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    bank capacitors

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    kost

    Posts : 33
    Join date : 2009-05-12
    Age : 52
    Location : athens

    bank capacitors

    Post by kost on Sun Apr 06, 2014 3:35 am

    f
    hi to all
    I wonder if i can increase the bank 
    capacitors values but i dont know how much.
    I am using Mundord non polar capacitors
    100 mf to the output transformers
    47 mf to the diode rectifier and 30 mf to the B+
    Last night i added an 68 mf to the 47 mf that goes to the diode rectifier
    with very good results.
    Can you advise how much i can exceed
    in all sections???

    cheers

    DarthBubba

    Posts : 81
    Join date : 2012-05-05

    Re: bank capacitors

    Post by DarthBubba on Sun Apr 06, 2014 3:04 pm

    What amplifier? Tube diode/rectifier or solid state?

    Upload a picture of your work or at least tell us the brand and model of amplifier.

    It should be a Dynaco, this is the Dynaco Tube Audio forum after all.

    Bob Latino
    Admin

    Posts : 2374
    Join date : 2008-11-26
    Location : Massachusetts

    Re: bank capacitors

    Post by Bob Latino on Sun Apr 06, 2014 9:04 pm

    Kost,

    What happened was that in your first post you did not state what kind of amplifier you were working with? The people reading the forum DID NOT KNOW whether you had a STOCK original ST-70, or a VTA ST-70 or a VTA ST-120 or what "Dynaco type" amp ? Now we know that you have a VTA ST-70.

    To try to answer your question ... Adding extra capacitance to the B+ high voltage system of a tube amp is OK UP TO A POINT. If you add too much then eventually some would be wasted because the amp just can't use that much AND extra capacitance (beyond a certain point) can SLOW DOWN the discharge and recharge rate of your bank of capacitors. This last part can cause problems. If you add a lot of extra capacitance you should add a "bypass capacitor" which provides a low impedance path to ground for the whole high voltage system. A BYPASS capacitor is a small value capacitor which allows the B+ system to discharge and recharge at a faster rate. On the VTA ST-120 and M-125 amp kits this cap is a 1 uF @ 630 volt cap. I think this bypass cap helps with transient response on the ST-120 and M-125 amps.

    Another thing ... Always add extra capacitance AFTER THE CHOKE. Too much capacitance (over 50 uF or 60 uF BEFORE the choke) can put an extra strain on the rectifier tube and cause your rectifier to have a short life.

    Bob

    kost

    Posts : 33
    Join date : 2009-05-12
    Age : 52
    Location : athens

    capacitors bank vta st70

    Post by kost on Mon Apr 07, 2014 5:18 am

    Hi Bob
    thank you for the fast responce.
    Please let me describe my amplifier s set up:
    I am using the vta old version 12AT7 and kt88 output.
    There is no rectifier tube,i am using SS rectification
    and i have a 100mf going to the output transformer,
    47mf going to the ss rectification and 30mf going to B+
    and i am driving ESL 57.
    According to your experience How much do you think that
    i can exceed the capacitance  without causing any harm
    in terms of funtionality or sound quality??

    regards

    Bob Latino
    Admin

    Posts : 2374
    Join date : 2008-11-26
    Location : Massachusetts

    Re: bank capacitors

    Post by Bob Latino on Mon Apr 07, 2014 8:11 am

    Hi Kost,

    1. Do not go any higher than the 47 uF to the rectifier.
    2. You can go to at least 200 uF to the two output transformers (after the choke)
       Both of these should be at least 500 volt rated on an ST-70

    Personally, I did things like this years ago on an ST-70 and found that after about the 100 uF you have on the output transformers now, adding more won't really help much.

    Understand that on an ORIGINAL Dynaco ST-70 just the quad cap ran the whole B+ system for the amp - driver board + output transformers. Dynaco used a 30, 20, 20, 20 cap with 30 uF for the rectifier and a VERY SMALL 20 uF to run the TWO output transformers. The other two 20 uF sections powered the driver board. The whole amp ran on 90 uF total.

