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    High Voltage Quad Cap and Mk3s To Replace or Not...

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    bubbasweet

    Posts : 53
    Join date : 2016-03-14

    High Voltage Quad Cap and Mk3s To Replace or Not...

    Post by bubbasweet on Mon Jul 18, 2016 12:02 pm

    I have 2 Mk3s that are dated 1959 and 1960 according to bias pots. Both are working well. Zero hum. Do I replace the Quad Cans or leave em.. I remember doing this once on my ST70 and it actually hummed more and I put the original can back. It was an Aero cap. Are the new replacements as good quality as the origial cans? I just hate to fix what ain't broken. I am a tech so I know damn well caps get old and the possible issues it brings. Do they replenish with a lot of use or reform? Curious to hear your thoughts on the issue. Also what current replacement brands are the best. NO Cap salesman please.. lol.

    stewdan

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    Age : 78
    Location : Houston Texas

    Quad Caps

    Post by stewdan on Mon Jul 18, 2016 1:12 pm

    Hi --- I have rebuilt multiple Mark 3s and the first thing I did was replace the 50+ year old Quad Caps.  You can reform the old caps, but 50 year old capacitors are prone to failure and when they go, they can take out something else.  So, it is cost effective to replace them.

    Usually, I use the 80-40-30-20 at 550V/600v cap from Dynakitparts when they are available. When not available, I use the SDS Cap Boards that Triode Electronics in Chicago sells or build a cap board of my own using ten 47MF @450 volt radial caps which gives me a 25-50-25-25MF at 800+ volts.  Forum member "I Beede" also builds his own cap boards and I got the idea from him after I saw his Forum Post.  There are also other quad brands available that are good.  I think Roy still lists a quad on the Tubes4Hifi Website. Dynakitparts lists several different ones.  Scan ebay and see what pops up when you search for "Dynaco Quad Cap" just to give you an idea of what is out there quad cap-wise.

    There was also an earlier post (last month, I think) from someone who was using a Mark 3 Cap Board sold by ebay seller "tubes4pro".  I have bought other cap boards from this seller and have been extremely happy with them.  Currently, he is selling a cap board for the PAS Preamp.  I inquired about the Mark 3 Cap Boards, but he was out of stock but expecting them in.

    Hope this info helps.  Any questions, just ask.
    Stew

    peterh

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    Re: High Voltage Quad Cap and Mk3s To Replace or Not...

    Post by peterh on Mon Jul 18, 2016 3:27 pm

    bubbasweet wrote:I have 2 Mk3s that are dated 1959 and 1960 according to bias pots. Both are working well. Zero hum. Do I replace the Quad Cans or leave em..  I remember doing this once on my ST70 and it actually hummed more and I put the original can back. It was an Aero cap. Are the new replacements as good quality as the origial cans? I just hate to fix what ain't broken. I am a tech so I know damn well caps get old and the possible issues it brings. Do they replenish with a lot of use or reform? Curious to hear your thoughts on the issue. Also what current replacement brands are the best. NO Cap salesman please.. lol.
    Leave them. Don't mess with working amps unless they hum or oscillates.
    If replacing them, dynakitparts tubes4hifi and triode has correkt parts.

    zx

    Posts : 194
    Join date : 2011-08-05

    Re: High Voltage Quad Cap and Mk3s To Replace or Not...

    Post by zx on Mon Jul 18, 2016 3:52 pm

    If you are using a Varic ....you can run older can caps in MK3...for ever...hehe







    thanks for the site Bob.....

    Jim McShane

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    Location : South Suburban Chicago

    Re: High Voltage Quad Cap and Mk3s To Replace or Not...

    Post by Jim McShane on Mon Jul 18, 2016 4:01 pm

    peterh wrote:Leave them. Don't mess with working amps unless they hum or oscillates.
    If replacing them, dynakitparts tubes4hifi and triode has correkt parts.

    I have to disagree strongly, since power supply cap failures can cause expensive damage; it almost certainly will take out the rectifier tube and may do other harm. As well, this cap has been in service well past its normal lifespan, so while it works (at this moment) it may not work as well as a fresh cap that is operating with less leakage and quite often much more capacitance than the old deteriorated original.

    Reforming is of no value in a case like this. Reforming is done when a cap hasn't been in use for a good while. Electrolytic capacitors use a chemical process to provide the insulating layer between the cap plates. This process can degrade over time if the cap has not had power applied. The the "re-forming" process is designed to reestablish the layer inside the cap without doing internal damage. If the cap has been in fairly recent use at anywhere near its rated voltage (like in the Dynas) there is no benefit to reforming.

    Replace the cap - it's cheap insurance!

    bubbasweet

    Posts : 53
    Join date : 2016-03-14

    Re: High Voltage Quad Cap and Mk3s To Replace or Not...

