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Old 2nd August 2006, 05:21 AM   #1
KBK is offline KBK  Canada
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Default An interesting capacitor question

I bought these russian mil caps off ebay.

They were listed as being polystyrene, 250V, 0.47uf. The values are fine, well in spec. no problemo.

I took one apart, after I had bought 75 of them off the guy. I felt it was film, and I was done. The film felt 'metal like' and there was a nice polystyrene feeling thin layer on either side. Good enough I said,and emailed him back,asking for more, if he could find them.

He found more. About 400 more, in total. 0.5uf (141) 0.399uf (200) and 0.3uf (100). I set it up to buy the rest. All rated at 250V (apparently, who knows what 250B means in russian)

I decided I wanted to use them to so some bypass in my phono section, in my preamp. I checked,and one side is biased at 180-190V, for the signal passing caps.

So, I found my dismembered cap I killed for my little 'truth' test, and proceeded to take it apart in a more detailed way. I wanted to see if a thicker film was in evidence, and the cap might be applicable in a circuit where Mr. Moore decided that 600v caps were needed. Mil spec is like that, and can be far under rated compared to a commercial rating system. I get the feeling that these caps can take repeated and constant abuse at something like 500V, not 250. Just a feeling. Or that the '250B' means 250VAC, not DC.

What I found was a film that was metallized on BOTH sides, and to a very high level of metalization. In comparison, you can use a solen cap film to make dark sunglasses,and the coating ona solen is on one side only. This stuff, you can't see through at all, but the impedance on one given side is about the same as the solen, across a given distance on the metalized side. What I mean is, if you take a bit of the metallized from the solen cap, measure the resistance across a given length. Lets say you get 3.5ohms. Take the film from the USSR mil cap,and get about the same, maybe a touch less. 10%-20% less. Then, the russian one is conductive on both sides. so cut that number in half again. The metalization is also very solid, or thick. On either side.

The separator film is on either side of the metal film on the russian cap and it is also a separate piece. so in triplicate, and far thicker feeling than on the solen, as well. It also does not feel like polyproplyne, it feels like polystyrene. I guess I'd better take apart a mylar cap and compare the film 'feel', maybe....

So it's a double metallized thick coated film, with polystyrene separators.

It's a metallized film polystyrene cap!!!It 'sounds' like a metal film cap, to a very large extent and has the advandatge of being polystyrene, as well. This is weird.

I had done some preliminary listening tests by putting it in some different places, and in each instance there was a notable increase in fidelity, so I didn't bother to investigate further and thought of it as a proper metal film polystyrene cap. But it isn't.

But it IS very, very, good! Better than any metallized cap I've ever used, and I've just about had my fill of all metallized caps, period.

The packaging also says 'polystyrne' according to the USSR designation system. The price I'm paying, which is very low, means that it is terrifically unlikely someone made new labels just for me.


I'm a bit confused in this one, this cap is a new one on me.

Anyone have experience with such a beast?

I gave Anatech (Chris) 8 of tehm to play with, when I was at his place last week. What I need to do, is to get him to run the Diss fator test again, (Hello Chris!) at 100khz, and check these puppies. Then compare that to a real polyprop film cap and to a polystyrne film cap. Then maybe I can get a least some understanding of what the heck is going on insofar as the numbers go.
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Old 2nd August 2006, 01:15 PM   #2
SY is offline SY  United States
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Is there continuity from one side of the film to the other?
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Old 2nd August 2006, 01:21 PM   #3
AndrewT is offline AndrewT  Scotland
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Hi,
is this Russian cap of folded construction or rolled?
Are there multiple lead outs commoned to the output pair?

But, back to the capacitance.
The double metalised film will form a capacitor in it's own right.
The adjacent layers whether folded or rolled will have dual separators between the metallised layers.
I would guess that the double separator layers will be thicker than the single metallised film.

Now, here is the difference between rolled and folded.

