(MONEY Magazine) – As millions of compact-disk owners toss their old 45s and LP vinyl records, other consumers are snapping up those platters for a song. "Right now is the best time investors will ever have to search out classic records of the '50s, '60s and '70s," says John Koenig of Discoveries, a record collectors' magazine (800-364-5593; $19 for 12 issues). In the past six years, say experts, prices on collectible vinyl have jumped 30% to 40%. But only a small number -- perhaps 5% -- of the millions of records produced from the '50s through the '70s are worth collecting. If you're tempted, take these tips: -- Buy the rarest records by the biggest names. Elvis attracts the most collectors, and the Beatles come close. Elvis' earliest 45s on the Sun label | go for $200 to $300 today and may command $500 to $600 within a few years, says Doug Hanners, promoter of the U.S.' largest record collector convention in Austin (512-288-7288). The most valuable Beatles singles, worth $500 or more apiece, are those released on Decca, Swan and Vee Jay labels in 1962 and '63, before the Fab Four's '64 deal with Capitol. -- Concentrate on the uncommon. Value in record collecting is largely a function of scarcity. Look for obscure bands on small labels, local or regional artists, duds by big-name artists and promotional releases. Most albums from the 1950s are good bets because, says Les Harris, a San Antonio dealer, "back in the '50s, records weren't mass-produced, even your top groups." -- Look for bargains at tag sales, thrift shops and used-book stores. Check your find's value in The Official Price Guide to Records by Jerry Osborne (House of Collectibles, $20). -- Packaging counts. "There's a resurgence of interest in '60s and '70s albums with gatefold covers and expansive artwork," reports Koenig. Examples: the 1969 Bee Gees' Odessa album ($30 to $50 now; $4 when new) and the Stones' 3-D cover (above). -- Condition is key. Look for record jackets that are sharp and crisp, with no dinged corners. Check records for scratches. "People partied with the '60s and '70s classic albums and really trashed them," says Koenig, "which has increased the market for good ones." -- And be alert: Recently, Harris was browsing in a store. Out fell a Beatles promotional 45 labeled "Sie Liebt Dich" ("She Loves You," in German). It's worth $300, but Harris bagged it for a quarter.