Tropical fish caps reliability

[GP]

Hi all...

this isn't entirely stompbox related since it's not actually a stompbox i'm working on at the moment. However, i thought all you knowledgeable people would have some insights for me since so much mojo is attached to tropical fish caps.

anyway, i'm currently servicing an old (70s) combi organ and, whilst checking all the various boards for issues, i found at least one tropical fish cap that had simply crumbled where the leads are attached (one of which was completely detached). Upon closer inspection, I notice virtually all of the tropical fish caps have cracks developing where the leads are attached and i take this to be a sign of them heading towards the same fate. I'm more interested in reliability than mojo so i'll be replacing any i find that look suspect with modern film caps but this leads me to my question:

Are there known reliability issues with tropical fish caps in the manner i have described? I did some googling but nothing jumped out at me as a confirmation of this. It's obvious that there are some issues in this particular organ but out of hundreds of film type caps in this organ, only the tropical caps are cracking.

[R.G.]

Use the Master Sergeant's Rule: once is an accident, twice is a coincidence, three times is enemy action.

My personal opinion is not that you've found a reliability issue with so-called tropical fish caps, but that you have certainly uncovered a reliability issue with those tropical fish caps right there in that box. If a number of the TF caps out of the hundreds in that box are cracking, I'd say that it definitely indicates a problem with that box. Generalizing this is hard. It may be that the TF caps all came from the same manufacturer (which is by now impossible to figure out) or not. It may be that the folks who manufactured that box mistreated all of their TF caps that way. Or they mistreated all their caps and the TF took it less well. Or it may be that the assembly tech on that box (or line of boxes or at that manufacturing site) had a bad day, month or year.

There is a very strong need in the human psyche to generalize based on incomplete information. It's a very useful trait. But we have to keep it in bounds by testing against the real data. In this case, I would say that you can generalize to the box: replace all the TF, and inspect the others. But I personally don't think I would generalize to all TFs. It's possible, but only one of the possibilities without more data.

[GP]

Thanks RG.

I was taking the lack of information i could find to mean that there wasn't a well documented reliability issue. I simply felt it worth asking to see if those in the know would be able to impart any of their knowledge. I also felt it worth posting here because what IS well documented is the popular love of TF caps for stompbox use. If there was a known reliability issue, it might be worth bringing that out into the open so that those wishing to use said caps would be aware of the issue.

With respect to what you posted about mistreatment. I don't think this is a question of mishandling... it looks more like the epoxy (i'm assuming the material between the paint and the actual cap is epoxy but do please correct me if wrong) has simply cracked or completely cracked off and it's always at the sides where the legs actually attach to the cap inside. There are a number of different types of caps inside the unit of which there are maybe 30 or 40 TF caps. None of the other types exhibit any form of cracking whereas virutally all of the TF caps do. As you say, this is more likely indicative of the manufacturer of the caps or the manufacturer/assembler of the unit but I felt it was worth asking if anyone else has found a similar situation when opening up an old electronic unit. Just because there isn't a well documented reliability issue, it doesn't actually mean there isn't one...

[SpencerPedals]

My experience with NOS tropical fish caps has been that they are indeed very brittle and easily break near the leads.  In fact, the last shipment I got of them had one or two with a few chipped in that area.  I've also heard about sellers on boards throwing in a few extra with orders, for that very reason.  On the flip side, I've never come across any in my parts-scavenging that were dissolving in the way you had described.  In short, they're rather fragile, but there's something really wrong with what's going on in there.

[zombiwoof]

Many of us have had problems with the Trop Fish caps, I had a lead break off one early on, I learned to handle them with care, and I've heard of others having similar problems.  The fact is that they are old components, and are fragile.  There is really no need to use them over other metallized polyester caps (which is what I've read is what they are in fact), other than cosmetic "mojo", not any sonic benefits.  People use them in wah and Fuzz Face builds when they are trying to use the exact components used in the early pedals, not for any other reason.  Just use a good metalliized polyester cap and you're there.  One article said that the Orange Drop PS series is a direct descendant of those Trop Fish caps, but any similar cap will work just as well.

Al

[GP]

Ah... so there is some colloquial evidence of this then!

My hypotheses were either (1) they've sort of dried out and crumbled - heating/cooling cycles causing expansion and contraction around the leads which the expoxy can't handle (epoxy being notorious brittle)? or (2) there's an onboard power amp and speaker so maybe this is a vibration issue?

As I say, i don't think these have been mishandled. They are obviously as old as the other film type caps in the unit, however they are perhaps of materials or construction that simply doesn't stand the test of time/usage.

Whilst I accept what RG says, there are 30+ caps exhibiting the same sort of behaviour to various degrees so my human pattern-spotting capabilities see this as more than simply coincidence and my science graduate capabilities see this as something of statistical significance. Of course, as RG states, this could be simply down to manufacturer.

As for whether they are worth having in the circuit or not, I personally don't care for the mojo. I want a working organ that will last for as long as i can keep it working for. To this end, i'll be subbing them all for box caps or whatever i've got that fits the job they've been put in the circuit to do. I felt it was worth (given the lack of documentary evidence i could find) documenting something if there is enough evidence to support my observations. Since there are already two more posters testifying to fragility, i think it worth beginning the documentation here... As a stompbox builder, if i find a customer who simply MUST have NOS TF caps in his pedal, I'd like to be able to say "well, i have some well founded evidence to suggest these might not stand the test of time. Perhaps you might consider something more up to the job". I'm not really into selling mojo for mojo's sake. I'll happily steer customers away from this if there is a good reason to do so. I want my pedals to last.