    Post by bubbasweet on Mon Jul 18, 2016 4:09 pm

    Thx for input. I agree with all of you. To add fuel, how many NEW components have I see bad out of box or fail... A few.. I certainly do not want to fry a Transformer. Maybe I will get 3 of the 80 40 30 20s for the MK3s and the ST70.. All are working fine with ZERO hum. I hear Peter H also though... Hate f*ing with perfect running amps. What is the lowest value fuse you can run in these. I like running them really low, so they blow easily if there is a problem. 1.5A or 2A Slow blow? 3 is a little too high.

    Jim McShane

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    Re: High Voltage Quad Cap and Mk3s To Replace or Not...

    Post by Jim McShane on Mon Jul 18, 2016 4:57 pm

    zx wrote:If you are using a Varic ....you can run older can caps in MK3...for ever...hehe

    But why would you want to? You've got a classic amp that's worth 100s of dollars and you really enjoy listening to - and an investment of a few bucks to keep it running its best isn't worth it? To each their own of course, but I must confess that is hard for me to get my head around.

    bubbasweet

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    Join date : 2016-03-14

    Re: High Voltage Quad Cap and Mk3s To Replace or Not...

    Post by bubbasweet on Mon Jul 18, 2016 5:47 pm

    Problem with Variac also is they lower the voltage so B+ goes down which is fine, but so does filament with it. Need proper filament voltage on the tubes.

    j beede

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

    Re: High Voltage Quad Cap and Mk3s To Replace or Not...

    Post by j beede on Mon Jul 18, 2016 6:47 pm

    bubbasweet wrote:Problem with Variac also is they lower the voltage so B+ goes down which is fine, but so does filament with it. Need proper filament voltage on the tubes.

    If your mains supply is like mine (118-123V) you are running your MkIII filaments hotter than then were run back in the 1960s. Probably not much of an issue there. But elevated B+ in a MkIII is a reliability issue as the stock quad cap had a small safety margin even when the mains supplies were referred to as "110" and "220".

    A VARIAC or bucking transformer is a good idea with the MkIII. Since the supply filtering is a reliability weak link in the MkIII I prefer to replace the quad cap with (much) higher voltage components. If you care to run your MkIII with (unbuffered) solid state rectification upgrading to higher voltage caps makes even more sense.

    ...j

    PeterCapo

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    Re: High Voltage Quad Cap and Mk3s To Replace or Not...

    Post by PeterCapo on Mon Jul 18, 2016 9:18 pm

    Though I have advocated for maintaining originality where possible, and where desired, and while I also believe "if it ain't broke don’t fix it," Jim McShane’s reasoning is undeniable.  The original quad caps are long past their service life.  It’s remarkable they work at all after all these years.

    It’s up to the individual owner what kind of chance they want to take.  It’s possible there could be a catastrophic failure, or it might not be catastrophic.  When the original quad cap in one of my Stereo 70s "went," it didn’t take anything else with it, but I also think I was lucky.

    It would be interesting to see one of the new, higher voltage quad caps taken apart.  The one with the higher voltage rating has discrete electrolytics inside – would be interesting to see them and their respective markings.  Over time I have read of some early failures with these as well as with the reissues of the traditional Swiss roll type of quad cap, but who knows why.  I suppose I would tend to favor an under-chassis cap board but a new quad cap should likely be fine provided the amplifier is otherwise functioning properly and within its design limits.

    tubes4hifi
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    Re: High Voltage Quad Cap and Mk3s To Replace or Not...

    Post by tubes4hifi on Thu Jul 21, 2016 11:06 pm

    I personally would not even consider powering up a tube amp with a quad cap that is more than ten years old !!!!!!!!!!!
    That is the very first and #1 replacement part, other than a rectifier tube (which probably goes bad due to a leaky quad cap)

    PeterCapo

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    Re: High Voltage Quad Cap and Mk3s To Replace or Not...

    Post by PeterCapo on Thu Jul 21, 2016 11:41 pm

    One complication is that whether we're talking about "new" multi-section cans from either Authenticap or CE Manufacturing, how would anyone know how long they might have been sitting on a shelf? I don’t recall if they come with a manufacturing date code printed on them anywhere. If not, it makes a good case for buying a variac, too.

    Bob Latino
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    Re: High Voltage Quad Cap and Mk3s To Replace or Not...

    Post by Bob Latino on Fri Jul 22, 2016 6:59 am

    PeterCapo wrote:One complication is that whether we're talking about "new" multi-section cans from either Authenticap or CE Manufacturing, how would anyone know how long they might have been sitting on a shelf?  I don’t recall if they come with a manufacturing date code printed on them anywhere.  If not, it makes a good case for buying a variac, too.

    All the Authenticaps (Made in Germany) come with a date code of month and year of manufacture. I have some here that say "18 16" which is the 18th week of 2016 which is May of 2016. I believe that the CE caps have a similar date of manufacture code on them but I do not have a CE cap here to check it.

