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    Repopulating an original ST-70 PCB

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    quadaptor

    Posts : 59
    Join date : 2009-05-04

    Repopulating an original ST-70 PCB

    Post by quadaptor on Sun May 23, 2010 1:41 pm

    Here's a quick and basic question. Lately I've been thinking about rebuilding the PCB in my stock ST-70 and would like some opinions on components. What are the best resistors - metal film or carbon, and is there much difference in the sound they produce. Also, reccomendations for capicitors are appreciated.

    I know there are aftermarket boards available, but I thought this project would be relatively inexpensive and one in which I too could practice my soldering and assembly skills. Thanks

    PS - Also, any comments on resistor values, ratings, percents, etc..?


    Last edited by quadaptor on Sun May 23, 2010 8:45 pm; edited 1 time in total

    kost

    Posts : 33
    Join date : 2009-05-12
    Age : 53
    Location : athens

    Re: Repopulating an original ST-70 PCB

    Post by kost on Sun May 23, 2010 3:02 pm

    Try the VTA modification.
    With the K40-Y PAPER IN OIL capacitors the st 70 is one of the
    best amplifiers i ve ever heard.

    regards
    kost

    quadaptor

    Posts : 59
    Join date : 2009-05-04

    Re: Repopulating an original ST-70 PCB

    Post by quadaptor on Sun May 23, 2010 4:03 pm

    Kost,

    Actually I have a VTA mod project with the K40-Y PIO caps in the works. I also happen to have a second ST-70 I'd like to keep fairly stock just to explore how well the original amps actually performed. I changed out the old selinium rectifier and added one of the dynakitparts bias kits a couple months back which made bias adjusing much more flexible. I also upgraded the quad cap to one of the larger dynakitparts caps. I've had both amps for nearly 25-years and frankly enjoy the sound of both stock and VTA modified ST-70s. I know its subjective, but I find the VTA modded amps have improved highs and lows, and create a plane of sound like that projected from a stage. In contrast, I too find that music played from a stock ST-70 sounds more like it's projected from a smaller format or room - this is just my opinion. Anyway, I like them both and appreciate advice on resistors and caps. Thanks again -

    kost

    Posts : 33
    Join date : 2009-05-12
    Age : 53
    Location : athens

    Re: Repopulating an original ST-70 PCB

    Post by kost on Mon May 24, 2010 4:15 am

    Hi

    I think that carbon composition resistors are the
    best for a vintage amplifier.
    Very good resistors are the KIWAME,with warm but slightly more modern sound
    than ALAN BRANDLEY.
    If you are interested i can send you a schematic.
    with all resistors and caps values.
    About caps ,avoid any modern capacitors,even the most expensive dont sound right to
    the st70.
    Try the k40 or MULLARD 0.1 400V.

    KOST

    quadaptor

    Posts : 59
    Join date : 2009-05-04

    Re: Repopulating an original ST-70 PCB

    Post by quadaptor on Mon May 24, 2010 11:22 pm

    Kost,

    I've been researching resistors and caps based on your advice. In the meatime, does the percentage tolerance and wattage ratings of resistors make a big difference? Should the russian K-40Y caps be of the same value as those used in the VTA boards? Also, can you reccomend a good source for purchasing caps and resistors? Thanks again

    kost

    Posts : 33
    Join date : 2009-05-12
    Age : 53
    Location : athens

    Re: Repopulating an original ST-70 PCB

    Post by kost on Tue May 25, 2010 5:37 am

    Hi

    I finaly think that the best solution for you
    is this...

    http://www.dynakitparts.com/store/product.aspx?id=19

    Very good quality parts,but dont forget to choose the
    carbon composition resistors option

    regards

    kost

    Aljaheejus

    Posts : 37
    Join date : 2010-01-03

    Original PCB schematic with values

    Post by Aljaheejus on Wed Aug 25, 2010 9:02 pm

    kost wrote:Hi

    I think that carbon composition resistors are the
    best for a vintage amplifier.
    Very good resistors are the KIWAME,with warm but slightly more modern sound
    than ALAN BRANDLEY.
    If you are interested i can send you a schematic.
    with all resistors and caps values.
    About caps ,avoid any modern capacitors,even the most expensive dont sound right to
    the st70.
    Try the k40 or MULLARD 0.1 400V.

    KOST

    May I request your schematic with values? I have rebuilt my original board with stock values, but I am not clear on the wattage rating the various resistors should have. Does your documentation address that?

    Thanks, David

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