Here is a visual comparison of the response of each individual tube, measured in lows, mids and highs.
Test conducted by Kurt Prange.
Kurt Prange (BSEE) is the Sales Engineer for Amplified Parts (www.amplifiedparts.com) in Tempe, Arizona, United States. Kurt began playing guitar at the age of nine in Kalamazoo, Michigan. He is a guitar DIY'er and tube amp designer who enjoys helping other musicians along in the endless pursuit of tone.