Dubilier/RS white axial caps - which dielectric? - UK Vintage Radio Repair and Restoration Discussion Forum

whiskas · 7th Jan 2019, 12:27 pm

Hi All,

I have some 0.015uF 400V white caps here, some marked Dubilier, some marked RS.
Does anyone have knowledge or an old RS catalogue which gives details of the actual dielectric type used in these caps?
I have encountered there were several colour versions of these caps: white, grey, two tone blue, white/blue.. so I just want to know what dielectric was, it would be useful to know what the other colours' dielectric was too ...
I've attached a photo of the cap in question
Thanks for any help chaps!

Nuvistor · 7th Jan 2019, 12:32 pm

They are mixed dielectric, paper and some type of plastic. I would not use them, they were better than paper only types but still failed, especially in pulse circuits.

whiskas · 7th Jan 2019, 12:40 pm

Thanks for that info Frank!

Were they grey ones any better?

ms660 · 7th Jan 2019, 12:41 pm

https://www.americanradiohistory.com...ch=%22dubilier mixed dielectric%22

Lawrence.

whiskas · 7th Jan 2019, 2:02 pm

Thanks again chaps, now that you mention the term 'mixed dielectric' it has jogged my memory - thanks for the details which further expand my knowledge!

barrymagrec · 7th Jan 2019, 2:27 pm

Quote:

Originally Posted by whiskas

Thanks for that info Frank!

Were they grey ones any better?

The grey ones were dire on anything involving AC - avoid.

Hartley118 · 7th Jan 2019, 3:27 pm

I recently bought an old valve amplifier which included some of the two-tone version of these caps. I thought that they looked quite promising with their smart intact encapsulation, but leakage measurements suggest that they use a dielectric of damp paper. Some of mine measured around 10Kohms!

Martin

kalee20 · 7th Jan 2019, 3:28 pm

I've got a few, half blue / half grey moulding. Came from Electrovalue in the 1970's, catalogued as 'mixed dielectric.'

I have come to understand that they are paper/plastic. But anything paper in a capacitor is to me now, a recipe for leakage at some point in the future - in short, a no-no!

David G4EBT · 7th Jan 2019, 3:49 pm

Maybe these jobbies?

dazzlevision · 7th Jan 2019, 4:44 pm

Fourth picture in post #1.

https://www.vintage-radio.net/forum/...ad.php?t=98964

Philips210 · 7th Jan 2019, 5:18 pm

Hi

These mixed dielectric capacitors were often used in mains filter circuits and as the boost capacitor in valve line output stages. They weren't all that good back in the day but mustn't complain as they used to keep us a busy with simple repairs.

I have quite a few in my collection but wouldn't use them. A fair number exhibit swelling and cracking probably due to the paper being hygroscopic.

From memory, the blue/yellow ones as in David's post, were used in BRC TVs such as the 1400 chassis. I never did find out if the colours of the case were of any significance.

Regards
Symon

m0cemdave · 7th Jan 2019, 11:06 pm

I think the usual problem with these was that the plastic case was moulded in two halves and would crack at the seam and allow moisture ingress. It's very common to see this, even in unused old stock examples.
I am guessing that the plastic was affected by temperature cycling. A bit like the problem with the dreaded Hunts types.

Boater Sam · 8th Jan 2019, 5:35 am

I have bins full of the white ones, all new, look perfect, in various values and voltages.
I was hoping to sell them to the audiophools on ebay and buy a mansion, a Ferrari and another boat.
Please don't tell anyone else that they are useless, keep it between you and me.

Diabolical Artificer · 9th Jan 2019, 8:05 am

Interesting, I too too have a few of these types but mine are dark blue/light blue. I have some big ones rated at 1kv, usually use this sort of thing when fault finding on scopes say to temp replace components to get a circuit working.

Not all paper caps are KO'd, I have some Dubilier 1u 600v, these are rather useful, it ain't easy to find similar rated caps. Out of a jar of about 20, 2 were leaky.

Andy.

Neil Purling · 9th Jan 2019, 4:14 pm

One of those Dubilier yellow & blue jobbies in a Ferguson CTV with the Thorm 8500 series chassis gave me the biggest fright of my life, ever. The shock as it exploded literally made be jump. Both of my feet left the ground. It went off six inches from my right ear hole.
Split the case wide open of course.

7th Jan 2019, 12:32 pm	#2
Nuvistor Dekatron Join Date: Aug 2013 Location: Wigan, Greater Manchester, UK. Posts: 9,433	Re: Dubilier/RS white axial caps - which dielectric? They are mixed dielectric, paper and some type of plastic. I would not use them, they were better than paper only types but still failed, especially in pulse circuits. __________________ Frank

7th Jan 2019, 12:40 pm	#3
whiskas Octode Join Date: Mar 2016 Location: Knutsford, Cheshire, UK. Posts: 1,500	Re: Dubilier/RS white axial caps - which dielectric? Thanks for that info Frank! Were they grey ones any better? __________________ ...where on earth did that spring/screw go??

7th Jan 2019, 12:41 pm	#4
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: Dubilier/RS white axial caps - which dielectric? https://www.americanradiohistory.com...ch=%22dubilier mixed dielectric%22 Lawrence.

7th Jan 2019, 2:02 pm	#5
whiskas Octode Join Date: Mar 2016 Location: Knutsford, Cheshire, UK. Posts: 1,500	Re: Dubilier/RS white axial caps - which dielectric? Thanks again chaps, now that you mention the term 'mixed dielectric' it has jogged my memory - thanks for the details which further expand my knowledge! __________________ ...where on earth did that spring/screw go??

