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Components and Circuits For discussions about component types, alternatives and availability, circuit configurations and modifications etc. Discussions here should be of a general nature and not about specific sets. |
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12th Jan 2019, 10:30 am | #21 |
Hexode
Join Date: Jul 2009
Location: Wokingham, Berkshire, UK.
Posts: 437
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Re: Can a capacitor's value increase with time?
Martin asked "Can a capacitor's value increase with time?"
As far as I am concerned that answer is an unequivocal yes. I have just overhauled a Quad 22 control unit and every small brown tubular capacitor, Dubilier, I think, in the tone and phono equalisation circuitry had changed value upwards. eg a 5000pF - 5nF had changed to 33nF. Most were replaced by polystyrene and/or polyester types. Interestingly the "notorious" black Hunts capacitors were all perfectly OK as far as value and leakage were concerned. All the electrolytics had changed both in value and ESR so of course were replaced, and the switch suppressors were both s/c, replaced with modern R/C combinations from CPC/Farnell. John |
12th Jan 2019, 12:18 pm | #22 |
Nonode
Join Date: Jun 2009
Location: Herefordshire, UK.
Posts: 2,495
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Re: Can a capacitor's value increase with time?
Re post no. 21:
Yes John, I had the same experience with a Quad 22 control unit a few years ago. Since Acoustical (Quad) gave treble/bass cut and lift plots in their documentation I thought I'd check them out on this unit. And to cut a long story short I found that those capacitors had gone up in value. I replaced them and the treble/bass lift then was as Quad had said. I must admit though that I never checked to see if the originals were electrically leaky - At the time I knew about older paper capacitors going leaky but I had not learnt about the extent of the problem until joining this forum. |
13th Jan 2019, 7:42 pm | #23 | |
Dekatron
Join Date: Dec 2007
Location: Haarlem, Netherlands
Posts: 4,203
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Re: Can a capacitor's value increase with time?
Quote:
Later, polypropylene was the material of choice, having better specs than polyester and paper. However it was much harder to get the sputtered plate materials to stick to polypropylene so they were often foil wound and/or also mixed dielectric. Only in the mid to late 1970's polypropylene capacitor technology had matured sufficiently to replace all paper capacitors, but not every component manuacturer chose to do so (Philips/Mullard was probably one of the first in Europe, as they had been with the introduction of polyester film). Last edited by Maarten; 13th Jan 2019 at 7:49 pm. |
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