In 1972 LEGO released the 4.5V and 12V train sets as part of the Blue Era which was named because of the rail color. These train sets used additional conductor rails mounted between the standard 4.5V rails and 12V motors contained in the same housings as the 4.5V motors, but with additional metal contacts attached to the bottom of the housings.
4.5V / 12V consists of 83 sets that ran from 1972 to 1986. As of today,
7750 Steam Engine with Tender is the most valuable 4.5V / 12V set with an estimated new/factory sealed value of $5,446.
Summary
Trains 4.5V / 12V Push-Along Play Train set 170 was released in April 1973, retailing for $5, but has since been retired. New, unopened Push-Along Play Train sets are valued at $235, while used sets can be found for $44.
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