Dyeing colourless heatshrink blue to match small vintage electrolytics

[GrimJosef]

In the 50's and 60's, and maybe at other times too, several manufacturers sold small-ish axial electrolytic capacitors which were wrapped in transparent blue insulating film. Among them were Philips and Hunts and I care about the Hunts ones because Quad used them in the C5 position (KT66 cathode resistor bypass) in their Quad II amplifier. This capacitor has reached the end of its useful life in almost all the Quad IIs I see and I would like to be able to replace it with something that looks similar. But modern electrolytics always seem to be clad in opaque, often dark coloured and patterned film. They're not convincing in terms of their look.

I've searched on-and-off for transparent blue heatshrink with which I might strip and re-insulate modern caps. But I've never found any (opaque yes, transparent no). So in the end I've had a go at dyeing some of my own. It turns out that the effectiveness of dyeing depends on absolutely everything - the dyestuff, the material being dyed, the temperature of the dye, its concentration and the length of time the material is immersed in it. After a deal of experimentation I've finally found a parameter set which seems to work.

I started out with this colourless heatshrink https://uk.farnell.com/pro-power/150...-5m/dp/1008472. One of its features is that it shrinks at a relatively low temperature, which minimises the risk of cooking temperature-sensitive electrolytics with the heat-gun. It's described as being made of halogen-free polyolefin but I don't know any more about the material than that.

Dyeing plastics isn't always easy, so I chose a specialist plastic dye - Jacquard iDye Poly https://www.jacquardproducts.com/idye-poly. Their colour range includes two blues, Blue 451 and Turquoise 459. I started out with Blue, but that turned out to be too violet. Turquoise is very much closer and that's what I ended up using. It's readily available from online UK craft retailers.

Long story short - I dissolved all of the dye powder (but not the sachet, even though Jacquard say it's soluble) and the colour enhancer in 800ml of water. I then heated that up. I found that 3 minutes immersion at a dye temperature of 70-75C gave me the colour depth I wanted. The picture shows four capacitors. From the left, the first and third are Hunts ones removed from two Quad IIs of different dates. The fourth one is an old stock Philips. The second one is a modern Sprague TE1410 (25uF, 100V) which is what I wanted to use in the Quad IIs. These arrive with a very thin colourless film stuck (very tenaciously !) over the legend which is printed direct onto the aluminium can. I've slipped my dyed heatshrink over the top of this and shrunk it down. I have to say I'm quite pleased with it.

Things I learned on the way:

1. I cut the heatshrink to a little over the length I wanted and preshrunk it slightly to form it into rough tubes, so the dye could get to the inside as well as the outside.

2. Below 75C the heatshrink didn't contract significantly during the dyeing. At 85C it shrunk right down to minimum (too small to stretch over the caps) in a couple of minutes.

3. I sewed a length of thread through a hole at the very end of the heatshrink which let me dip it into the dye and pull it out again.

4. I heated the dye in a glass jar in the microwave. Needless to say it's vital to keep splashes and and spitting off surfaces you don't want to change colour. The colour enhancer smells too and is probably not safe to eat/drink, so maybe don't use the kitchen microwave !

5. I did the dyeing in a good quality stainless steel thermos flask and the temperature stayed stable (maybe 2C cooling) for tens of minutes.

6. Different dyes dye very differently. It took 3 minutes to achieve the colour depth I wanted with Turquoise. I could get the same colour depth with Blue in less than 10 seconds, albeit using twice the concentration.

7. The manufacturers say the made-up dye can be stored cold but the more times it's used, the more pigment will be lost to the plastic, so the dyeing time may need to be lengthened.

8. It would be good to find thinner-walled heatshrink, to replicate the original film more closely, but all the thinner-walled stuff I've come across had a much higher shrink temperature, and generally wasn't polyolefin.

9. Cutting the dyed tube to final length is a faff. It ideally needs to be only very slightly longer than the cap, allowing for any length contraction during the final shrink. If it's too long the shrunk ends look thick and clumsy.

