Instruct: Classify the given Amazon review into positive or negative sentiment.
Query: Much like the christian bible, this tube "bible" is not reliable.

Buy Groove Tubes. That's the only lesson you will learn from this overpriced book.Save your money. Use it for gas to travel to as many new and used stores as possible and play as many amps as you can. There are great amps being made today, just as there were many great amps made long ago.And there are MANY sources for good info on tubes aside from Groove Tubes. I mean, it's a great, really catchy company name and they have done much to encourage the use of tubes in the larger "chain" guitar stores...meaning the only large chain store of Guitar Center. But you must know that Guitar Center and Groove Tubes are only one small window into the cool world of instruments and amps.