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742 LEGO Trains 12v Transformer thumbnail image

742 LEGO Trains 12v Transformer
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742 LEGO Trains 12v Transformer
  • 12v Transformer thumbnail
  • 12v Transformer thumbnail

LEGO 742 12v Transformer is a vintage Trains set from 1970 valued at $10 for new and sealed sets, up 0% from an original retail price of $9.99. Used copies are valued between $8 and $9 depending on condition.

LEGO 742-1 12v Transformer is a Trains 12V accessory set released in 1970, containing 1 piece. It is a mains-powered unit used to supply and regulate 12V power for LEGO trains of the era, featuring variable speed control and connections for the 12V track system. Also known as “12V Transformer – for 100V Mains,” the model was issued in regional voltage versions, including a blue 110V Type 1 unit. It served as a core power component for early LEGO 12V train layouts. Based on current trends, this set could be valued near $10 within the next year.
12v Transformer is a vintage and hard-to-find LEGO set. Set 742-1 has not been available for sale online or in retail stores in new or well-preserved condition for many years. Collectors prize complete sets from this era, as boxes and sealed contents are especially difficult to track down today. Its true market value is difficult to assess with confidence due to its rarity.
There are currently no new/sealed listings available for 12v Transformer at this time.
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Sets in Trains / 12V

720-2 Train with 12V Electric Motor

Theme / Subtheme Trains / 12V
Year 1969
Pieces 369
Availability Retired
720-2 LEGO Train with 12V Electric Motor
Retail $24.50
Value $879.49
Growth  +3489.8%
Annual growth 6.5%

722-2 12V Electric Train with 2 Wagons

Theme / Subtheme Trains / 12V
Year 1970
Pieces 151
Availability Retired
722-2 LEGO 12V Electric Train with 2 Wagons
Retail $15.25
Value $1,249.77
Growth  +8095.2%
Annual growth 4.6%

721 Steam Locomotive

Theme / Subtheme Trains / 12V
Year 1969
Pieces 126
Availability Retired
721 LEGO Trains Steam Locomotive
Retail $11.50
Value $793.14
Growth  +6796.9%
Annual growth 5.1%

723 Diesel Locomotive

Theme / Subtheme Trains / 12V
Year 1970
Pieces 95
Availability Retired
723 LEGO Trains Diesel Locomotive
Retail $8.50
Value $606.68
Growth  +7037.4%
Annual growth 6.3%

702 12V Motor with Accessories Pack

Theme / Subtheme Trains / 12V
Year 1969
Pieces 28
Availability Retired
702 LEGO Trains 12V Motor with Accessories Pack
Retail $7.25
Value $233.37
Growth  +3118.9%
Annual growth 3.6%

750 8 Straight 12V Conducting Rails

Theme / Subtheme Trains / 12V
Year 1969
Pieces 8
Availability Retired
750 LEGO Trains 8 Straight 12V Conducting Rails
Retail $1.49
Value $20.56
Growth  +1279.9%
Annual growth 2.7%

751 8 Curved 12V Conducting Rails

Theme / Subtheme Trains / 12V
Year 1969
Pieces 8
Availability Retired
751 LEGO Trains 8 Curved 12V Conducting Rails
Retail $1.49
Value $11.66
Growth  +682.6%
Annual growth 3.0%

753 Automatic Right Electric Switch

Theme / Subtheme Trains / 12V
Year 1969
Pieces 5
Availability Retired
753 LEGO Trains Automatic Right Electric Switch
Retail $4.75
Value $80.93
Growth  +1603.8%
Annual growth 4.8%

754 Automatic Left Electric Switch

Theme / Subtheme Trains / 12V
Year 1969
Pieces 5
Availability Retired
754 LEGO Trains Automatic Left Electric Switch
Retail $4.75
Value $86.50
Growth  +1721.1%
Annual growth 5.2%

705 Motor Bushings

Theme / Subtheme Trains / 12V
Year 1969
Pieces 4
Availability Retired
705 LEGO Trains Motor Bushings
Retail $0.50
Value $5.82
Growth  +1064.0%
Annual growth 3.9%

704 12V Sleeper Track Contacts

Theme / Subtheme Trains / 12V
Year 1969
Pieces 2
Availability Retired
704 LEGO Trains 12V Sleeper Track Contacts
Retail $0.75
Value $31.15
Growth  +4053.3%
Annual growth 6.2%

703 12V Replacement Motor

Theme / Subtheme Trains / 12V
Year 1969
Pieces 1
Availability Retired
703 LEGO Trains 12V Replacement Motor
Retail $2.25
Value $43.73
Growth  +1843.6%
Annual growth 5.3%

706 Rail Contact Wires

Theme / Subtheme Trains / 12V
Year 1969
Pieces 1
Availability Retired
706 LEGO Trains Rail Contact Wires
Retail $0.75
Value $25.98
Growth  +3364.0%
Annual growth 5.9%

708 2m Extension Cord for Points

Theme / Subtheme Trains / 12V
Year 1970
Pieces 1
Availability Retired
708 LEGO Trains 2m Extension Cord for Points
Retail $1.00
Value $16.69
Growth  +1569.0%
Annual growth 3.1%

740-2 12V Transformer for 220V Pack

Theme / Subtheme Trains / 12V
Year 1969
Pieces 1
Availability Retired
740-2 LEGO Trains 12V Transformer for 220V Pack
Retail $12.50
Value $44.68
Growth  +257.4%
Annual growth 2.3%

707-2 12V Train Replacement Parts Retailer Pack

Theme / Subtheme Trains / 12V
Year 1969
Availability Retired
707-2 LEGO 12V Train Replacement Parts Retailer Pack
Retail $99.50
Value $957.95
Growth  +862.8%
Annual growth 4.1%

My Collection

12v Transformer Reviews

29 reviews
4.7
Collectors
Investors
BrickTrains-Sets
“The Lego 742 12v Transformer for 100 volt mains is basically a universal remote for all the things going on in your train track. There are ports in the transformer that controls the train, of course, one for the switch tracks, and one for the signals. It is great because all... More these devices to control the switch track snaps onto place on the transformer, so you can have a neater train station.”
Full review at bricktrains-sets.com

About Trains 12V

In 1969 LEGO released the 12 volt train sets as part of the Blue Era which was named because of the rail color. These 12V 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.

12V consists of 17 sets that ran from 1969 to 1970. As of today, 722-2 12V Electric Train with 2 Wagons is the most valuable 12V set with an estimated new/factory sealed value of $1,250.
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