Cheers,

GJ

[Kentode]

I doff my cap to you GJ, that is truly a labour of love, excellent work!

[joebog1]

I agree !!! even a close look suggests Philips!! Excellent.

Joe

[Argus25]

Great work and a tribute to the nature of the Art & Science that is the cornerstone of excellence in vintage electronic equipment restorations. A+ in my book.

[Philips210]

Hi.

That's an excellent result and well worth the effort.
I tried to find something similar a while back but had no luck. A search for coloured transparent polyolefin didn't throw up much. A search for polyolefin translucent colours was more successful. This company http://www.insultab.com/products/dec...ink-specs.html looks to stock a wide range of various polyolefin finishes.

Regards,
Symon

[GrimJosef]

Thanks for the kind words folks !

I sounds as though the insultab stuff would be OK if translucent would meet your needs. But the original capacitor coating films were clearly (no pun intended ) transparent i.e. you could read the legend printed on the capacitors through them. I understand translucent to mean that some light will come through but that it will be diffused so that any detail on the far side will be obscured.

The main drawbacks with the relatively thick polyolefin tubing I've used are that it is a bit scattery/milky and that its surface is rather dull, not shiny. The unused Philips cap in my previous picture is noticeably shiny looking.

Cheers,

GJ

[Philips210]

Hi.

This product https://www.ebay.co.uk/itm/100PCS-Tu...qvOUPSdiBZj5hA for sleeving cells may be suitable.

It appears a transparent blue sleeve is included in the range but this looks somewhat darker than the type used on the Philips and Hunts electrolytics.

Regards,
Symon

[GrimJosef]

Thanks Symon, I checked the listing but although I can see a Transparent sleeve and I can also see two blue ones, one called Blue and one called Purple-Blue (or Blue-violet in the drop-down ordering menu) I can't see any transparent blue ones. I've attached a screen shot showing the picture of all the different colours and also showing the drop-down menu. The one I've pointed to as transparent is, I'm sure, transparent. But I'm also sure it's colourless (or Transparent white, if you like). The others are coloured, but they are not transparent. Or have I missed one ?

Cheers,

GJ

[Philips210]

Hi GJ

I was going by the main listing pic of the 7 cells. The centre one appears to be transparent blue. There seems to be an inconsistency in the drop down menu and the pic of available colours in the main pic.

I also found this listing https://www.ebay.co.uk/itm/152852046...MakeTrack=true which may be better. They also stock clear yellow, clear green, clear purple and transparent sleeves.

I've also seen clear gold sleeve listed on ebay which was often seen on some old electrolytics.

Regards,
Symon

[GrimJosef]

The latest listing does indeed include transparent blue. So someone somewhere has a tube extruder fed with transparent blue PVC. The retail market seems to be for customising vape machine batteries, which seem to be wider than the capacitors I need to clad. But maybe the tubing is also manufactured in smaller sizes ?

Cheers,

GJ

[Philips210]

Hi.

I was wondering if the sleeve was cut down its length and maybe a strip taken off to reduce its circumference, then shrink this on a smaller diameter cap. The join being out of view but I wonder how well it would grip the cap. Just a thought.

Regards,
Symon.

[GrimJosef]

In my limited experience of slitting heatshrink Symon (confined mostly to making a small hole in the stuff as a 'breakout' to feed a wire through) any cut opens up enormously when you start the shrinking. I'd struggle to believe that a tube which is still too large when fully shrunk could be modded to an even smaller size.

As a follow-up to my earlier posts I thought I would try a thinner, shinier, less scattery/milky heatshrink material. There is a family of these based on 'modified fluoropolymer' (a form of PVDF - polyvinylidene fluoride - I believe). What put me off them originally was a) that I know PVDF to be chemically very unreactive, so perhaps unusually difficult to dye and b) that the shrink temperature is much higher than the polyolefins. As it was, though, neither of these factors turned out to be a showstopper.

