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    ST-70 age and care

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    chrisj

    Posts : 2
    Join date : 2014-08-10

    ST-70 age and care

    Post by chrisj on Sat Aug 16, 2014 8:45 am

    I have just bought a ST-70 amp and would like to know if there is a way to tell what year it was built. Its all original except for the rectifier and output tubes. I am currently using a rotel turntable with an AT cart and an AMBER preamp driving a pair of magnepan 1.6 speakers. There is no hum or hiss so I dont know if there are any changes I need to make to the amp to have it last. I have read about all kinds of mods to make to the amp but would like to keep it as stock as possible.

    Bob Latino
    Admin

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

    Re: ST-70 age and care

    Post by Bob Latino on Sat Aug 16, 2014 8:51 am

    A rough idea of the age of any Dynaco tube amp with bias pots is to check the number on the bias pot. This number indicates when the bias pot was made. Since Dynaco used parts fairly quickly, the amp was probably shipped as a kit or a factory wired amp within a month or two of the date mentioned.

    Early Dynaco bias pots had a 7 number bias pot code. On the photo below "137" was the part number, the next two digits "64" was the year of manufacture and the "30" was the 30th week of 1964 - sometime in August of 1964. This amp was probably shipped sometime in the fall of 1964.



    Later in production, these bias pots had a SIX number code and were sometimes stamped on the back OR the edge of the bias pot. It is possible that Dynaco had 2 or 3 vendors of these bias pots who stamped these pots in a different manner. Below are two photos of pots possibly from a later production or from other vendors? It is just conjecture, but maybe the company (or companies ?) that made these pots dropped the "6" from the date and the two pots below were made in the 52nd week of 1969 and the other made in 8th week of 1968?





    chrisj

    Posts : 2
    Join date : 2014-08-10

    Re: ST-70 age and care

    Post by chrisj on Sat Aug 16, 2014 9:39 am

    The numbers on one of the pots is 1376021 which would make it about mid 1960. Thanks for the info.

    MontanaWay

    Posts : 767
    Join date : 2014-02-06
    Age : 58
    Location : Cameron, Montana

    Re: ST-70 age and care

    Post by MontanaWay on Sat Aug 16, 2014 10:21 am

    WELL!....ya learn something new every day!  Smile never knew that!

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