Fake Axial Caps!

[tedmich]

that I made!

wanted a big beefy axial filter cap and didn't want to shell of the $27 Mouser wants for a 100uf/450v Atom. Sure some places say they have these for ~$10 but what do I know about them? Even Sprague lists no ESR or RIPPLE CURRENT or LIFETIME data.

I had 2 excellent CDE caps, the 220uf 250v 381lx units which are rated to 12,000h ripple life at 85C, with decent ESR and a full 105C rating. They are also among the most compact caps for their capacity, a scant 1" x1".

But they are snap-in, thus was born the Snap in to Axial (SITA) project.

I made 2 little PCBs

and then added equalizing resistors and tied them in series with some stout copper tape and 22awg PTFE/Cu/Ag wire

and closed them up in a nice piece of shrink tube Harbor freight sells


it looks (on paper) better than the Atom and other axials from the Mouse

[Chuck H]

Pretty. looks real pro. I too am sick of paying so much for Atom's while it's near impossible to find comprehensive specs on the damn things and so many fake, knockoff, etc. shinanigans have been aired. I've only had trouble with Atoms twice. An old batch that was never rotated was shipped to me all dried up (I don't trouble to "form" my caps. I just stick 'em in and turn on). And I do have a recent build that is "ghosting" for no good reason. I've built the same amp without this problem. Other than that Atoms have been good to me. But I can't help but wonder why they don't provide specs??? The recent esr (probably the reason for the ghosting) problem and the cavalier attitude has me looking for alternatives. I probably won't make snap in's into axial caps as you have (but nice job). I'll more likely revamp my build strategy to accomodate radial caps. I'm spying the Nichicon PW's. They DO publish spec sheets. And the spec sheets look good.

Chuck

[tedmich]

yeah everything (cept tube amps) is radial and usually snap in too.

don't miss the CDE 381LX470M450H022 (47uf/450Vdc) at Mouser (180 in stock); its a non stock item that doesn't even show up in the CDE spec sheet but for $23/10 its quite a bargain, figuring it will last ~33 years at 1h a day 85C, ESR is decent, not great but I am unsure this matters in tube amps.

and for axials the $9.34 Kemet PEG124YL2470QL1 has lower ESR than my SITA cap, even though its only 47uF! Smaller too...

[bob p]

I like the 380/381 series CDE caps. I'm building all of my new amp designs around them, because the writing is on the wall when it comes to caps -- snap in caps may be the only choice that we have in the future, so it makes sense to design around them now.

I've also retro-fitted these caps into older amps by fabbing little PCBs. I hadn't thought about putting them head to head in a heatshrinked package. It looks really great. But I tend to worry a lot, so here are my concerns:

It looks like you've put the vents end to end, and then sealed them in the heatshrink tube. I wonder if enclosing the caps in the heat shrink tubing and sealing them up might create a problem / impediment to gas venting, or if it might tend to hide a problem from detection if the cap starts to vent. Perhaps an annular spacer between the vent surfaces, and some sort of exhaust port could solve this problem.

I also wonder if the heatshrink tubing will cause any significant rise in the cap's operating temperature. I'm thinking that the combination of the heatshrink tube and the head-to-head configuration will decrease the available surface area for cooling, and result in heat retention in the cap, and shortened cap life.

Please keep us posted on how this works out for you. From a visual standpoint, it's a very appealing solution.

[tedmich]

I like the 380/381 series CDE caps. I'm building all of my new amp designs around them, because the writing is on the wall when it comes to caps -- snap in caps may be the only choice that we have in the future, so it makes sense to design around them now.

I've also retro-fitted these caps into older amps by fabbing little PCBs. I hadn't thought about putting them head to head in a heatshrinked package. It looks really great. But I tend to worry a lot, so here are my concerns:

It looks like you've put the vents end to end, and then sealed them in the heatshrink tube. I wonder if enclosing the caps in the heat shrink tubing and sealing them up might create a problem / impediment to gas venting, or if it might tend to hide a problem from detection if the cap starts to vent. Perhaps an annular spacer between the vent surfaces, and some sort of exhaust port could solve this problem.

I also wonder if the heatshrink tubing will cause any significant rise in the cap's operating temperature. I'm thinking that the combination of the heatshrink tube and the head-to-head configuration will decrease the available surface area for cooling, and result in heat retention in the cap, and shortened cap life.

Please keep us posted on how this works out for you. From a visual standpoint, it's a very appealing solution.

Those are valid concerns Bob, a few thoughts I have:

The 381lx series are so ridiculously long lived you could heat them quite a bit and still not live to see them fail; 5kh at +1A ripple at 105C translates to huge lifespan even if I half their thermal loss ability. The heatshrink I used was from Harbor Freight and just for convenience as it was a $1 pack of 1 3/16" ID x 3.6" (2) pieces in black and red and (unfortunately) inner melt. Thus it is pretty darn thick when shrunk; a better choice is the really thin polyolefin or PVC shrink tubing which is only 0.04 thick after shrinking; pretty much like the shrink tube they are made with. You could even strip that original shrink tube and have the dual caps "naked" under as much plastic as before. ELs used to be naked silver with a coating to keep their skin from conducting; the coating is still there and their shrink tube added as a safety factor and handy labeling system (much easier to run unshrunk tube through printers than cans!)

A clean hole at the midpoint (either hole punched before shrink or carefully drilled after) of the dual cap would make a nice aux. vent hole. I'd take pains to have this hole carefully pointed down at the board when mounting, not having the caps spew all over the board is ok in my book but I understand if you'd like the full cap functionality in the SITA cap.

[Ronsonic]

I just want to invite you all to join my campaign to correct the confusing and misleading terminology used to describe electronic components, especially capacitors. It is a simple change that will clear away confusion and misunderstanding in our daily electronical lives.

From now on we do away with the terms Radial and Axial, and replace them with the more technically precise and descriptive terms Walkies and Rollies.

Thanks you very much.

[rockin roy]

Turning walkies into rollies for mounting considerations is fine. Doing it for increased voltage....well.
The balancing resistors should be stressed a little more. They keep the voltage drop across each cap, witch will be related to the individual caps leakage, in check.
I guess your circuit is also dc coupled now. Will the cases see 250 volts as designed or 450?