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    What's an appropriate amount of capacitance for the quad cap in a MK IV amp?

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    howlin' hoosier

    Posts : 29
    Join date : 2012-04-30

    What's an appropriate amount of capacitance for the quad cap in a MK IV amp?

    Post by howlin' hoosier on Fri Feb 19, 2016 4:05 pm

    I managed to get my finicky MK IV up and running after a bout with runaway bias (new diode, new resistors and caps in the bias circuitry, Wima .1 caps on the driver board with some PIO .047 caps on the way) - the amp has the 550 volt German quad cap with the 80/40/30/20 sections. The cap is oriented so the 80 mfd section is away from the GZ34 rectifier tube (40 mfd section is wired there). The amp sounds better than my other MK IV which has the stock 525 volt quad cap and inexpensive poly caps on the driver board (when I shut off the stock cap amp the music stops abruptly after a couple seconds, the amp with the uprated cap plays on for awhile before fading away).

    How much is enough capacitance for a MK IV amp as far as the quad cap is concerned? Is there a point where the sound suffers because an ideal amount of capacitance has been reached?

    Bob Latino
    Admin

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    Join date : 2008-11-26
    Location : Massachusetts

    Re: What's an appropriate amount of capacitance for the quad cap in a MK IV amp?

    Post by Bob Latino on Fri Feb 19, 2016 6:14 pm

    howlin' hoosier wrote:I managed to get my finicky MK IV up and running after a bout with runaway bias (new diode, new resistors and caps in the bias circuitry, Wima .1 caps on the driver board with some PIO .047 caps on the way) - the amp has the 550 volt German quad cap with the 80/40/30/20 sections.  The cap is oriented so the 80 mfd section is away from the GZ34 rectifier tube (40 mfd section is wired there).  The amp sounds better than my other MK IV which has the stock 525 volt quad cap and inexpensive poly caps on the driver board (when I shut off the stock cap amp the music stops abruptly after a couple seconds, the amp with the uprated cap plays on for awhile before fading away).

    How much is enough capacitance for a MK IV amp as far as the quad cap is concerned?  Is there a point where the sound suffers because an ideal amount of capacitance has been reached?

    That 80, 40, 30, 20 uF @ 550 volt German quad cap is a much better cap than the original Dynaco 30, 20, 20, 20 uF cap @ 525 volt cap that you have in the other amp. You should replace the stock 525 volt cap in the other amp. The newer quad cap allows the amp to play longer after turn off because it is storing 170 uF vs 90 uF for the original quad cap. The 170 uF of DC storage in that cap is more than enough to run a single Mark IV amp.

    If anyone acquires an older tube amp that is 40+ years old, you should replace, at the very minimum, all electrolytic caps in the amp. Electrolytic caps do go bad in time and do not last forever.

    Bob

    howlin' hoosier

    Posts : 29
    Join date : 2012-04-30

    Re: What's an appropriate amount of capacitance for the quad cap in a MK IV amp?

    Post by howlin' hoosier on Fri Feb 19, 2016 6:50 pm

    The cap in my other amp is a new production cap that I got before the 80/40/30/20 quad caps showed up. It's on the need to buy list - it never ends, does it?

    j beede

    Posts : 316
    Join date : 2011-02-07
    Location : California

    Re: What's an appropriate amount of capacitance for the quad cap in a MK IV amp?

    Post by j beede on Fri Feb 19, 2016 8:52 pm

    Precisely what exactly would a "German quad cap" be? Maybe Panasonic caps stuffed into a Teutonic tin can? If you can hear the difference between two otherwise identical mono tube amps that differ only in the country of origin of their power supply filter caps...

    You changed the ac coupling (signal path) caps to Wima. I suppose that difference might be audible.

    Bob Latino
    Admin

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    Location : Massachusetts

    Re: What's an appropriate amount of capacitance for the quad cap in a MK IV amp?

