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Just two more data points: I have two 1968 Adler Tippa S made in W, Germany by Grundig and both have the serial number stamped into the top of the frame under the right end of the carriage. These frames are non-ferrous castings, probably aluminum, and apparently painted after the serial numbers were stamped, which might be a clue to the manufacturing sequence. Have fun with this info, guys.
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I just checked a few T/A portables, limited to early '60s onward. All of the '60s models had serial numbers under the carriage - some on the left side by the drawband drum, some on the right side - and an early '70s was the same. On a Contessa De Luxe I found the serial number under the keyboard; I don't know the exact year of manufacture for this machine other than it's from the '70s. Again, this is a super-small sample size, but so far the year theory is holding up.
With respect to Michael's observations, some of the T/A machines I looked at had serial numbers engraved on a separate plate that was riveted to the frame, but most match his description.
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Some more datapoints: from the 8 Tippa's I have owned, only the 1973 model has the serial in the front. The other 7 were produced between 1961-1971.
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My 1964 Triumph Tippa has it SN's placed under the right side of the carriage. It is a West Germany made machine.
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