Great memories! Used to listen to him and many other rock/metal bands in high school and college in the 80's. Yngwie Malmsteen is one of the best rock/metal guitarists of all time!
Finally, something we can agree on.
His most famous Stratocaster is his 1972 blonde Strat, nicknamed "The Duck" because of its yellow finish and the Donald Duck stickers on the headstock. An alternative nickname for this guitar is "Play Loud" due to a sticker on the upper horn of the guitar. Fender made 100 replica copies of this guitar and marketed it as the "Play Loud Guitar". He also has a signature Stratocaster. It comes in a Vintage White finish with a maple neck, either a maple or rosewood fretboard with scalloped frets and, from 2010, Seymour Duncan STK-S10 YJM "Fury" Model pickups. There is also a signature YJM100 Marshall amplifier, based on the '1959' amplifier range.
Malmsteen has stated that he prefers the Stratocaster (from 1968-1972) he claims that the bigger headstock on these generates more sustain. Yngwie customizes his guitars by fitting a brass nut, removing the middle string tree and scalloping the fretboard. He previously disconnected the tone controls on his guitars but has said that he no longer does this. He now uses his signature Seymour Duncan YJM Fury pickups. Before using the YJM's, he used DiMarzio pickups - most notably the HS3 model and the HS4 model and would use a HS3 in the bridge and HS4s in the middle and neck positions. In even earlier recordings, Malmsteen instead used the HS3 model in the neck and bridge positions and a disconnected stock Fender single coil pickup in the middle.
Outside of his Stratocasters, Yngwie has played non-Fender guitars (like Aria Pro II's in the early 1980s) and non-Strat-shaped guitars (like Flying V's), particularly early in his career. For acoustic and nylon string guitars, today Malmsteen plays his signature Ovation YM68's.