There is absolutely NO danger in swopping the tubes you have mentioned. You will not damage anything, and 9 times out of 10 it will run OK, and give you the gain lowereing you desire.
But it may not sound as good as it would if the stage had been designed to take the tube you use - but it won't harm anything - and may work perfectly!
Of the tubes that you can sustitute, the 12AU7 has by far the lowest gain.
Just don't try fitting something that uses different pin connections - or uses far more heater current than the ones it was designed for.
Regards, Allen (Vacuum State)
But it may not sound as good as it would if the stage had been designed to take the tube you use - but it won't harm anything - and may work perfectly!
Of the tubes that you can sustitute, the 12AU7 has by far the lowest gain.
Just don't try fitting something that uses different pin connections - or uses far more heater current than the ones it was designed for.
Regards, Allen (Vacuum State)