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The Dynaco Tube Audio Forum

Dedicated to the restoration and preservation of all original Dynaco tube audio equipment - Customer support for Tubes4hifi VTA tube amp and preamp kits and all Dynakitparts.com products


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Earl
vtshopdog
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    Coupling Cap Substitutions?

    vtshopdog
    vtshopdog

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    Coupling Cap Substitutions? Empty Coupling Cap Substitutions?

    Post by vtshopdog Sat Aug 28, 2021 4:40 pm

    Anyone played with swapping coupling caps in an ST-120 or M-125 willing to share thoughts?  

    I have only used the stock Russian PIO KY40 the came with the M-125 kits I built 6 years ago.  Doing a mini rebuild right now and I have the driver boards pulled so would be easy to swap something in.  Not unhappy with how things sound but have been surprised in past with changes to other gear from component upgrades.  (real or imagined)

    Any impressions from swaps people have made appreciated.

    Thanks
    Earl
    Earl

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    Post by Earl Sat Aug 28, 2021 8:00 pm

    The only way to know for sure if there are changes with a cap swap would be to build two identical amps with identical parts. The only difference, of course, would be the disparate caps. And then hook them up to a comparator.
    corndog71
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    Post by corndog71 Sat Aug 28, 2021 11:55 pm

    C5-C8 are the main caps to look at for upgrades. C1 and C2 might be worth playing with as well.

    Here are the caps I’m familiar with. These are my observations and opinions.

    Sonicap Gen 1 - Neutral on the side of cool. A solid choice for detail and affordable.

    Clarity Cap
    CMR - A very transparent, detailed, and dynamic cap. Similar to V-Cap TFTF and less cost.
    CSA - Similar to the CMR but with somewhat less extension in the treble. Very good midrange and affordable.
    MR - Similar to CMR but slightly less transparent.
    ESA - Similar to CSA but slightly less transparent and also more muted in the upper treble. Not recommended.

    Dayton Audio - Fairly generic and kind of dull sounding. Not recommended.

    Audyn Q4 - Another generic cap that lacks transparency. Not recommended.

    Erse Pulse X - A little dark sounding over all but ok detail. Just needs to be turned up. Cheap!

    Solen Fast Cap - Not the ultimate in resolution but actually very good detail. Cheap!

    Russian
    K40Y - A very nice detailed and warm cap though not the most transparent.
    K42Y - Similar to K40Y.

    V-Cap
    TFTF - Pricey but an excellent cap. Very spacious, detailed and neutral.
    OIMP - Slightly warmer sounding than TFTF. Very good detail but not sure if as transparent as TFTF.
    CUTF - Another pricey and excellent choice. Better than TFTF.

    Miflex
    KFPM - An inexpensive and very good sounding cap. Recommended.
    KPCU - Very similar to the Jupiter copper foil. Excellent detail and transparency and still reasonably priced.

    Jupiter JCW-060 copper foil, paper and wax - Pricey and excellent cap. Vey transparent, detailed with just a hint of warmth.
    WLT
    WLT

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    Coupling Cap Substitutions? Empty my 2 cents

    Post by WLT Sun Aug 29, 2021 9:29 am

    I do not have the VTA but the original vintage amps. As such they still have the normal output section coupling caps but no C1,C2 inter stage caps. Regardless I have tried a number of different caps on my restored amps. A few opinions of mine to add to Corndog71…

    Russian K40/K42 in ST70 and MK IV – both similar and a real value. Smooth mids are their best quality. Modest cost and recommended as such.

    Sprague Vit Q in MK III - similar to the Russian K40/K42 type but getting a little pricey. Nice

    Jantzen Suprior Z Cap in MK IV – A little bright on top but maybe still braking in. More detailed top end than the Vit Q.

    Audio Cap (by Rel cap) in MK III – very detailed and clean top to bottom. Nice match to the amp. Highest rating my me and worth the higher cost.

    Solon Fast Cap in ST 35 – to bright and sibilant. Will be trying something else.

    JFX Premium in SCA 35 - typical MKP with bright top end. Nice for economical project.

    Obbligato Gold Ultra Premium -in MK VI. Smooth and extended. not harsh at all. A good value

    The next few caps were tried in crossovers not coupling caps so opinion may not be of value.

    Clarity Cap CSA -  agree with corndog71 on sound and cost

    Erse Pulse X – seemed fine with good and not overly bright top end. Cheap.

    Corndog71 – thanks for the info. I may try your Miflex recommendations.
    vtshopdog
    vtshopdog

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    Post by vtshopdog Sun Aug 29, 2021 4:03 pm

    Thanks to both of you, this is a good start to what ultimately will be throwing a (possibly semi-costly) dart at what is pretty much a whim project.  My general go to caps are Cornell Dublier 940-C for "nice but affordable" and Mundorf Silver Oil (not gold) if I'm feeling "urge-to-splurge" but they have vague reputation of not holding up particularly well in higher heat so hadn't really considered them for this use.  I doubt the 940's will improve over the Russian PIO.

    Corn Dog:
    The Miflex look interesting, but appears they are rated at 70c which might be of concern mounted inside chassis near a quad of KT-120s.  Are you using them in the coupling cap position and if so how long have they been installed?
    (besides the temp rating they are right at limit dimensionally and their thick leads will require enlarging through holes .... Hmm, multiple flags going up, I think the world is speaking to me)

    The V-cap TFTF's are being discontinued and available at 40% discount which is very tempting, going to look at those a bit closer.  Correct value might be sold out, will check with vendor this week.
    corndog71
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    Post by corndog71 Sun Aug 29, 2021 7:38 pm

    Oh yeah, I forgot to mention some of those caps are big.  Always double check dimensions before ordering.  The Miflex leads shouldn’t be an issue but Clarity and V-Caps do have thicker leads.  On other kits I’ve used a 1/16” bit to open up the pcb hole which usually works.

    I have used the the Miflex caps in my custom ST35 for over a year with no issues.  I have also used the Jupiter’s in my custom M125 amps for a couple of years and again no issue.  I don’t think the inside of the tube amp chassis should be a problem if it’s vented well enough.  Most of the heat comes from the tubes and the PT which are outside of the chassis.
    JunkyJan
    JunkyJan

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    Post by JunkyJan Wed Sep 01, 2021 5:40 pm

    I have been running a "full" set of Audience Auricap capacitors on a pair of Mark 3s (with VTA driver boards) I built some years ago. I love the detail it adds. Been running without any issues for about 10 years now, however at the time the added cost did hurt a bit (nowhere near the $$$ I have seen for some of the "boutique" couplings caps that seem to be popular):

    Coupling Cap Substitutions? IMG_8403
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    EWALAA

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    Post by EWALAA Fri Sep 10, 2021 1:08 pm

    Has anyone ever tried Kimber Kaps?
    I have a set leftover from another amp. I might install them in the MarkIIIs.

    E.
    corndog71
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    Post by corndog71 Sat Sep 11, 2021 11:39 am

    Oh yeah, I’ve tried Kimber Kaps too. Still have a couple pairs in a box. I didn’t mention them since they’re discontinued. They were ok as far as can remember but it’s been a long time since I’ve heard them. Try them and report back.

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