Tube Rolling

Look at the getter (the chrome-like coating on the inside of the top end of the glass envelope) of each tube. As the tube is used, that "flash" is burned off.

HI,
Getter is the metal (various shapes) that is connected to a hot electrode and is to collect free gases for tube to work in a vacuum, they are coated and loose some shining with use. The underside top of glass is metal particles (silver colouring) induced when sealing the tube. In power tubes they fade away with use. Driver or signal tubes get hazy marks or spots and a white ring at nipple base.

I replace tubes well before the getter "flashing" gets funky, and often simply because I want to try a different tube...generally the power tubes get the most attention, but my amp has only 2 (single ended pentode) so it's cheap. Preamp tubes seem to last a very long time in my Freya (4 6SN7GTYBs), and there's only one of those in the amp that also lasts...I check tubes by simply replacing one from my pile of new spares.

I have 3 power tube sets for my PrimaLuna Dialogue integrated amp: Tung Sol KT120, Gold Lion KT77 and TungSol 7581A. Each produces a different sonic signature and I swap sets about every 3 to 4 months. Now that's rolling!