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    Stereo 70 Series II capacitor question


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    Stereo 70 Series II capacitor question

    Post by mainstream-deluxe on Sun Mar 29, 2015 10:57 am

    Hello everbody,

    my name is Thomas. I'm a new member in this forum.
    I owned a Stereo 70 Series II a few days ago.
    The amplifier is in working condition, but i want to replace the capacitors C1-C4 and C5, C6 & C9.
    As you can see in the schematics C1 & C2 are 68µf @ 450V capacitors, and C3 &C4 are 100µf @ 400V caps.
    On the board of my amplifier C1-C4 are 150µf @ 450V Sprague caps.
    I'm a bit confused.  confused Which capacitors are the right ones? Are there different versions of the ST 70 Series II?
    My be someone can help.  Very Happy

    My amp:



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    Re: Stereo 70 Series II capacitor question

    Post by stewdan on Sun Mar 29, 2015 11:51 am

    Hi Thomas --- I looked at the ST70 Series II Schematic that Bob has placed in the schematics file.

    The stock Series II has C1-C2 as 68MF @ 450V and C3-C4 as 100MF @ 400V.
    Whoever owned the amplifier before you got it, apparently changed out C1-C4 to 150MF @ 450V caps or maybe a later Series II amp was produced with the 150MF caps.

    On the original ST70 (circa 1965) the main cap was a 4-section 30MF-20MF-20MF-20MF can cap rated at 525V. This older functionally was like your C1-C4 caps, but all in one container(Quad Cap).

    Over the years that can cap has been replaced by different 4-section can caps or by 4-individual or 2-individual caps. (40-40-20-20,80-40-30-20, etc). I have seen amps with larger capacitance in the C1 & C2 stages, like the 150MF caps that you have.

    The intent of the large capacitance caps is to allow the amp to store more energy as it plays, thus giving you a smoother, larger sound.

    At some point, how large a capacitance is overkill?  The philosophy is that C1 & C2 should be large and C3 & C4 smaller. But what happens when you don't have the smaller caps available, well, I guess that you use 4 caps of the same size.

    There has been some discussion on the Forum about the Can or Quad Cap replacement, so if you do a search, some info will turn up,

    Hope that helps and does not confuse.

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    Re: Stereo 70 Series II capacitor question

    Post by tubes4hifi on Wed Apr 01, 2015 6:30 pm

    if it works, dont' fix it !!!


    Re: Stereo 70 Series II capacitor question

    Post by Guest on Wed Apr 01, 2015 8:00 pm

    as tubes4hifi said, if it works and sounds fine to you, why change them.
    What is the reason you wish to change them in the first place, do you wish to go back to stock?
    Those values that are in now should be just fine.

    by the way Willkommen, ich hoffe das Du unser Forum sehr Interessant findest!

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    Re: Stereo 70 Series II capacitor question

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