Good source of 400V electrolytics for stuffing

[Yorkie]

Ordered some caps yesterday - they arrived today. In looking at the e-bay suppliers 'shop' I note that he has 112 pages of very useful components from caps to transistors, ICs, opto isolators, diodes - all sorts of stuff, but what especially caught my eye were the electrolytics on offer at reasonable prices, which look eminently sultable for stuffing. They're 400V and unusually, the ripple rating is stated, which is more than adequate for our needs. I've highlighted a few here:

6.8 uF 400V, 220mA AC Ripple Current: £1.35 each, radial leads:

http://www.ebay.co.uk/itm/6-8UF-400v-105...upplies_ET&hash=item4605d6a25e

10uF 400V, 300mA AC Ripple Current: Five for £2.75, radial leads:

http://www.ebay.co.uk/itm/10UF-400V-105c...upplies_ET&hash=item43b34654b7

22uF 400V, 760mA AC Ripple Current: £1.50 each, radial leads:

http://www.ebay.co.uk/itm/22uf-400v-105c...upplies_ET&hash=item43a0f22721

47uF 400V, (No ripple rating stated), ‘snap-in’ type, £1.75 each:

http://www.ebay.co.uk/itm/47uf-400v-105c...upplies_ET&hash=item439a5ad1b8

Well worth a look at his e-bay 'shop'.

Hope that's of interest to someone.

[dennishoy]

Excellent David; thank you.

[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

[Retired]

Hi,

Many thanks for this information David.

I'm still very much a novice when it comes to restoring a radio chassis unlike Gary who is well clued up on the subject.

I've always replaced caps with equal or higher voltage ratings and as long as the set worked it was good enough for me because once a set is restored then I lose interest in it.

Most of the basket cases I've restored had duff electrolytic's with many being the 8uF size so rather than keep buying a couple I bought a job lot of 250 motor run types through eBay. Looking at one of these now I note 8uF +/- 5% 425/500V. They are single nut fixing.

If my sets were as expensive as the sets Gary restores then I think I would try to keep the set as original as possible.

Kind regards, Col.

[pwdrive]

Gary wrote "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"

Wise words.

Lawrence.

[Radio Fixer]

No probs with ripple current with motor run caps Colin.

I restored a Stewart Warner once that had an electro capacitor box. The values werent that high and if I'd have given it more thought I could have easily built the values up with poly types, plenty of room in the box. But I used good, well over speced, electros. Someone might curse me in 50 years time .

Gary

[pwdrive]

The RCA AR88 shoots up near 500v when the HT switch is in the transmitt position.
The Hallicrafters SX28 has a nominal 280v HT when running but at switch on from cold it rises almost to 450v, I used 500v jobs in that receiver, Not done the AR88 HT filter caps yet, they are paper in oil and will be replaced with suitably rated non electrolytic types.

Lawrence.

[Yorkie]

Thanks for the words of wisdom Gary.

The question of ripple rating is always something that's concerned me, but then when I've occasionally considered the disgorging and re-stuffing the smoothing caps of some old radios - in one case, a triple section cap in a Pye R33, ( 8+32+32uF @ 275V) - the originals have been really quite puny and there was no chance of modern ones of the same value fitting inside the can. In that instance, only the 8uF section wouldn't reform, so I fitted a replacement under the chassis and left the can alone with the two 32uF sections working quite nicely. Incidentally, that radio has a half-wave contact cooled selnium rectifier (quaintly refered to on the data sheet as 'V4'!), so in that instance, the frequency would be 50Hz rather than 100Hz in a full-wave rectifier.

You're right about the BVWS caps. The smaller (25mm diam) can types for re-stuffing, in 8, 16 & 32uF at 500V aren't bad value at £4.50 each.

[Joe]

HOW MUCH!?

- Joe

[Nick]

The question of ripple rating is always something that's concerned me,

Ripple rating is directly related to low ESR. Low ESR small caps are around, but the original caps in these radios were pretty rubbish - modern expectation of "low ESR" are in the low 10s of milli-ohms range... so I suspect that any decent modern capacitor from a reputable manufacturer will be better than that originally installed and a fraction of the size... Remember, V=I*R where V is the ripple voltage and R is the capacitor's ESR.

A REALLY simple trick to get lower ESR at a cheap price, if you have the room, is to simple parallel up a couple of capacitors of half the value you want. e.g. If you want a 16uF 400V capacitor, use 2 x 8uF in parallel (if they'll fit in the can) - you'll get half the ESR at a cheaper price. Of course, you can put any number in parallel to lower the effective ESR accordingly...

Low ESR HV caps can be VERY expensive. I have boxes of ex-equipment-but-unused 2200uF & 3300uF 450V ultra-low ESR caps (10-15mOhms) left over from a project (several other values too) - they are BEASTS (weigh 1.4kg each!) - Farnell & RS have them at over £90 a pop - Going on an auction site RSN (real soon now) as I need the space...