Have to agree with Adam, but here's the timeline:
Early 90's till 2000...OSB but great sounding speakers, US made.
2000-2005...OSB, dark speakers, US made.
Sometime in 2006...plywood, dark speakers but still sounds a little brighter than the 2000-2005 cabs...US made.
2007-present...plywood, brighter speakers, foreign made.
Ampeg Portaflex Club #1