    Post by Bob Latino on Fri Feb 19, 2016 9:07 pm

    j beede wrote:Precisely what exactly would a "German quad cap" be? Maybe Panasonic caps stuffed into a Teutonic tin can? If you can hear the difference between two otherwise identical mono tube amps that differ only in the country of origin of their power supply filter caps...

    You changed the ac coupling (signal path) caps to Wima. I suppose that difference might be audible.

    The German cap is the KTL25 "Authenticap". I buy them directly from the distributor in Germany. You can also get them from Kevin at Dynakitparts at the link below ..

    German 80, 40, 30, 20 uF quad cap

    Bob

    howlin' hoosier

    Posts : 29
    Join date : 2012-04-30

    Re: What's an appropriate amount of capacitance for the quad cap in a MK IV amp?

    Post by howlin' hoosier on Fri Feb 19, 2016 9:32 pm

    j beede wrote:Precisely what exactly would a "German quad cap" be? Maybe Panasonic caps stuffed into a Teutonic tin can? If you can hear the difference between two otherwise identical mono tube amps that differ only in the country of origin of their power supply filter caps...

    You changed the ac coupling (signal path) caps to Wima. I suppose that difference might be audible.

    I assume "German" caps mean they were manufactured in Germany - they're too expensive to pry one open to see what's inside.  They're more expensive than the made in the U.S. caps made on old Mallory tooling that haven't proven to be very reliable for me. The higher rating and 600 volt surge are nice insurance against failure.

    Yep - the Wima coupling caps are an improvement over the cheapie caps the board came with - less tizzy highs for starters.  I'll credit those for making the initial difference in sonics more than anything.  I use them in Musical Fidelity X-10D buffer stages I resell, and have used them for other projects - they're a consistently reliable cap that doesn't cost 50 or more dollars a pop.  The quad cap stiffens up the power supply tremendously - the German cap amp plays on well after the power is cut (compared to the couple seconds and gone that the other amp is capable of doing).  The bass isn't as flabby as the amp with the smaller cap.  I ran a cd with test tones, hit the mono button on my preamp and watched how the cones reacted and sounded - the mid-woofer doesn't flap as much on the stiffened power supply amp side.  I can hear the difference as well.

    I'm very familiar with the sound of my Dyna gear - I grew up with a ST-70/PAS 2 combo my dad built, continued on when my brother snagged the gear from my dad, and goes on with me rebuilding my MK IVs, a MK II, and a ST-70.  I run my amps through Dynaudio monitors - they give back whatever's fed to them, they're ruthless in exposing details - I can walk ten feet, put my ear right up to the speaker and hear those differences easily.  The differences aren't night and day, but I know what to listen for and watch for and there is a difference I prefer so far.

    MontanaWay

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    Age : 58
    Location : Cameron, Montana

    Re: What's an appropriate amount of capacitance for the quad cap in a MK IV amp?

    Post by MontanaWay on Fri Feb 19, 2016 10:50 pm

    j beede wrote:Precisely what exactly would a "German quad cap" be? Maybe Panasonic caps stuffed into a Teutonic tin can? If you can hear the difference between two otherwise identical mono tube amps that differ only in the country of origin of their power supply filter caps...

    You changed the ac coupling (signal path) caps to Wima. I suppose that difference might be audible.

    not sure if the Germans are quite up to what some Asian suppliers will do to make a buck or two.....it is good to be cautious, but one can perhaps be somewhat uber cautious as well.....

    Bob Latino
    Admin

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    Join date : 2008-11-26
    Location : Massachusetts

    Re: What's an appropriate amount of capacitance for the quad cap in a MK IV amp?

    Post by Bob Latino on Sat Feb 20, 2016 8:47 am

    Not trying to cause thread drift here but sometimes Asian suppliers have been known to FAKE parts. We have had a few posts on the forum here about this ... See below ...

    Fake Chinese capacitors

    Fake Chinese "tube" amp

    Tube buffer fraud

    Bob

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    Re: What's an appropriate amount of capacitance for the quad cap in a MK IV amp?

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