RCL? Polycarbonate capacitors

[Julesomega]

I found a pack of 100nF 100V axial capacitors dating from 1986. They bear the moulded inscription >RCL PMT/2R< and I have a few questions about these

Was RCL a known brand? I can't find them in RS or FEC catalogues from the period?

The Stores card with them is annotated "Polycarb" - is that like to be correct? There were capacitors in this style in both polycarbonate and polypropylene

Is there any benefit of using Polycarb over polyprop?

[Radio Wrangler]

Known maker. Likely to be OK

Polycarbs were high stability and often available in tight tolerance for low-medium freq filters etc. They avoid the one-shot value shift at 70C that plagues polystyrene. They pre-date polypropylene so I never compared them directly. Polypropylene are lowish loss, but not, I think, such high stability.

David

[dazzlevision]

RCL Components Ltd, Ash Road, Wrexham Industrial Estate, Wrexham, Clywd, LL13 9UN. Maker of capacitors (now defunct?). Tel: 01978 661201.

The PMT designation was originally used on STC/ITT capacitors that otherwise looked identical.

Photo attached.

[dazzlevision]

I expect that RCL took over the rights to this former STC/ITT product when Standard Telephones and Cables (STC) was spun out of ITT Europe in 1982 (and subsequently acquired by Northern Telecom in 1991).

the one-shot value shift at 70C that plagues polystyrene

What is that all about?

[Craig Sawyers]

(something) Capacitors Ltd?

It looks like ITT made physically identical parts.

Craig

[Craig Sawyers]

Originally Posted by dazzlevision

RCL Components Ltd, Ash Road, Wrexham Industrial Estate, Wrexham, Clywd, LL13 9UN. Maker of capacitors (now defunct?). Tel: 01978 661201.

The PMT designation was originally used on STC/ITT capacitors that otherwise looked identical.

Photo attached.

Perhaps a later iteration is ICW, also in Wrexham http://www.icwltd.co.uk/about-us/

Craig

[dazzlevision]

Originally Posted by Craig Sawyers

Perhaps a later iteration is ICW, also in Wrexham http://www.icwltd.co.uk/about-us/

Craig

Possibly, although the Wrexham area seems to have been something of a capacitor "hot spot", with A H Hunt, Advance Filmcap (later Gould), BHC and MFD all having factories there at one time or other.

[ms660]

Originally Posted by merlinmaxwell

What is that all about?

The polystyrene starts to soften, had to be quick with the soldering iron when I used to solder them.

Lawrence.

[dazzlevision]

Originally Posted by Craig Sawyers

(something) Capacitors Ltd?

It looks like ITT made physically identical parts.

Craig

When ITT pulled out of Europe (in the early 80s), all the UK made "ITT" capacitors were then rebranded STC.

As an aside, in the mid-1970s, ITT acquired Erie Electronics (in the UK) and their parts were then rebranded ITT....until STC was spun out of the ITT empire in the early 80s.

ITT/STC plastic film and mica capacitors were made in their Paignton factory.

Looking at the relevant ITT/STC data, the PMT range is Polyester dielectric.

[kalee20]

Originally Posted by Julesomega

Is there any benefit of using Polycarb over polyprop?

They'll withstand higher temperatures - and they're smaller. But as David says, they're more lossy.

Basically, somewhere between polypropylene and polyester.

Nobody makes polycarbonate capacitors now, though - the sole manufacturer of capacitor-grade polycarbonate film (Bayer) stopped making the stuff because their machines needed refurbishing and they reckoned that the sales didn't justify it. So all the manufacturers of polycarbonate capacitors (Wima, Roederstein, Philips, etc) withdrew their polycarbonate ranges at the same time.

Originally Posted by Craig Sawyers

(something) Capacitors Ltd?

Yes. Recsam Capacitors Ltd.

[Julesomega]

Thanks everyone, everything I wanted to know
So mine are Polyester and from North Wales, which explains why there were delivery notes in the box from a distributor in LLanwrtyd Wells

What is the reputation of Polyester?

[kalee20]

Polyester... It's a tough, stable film. You know when you read about litter-droppers, the crisp packets they through in the hedge won't deteriorate for 1,000 years? Well, that's how long the capacitors will last, too. Good news!

Electrically, it has a very high insulation resistance; it's easy to metallise, so capacitors can be small and low-inductance. It's fairly stable. Loss isn't as low as polystyrene or polycarbonate, so not so good for high-Q tuned circuits. It's far superior to paper.

[Radio Wrangler]

Watch out with polyester about dielectric absorption.

David

[turretslug]

Originally Posted by kalee20

Polyester... It's a tough, stable film. You know when you read about litter-droppers, the crisp packets they through in the hedge won't deteriorate for 1,000 years? Well, that's how long the capacitors will last, too. Good news!

And the capacitors won't be subject to the same degree of sunlight UV, wind/dust erosion, rain that even nowadays is still slightly acidic etc. that the crisp packets will. Better news!

I recall buying a big bag of ITT-branded 100nF 400V PMT/2R caps from Birketts for very few shekels many moons ago. I've seen this type of "butterscotch" hard plastic encapsulated capacitor with several brand-names- sometimes in black or blue print rather than moulded in.

[dazzlevision]

Such as this one - Telegraph Condenser Company (Plessey).

[Radio Wrangler]

Originally Posted by merlinmaxwell

What is that all about?

It's a stress relief effect in the dielectric material itself and happens somewhat under the melting point.

David

[Craig Sawyers]

The Welsh connection continues. ICW (Industrial Capacitors Wrexham) have been acquired by Charcroft https://www.charcroft.com/ .

The reasoning is that part of Charcroft supplies the audio industry ( https://www.charcroft.com/markets/audio/ ), and 80% of ICW's production is now to the audio industry (mainly loudspeaker crossovers, but also amplifier use).

There is a good series of visit photos of the ICW plant and high quality polypropylene film capacitor manufacture here https://www.hificollective.co.uk/blo...cap-visit.html

Craig

[Julesomega]

I've dug out the despatch note which shows they came in 1995 from Charcroft Electronics Ltd, Dol-y-Coed, Llanwrtyd Wells who are still there and trading in splendid isolation on Google maps

Thanks for the replies, much indebted, and as I have a lifetime's stock of these, and a few 0.47 and 1µF (63V) you are welcome to a few for the cost of postage

The value of these things is not as high as I had thought: CPC have Wima 100n 100V dc at 18p ea. A SMT equivalent is however quite costly: Mouser list a 2220 package Wima for 69p inc. VAT so expect to see radial leaded types in modern products for some time yet