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Old 18th Sep 2019, 11:31 am   #1
Tractionist
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Default Translucent Tuning Dial 'knobs' - re-manufacture?

Does anyone have experience of casting [or 3D printing] TRANSLUCENT tuning dial 'knobs'?

We all know about the 'cloudy' TR82 'knobs' ..... but I'm currently interested in those associated with the Nordmende 'Clipper', 'Transita'', and 'Mambo' sets i.e. the 603F's etc. These are very rare and just don't 'turn up'!

I have one knob to copy [which is a good start] ..... but wonder how successful people have been [if at all] in re-manufacturing these optically translucent components.
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Old 10th Nov 2019, 9:56 am   #2
pbengtech
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Default Re: Translucent Tuning Dial 'knobs' - re-manufacture?

Hi Tractionist,
Have you seen any of the Repair Shop programmes on the TV?
In one program Steve the clock maker made a clear knob for a GEC portable radio by finding a clear plastic pot, cutting off the rim and making a brass adaptor to fix it to the shaft. Luckily the radio needed a brass centre to match the other one.
If you really are stuck, you could make a rubber mould from a good knob and cast more out of clear casting resin.
I have needed to make rectangular wave change press type knobs in the past, and made them out of solid black acrylic plastic. Cut and polished by hand.
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Old 11th Nov 2019, 9:37 am   #3
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Default Re: Translucent Tuning Dial 'knobs' - re-manufacture?

This is a problem I have faced many times with vintage radio restorations. And I have been developing techniques since the mid 1970's to solve radio and TV restoration issues. I have not published this one though.

I only do this for my own beloved radios. This is because it is a time consuming process. Mind you most of my restorations fall into that category, so I get accused of over doing it often.

Many vintage transistor radios have opacified (once clear plastic) knobs.

Good examples are he NZ made Pacemaker radio, the Classic Sony TR-72 and you guessed it, the Nordmende Clipper.

In these radios you have to look via the clear knob (if it is clear) to see the dial markings.

My preferred technique for restoration is to accept the central and peripheral parts of the knob are cloudy, and replace the central window with crystal clear acrylic. In the case of the Clipper, you would have to accept the loss of the small taper on the surface.

The central area is machined out (on my hobby lathe) and and exactly fitting disc of acrylic is substituted. Keeping the outer knob perimeter and the central fitting. I don't use acrylic glue because it has an indeterminate chemical reaction with the old plastic, instead I use non chemically reactive 24hr two part expoxy resin.

I have attached a photo of a tuning knob restored this way.
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Old 11th Nov 2019, 10:23 am   #4
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Default Re: Translucent Tuning Dial 'knobs' - re-manufacture?

Fascinating [and ingenious] solutions guys .... keep 'em coming!
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Old 19th Nov 2019, 1:21 am   #5
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Default Re: Translucent Tuning Dial 'knobs' - re-manufacture?

I am modifying a KB Rhapsody radio but have some questions on restoring its appearance. It was not look after properly and had multiple breaks and cracks, most of which I've patched up. The plastic dial is ok and still very transparent after more than 60 years, the red is still red but the golden paint on the rotary dial has turned coppery and the speaker grille has tarnished. So has the handle and its brass fittings. The golden KB and Rhapsody letterings have faded. Any tips on restoring the colour of the dial to golden would be much appreciated. I am afraid of using spray paint, but maybe there are special pens for this purpose ?
I think the flaky dial markings are prints on a piece of golden paper so maybe not too difficult to reproduce ? Is it possible to custom make circular golden labels, something similar to stickers ?
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Old 19th Nov 2019, 2:30 am   #6
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Default Re: Translucent Tuning Dial 'knobs' - re-manufacture?

If you look on post #3, you will see the cone shaped central nut looks perfect. It didn't look like this when I started.

I hold these in a lathe's chuck and polish them while they rotate, then de-grease them with contact cleaner , leave for 24-48 hrs to acquire a golden look then spray with Holts duplicolour automotive clear. The Holts sprays are a very fine droplet lacquer with a quick drying solvent.

There is also a metallic gold Holts that can be used to restore previously gold painted surfaces. You certainly don't want to use any old paint for this task, it must be one like the Holts that can be applied progressively in very fine layers until it is just enough. Enamel spray is totally unsuitable.
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Old 19th Nov 2019, 2:12 pm   #7
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Default Re: Translucent Tuning Dial 'knobs' - re-manufacture?

