The stock EL34 Power Tubes of the Marshall 1987X are compared to KT66 Power tubes. The EL34 are Telefunkens and the KT66 are TAD. The 1987X is played through a 1971 Marshall 4x12 model 1960A with stock G12M25 75Hz Pulsonic Celestion Greenbacks. The guitar is a Gibson SG Custom Shop.