I agree with Albert too. Having said that, I will now proceed to step on some toes so please excuse me for a moment :) :
6DJ8/6922s are not a good tube for audio despite what you might hear here. The reason is they have a tendancy to microphonics (they were built more for instrumentation and not audio), despite their otherwise excellent characteristics. You *really* have to hunt to find one that is low microphonics. The 12AT7 is a lot easier to use and so is the 6SN7 for many of the purposes that you might use a 6DJ8 for.
The 6SN7 is the octal equivilent of the 6CG7, but is usually smoother sounding because again there are less microphonics (my guess is due to the more robust structure).
12AX7s can be very nice but do not expect a wide bandwidth circuit! So from 12AX7s you will get an older-fashioned tube sound as mid and treble artifacts will be audible due to phase shift caused by the upper frequency cutoff. Its not a bad sound- just not very fast. Incidently this is something that 6DJ8s do better (they have plenty of bandwidth) but now you have an 'iridescence' caused by their microphonics.
12AU7s can be very nice as they have good bandwidth, but they are more prone to microphonics again, however with less of the 'bell ringing' issues of the 6DJ8 family (which includes the 6H30).
IF it seems that microphonics is a major problem, you are right. Tubes designed for audio do seem to have less in that department then those designed for instrumentation. There are other more subtle effects caused by means of construction, some of which are lost to time: Telefunken 12AX7s and Mullard tubes are sought due to the excellent contruction techniques employed during the hey day of tubes.
So, while I have offered some general pointers on some tubes, the individual tubes of the specific types will vary enough for considerable overlap! This is why Albert is correct in his assertion. If you are dealing with the best of the best in all tube types you will find them all very close. It is the generel average tubes where the foibles that seperate them become evident- for example the average 6DJ8 will sound pretty bad compared to the average 6SN7.
My advice if you are tube rolling is to be careful about documenting what you are doing, and make sure you can return tubes that you buy from NOS/antique dealers! *Above all* remember that you are supposed to be having fun and don't go off the deep end. Its not pretty :)
6DJ8/6922s are not a good tube for audio despite what you might hear here. The reason is they have a tendancy to microphonics (they were built more for instrumentation and not audio), despite their otherwise excellent characteristics. You *really* have to hunt to find one that is low microphonics. The 12AT7 is a lot easier to use and so is the 6SN7 for many of the purposes that you might use a 6DJ8 for.
The 6SN7 is the octal equivilent of the 6CG7, but is usually smoother sounding because again there are less microphonics (my guess is due to the more robust structure).
12AX7s can be very nice but do not expect a wide bandwidth circuit! So from 12AX7s you will get an older-fashioned tube sound as mid and treble artifacts will be audible due to phase shift caused by the upper frequency cutoff. Its not a bad sound- just not very fast. Incidently this is something that 6DJ8s do better (they have plenty of bandwidth) but now you have an 'iridescence' caused by their microphonics.
12AU7s can be very nice as they have good bandwidth, but they are more prone to microphonics again, however with less of the 'bell ringing' issues of the 6DJ8 family (which includes the 6H30).
IF it seems that microphonics is a major problem, you are right. Tubes designed for audio do seem to have less in that department then those designed for instrumentation. There are other more subtle effects caused by means of construction, some of which are lost to time: Telefunken 12AX7s and Mullard tubes are sought due to the excellent contruction techniques employed during the hey day of tubes.
So, while I have offered some general pointers on some tubes, the individual tubes of the specific types will vary enough for considerable overlap! This is why Albert is correct in his assertion. If you are dealing with the best of the best in all tube types you will find them all very close. It is the generel average tubes where the foibles that seperate them become evident- for example the average 6DJ8 will sound pretty bad compared to the average 6SN7.
My advice if you are tube rolling is to be careful about documenting what you are doing, and make sure you can return tubes that you buy from NOS/antique dealers! *Above all* remember that you are supposed to be having fun and don't go off the deep end. Its not pretty :)
