The oil and paper cap in the DeCappo

Terry · « **on:** 11 Feb 2004, 05:39 pm »

A friend of mine owns a pair of Antique Sound Lab Hurricane amplifiers. These amps use an oil and paper capacitor that I understand is very similar to that used in the DeCappo-i. Recently, his Hurricanes required servicing and, upon removing the lower cover, the technician discovered that many of the oil and paper caps were leaking, some of them very badly. I have spoken to a couple of knowledgeable people about these caps and they have all stated that these caps have a bad reputation developing leaks. I have not investigated my own DeCappos but I think I will. If anybody has any information on this, please share it.

cyounkman · « **Reply #1 on:** 11 Feb 2004, 06:16 pm »

Quote from: Terry

A friend of mine owns a pair of Antique Sound Lab Hurricane amplifiers. These amps use an oil and paper capacitor that I understand is very similar to that used in the DeCappo-i. Recently, his Hurricanes required servicing and, upon removing the lower cover, the technician discovered that many of the oil and paper caps were leaking, some of them very badly. I have spoken to a couple of knowledgeable people about these caps and they have all stated that these caps have a bad reputation developing leaks.

Well, I'm sure Anthony will be thrilled to see this post, as it's more reason for him to open up my DC's and 'check for leaks' and install some $300 cap instead... Not that I should mind, I guess...

Seriously, though: I did the upgrade to the new tweeter and cap a few months ago, and it's certainly been fine sonically, I guess I wouldn't have any way of knowing if it's leaking unless the sound starts to change or I find an oily puddle on the rug. Am I more likely to spring a leak since I blast mine with a 175-w Plinius?

Terry · « **Reply #2 on:** 11 Feb 2004, 10:06 pm »

Hi Chris,

I reported this because it should be something that DeCappo-i owners can check quite easily. I have certainly not observed any deterioration in sound which, I imagine, would happen if the caps were breaking down. Nevertheless, it is worth checking out.

I am curious about caps in general. I recently replaced the caps in my Audible Illusions M3A with TRT DynamiCaps and REL Teflon and foils and the improvement is quite noticable. However, I have always understood that the oil and paper caps, apart from prone to leakage, sound very good. What would you replace these caps with in the DeCappos?

mcrespo71 · « **Reply #3 on:** 11 Feb 2004, 11:23 pm »

How are you planning at getting at the cap? Are you going to take out the woofer?

Michael

Terry · « **Reply #4 on:** 11 Feb 2004, 11:37 pm »

I have never been inside the DeCappos but I had assumed that you could get at this cap by removing the tweeter. If I'm wrong, please tell me.

mcrespo71 · « **Reply #5 on:** 12 Feb 2004, 12:20 am »

I have no idea. That's why I was asking you!

It seems to me that Chris was able to access the cap when he did the tweeter replacement.

Michael

he46570 · « **Reply #6 on:** 12 Feb 2004, 01:57 am »

You'll need to remove the woofer at least. The cap is either taped or tied to one of the internal braces, which is situated behind the woofer.

From memory the value is around 5.0uF. You could replace this with a plastic cap like Hovland, or go exotic with an axial paper-in-oil like AudioNote. I'd replicate the value by using a 4.7uF bypassed with a 0.47uF or whatever is necessary.

I've used these caps before, but in power supply applications rather than coupling. I honestly don't like if substitution will be an improvement or not. Seeing that decent replacements would cost under $100, you won't break the bank if results are less than optimal.

JoshK · « **Reply #7 on:** 12 Feb 2004, 02:15 am »

Michael,

I can help you check yours out if you are worried.

Terry · « **Reply #8 on:** 12 Feb 2004, 02:16 am »

Thanks for the info. I will check the caps this weekend and decide if they should be replaced. If they are not leaking, I am guessing that they will probably be good for a long time (I don't drive my DeCappos like our esteemed moderator does

). Can you explain a little more about using the bypass caps? I understand that bypassing is used to smooth out the top end. Is this correct? Thanks again.

mcrespo71 · « **Reply #9 on:** 12 Feb 2004, 02:23 am »

Thanks, Josh! I may take you up on this.

Michael

he46570 · « **Reply #10 on:** 12 Feb 2004, 03:03 am »

Firstly, it's unlikely these caps will be leaking. Though it looks like a 50 year old cap, it appears it is new production (just in an older-style can). I've used 50-60 year old caps far larger than the one in the Ref 3A without any difficulty - in fact, they have a far greater shelf life than all modern day electrolytics.

Bypassing is a fairly complex issue. Why I recommended bypassing here was to replicate the value of the cap already in there. For example, if you have a cap value of say 5.17uF, and you can't find a 5.17uF cap to replace it, then you can use a 4.7uF and a 0.47uF to replicate the value. The general rule with capacitance is that paralleled caps add, and series caps have an inverse relationship. This is the opposite for resistance, in case you're interested.

So to replicate 5.17uF, you take a 4.7uF cap and parallel it with a 0.47uF cap. It is important to get the right value, since the differences you hear may be more due to the changed value (therefore changing crossover point of the tweeter) rather than the different type of capacitor.