In rolled the common metallised layers are alternate with the two different metallised layers forming capacitors first across the dual separator AND secondly across the film. If the dual separator is thick then the metallised film will dominate the capacitance. Why double the separators, it appears to reduce capacitance for little benefit.

In folded construction the common metal layers are adjacent and then the next pair of metal layers are common.

The capacitance, in this case is only across the metallised film. There is no additional capacitance across the dual separator since the metal layers are common. In the folded case you do not need any separators.

If my imaginations are correct then folded constructionachieves no extra capacitance and due to redundant separators is far bulkier than needed in return for reduced inductance.
The rolled construction reduces the effectiveness by dualling the separators, when one would be sufficient.

There is another senario. Maybe the separators are extremely thin and of a high dielectric constant and low insulation value. Forcing dual separators to achieve the voltage rating. Then the separators start to have a beneficial influence. But polystyrene does not have a high dielectric constant, so that does not seem feasible.
A conundrum. I am no further forward and I suspect my post does not help you either.
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Old 2nd August 2006, 06:47 PM   #4
KBK is offline KBK  Canada
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Quote:
Originally posted by SY
Is there continuity from one side of the film to the other?

After a bit more investigation, it appears there is only the one separator film, it being apparently, polystyrene. The metallized film is definitely identially conductive (relatively speaking, simple tests) on either side, but not through to the other side.

So, conductive on both sides, likely a polyproplyne film, and then the styrene separator. Each cap is made up of two of these windings per capacitor. So, internally doubled up on the highly metallized film (parallel paths) and then two of these in parallel in each actual 'capacitor' body. For example, the 0.5uf caps I'm getting from this guy, will have two 0.25uf caps in the case, parallel stacked. They are approx twice as long as their diameter, each round roll, that is.

I also noted that the oxide layer from the Solen caps can easily be removed via rubbing. The russian cap? This stuff is so well attached or layered that this is VERY difficult to do. Sometimes the metallized layer comes partially off in a clean layer, onto the styrene separator layer. So it is quite well constructed and has a definite depth (the metal layer).

All in all, a very nice cap, but not exactly what I was led to believe I was getting. Polystyrene is always film/foil, to my recollection, this is an exception to that rule. To be fair, the guy selling them to me has no idea either, I'm sure, and I'm not about to alert him to possibilities.

When I get this batch in, I'll send a few off to you guys (only a few guys!) to garner an opinion. I'm pretty darned firm (a relatively educated opinion) about them being quality in terms of sonics and a general improvement overall, and roughly comparable to a true metal cap, but I'm not stupid enough to rely on my opinion alone.

At worst, I expect that folks will find they compare to the best that metallized film has to offer- but just a clearly noticable hair better. I just put them as bypass on a 12.22uf cap bundle in the main signal pass point in my MFA phono section. That bundle is a 3 piece affair, at 2x 6.0uf Rel-cap PPMT, and a .22uf RT rel-cap. There was a definite change (duh!), with the 0.477uf Russian cap put in there, but I'll have to let it sit for a few days to really get an idea of where things stand. More complimentary than destructive, so It seems to agree fairly well with the Rel-cap Styrene/tin foil cap that is in there (the 'RT' designation Rel-cap)

I/we will hopefully be isuing speakers soon, and I'll likely keep most to do bypass work on differing sections of the first issuance of any given model's passive crossover. This can save us a ton of cash, comparatively speaking, at the same time the speaker can be quite sweeteend and cleared up, compared to equivalent $$$ competition. These units seem to be designed for high frequency and high peak current.
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Old 2nd August 2006, 10:50 PM   #5
KBK is offline KBK  Canada
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Well..... tomorrow I get my pricing on 5N copper and silver foils, and teflon films..and then the fun begins. Time to experiment!

I plan to design and execute a new type of inductor, a new type of capacitor, and a new type of wire. All three having a design and geometry that has not been seen yet. See what happens when you start playing with this stuff?