Thanks for the tips. I think I will try my Montana Gold spray paint when its a bit warmer in the spring. The paint seems to be lacquer based and is suitable for use on plastic.
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Old 19th Nov 2019, 6:27 pm   #8
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Default Re: Translucent Tuning Dial 'knobs' - re-manufacture?

You dial looks to be scan-able - and then maybe re-touch'able with paintbox or some other programme? The most important part of the image is the actual scale markings - these seem to be pretty legible and should come out in a scan. One you have a good clean image of the scale elements [with the background gold omitted] - you could then get them printed onto transfer paper and stick that onto a thin gold disc [could even be gold foil]. BUT - half the scales 'colour' is white - so you will not be able to do that on a simple ink jet printer.
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Old 20th Nov 2019, 6:54 pm   #9
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Default Re: Translucent Tuning Dial 'knobs' - re-manufacture?

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You dial looks to be scan-able - and then maybe re-touch'able with paintbox or some other programme? The most important part of the image is the actual scale markings - these seem to be pretty legible and should come out in a scan. One you have a good clean image of the scale elements [with the background gold omitted] - you could then get them printed onto transfer paper and stick that onto a thin gold disc [could even be gold foil]. BUT - half the scales 'colour' is white - so you will not be able to do that on a simple ink jet printer.
Thanks. Great idea, I hadn't thought of transfer paper. Maybe a compromise would be to Photoshop the white lettering to black before printing.
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Old 20th Nov 2019, 9:58 pm   #10
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Default Re: Translucent Tuning Dial 'knobs' - re-manufacture?

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You dial looks to be scan-able - and then maybe re-touch'able with paintbox or some other programme? The most important part of the image is the actual scale markings - these seem to be pretty legible and should come out in a scan. One you have a good clean image of the scale elements [with the background gold omitted] - you could then get them printed onto transfer paper and stick that onto a thin gold disc [could even be gold foil]. BUT - half the scales 'colour' is white - so you will not be able to do that on a simple ink jet printer.
If you use white decal paper you can in fact create white lettering on ink jet waterslide transfer ('decal') paper using an ordinary domestic ink jet printer. (Or on a laser with laser decal paper). With careful colour selection, you can also mimic 'gold'.

Looking at the state of the dial, I think you'd have to use it as a guide to create a new one in Photoshop or whatever as it looks rather too far-gone to clean up a scan. Waterslide transfers have to be sprayed with several coats of clear gloss acrylic lacquer before they're applied, so the 'gold' background would I think, create a good likeness - certainly far better than what you have now.

If all the lettering was black, red, blue, green - whatever (anything but white), you could create a waterslide transfer on clear decal paper and apply that to gold foil paper on a replica dial. No-one is going to look at the replica dial and say 'it's not genuine' - how would anyone know without a genuine example alongside with which to compare it?

Rather than repeat what I've written in previous threads when this topic has cropped up before, the link below might be of interest. All of the images in the quick examples shown were created from the top one, which was black letters on a white background. If you look at the third image down, you'll see that its a reasonable approximation to white lettering on a gold background.

https://www.vintage-radio.net/forum/...lide+Transfers

It's also often said that we can't print white lettering on labels etc, such as for replica radio backs. The label on the replica back at the picture below, which I made for a little Maestro, printed on ordinary paper in an ink-jet printer is, I think, passable as white lettering on a dark brown background. Simple to do - the lettering was created black, then the image was 'inverted' so that the lettering showed up as white on a black background. The background could easily have been changed to another colour in a few seconds - dark brown for example, but I was happy with it as it was.

Hope that might help a bit.
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Old 21st Nov 2019, 7:45 am   #11
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Default Re: Translucent Tuning Dial 'knobs' - re-manufacture?

Quote:
Originally Posted by Jolly 7 View Post
I am modifying a KB Rhapsody radio......
......the golden paint on the rotary dial has turned coppery and the speaker grille has tarnished. So has the handle and its brass fittings. ?
The rim and the centre boss cover on this knob is made from brass, if you can remove them they are easy to polish with brasso wadding. Once cleaned to shiny brass and all residue of the polish has ben removed, the brass parts can be sprayed with clear lacquer to help stop further tarnishing.
The speaker grill is painted plastic and it tends to rub off over time. The grill can be removed by careful releasing all the melted lugs which go through the case to "weld" it in position. Then it can be sprayed gold. The handle fittings on the early radios are also brass and can also be removed for polishing.