Now, modders in the 70s and 80s were obsessed with parallelling caps since, in general, smaller value caps have better performance characteristics (ESR etc). This applied to both power supply and signal capacitors. Therefore, if you say had a 0.47uF coupling capacitor, people would parallel this with a 0.047uF, and possibly even smaller value caps. Supposedly you hear more 'air'. I've had variable results from this technique, and prefer instead to just use a high quality cap suitable for the application at the start.

Hope this helps.

Robert

wongstein · « **Reply #11 on:** 12 Feb 2004, 10:21 am »

Hey, y'all didn't think you could have this conversation without me chiming in, didja?

The caps on the non-i model were right behind the speaker post plate on the back, and that's where the upgraded caps went too. Not sure about the factory i model, but I can't see why they wouldn't be in the same place.

Are we sure that we're talking about mechanical leaks and not electircal leaks? All caps dissipate their charge eventually, but if it loses its charge in the relative short term, that's commonly called a leak by electical engineers, I believe. That proabably occurs more often than oil coming out of the cannister.

Lastly, for what it's worth, I read in TAS that ASL used to use Multicaps in the Hurricane before they switched to a paper in oil, and then a different paper-in-oil cap, and I think HP says that he really preferred the Multicap, so they still make "The HP version" with the polystrene caps by request. Multicap has been highly recommended to try in the De Capos, and at $30 each, it doesn't seem so crazy. I'd really like to know which paper-in-oil caps the latest Hurricane uses however, so if anyone can let me in on it, please do.

Terry · « **Reply #12 on:** 12 Feb 2004, 12:59 pm »

Quote

Bypassing is a fairly complex issue. Why I recommended bypassing here was to replicate the value of the cap already in there. For example, if you have a cap value of say 5.17uF, an ...

Robert, Thank you! Bypassing has always been a mystery to me and you have provided an excellent explanation.

Terry · « **Reply #13 on:** 12 Feb 2004, 01:19 pm »

Quote from: wongstein

Are we sure that we're talking about mechanical leaks and not electircal leaks? All caps dissipate their charge eventually, but if it loses its charge in the relative short term, that's commonly ca ...

This was definitely mechanical leaks. In this particular pair of Hurricanes, a total of 10 of the paper and oil caps leaked oil onto the inside bottom plate. Fortunately, the plate prevented a major spill on an expensive carpet.

I should mention that Divergent was very prompt in replacing the caps and the amps were only out of service for about one week.

I will try to find out what make and value those caps in the Hurrican are and relay this information to you.

he46570 · « **Reply #14 on:** 13 Feb 2004, 10:45 pm »

If there were that many leaks, I suspect they either used a faultly batch of caps, or, more likely, heat caused the caps to operate in an environment they are not specified for (whether this is a design flaw or operating out of spec I don't know)...

wongstein · « **Reply #15 on:** 18 Feb 2004, 12:30 am »

FYI, I found that article in TAS, and interestingly, the paper/oil caps that were first used, that he and his "panel" did not like at all were Illusion caps. The Decapo i uses Illusion caps. I wonder if these were the leaky caps. I guess it doesn't matter to De Capo owners since speakers do not get hot.

The mystery cap that I'm curious about is the cap that ASL used to replace the Illusion caps, which supposedly sounded better, although HP still prefered the Multicap polystrenes, for what it's worth. What brand are they? Are these be the leaky caps?

As an aside, I can't say that TAS is not credible, because at the moment, Chris' setup is just components that were TAS Golden Ear winners, and it does indeed sound great.

Anthony

Terry · « **Reply #16 on:** 18 Feb 2004, 10:56 pm »

Quote from: wongstein

The mystery cap that I'm curious about is the cap that ASL used to replace the Illusion caps, which supposedly sounded better, although HP still prefered the Multicap polystrenes, for what it's worth. ...

I can't quite figure out what Multicap HP was referring to. The max. Multicap that is available is only 1.5 uf whereas the paper and oil cap in the DeCappo is 5 uf. I can't see how you could just swap these and expect the Multicap to work. Could someone shed some light on this?

wongstein · « **Reply #17 on:** 9 Mar 2004, 06:52 am »

I don't know what values of caps are in the ASL Hurricanes, but there are different Multicap series. Terry, I think you're referring to the RTX series, probably the highest level of cap from them (certainly if price is the indicator). You can't commonly find values higher than 1.5, but 3uF exist, or so I've seen advertised. Steve Nugent of Empirical Mods recommended this cap in particular when I solicited cap suggestions for the De Capos. I don't know if he knew that this cap only goes up to 1.5 or 3 uF, but putting several caps together in parallel yields total capacitance equal to the sum, so maybe that's what he was suggesting. Some say that putting caps in parallel gives better sound than a single cap of the same quality in some applications. Some even say that your best cap in that configuration shines through to some extent, and it makes some sense since they're in parallel; the idea is that for instance you could use a less expensive 4.7 uF cap and a top-quality .3 uF cap as a "trimmer cap" which is much cheaper than the equivalent grade 5 uF cap for better results for the dollar.

There are also MultiCap - PPFXS, Polypropylene Film & Tin Foil which are available up to 12uF rated for 200V, and there's the MultiCap - PPMFX Metallized Polypropylene that can be had up to 30uF rated for 200V. I don't know what these sound like. http://www.partsconnexion.com/catalog/CapacitorsFilm.html">http://www.partsconnexion.com/catalog/CapacitorsFilm.html

Anthony