7th Jan 2019, 3:27 pm	#7
Hartley118 Nonode Join Date: Aug 2015 Location: Cambridge, Cambs. UK. Posts: 2,198	Re: Dubilier/RS white axial caps - which dielectric? I recently bought an old valve amplifier which included some of the two-tone version of these caps. I thought that they looked quite promising with their smart intact encapsulation, but leakage measurements suggest that they use a dielectric of damp paper. Some of mine measured around 10Kohms! Martin __________________ BVWS Member

7th Jan 2019, 12:27 pm	#1
whiskas Octode Join Date: Mar 2016 Location: Knutsford, Cheshire, UK. Posts: 1,500	Dubilier/RS white axial caps - which dielectric? Hi All, I have some 0.015uF 400V white caps here, some marked Dubilier, some marked RS. Does anyone have knowledge or an old RS catalogue which gives details of the actual dielectric type used in these caps? I have encountered there were several colour versions of these caps: white, grey, two tone blue, white/blue.. so I just want to know what dielectric was, it would be useful to know what the other colours' dielectric was too ... I've attached a photo of the cap in question Thanks for any help chaps! Attached Thumbnails __________________ ...where on earth did that spring/screw go??

7th Jan 2019, 3:28 pm	#8
kalee20 Dekatron Join Date: Feb 2007 Location: Lynton, N. Devon, UK. Posts: 7,088	Re: Dubilier/RS white axial caps - which dielectric? I've got a few, half blue / half grey moulding. Came from Electrovalue in the 1970's, catalogued as 'mixed dielectric.' I have come to understand that they are paper/plastic. But anything paper in a capacitor is to me now, a recipe for leakage at some point in the future - in short, a no-no!

7th Jan 2019, 3:49 pm	#9
David G4EBT Dekatron Join Date: Feb 2003 Location: Cottingham, East Yorkshire, UK. Posts: 5,766	Re: Dubilier/RS white axial caps - which dielectric? Maybe these jobbies? Attached Thumbnails __________________ David. BVWS Member. G-QRP Club member 1339.

7th Jan 2019, 4:44 pm	#10
dazzlevision Dekatron Join Date: Sep 2003 Location: Near Swindon, North Wiltshire, UK. Posts: 3,621	Re: Dubilier/RS white axial caps - which dielectric? Fourth picture in post #1. https://www.vintage-radio.net/forum/...ad.php?t=98964

7th Jan 2019, 5:18 pm	#11
Philips210 Nonode Join Date: May 2007 Location: Redruth, Cornwall, UK. Posts: 2,580	Re: Dubilier/RS white axial caps - which dielectric? Hi These mixed dielectric capacitors were often used in mains filter circuits and as the boost capacitor in valve line output stages. They weren't all that good back in the day but mustn't complain as they used to keep us a busy with simple repairs. I have quite a few in my collection but wouldn't use them. A fair number exhibit swelling and cracking probably due to the paper being hygroscopic. From memory, the blue/yellow ones as in David's post, were used in BRC TVs such as the 1400 chassis. I never did find out if the colours of the case were of any significance. Regards Symon

7th Jan 2019, 11:06 pm	#12
m0cemdave Octode Join Date: Feb 2009 Location: Bletchley, Buckinghamshire, UK. Posts: 1,223	Re: Dubilier/RS white axial caps - which dielectric? I think the usual problem with these was that the plastic case was moulded in two halves and would crack at the seam and allow moisture ingress. It's very common to see this, even in unused old stock examples. I am guessing that the plastic was affected by temperature cycling. A bit like the problem with the dreaded Hunts types.

8th Jan 2019, 5:35 am	#13
Boater Sam Banned Join Date: Dec 2013 Location: Middlewich, Cheshire, UK. & Winter in the Philippines. Posts: 3,897	Re: Dubilier/RS white axial caps - which dielectric? I have bins full of the white ones, all new, look perfect, in various values and voltages. I was hoping to sell them to the audiophools on ebay and buy a mansion, a Ferrari and another boat. Please don't tell anyone else that they are useless, keep it between you and me.

9th Jan 2019, 8:05 am	#14
Diabolical Artificer Dekatron Join Date: Jul 2009 Location: Sleaford, Lincs. UK. Posts: 7,669	Re: Dubilier/RS white axial caps - which dielectric? Interesting, I too too have a few of these types but mine are dark blue/light blue. I have some big ones rated at 1kv, usually use this sort of thing when fault finding on scopes say to temp replace components to get a circuit working. Not all paper caps are KO'd, I have some Dubilier 1u 600v, these are rather useful, it ain't easy to find similar rated caps. Out of a jar of about 20, 2 were leaky. Andy. __________________ Curiosity hasn't killed this cat...so far.

9th Jan 2019, 4:14 pm	#15
Neil Purling Nonode Join Date: Jul 2005 Location: Hull, East Yorkshire, UK. Posts: 2,087	Re: Dubilier/RS white axial caps - which dielectric? One of those Dubilier yellow & blue jobbies in a Ferguson CTV with the Thorm 8500 series chassis gave me the biggest fright of my life, ever. The shock as it exploded literally made be jump. Both of my feet left the ground. It went off six inches from my right ear hole. Split the case wide open of course.