Wima 'Toffee' Capacitors

[factory]

Originally Posted by Lucien Nunes

Agreed. Tropyfol 'M' types are metallised paper and therefore suspect. Tropyfol 'F' are polyester and seem to be holding up well. They just look similar to phool the audiophools. Imagine if Mustards could be either paper or polyester!

See thread here where I was trying to find reasons not to change 200+ apparently good caps in an organ: https://www.vintage-radio.net/forum/...ad.php?t=98383

I had very few problems with the yellow Tropyfol 'F' types at work from the 1970's, sometimes the insulation was cracked or peeling off at the surface so they got replaced, I suspect this was mainly caused by the drying part of the ultrasonic cleaning plant.
Another problem was one that was located next to a dropper resistor for the Zener powering the board, it would cause that quarter of that circuit to drift out of calibration with the heat.
The problems were very rare though, many are still in service in trains at the moment and probably will be till the trains are eventually withdrawn from service & replaced.

Now that I no longer repair electronics for a living I was able to buy the components that were to be binned with the closure of the department, so I now have many NOS WIMA yellow capacitors for use in my own repairs, most are lower voltage ones though.

David

[G6Tanuki]

Originally Posted by radioman

Do you think that putting heatshrink over them before fitting would help to prolong their lifes ?
I have seen a few on old computer boards (stored in less than ideal conditions) that are covered in cracks... and measure faulty after I've removed them.

I wouldn't consider heatshrinking them: indeed I'd think that the high temperature-gradient involved in heatshrinking would exacerbate the cracking of the resin encapsulation, so degrading the underlying moisture-sealing and if anything it would be hastening failure!

Why go to the hassle?? When yellow MKT-caps are available for pennies??

If you're faced with suspect components [either in-circuit or in your spares-racks] it only ever makes sense to replace them with currently-most-reliable-technology parts.

Good-quality, reliable parts are dirt-cheap these days. Your time is expensive!

[m0cemdave]

Originally Posted by Heatercathodeshort

They can be confused with the type manufactured by Plessey. They look identical but never appear to be faulty, not even leaky but that is Plessey quality for you. John.

I'm not sure about that. I have seen plenty of Plesseal types with badly cracked encapsulaton - including some where it has fallen off completely, leaving just the capacitor winding.

[pmmunro]

EMI 201 vidicon cameras https://www.tvcameramuseum.org/emi/201/201p1.htm used large numbers of dark toffee coloured Wima capacitors. The encapsulating resin of these developed severe cracking often causing the resin to fall off leaving the wound foil exposed. I don't know how many types were involved, nor can I remember the foil material. I also seem to remember a fungus like discolouring along the cracks which made them look diseased, not at all pleasant.

Kits were issued for their wholesale replacement in the camera head, CCU and power supply but I don't know if these kits came from EMI or the BBC Equipment Department. It must have cost someone a lot of money, possibly WIMA or the resin supplier, even if only through damage to their reputation.

PMM

[stevehertz]

Is it these that are found in the large, high quality Grundig late 50s radios? I remember changing a load of them last time I restored a model 3028, but I don't recall the brand?

[Nuvistor]

Yes, Grundig used these in the late 50’s early 60’s.