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Old 13th Jul 2019, 12:43 pm   #1
jubilado
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Default Armstrong 626 capacitor question.

While waiting for parts to arrive for my Armstrong 626 (subject of another thread on here) I have just been given another of the same. On opening I found that the power reservoir capacitor(?) has a large bulge where I presume there is a safety vent. On majority of the circuit diagrams I have seen for this model this capacitor is 85v 3300uF but this is fitted with 85v 7500uF. I believe this change was made in later models.. Anyway... the nearest equivalent I can find is 100v 8200uF. Can I safely use this as a replacement?
Neil
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Old 14th Jul 2019, 2:30 pm   #2
jamesperrett
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Default Re: Armstrong 626 capacitor question.

Yes, provided it physically fits it will be OK. Electrolytic capacitors have fairly wide tolerances so the difference between 7500 and 8200 is probably within the normal range of the capacitor's tolerance.
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Old 15th Jul 2019, 12:04 am   #3
jubilado
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Default Re: Armstrong 626 capacitor question.

Thanks, duly ordered!
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Old 17th Jul 2019, 5:03 pm   #4
jubilado
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Default Re: Armstrong 626 capacitor question.

Oooooops NOT ordered. I checked the space and all the 100v capacitors are too large(too long!)!!
Can anyone help with any suitable solution / alternative to this? or as to why Armstrong changed the value of this cap?? from 3300 to 7500?
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Old 17th Jul 2019, 5:31 pm   #5
G6Tanuki
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Default Re: Armstrong 626 capacitor question.

The change of value could have a number of reasons:

Larger capacitance, hence giving better smoothing.

Smaller-value part discontinued by supplier, larger one offered by supplier as replacement at no extra cost, or smaller-value part discontinued and larger-value part fitted because it was physically the same size as superseded part, so avoiding also having to also redesign/replace existing style of mounting-brackets etc.

Another product used the larger-value part and there were 'economies of scale' to be had by standardising on one part across several product-ranges.

Changes such as these are just as often driven by the needs of production-engineering and buying-departments than by any technical-electronic matters!
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Old 17th Jul 2019, 5:55 pm   #6
Granitehill
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Default Re: Armstrong 626 capacitor question.

Just for some reassurance - my ex-Ebay 625 was fitted with a (faulty) 7500uF. I had a rather nice 3500uF 100V high ripple Aerovox capacitor for another project, so I used that. It works perfectly. I can detect NO audible difference whatsoever between the 625 and my 626 which has a 7500uF capacitor fitted.
(I like Armstrongs, by the way...)
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Old 18th Jul 2019, 7:10 am   #7
snowman_al
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Default Re: Armstrong 626 capacitor question.

A 6800uF (or 5600uF even) 100 volt cap will be fine if it is the right size.
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Old 21st Jul 2019, 10:55 pm   #8
jubilado
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Default Re: Armstrong 626 capacitor question.

Thanks folks, I 've been away for a few days but have returned to find 6800uF cap awaiting. I'll get it fitted and take things from there.
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Old 6th Aug 2019, 10:37 am   #9
jubilado
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Default Re: Armstrong 626 capacitor question.

Thanks for the help.... 6800uF 100v cap fitted and amp sounds OK
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