What type of capacitor is this? - UK Vintage Radio Repair and Restoration Discussion Forum

agardiner · 1st Mar 2021, 12:10 pm

Hi,

Just when I thought I had seen them all, a different type of capacitor turns up!

Can anyone identify the type of capacitor in the image? The set concerned is very well built and probably ex military. There are 4 of these 2uF caps and one similar one at 8uF. Are they early electrolytics or high value non polarized? They test fine on my ESR meter; should then be replaced or left alone?

Many thanks....

Adrian.

Radio Tech · 1st Mar 2021, 12:17 pm

Hi Adrian

I think these will be electrolytic types and as you found they test ok I would be inclined to leave well alone

Ken

HamishBoxer · 1st Mar 2021, 12:20 pm

Agreed!

Herald1360 · 1st Mar 2021, 12:22 pm

They're oil filled paper types. They should be perfectly OK but it would be sensible to check them for leakage (both electrical and physical) using a high voltage insulation tester ("megger") and a British Standard eyeball.

ms660 · 1st Mar 2021, 12:22 pm

They look like non polarized types (paper)

Lawrence.

agardiner · 1st Mar 2021, 12:23 pm

Quote:

Originally Posted by ms660

They look like non polarized types (paper)

Lawrence.

They are in metal cans if that helps? If paper, would you leave alone?

Herald1360 · 1st Mar 2021, 12:24 pm

Quote:

Originally Posted by Radio Tech

Hi Adrian

I think these will be electrolytic types and as you found they test ok I would be inclined to leave well alone

Ken

Shouldn't this be "non-electrolytic"?

ms660 · 1st Mar 2021, 12:27 pm

You might find that they're ok if you test them for leakage at the proper voltage.

EDIT: Post crossed.

Lawrence.

newlite4 · 1st Mar 2021, 12:28 pm

To me, these look more like the non-polarised types typically used for filtering or motor-start or power factor correction. This type of capacitor is of the oil filled variety. Earlier versions were often labelled "visconol" and would have contained PCBs. Normally, these capacitors are very reliable in the long term and can be left unless they begin to leak fluid.
Neil

Silicon · 1st Mar 2021, 12:28 pm

They are probably non polarized paper insulated capacitors.

They were regarded as more reliable than electrolytics and were used in military and high quality equipment.

They could also be plastic film insulation capacitors if the equipment was made or refurbished in the last sixty years.

I would test them by connecting them to a 200V supply via a 10K resistor and measuring the voltage across the resistor.

If there is no leakage current there will be no voltage across the resistor.

I would expect some leakage if they were electrolytics.

Dave Moll · 1st Mar 2021, 12:29 pm

Unlike the waxed paper capacitors, these don't tend to suffer from the same problems of moisture ingress. I would be inclined to leave well alone unless they prove problematic.

edit: Wow - lots more posts while I was typing?

agardiner · 1st Mar 2021, 12:33 pm

Seems like varies opinions as to their construction! Many thanks everyone though for your input. It tends to concur with my thoughts which are that they are military grade non polarized.

I will check for leakage and if OK leave alone!

Techman · 1st Mar 2021, 2:41 pm

I'm surprised people find these unusual. I always call them 'block paper' types.

My Dynatron radiogram has a few of them - all original, but higher working voltage rated than those shown.

I've never known one of these to be faulty, except once in a Grampian record player where it was mounted next to very hot components (droppers and valves) and had virtually zero ventilation within the case of the player (typical Grampian design, over engineered in some places, yet in others absolutely no regard for safety whatsoever) and had ruptured and was soaked in oil and lost its capacitance.

I wouldn't even bother to test these if they 'look' ok. These capacitors are likely to be better than anything you could replace them with now and they're very 'period'. I even keep a small stock of new ones - well 60 year old new ones. I tested one a while ago with the DMM and nothing shown on the 20 meg range and it's still holding the charge from the meter perfectly now. I may test it on an HT supply later just for interest sake, but I don't expect any surprises...new old stock shown below:-

agardiner · 1st Mar 2021, 2:45 pm

Thanks Techman!

rontech · 1st Mar 2021, 2:52 pm

I have used these in the past from a WW2 RAF monitor amp. I assumed they were paper / oil and had no problem with them at 400 V DC

turretslug · 1st Mar 2021, 3:08 pm

I agree with Silicon's post- they are high-qality and well-sealed types that are probably still fine, but a leakage check at representative voltage makes sense.

Something about those 3 caps and the 22k filter resistors says "GEC BRT400 -100V rail (AGC generator supply)", the Berco (cookers!) pot and hefty pitch-covered choke visible also hint- but there is probably a lot of professional kit of the era that has similar innards.

