18-01-2013, 08:36 AM
(This post was last modified: 18-01-2013, 08:41 AM by Radio Fixer.)
Thanks David but ...
Personally I wouldnt use them. Restuffing takes time and patience and I cant abide rework. I have in the past bought from AES in the US, Farnell and BVWS all having an excellent pedigree. Costs a bit more but I'm not looking to do the lowest cost restorations.
Also in some cases 400V isnt really enough, say with directly heated rectifiers when the HT can rise to high values before the O/P valve conducts. Or if a wiring fault leaves a disconnected HT line, Yep! I did it once. So for me its 450V minimum but I look for 475V and 500V types which are available.
Ripple current ratings also have to be looked at carefully. Here's an extract from an article I did for the BVWS on a Philips 834C back in 2011. There's much more in that if you have it including references to manufacturers data:
"Beware of small components quoted at a too good to be true ripple current rating. For example, Maplin Electronics have a 47mF, 450V rated at 1.279A (how did they come up with that figure?) in their catalogue. No frequency is quoted but the most likely is 100kHz, as might be the case for Switch Mode power supplies (I did ask by e-mail three times but didn’t get a reply). The rating has to be downgraded, as ESR increases with fall in frequency, maybe to 1/3 for 100Hz (and slightly less for 50Hz). Actually, even this seems most generous as that would make it have a ripple current rating of about the same as the 100mF above in a quarter of the volume."
Some of the caps I have have large volumes and that gives me confidence that they really will stand the ripple current at 100 HZ even enclosed in another can and probable stuffed out with paper, rather than free air as they are speced.
Gary
Personally I wouldnt use them. Restuffing takes time and patience and I cant abide rework. I have in the past bought from AES in the US, Farnell and BVWS all having an excellent pedigree. Costs a bit more but I'm not looking to do the lowest cost restorations.
Also in some cases 400V isnt really enough, say with directly heated rectifiers when the HT can rise to high values before the O/P valve conducts. Or if a wiring fault leaves a disconnected HT line, Yep! I did it once. So for me its 450V minimum but I look for 475V and 500V types which are available.
Ripple current ratings also have to be looked at carefully. Here's an extract from an article I did for the BVWS on a Philips 834C back in 2011. There's much more in that if you have it including references to manufacturers data:
"Beware of small components quoted at a too good to be true ripple current rating. For example, Maplin Electronics have a 47mF, 450V rated at 1.279A (how did they come up with that figure?) in their catalogue. No frequency is quoted but the most likely is 100kHz, as might be the case for Switch Mode power supplies (I did ask by e-mail three times but didn’t get a reply). The rating has to be downgraded, as ESR increases with fall in frequency, maybe to 1/3 for 100Hz (and slightly less for 50Hz). Actually, even this seems most generous as that would make it have a ripple current rating of about the same as the 100mF above in a quarter of the volume."
Some of the caps I have have large volumes and that gives me confidence that they really will stand the ripple current at 100 HZ even enclosed in another can and probable stuffed out with paper, rather than free air as they are speced.
Gary