The attached picture shows the result. The lower capacitor is the one whose cladding I dyed a couple of weeks ago. The upper one is the latest result with the fluoropolymer. The colour is just as good but the upper film is indeed a lot thinner, shinier and clearer than the lower one. The picture clouds the distinction slightly because there is a little bit of camera defocus in the foreground. But that's certainly not the only reason for the clearer typescript visible on the upper capacitor (you can judge the defocus by looking at the leadout wires at the ends of the two caps).

The actual tubing I cose was Raychem RT-375-3/8-X-STK, available from Farnell, at least while stock lasts (their UK order code 1210450). This hardly needed to be shrunk at all to fit onto my caps, so heating wasn't as much of an issue as it might have been. But the thinner material and the lack of dye concentration during shrinkage meant I did need to load a lot of dye into the plastic. To do this I extended the soaking time to 10 minutes and raised the dye temperature to ~92C (94C at the start of the soak, 90C by the end). The tube didn't shrink detectably during the soak.

I think this is probably as close as I am going to get to the look of the original film. I really struggle to tell the difference fom old stock caps. I now need to set to work soaking a fair number of sleeves !

Cheers,

GJ

[Radio Wrangler]

They both look good. Philips must have had batch variation in making theirs, as well. You might as well choose on material availability and difficulty of your processes.

David

[joebog1]

I must say you are a stickler for perfection!! I thought the fist effort was quite good, but this new experiment is excellent. I must say though, In another thread I am looking for Philips axial caps. While desoldering some from the PCB, I used a tad too much heat to prevent pulling out the plate throughs and found that the heatshrink on my Philips caps are actually wound onto the cap like tape, rather than a heat shrunk tube. See photo. Also, the printing is on the plastic sleeve, NOT the cap itself as they used to be.

Joe

[Argus25]

This thread reminded me of something, aside from the excellent work being done here that I have already remarked on.

Back in the early 1970's my brother worked at a transformer manufacturing company. This was before heat shrink was in general use. They would get an effect exactly like heatshrink, but with no heat. The tubing was effectively already shrunk, then they would dip it in a solvent (I think it was toluene), the sleeve would then swell up to 3 or 4 times in size and go all rubbery and slippery, I remember playing around with it and probably sniffing up more toluene than was recommended.

In any case when it evaporated the tubing tried to shrink back to its original size and it would wrap itself around things, just like heat shrink sleeve.

I don't remember seeing any clear or blue sleeve though, only yellow & white.

The method may be of some use, but further research would be required to see if it could be anywhere near as good as what has been done here with the heat shrink sleeve.

[joebog1]

Argus!! I remember only red sleeving. It still reminds me of early silicon. The "dilating" fluid as it was "labelled" came with the tubing. This memory is from the Snowy Mountains Hydro Scheme radio workshop. Sleeving itself was not smooth, but sort of roughish if I may use that term. I still have bits of it today on various bits of kit. IF you dont disturb it, it functions like it did in the 1960,s. IF you "stress" it, it will split and doesnt insulate so well anymore. I also seem to remember ( but cant quote figures) that it was suitable up to several thousand volts.

Sheesh you make me think WAY back !!!

Regards
Joe

[daviddeakin]

Maybe I missed some explanation, but are you saying those are modern capacitors with their labelling removed and replaced with your blue dyed heatshrink? How did you do the lettering?

[GrimJosef]

Yes, they are modern capacitors. The ones I wanted to cover were made by Vishay Sprague who print the lettering onto the capacitor can and then wrap it in a very thin, very durable and very, very adhesive colourless transparent film (think Sellotape only stronger and stickier). So I don't have to do any labelling with these. I just slip the blue-dyed heatshrink over and shrink it.

I have, in the past, stripped the outer opaque film off other modern capacitors and then labelled them using water-slide transfers before re-covering them in colourless heatshrink. This can work quite well but now the faff comes in producing a convincing label and in positioning it around any grooves in the capacitor can. Grooves half-way along the can are sometimes present these days unlike in times past.

Cheers,

GJ