Sorry for the answer in English. This actually involves a rebuild: a new body was put on the chassis of an older two-axle tram. This is the reason why this series (like the articulated series 4000) barely served 20 years. Delivery of new trams had already started in 1958 (with the PCC series 7000) and was completed 20 years later with the delivery of the last articulated tram series 7900. It is to cover this intermediate period that a small part of the older trams were modernised.
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