolex around the corners.
Renewing brass parts, using sanding paper, abrasive pads and metal polish. A drill speeds up the process.
The old plastic strap was cracked and extremely yellowed, so I made a new one of faux leather.
On the inside, the radio first and foremost needed a good cleaning. Dust removal using a paint brush and a vacuum cleaner. Contact cleaner for the switches.
Some capacitors were leaky or dried out, and had to be replaced. The mustard caps, however, seems to last forever 🙂

There were some scraping noises in the loudspeaker when tuning radio frequency, which turned out to be caused by a slightly bent plate on the tuning capacitor.

The dial string was slipping, and needed to be tightened.

The alignment was grossly off. Someone must have turned the trimmers randomly.

Final assembly. The old plastic strings covering the gaps between the vinyl sheets, were replaced with brass wire. On the bottom of the radio, we can see a connector that interfaces with the car mounting kit.
The finished restoration. An ugly old piece of junk had turned into a beauty.
, ,

Posted by:

retronics.no

2 responses to “Plastic fantastic”

  1. Stein Roger Bang avatar
    Stein Roger Bang

    Fantastisk jobb! Nydelig! Jeg kjøpte nylig en liten samling Radionetter, og denne modellen var overraskelsen blant dem. Det var bare å kjøpe batterier, så strømmer det inn radio i fin lyde fra hele verden! Tanken med innkjøpet var å ha det litt gøy med montering av Bluetooth og lignende, men når denne fungerte så bra så beholder jeg den original. Bytter bare elektrolytter for ordens skyld. Men kabinettet er en utfordring. Vinylen jobber jeg med, beholder patinaen men får vekk skitten. Dreieknotter får jeg tak i. Men plasten…gul og porøs. Du kunne ikke tenke deg å dele printefilene dine? Uansett, gratulerer med en imponerende jobb og takk for at du deler historien og inspirerer!

    Liked by 1 person

    Reply
    1. retronics.no avatar
      retronics.no

      Hei! Jeg kan sende .stl-filer til deg på mail, hvis du lover at de kun er til bruk for egne radioer (det er enkelte kremmere som forsøker å tjene penger på slikt). Send mail til retronics_no krøllalfa protonmail.com, så svarer jeg på den 🙂

      Like

      Reply

Leave a comment