1st Mar 2021, 12:10 pm	#1
agardiner Octode Join Date: Sep 2020 Location: Thetford, Norfolk, UK. Posts: 1,741	What type of capacitor is this? Hi, Just when I thought I had seen them all, a different type of capacitor turns up! Can anyone identify the type of capacitor in the image? The set concerned is very well built and probably ex military. There are 4 of these 2uF caps and one similar one at 8uF. Are they early electrolytics or high value non polarized? They test fine on my ESR meter; should then be replaced or left alone? Many thanks.... Adrian. Attached Thumbnails

1st Mar 2021, 12:17 pm	#2
Radio Tech Nonode Join Date: Dec 2012 Location: Bocking, near Braintree, Essex, UK. Posts: 2,071	Re: What type of capacitor is this? Hi Adrian I think these will be electrolytic types and as you found they test ok I would be inclined to leave well alone Ken

1st Mar 2021, 12:20 pm	#3
HamishBoxer Dekatron Join Date: Aug 2007 Location: W.Butterwick, near Doncaster UK. Posts: 8,932	Re: What type of capacitor is this? Agreed! __________________ G8JET BVWS Archivist and Member V.M.A.R.S

1st Mar 2021, 12:22 pm	#4
Herald1360 Dekatron Join Date: Feb 2007 Location: Leominster, Herefordshire, UK. Posts: 16,535	Re: What type of capacitor is this? They're oil filled paper types. They should be perfectly OK but it would be sensible to check them for leakage (both electrical and physical) using a high voltage insulation tester ("megger") and a British Standard eyeball. __________________ ....__________ ....\|____\|\|__\|__\_____ .=.\| _---\__\|__\|_---_\|. .........O..Chris....O

1st Mar 2021, 12:22 pm	#5
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: What type of capacitor is this? They look like non polarized types (paper) Lawrence.

1st Mar 2021, 12:27 pm	#8
ms660 Dekatron Join Date: Apr 2011 Location: Cornwall, UK. Posts: 13,454	Re: What type of capacitor is this? You might find that they're ok if you test them for leakage at the proper voltage. EDIT: Post crossed. Lawrence.

1st Mar 2021, 12:28 pm	#9
newlite4 Octode Join Date: Nov 2003 Location: Bath, Somerset, UK. Posts: 1,805	Re: What type of capacitor is this? To me, these look more like the non-polarised types typically used for filtering or motor-start or power factor correction. This type of capacitor is of the oil filled variety. Earlier versions were often labelled "visconol" and would have contained PCBs. Normally, these capacitors are very reliable in the long term and can be left unless they begin to leak fluid. Neil __________________ preserving the recent past, for the distant future.

1st Mar 2021, 12:28 pm	#10
Silicon Nonode Join Date: Jun 2007 Location: Coulsdon, London, UK. Posts: 2,163	Re: What type of capacitor is this? They are probably non polarized paper insulated capacitors. They were regarded as more reliable than electrolytics and were used in military and high quality equipment. They could also be plastic film insulation capacitors if the equipment was made or refurbished in the last sixty years. I would test them by connecting them to a 200V supply via a 10K resistor and measuring the voltage across the resistor. If there is no leakage current there will be no voltage across the resistor. I would expect some leakage if they were electrolytics.

1st Mar 2021, 12:29 pm	#11
Dave Moll Dekatron Join Date: Feb 2005 Location: West Cumbria (CA13), UK Posts: 6,127	Re: What type of capacitor is this? Unlike the waxed paper capacitors, these don't tend to suffer from the same problems of moisture ingress. I would be inclined to leave well alone unless they prove problematic. edit: Wow - lots more posts while I was typing? __________________ Mending is better than Ending (cf Brave New World by Aldous Huxley)

1st Mar 2021, 12:33 pm	#12
agardiner Octode Join Date: Sep 2020 Location: Thetford, Norfolk, UK. Posts: 1,741	Re: What type of capacitor is this? Seems like varies opinions as to their construction! Many thanks everyone though for your input. It tends to concur with my thoughts which are that they are military grade non polarized. I will check for leakage and if OK leave alone!

1st Mar 2021, 2:41 pm	#13
Techman Dekatron Join Date: Nov 2009 Location: Lincolnshire, UK. Posts: 5,000	Re: What type of capacitor is this? I'm surprised people find these unusual. I always call them 'block paper' types. My Dynatron radiogram has a few of them - all original, but higher working voltage rated than those shown. I've never known one of these to be faulty, except once in a Grampian record player where it was mounted next to very hot components (droppers and valves) and had virtually zero ventilation within the case of the player (typical Grampian design, over engineered in some places, yet in others absolutely no regard for safety whatsoever) and had ruptured and was soaked in oil and lost its capacitance. I wouldn't even bother to test these if they 'look' ok. These capacitors are likely to be better than anything you could replace them with now and they're very 'period'. I even keep a small stock of new ones - well 60 year old new ones. I tested one a while ago with the DMM and nothing shown on the 20 meg range and it's still holding the charge from the meter perfectly now. I may test it on an HT supply later just for interest sake, but I don't expect any surprises...new old stock shown below:- Attached Thumbnails

1st Mar 2021, 2:45 pm	#14
agardiner Octode Join Date: Sep 2020 Location: Thetford, Norfolk, UK. Posts: 1,741	Re: What type of capacitor is this? Thanks Techman!

1st Mar 2021, 2:52 pm	#15
rontech Heptode Join Date: Jun 2017 Location: Southport, Merseyside, UK. Posts: 646	Re: What type of capacitor is this? I have used these in the past from a WW2 RAF monitor amp. I assumed they were paper / oil and had no problem with them at 400 V DC __________________ Time flies like an arrow, fruit flies like a banana

1st Mar 2021, 3:08 pm	#16
turretslug Dekatron Join Date: Nov 2011 Location: Surrey, UK. Posts: 4,395	Re: What type of capacitor is this? I agree with Silicon's post- they are high-qality and well-sealed types that are probably still fine, but a leakage check at representative voltage makes sense. Something about those 3 caps and the 22k filter resistors says "GEC BRT400 -100V rail (AGC generator supply)", the Berco (cookers!) pot and hefty pitch-covered choke visible also hint- but there is probably a lot of professional kit of the era that has similar innards.