(truthfully, I've been sitting on these designs for over a decade. Time to get'er'done)
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Old 2nd August 2006, 11:22 PM   #6
anatech is offline anatech  Canada
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Hi Ken,
I am warming up the poor little HP to get you those figures. I'll just give you the average and any flyers.

Those other caps are amazing dude! (the ones you re-sealed).

-Chris
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Old 3rd August 2006, 01:30 AM   #7
anatech is offline anatech  Canada
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Default Capacitor test numbers

All right then.

At 10 KHz the readings very fairly stable. All capacitors measured a dissipation of 0.0004 or 0.0005. I had two caps that measured 0.0016 and 0.0009 respectively. I didn't bother working out the total uncertainty. It is plain to see these are rather good figures.

At 100 KHz the readings were unstable. Watching the changing numbers, dissipation seemed to run 0.0022 to 0.0033. Our previously misbehaving caps measuring in the area of 0.0075 and 0.0140. Still, the group measures well.

For comparison I tested some Polyestor 630 V capacitors at the same value. At 10 KHz they ran 0.0093 and 0.0169 at 100 KHz.

Ken, your 0.1 uF caps measured 0.0000 at 10 KHz and 0.0006 ish at 100 KHz. Not too shabby (next to bloody perfect).

The test leads (HP 16089B, Kelvin Clips) were zeroed just prior to each frequency test sequence. The meter used was an HP 4263A (LCR Meter). The 100 KHz test frequency is on the top edge of the frequency range for the test lead set.

-Chris
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Old 3rd August 2006, 02:52 AM   #8
KBK is offline KBK  Canada
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Ok. thanks for the figures and tests!

The caps tested were 8 of the 0.47uf russian caps I gave Chris when I last visited. (the green ones)

The ones that are vanishing low in DF, are a set of 4 of the russian Teflon 0.1uf/200V caps, with their metal cans removed, a new 'wrap' skin, and epoxyed end caps. They look 'just like' a professionally made cap. (the white ones)

In the photo, are the green ones I speak of that are metallized on both sides of the foil, with a polystyrene seperator. You can see what I mean about the construction. Poor Russian man's MIT multicap. Apparently it works, which it would be nice if the multicap did the same. The others, the white labeled ones, are the skinned and epoxyed russian teflon caps. They are easy to make!

The writing is on the next to last layer of the film (wrap) cover, so it won't come off. As you can see, a full pot of coffee was consumed before attempting to write on them.


Click the image to open in full size.
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Old 3rd August 2006, 03:46 AM   #9
KBK is offline KBK  Canada
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PS, the guy whom I am getting pricing on copper foil from. He just happens to be the exact and ONLY (my impression, not his words) US manufacturer of this thin a high purity copper foil, period. I run into the exact guy I need to run into. I can buy any size roll I want. any width and down to uh..a very thin foil. 0.0007" thin, to be exact. What is the real point of mentioning it? about 5 different grades, and I won't ber 'two stepped' in the pricing, as this is the actual manufacturer, which is the hardest place to get to.

Press a supplier hard, and you'll find out very quickly that your pricing isn't what it could be, especially on such rarely used and rarely manufactured items. This is because you can't seem to track down the actual manufucaturer, you get an extra pricing level(distributor pricing) , which cuts deeply into your ability to sell at a profit, as your pricing structure is being affected right at the bottom.

10lb roll, about $300, he said. More then enough to roll me a few, for test porpoises. Re-packaging those russian teflon caps made me hungry for mo'better caps, but throw some labour in, and I can do it on the cheap. Not $100-300-600 for one single capacitor, but with labour, maybe $20 each, maybe less. Now we're talkin.

Now to source the teflon film. Copper/teflon caps, yummy.
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Old 3rd August 2006, 04:39 AM   #10
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Ken, are the teflon capacitors an extended foil design?
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