When installing the 6550C or KT88 power tubes, match the numbers designated on the metal base of the tube or the tube boxes to the corresponding markings printed on the tube top (V5 through V8 and LV5 through LV8) and be sure the center pin key locator is in alignment with the slot in the center of the socket. Again push down the tube, rocking gently until it is firmly seated.
Note the locating center key and notch for proper alignment of tube and socket.
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