    On the VTA ST70 you have 40 uF to the rectifier, the 80 and 20 are wired together for 100 uF to the two output transformers and 324 uF (294 uF on the board + the 30 section of the quad cap) to run the driver board. Set up like this, the VTA ST-70 has plenty of B+ storage to run the amp. IMHO adding any more capacitance to the VTA ST-70 as set up like this will not help the amp. The VTA ST-70 amp kit (if used with the stock parts) has 494 uF of B+ storage vs. the 90 uF of the original amp. That is 5 times what the original amp had and IMHO is enough to bring out the best in this amp.

    Your question was about "capacitor banks" .. You CAN replace the quad cap with separate capacitor banks but then you run into the problem of where to place them and how to safely attach them to the chassis. I've seen the inside wiring of amps that people have added separate capacitors and sometimes they are well done but many times capacitors are glued in there with wires running all over the place. Sometimes I get flak on customer inquiries for not using a "cap board" in place of the quad cap - BUT - a quad cap is a good way to get a lot of capacitance at a reasonable price and the quad cap makes the amp look "original". A cap board like the Triode Electronics board designed by Sheldon Stokes gives more capacitance than the quad cap on the VTA ST-70 amp - BUT - the Triode cap board is rated at 500 volts and the VTA amp's quad cap is rated at 550 volts. You have more voltage "headroom" using the VTA ST-70's 550 volt quad cap.

    Bob

    kost

    Posts : 33
    Join date : 2009-05-12
    Age : 52
    Location : athens

    capacitors bank vta st70

    Post by kost on Mon Apr 07, 2014 8:23 am

    Thank you Bob

    If i dont use a rectifier tube can i go higher than the 47mf with a SS rectifier?
    will this have an audible effect?

    thank you for being so passionate

    tubes4hifi
    Admin

    Posts : 1261
    Join date : 2008-11-30

    Re: bank capacitors

    Post by tubes4hifi on Fri Apr 11, 2014 8:50 pm

    even using SS diodes instead of a tube rectifier, keep in mind that first capacitor affects how much surge current goes thru the diodes,
    so too much capacitance can kill the diodes just like they can kill a tube rectifier. Too much capacitance acts like a dead short to the power supply
    when you turn on the power. (when the lights dim, you'll know you've got too much capacitance).
    so IMHO, I'll agree with Bob, keep that first cap before the choke to 47uF or less . . .

    snav

    Posts : 18
    Join date : 2011-05-18

    Re: bank capacitors

    Post by snav on Sat Jun 07, 2014 2:49 pm

    tubes4hifi wrote:even using SS diodes instead of a tube rectifier, keep in mind that first capacitor affects how much surge current goes thru the diodes,
    so too much capacitance can kill the diodes just like they can kill a tube rectifier.  Too much capacitance acts like a dead short to the power supply
    when you turn on the power.   (when the lights dim, you'll know you've got too much capacitance).
    so IMHO, I'll agree with Bob, keep that first cap before the choke to 47uF or less . . .


    The rectifier cap and PT cap are always mentioned but I haven't found mentions of the Driver board caps on a MK3. Is there a recommended (point of diminishing returns) limit for each of the four PS caps?


    Fwiw I have a cap bank board and chose 3pr of 68uf-400v for 34uf-800v ea and one pair of 180uf-400v for 90uf-800v after choke. I use a 5U4-GB for the voltage drop and have 20s delay for loaded voltages of 512v after rect, 501 after choke, and 464v at splitter and 402v at driver of 6AN8.

    evgenibgr

    Posts : 12
    Join date : 2012-02-28

    Re: bank capacitors

    Post by evgenibgr on Mon Jun 09, 2014 2:54 am

    I use 30uF Mundorf Tubecap after rectifier, After 4H choke 220uF Mundorf M-lytic HV+, after R2,2K 100uF Mundorf M-lytic HV+. Good results




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