I have replaced a 12AX7 tube with ECC85 in my guitar amp. Seems to work great and sound great. The part that is questioning me is whether the sound is being at its best because it takes a good 20-30 seconds before the volume reaches a good level. This is probably because original heating gives 6.3v at only 300ma and the tube needs about 400ma. It works but the question... will it sound any different? better? How will it affect the tone of the vacuum tube?
In other words. Having lower voltage than recommenden on heaters - good or bad?