Originally Posted by Scooper
I believe all the early frames had second downtubes in both positions similar to the bike on the left in the attached illustration from the 1978 catalog.
Actually, before '64 the Schwinn tandems (Town & Country & Bicycle Built for Two) were "lady-back" designs with a horizontal front and "mixte" rear. '64 was the transition year leading up to the '65 Schwinn Twinns with the dual step-through frames. Through it all, the Paramount group was still doing custom tandems for racing and in '69 the Paramount tandems were reintroduced as production models with both a "conventional" full length horizontal top tube and a lady-back design.
Also, if the tandem is a very light blue, it could have been produced in the 70's as I noted that an "Opaque Blue" color showed up in '73:
http://www.geocities.com/sldbconsume.../73ccpg07b.jpg
Again, the serial number will quickly resolve the year of manufacture.
1972 - AH00000…
1973 - AJ00000…
1974 - AK00000…
1975 - AL00000…
1976 - AM00000…
1977 - AN00000…
1978 - AP00000…