Instruct: Classify Amazon reviews into positive or negative sentiment
Query: Classic Never Goes Out of Style

This is an interesting read, of historical value and a pretty good guide to some basic valve amplification circuits. The power amps described are all push/pull so if you're looking for a class-A single-ended design, this isn't your source. Still, it's worth keeping in your library. At sixty dollars it's a bit pricey but at the cover price of $16.95 would be quite reasonable if it were still available. Oh wait. It is still available from Parts Express and it's even discounted so now you don't have to agonize over the expense. I'm still kicking myself over that one.