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Thread: What was the build year of my PL 400?

  1. #1
    New Around These Parts silver_face's Avatar
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    What was the build year of my PL 400?

    I was wondering how to tell what year my PL 400 was built? The serial number is 4277 on the transformer. Transistors are XPL909 with 7452,
    and SJ2741 with 7439 on them.

    Click image for larger version. 

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  2. #2
    Forum Veteran 62vauxhall's Avatar
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    Quote Originally Posted by silver_face View Post
    I was wondering how to tell what year my PL 400 was built? The serial number is 4277 on the transformer. Transistors are XPL909 with 7452,
    and SJ2741 with 7439 on them.

    Click image for larger version. 

Name:	IMG_20180304_223054.jpg 
Views:	23 
Size:	72.8 KB 
ID:	31495
    I'm interested to learn from the experts too.

    I have a 4 fin PL400 with SN 343-323 and I was informed:

    First digit = month
    2nd digit = first numeral in power amp model number
    3rd digit = last number of build year

    The 3 number suffix denoted it's spot in the production run for that month.

    In my case, the 323rd PL400 amplifier built in March of 1973.

    Maybe your example, with 4 digits and no hyphen, means a different numbering system was in place?

    As it happens, I also have a 700B (too heavy and awkward to move at the moment) and the original board was date stamped May, 1974. I've intended for some time to have a look at the SN just to see if it's SN fits the formula.

  3. #3
    Quote Originally Posted by silver_face View Post
    I was wondering how to tell what year my PL 400 was built? The serial number is 4277 on the transformer. Transistors are XPL909 with 7452,
    and SJ2741 with 7439 on them.

    Click image for larger version. 

Name:	IMG_20180304_223054.jpg 
Views:	23 
Size:	72.8 KB 
ID:	31495
    In June 1974 Phase Linear went away from a date coded serial number to serial numbers starting at 1000.
    More than likely your amp was made sometime in early 1975 (a few months) after the XPL909 transistors were made.
    The 7452 on the XPL909's indicates the year 1974 and 52 would be the 52nd week or the last week of 1974.

    Ed

  4. #4
    New Around These Parts silver_face's Avatar
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    Quote Originally Posted by oldphaser View Post
    In June 1974 Phase Linear went away from a date coded serial number to serial numbers starting at 1000.
    More than likely your amp was made sometime in early 1975 (a few months) after the XPL909 transistors were made.
    The 7452 on the XPL909's indicates the year 1974 and 52 would be the 52nd week or the last week of 1974.

    Ed

    Ok, Thanks Ed

    Ron

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