    I totally agree with what Roy mentioned above .. If the quad caps says "Dynaco" on it just replace the cap. It has to be 40+ years old and has already outlived its usefulness. If you are not sure about the cap's age then continuing to run the amp with a cap of unknown age is (as the British would say) a "sketchy" situation.

    Bob

    Jim McShane

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    Location : South Suburban Chicago

    Re: High Voltage Quad Cap and Mk3s To Replace or Not...

    Post by Jim McShane on Fri Jul 22, 2016 11:17 am

    The CE caps I have that I just received are all date coded from 2015 as well. These are new production caps as Bob mentioned

    bubbasweet

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    Re: High Voltage Quad Cap and Mk3s To Replace or Not...

    Post by bubbasweet on Sat Jul 23, 2016 1:57 am

    I got mine from Germany.

    morrism

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    Join date : 2016-01-18

    Re: High Voltage Quad Cap and Mk3s To Replace or Not...

    Post by morrism on Sun Jul 24, 2016 1:42 pm

    I just got a CE cap. It has "1527-01" printed on it as well as 55C. When was it manufactured? Is it really temperature rated to only 55C?

    stewdan

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    Quad Cap

    Post by stewdan on Sun Jul 24, 2016 2:02 pm

    .............. "It has "1527-01" printed on it"

    Date --- 27th week of 2015
    Not sure what the 01 is.

    PeterCapo

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    Re: High Voltage Quad Cap and Mk3s To Replace or Not...

    Post by PeterCapo on Sun Jul 24, 2016 4:28 pm

    morrism wrote:Is it really temperature rated to only 55C?

    I believe the CE Manufacturing quad cans typically used in Dynacos are rated to 55C, which is not one of their strong points.

    The Authenticap quad can with the higher voltage rating has discrete electrolytics inside.  Discrete electrolytics are typically rated for 85C but some are rated lower.  Unfortunately, you can't see inside the can to know.  And, I looked at the datasheet for these but did not notice a temperature rating.

    I tend to prefer cap boards with discrete electrolytics known to be rated for at least 85C with others available at 105C.

    But, any of the current production quad cans should nevertheless work fine.


    Last edited by PeterCapo on Sun Jul 24, 2016 10:27 pm; edited 1 time in total (Reason for editing : Clarification.)

    bubbasweet

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    Join date : 2016-03-14

    Re: High Voltage Quad Cap and Mk3s To Replace or Not...

    Post by bubbasweet on Sun Jul 24, 2016 5:09 pm

    What temp were the original cans that are still working in my amp rated?

    PeterCapo

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    Re: High Voltage Quad Cap and Mk3s To Replace or Not...

    Post by PeterCapo on Sun Jul 24, 2016 5:13 pm

    Might be stamped right on the can - have a look.

    bubbasweet

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    Re: High Voltage Quad Cap and Mk3s To Replace or Not...

    Post by bubbasweet on Fri Jul 29, 2016 3:53 pm

    Replacing them anyway.

    PeterCapo

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    Re: High Voltage Quad Cap and Mk3s To Replace or Not...

    Post by PeterCapo on Fri Jul 29, 2016 6:46 pm

    Should work well. Looking forward to hearing about the results when you're done.

    bubbasweet

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    Join date : 2016-03-14

    Re: High Voltage Quad Cap and Mk3s To Replace or Not...

    Post by bubbasweet on Mon Aug 15, 2016 11:41 am

    Done, not noticing much. Piece of mind.

    Peter W.

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    Re: High Voltage Quad Cap and Mk3s To Replace or Not...

    Post by Peter W. on Mon Aug 15, 2016 3:23 pm

    bubbasweet wrote:Done, not noticing much. Piece of mind.

    Yes. But, one hopes "Peace" of mind. Writing for myself, I have so little that sparing a piece would be risky.

    One does not, typically, notice a bad cap until something slags. And that is generally no fun at all.

    Now, if one is very careful and has a very good octal or 4-pin socket and base, one can make a cap board and plug it into a socket for easy service. BUT (!!!) that socket had better be tight - high voltages and sketchy connections = heat.

    If one uses this expedient, it is useful to install small snubbing capacitors across each section. I use 0s .22 film caps at 600 V. I also put caps in series/parallel to get ~50 % more capacitance at 600V (the  iting factor being the film cap).

    IF one does choose to up the capacitance, CHECK THE B+ and make sure that the bias voltage is within tolerance. Due to increases in line voltage over the 1960s, what happens at the wallplate may be  up to 125 V, sometimes even more. And increased capacitance in itself can increase B+. So, have a care.

    Lethal voltages on those caps. Beware of exposure if above the chassis.

    Use 100 C (temperature) caps. Goes a long way towards longevity.

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