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    capacitors (polyprop) installed backwards?

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    corporalspiffy

    Posts : 15
    Join date : 2015-04-23

    capacitors (polyprop) installed backwards?

    Post by corporalspiffy on Mon May 18, 2015 2:52 pm

    i am watching this video and wondering about my st70.

    apparently caps used to come marked with a stripe indicating which end (outside foil end) should go to the low impedance side of the circuit but the modern orange/brown/greed dipped once dont.

    .

    is this a valid concern in the amount noise injected into the signal path on  my amp?

    Elrick

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    Join date : 2012-09-02
    Location : Bellingham WA

    Re: capacitors (polyprop) installed backwards?

    Post by Elrick on Mon May 18, 2015 3:29 pm

    Modern caps are made differently and do not show the foil side makings. Any cap that you see in old gear that shows the stripe indicating foil side, replace immediately. I don't think Dynaco products are old enough to have those type of caps but perhaps.

    corporalspiffy

    Posts : 15
    Join date : 2015-04-23

    Re: capacitors (polyprop) installed backwards?

    Post by corporalspiffy on Mon May 18, 2015 3:54 pm

    this video shows that there still is a foil side on modern caps but that they just arent marked

    sKiZo

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    Location : Michigan USA

    Re: capacitors (polyprop) installed backwards?

    Post by sKiZo on Mon May 18, 2015 5:50 pm

    More fodder for the anal retentive amongst us ...
    (come on ... you know who you are!)   ;-}

    Unlike electrolytics, the current in these caps crosses the same no matter the direction of travel, and there's no deforming issues to worry about. If there is any minimal difference in what comes out, keep in mind that capacitor tolerances tend to be quite large anyway. Most circuits will fire with no apparent degradation as long as it's within 20% of the design rating. Only real exception that may concern us audio types is tuner circuits where tolerance is much tighter.

    Most polys I see in a circuit are there to bypass any residual AC in a line level signal. I use anywhere from .1 to .22 for these applications - any voltage rating that meets or exceeds the design requirements - they all work the same as long as they don't explode.

    Still might be fun to take a peek at these ... picked them up to rebuild some crossovers, and I imagine any such issues would be more applicable with the larger values.


    Bob Latino
    Admin

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    Location : Massachusetts

    Re: capacitors (polyprop) installed backwards?

    Post by Bob Latino on Mon May 18, 2015 7:00 pm

    Unless it is an electrolytic cap, as sKiZo has mentioned, it doesn't really matter which way modern caps are oriented. I once pulled the Russian PIO main coupling caps out of a VTA ST-70 amp here and turned them around so that the printing on the cap went the other way. The audio signal from these caps goes from the inside lead to the outside lead. I had them in there with the printing on the cap going one way reading towards the four output tubes. I then reversed them and had the printing on the cap reading towards the center of the driver board. I could hear no difference in the sound of the amp with all four caps turned the other way. When you install the Russian PIO caps on the VTA driver board there is a sentence in the instructions that mentions that "it does not matter which way the caps are oriented". Below is a forum link from November of 2010 which shows what the inside of a Russian PIO cap looks like.

    Inside a Russian PIO cap

    Bob

    PeterCapo

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    Join date : 2008-12-05

    Re: capacitors (polyprop) installed backwards?

    Post by PeterCapo on Mon May 18, 2015 8:22 pm

    I've delved into this a bit.  Someone over at AA provided me with a procedure to find the outer foil of the K40Y-9 as well as other caps.  I confirmed what he said about the K40Y-9 being inconsistent in its markings.  The markings on the K40Y-9 do not have anything to do with which lead is connected to the outer foil – some of the K40s I checked had the outer foil one way, others were reversed regardless of the orientation of the markings on the body.  They're random.

    Dynaco did use capacitors with the outer foil marked, and, from what I have seen, they were consistent in how they oriented the outer foil.  Exactly why they did this I do not know.  Maybe there is a measurable, though perhaps not audible, difference in noise.  Other than any question about noise, some claim to hear a difference in the sound quality depending on which way the outer foil is oriented.  In the event there is a difference in the sound qualities, I think it is reasonable to at least keep the outer foil oriented consistently from channel-to-channel.

    sKiZo

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    Re: capacitors (polyprop) installed backwards?

    Post by sKiZo on Mon May 18, 2015 9:59 pm

    "some claim to hear a difference in the sound quality depending on which way the outer foil is oriented"

    Probably the same dummies who think the rectifier can make an amp sound different. clown

    PeterCapo

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    Join date : 2008-12-05

    Re: capacitors (polyprop) installed backwards?

    Post by PeterCapo on Mon May 18, 2015 10:13 pm

    It was actually a pretty interesting discovery.  Reading some sources on-line like jimmy's junkyard capacitor pages, and other sources, indicated the metal shell of the K40 makes it impossible to use a scope to find the outer foil like you can with a lot of other capacitors.  But, Steve O. on AA came up with a way of using a scope and signal generator.  I tried it, and it works.  The K40 outer foil is indeed random in relation to its markings http://www.audioasylum.com/forums/tubediy/messages/22/223689.html

    wildiowa

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    Join date : 2012-03-19

    Re: capacitors (polyprop) installed backwards?

    Post by wildiowa on Tue May 19, 2015 9:08 am

    All I know is in my first refirb I had the bias caps in backwards and the thing lit up like a firecracker. I put orange drops in other positions and there was no pos/neg markings and all went well. Can't tell you the difference or what applications but the electrolytics on the bias circuit were not happy with my mistake.

    Bob Latino
    Admin

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    Re: capacitors (polyprop) installed backwards?

    Post by Bob Latino on Tue May 19, 2015 10:48 am

    wildiowa wrote:All I know is in my first refirb I had the bias caps in backwards and the thing lit up like a firecracker. I put orange drops in other positions and there was no pos/neg markings and all went well. Can't tell you the difference or what applications but the electrolytics on the bias circuit were not happy with my mistake.

    The two 100 uF @ 100 volt bias power supply caps on the VTA amp kits are electrolytic caps. Electrolytic caps DO HAVE a positive and a negative side and MUST be installed ONE WAY ONLY. Other (film, PIO etc) caps do not have a positive and negative side and may be installed either way ..

    And yep .. If you do install them the wrong way, they usually self destruct pretty quickly ...

    Bob

    GP49

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    Re: capacitors (polyprop) installed backwards?

    Post by GP49 on Tue May 19, 2015 12:20 pm

    A lot of the issues with the electrolytics in the bias circuit are due to...of all things...too much experience with electronics! Nearly all unipolar power supply applications are positive-hot, negative-ground, and by instinct and habit, a tech or modifier may tend to wire in those capacitors with the negative side grounded. The bias supply in Dynacos is NEGATIVE so the capacitors must be POSITIVE-grounded.

    More people have done this than will admit it!

    Don't ask how I know.

    GP49

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    Re: capacitors (polyprop) installed backwards?

    Post by GP49 on Tue May 19, 2015 12:22 pm

    sKiZo wrote:More fodder for the anal retentive amongst us ...
    (come on ... you know who you are!)   ;-}

    Still might be fun to take a peek at these ... picked them up to rebuild some crossovers, and I imagine any such issues would be more applicable with the larger values.


    That BATTERY in the lower right corner probably won't work very well...!!! affraid

    deepee99

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    Location : Wallace, Idaho

    Re: capacitors (polyprop) installed backwards?

    Post by deepee99 on Wed May 20, 2015 7:02 pm

    Don't encourage him.

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