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Old 21st Nov 2019, 11:22 pm   #12
Jolly 7
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Default Re: Translucent Tuning Dial 'knobs' - re-manufacture?

.......or replica radio backs. The label on the replica back at the picture below, which I made for a little Maestro, printed on ordinary paper in an ink-jet printer is, I think, passable as white lettering on a dark brown background. Simple to do - the lettering was created black, then the image was 'inverted' so that the lettering showed up as white on a black background. The background could easily have been changed to another colour in a few seconds - dark brown for example, but I was happy with it as it was.

Hope that might help a bit.[

Thanks David ! That's so useful. I saw the Taytronics image with the white on gold lettering. I've never used decal paper before, so will surely give it a try.
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Old 21st Nov 2019, 11:26 pm   #13
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Default Re: Translucent Tuning Dial 'knobs' - re-manufacture?

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Quote:
Originally Posted by Jolly 7 View Post
I am modifying a KB Rhapsody radio......
......the golden paint on the rotary dial has turned coppery and the speaker grille has tarnished. So has the handle and its brass fittings. ?
The rim and the centre boss cover on this knob is made from brass, if you can remove them they are easy to polish with brasso wadding. Once cleaned to shiny brass and all residue of the polish has ben removed, the brass parts can be sprayed with clear lacquer to help stop further tarnishing.
The speaker grill is painted plastic and it tends to rub off over time. The grill can be removed by careful releasing all the melted lugs which go through the case to "weld" it in position. Then it can be sprayed gold. The handle fittings on the early radios are also brass and can also be removed for polishing.

Mike
Thanks again Mike. Since you are the KB expert, I have a question for you please. Do you know what the capacitance values of the gang condenser are in the Rhapsody ?
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Old 22nd Nov 2019, 1:24 pm   #14
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Default Re: Translucent Tuning Dial 'knobs' - re-manufacture?

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Do you know what the capacitance values of the gang condenser are in the Rhapsody ?
Jolly_7,

Your enthusiasm for AM radios is actually quite infectious and it makes me want to start building some AM radios again!

With your radio work it is very important that you have a good capacitance meter for measuring pF range capacitances, so you can check values yourself for your experimental work.

Over 15 years ago I got a very good meter from AES in the USA, they are not too expensive either. I had a look and they still sell exactly the same meter.

Because these work so well they have become very popular with vintage radio enthusiasts and radio restorers in the USA. There may be a supplier in the UK, but AES have a very good mail order system to ship worldwide:


https://www.tubesandmore.com/product...e-meter-yf-150

I recommend you get this meter and you will end up using it countless times.
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Old 23rd Nov 2019, 2:32 am   #15
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Default Re: Translucent Tuning Dial 'knobs' - re-manufacture?

Thank you. I hope you do build some high quality AM sets soon so that we can learn from your expertise. For me there's something about MW that's magical about not just how the different circuit types work, but also the manner in which signals can propagate over vast distances unpredictably. Shorwave was designed to propagate, but MW can also produce some interesting surprises. I guess I got addicted when I built my first superhet almost 35 years ago and started DXing shortly after.
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Old 23rd Nov 2019, 10:39 pm   #16
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Default Re: Translucent Tuning Dial 'knobs' - re-manufacture?

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For me there's something about MW that's magical about not just how the different circuit types work, but also the manner in which signals can propagate over vast distances unpredictably.
It is surprising how well and how far MW radio stations propagate, even locally. For example there is a station 4KQ in Brisbane on 693 kHz, if you are in Brisbane and start driving away from the transmitter for over an hour, all the FM radio stations vanish, but even over 100km away you can still get a good signal from 4KQ, which I can get with good reception, in most places in the town I live in 100km north from the transmitter, day or night. The FM stations are really only good line of sight. It is great if you are in the city where the transmitter is, but that is it. It is a shame that many AM stations are getting decommissioned.

Then at night with a good AM radio you can get all kinds of stations, both MW and and shortwave ones wordwide on a fairly small antenna.

One thing that might have saved some of these AM stations is that they are also on the internet and can therefore generate some revenue from that.

Also, one advantage of the AM transistor radio, is that you can have the ferrite rod antenna (the thing that made the "pocket radio" possible) and don't require a whip antenna like an FM radio, and the rod drastically reduces interference effects that exist in the electric component of the field.
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