Capacitors????

[brainstorm]

Hi Andy

I have recieved just one email from you and nothing in trash

Brian

[Turnip]

Hi Brian,

Guess you're right - substituting a well known name for another is hell for the over 70s.

I used to love Imps, Waggon wheels and that chewy woody stuff before realising years later my jolly memories were a bit suspect.

Still feel that big caps are good (sounds a bit Animal Farm)  - Chris

[jimca007]

Back in the middle ages when I was a boy and most things were either valve or solid state cap values were " near as damit does " as long as the working voltage was equal to or + up to 15 % of the original.
Laterly with the ever increasing use of high frequency applications such as in SMPS's the boffins at Manufacturers courses all seem to sing from the same hymn sheet... exact same replacement, voltage temp tolerance and capacitance.
I questioned the wisdom of this at a sony course and was told with the increasing use of feedback loops, opto sensors and error detection circuits the slightly increased charge/ discharge time of a higher voltage same capacitance replacement can cause instability in a PSU.
I can't vouch for the validity of this explanation but it is a possibility....that said I've often substituted higher voltage caps and never noticed it causing a problem...
I suppose the final nail in the coffin is the fact that all manufacturers insist you do not alter or modify any part of the circuit or component specification without express authorisation of teh designers in order to maintain operational and safety parameters so from that point of view I guess its like for like.....

[Ohm Supplies]

The main reason/ excuse for not changing the value of a capacitor would be explained by  the phrase “by changing the value of any component you change the characteristic of the circuit “
Although this is true as is “do not alter or modify any part of the circuit or component specification without express authorisation” you could argue that capacitors should not spew forth after 12 months.It would also call into question the practise of using equivalent or uprated parts. I can think of one psu supplied by a major supermarket that had a knock of smoothing capacitor in that a different value than that shown on its canister.
When subbing caps its wise to try to stick to the original values and types, uprating the voltage is a good idea as is using slightly better quality caps. I’m sure if manufacturers had tested all the sets for 12 months before launch most of the problems would be cleared up, its also worth pointing out the number of “stock faults” on a particular set compared to the amount of components fitted in the set.

Regards
Andy

[Turnip]

Hi folks,

Guess it's all health, safety and clip-boards - even when we as a country are going down the pan -

Bit too old to hold with that - puff - Chris.

[jimca007]

I'm afraid old duffers like me an lots others will continue to do what we have for years suck it and see ! if it works it can't be far off being right !

[Turnip]

Hi folks

Guess if some old duffers are still lose and mending -  rule of thumb applies 'till New/New Socialists re-house us for our own safety next election, and chuck the key.

Curiously, I'm a Socialist - just don't have the clip-board or pension  - born too late, and still working  -  Chris

[Ohm Supplies]

If an engineer is repairing sets with a high success rate, then its always wise to keep on with what you do.
An electronic circuit is often made up of smaller circuits designed for a particular part.

 If you look at the attached datasheet for use with an ic commonly used in sets most engineers will of worked on, it gives recommended values for the components and these are then used in the circuits, they’re not just doubled in size and a larger voltage used, its only after repeated use do common faults appear.

As modern devices are often designed to do the work of several parts, they’re designed to save on extra parts and space and therefore lowering the cost. A major reason for capacitors failing is heat, adding a larger sized part might increase temperature and cause problems with the part of the circuit its used in.
This why when we’re designing kits and repairing sets we use the correct value and sized parts.

That make sence?


regards
Andy

[Turnip]

Hi Andy,

Sense ?  - well not really, your third para is a problem - if replacing a capacitor with lower initial ESR than the original (selected initially mainly for economy with a limited service life in mind) Heat generated by new cap's reduced ESR will be less and reliabilty obviously greater.

Only go on about it as have chased reliabilty for a lot of years and am still in business - for some possibly good reason.

I make no observations on your kits, one way or the other, but would be happy to give 'em a go should I need to  - Chris.

[tv tony]

Just browsing through the various posts and this is possibly worth a mention, we have hot air guns, stereoscopes, digital meters, pattern generators etc, our workshops, i thought, were adequate, but if you can, buy an E.S.R. meter. Ours arrived yesterday, eighty pounds + VAT/p&p. Paid for itself already in PSU repairs, its worth every penny.
Tony Walker

[Turnip]

Hi Tony,

Got one of those Aussie ones years ago, loaned it to a chap in the trade and never got it back.

Saved enough eventually to buy a 'Peak' ESR60 (extending the leads as those fitted were so short they drove me nuts)

Guess without our duff 'Caps' most of us would be serving fries down at the roundabout - Chris.