How to tell vacuum tube is gone bad??


I recently purchased primaluna prologue 3 and I connect with dynaudio bm6a.

First I saw is lights of three vacuum tubes are dim and

other lights of three vacuum tubes are bright.

Among 6, 1 of vacuum tube has little soot on wall.
chunkichunky

Showing 1 response by montytx

The brightness of the various tubes are mostly a non-issue as this isn't an indication of the condition of the tube, but more related to where the plates and cathode are in relation to each other.

The soot on the glass is also of no concern. Mullards typically leave a very dark, smokey haze on the glass and that's normal. Small signal Mullards will often "flash" upon power up and that's just a design thing and not an indication of an arching tube.