Using 20uf filter capacitors instead of 16uf with 5Y3GT

[tubedood]

Good tip Chuck! As much as I thought the build would be a good use of leftover cool-mojo parts it is starting to look like new parts are in order for the caps that I need!

[christarak]

And!..

If you don't build/repair much and have electrolytic caps "on hand" you should take into account something I mentioned earlier. Electrolytic caps actually have a shelf life. They age faster unused than they do in circuit. I buy fresh caps for every build. If I did repairs I would literally write dates on my electrolytics and toss them after two years. Doing otherwise (IMHO) means risking problems that you don't want to have for the $$$ new caps cost. I literally have two electrolytic caps in my inventory right now. If they don't get used by December I'll toss them in January. Freshly purchased caps is NOT a guarantee, but it's likely better than using electrolytics you know to be many years in a drawer unused.

Oh great... :-( It Tax time here in Australia and I have just put in a huge order for caps and tubes from the USA (where they are much cheaper than here). I knew electrolytics had a shelf life but not that small a shelf.

[Chuck H]

Oh great... :-( It Tax time here in Australia and I have just put in a huge order for caps and tubes from the USA (where they are much cheaper than here). I knew electrolytics had a shelf life but not that small a shelf.

Well, the shelf life isn't THAT small. I get a little nutty because I've built amps with stored caps (and new actually) where the caps were bad. Or, less than good. I don't like rebuilding power supplies on new amps so I don't store caps anymore and I don't use the brand that gave me trouble with new caps anymore.

Back in the days of American electronic stores (that WEREN'T Fry's) electrolytic cap manufacturers use to recommend rotating stock. Like food in a grocery store. Some brands even had "best by" dates recorded for batch codes so the distributors could check if they were inclined.

A friend of mine that was a player in the amp game for awhile (as in, selling next to Fenders and Marshalls in the music stores) brought a couple of his old amps, still in original shipping boxes to his house one afternoon so we could give them a listen. 20 years stored! His assumption was that having not been used they would be "as new". I warned about the electrolytics and he was nonplussed. Sure enough the first one we plugged in hummed badly, made funny noises and smoked within five minutes. The second one was brought up slowly on a make shift current limiter for about four hours. It only hummed and just generally sounded bad for it. I replaced the electrolytic caps in both amps the following day.

Now, 20 years is ten times longer than two years, of course. If those amps had been in operation during those 20 years there's a good chance the caps would have still been working. Idle caps are sad caps is my point.

[pdf64]

If concerned about the ecaps you’ve got in storage deteriorating, I suspect that the risk of that may be much reduced by charging them up to rated voltage once in a while, eg every few months. Via a nigh value resistor, to limit current, eg 10k-100k.
It may be best to then store them in their charged state; obviously that needs some safety precautions.

[christarak]

That may be worth doing on the larger more expensive caps. Thanks for that idea.

[christarak]

electrolytic cap manufacturers use to recommend rotating stock. Like food in a grocery store. Some brands even had "best by" dates recorded for batch codes so the distributors could check if they were inclined.

Do modern caps, like the F&T, have a date encoded on them somehow? They used to be easy to decipher on the older caps and multi-Capcans, but what is an IEC60 384-4 ?

[Leo_Gnardo]

Do modern caps, like the F&T, have a date encoded on them somehow?

Date codes, AFAIK only on:

Sprague Atoms. I haven't bought any of them for a decade due to excessive cost AND they're now just shells holding stuffing and a "modern" cap inside.

BMI, the company that was started by some engineers that split from Sprague/Cornell-Dubilier. You find their caps in Mesa-Boogie amps. Mesa may sell you some if you ask. Generally good BUT I recently had to replace a series pair when one failed, the amp had only been made 2 years ago, a JP-2. Just to show ya, anything can go wrong, even with hi-reputation parts.

[christarak]

Thanks Leo. Every single time I come to this forum I learn something new.

I think I will just have to start a date code system myself on my purchases from now on, eg "6-18" on the base and hope that the stock we receive is reasonably fresh.