Since I often use my Alembic F-2B as a preamp for recording, I thought I would try some of my various 12AX7 tubes in it and compare them.
I used my Fender P Bass deluxe 4 string, which has a high output active circuit in it. I ran it into Channel B on the Alembic F-2B and then out the Channel B output right into my DAW. I played the same passage with each tube and recorded it, using of all 4 strings on my bass. I left the top off the unit and shut everything, incl. my computer off, in between tube changes.
Since all my tubes are used, and many are very old, results would vary from someone else doing this test with their own tubes.
My non-scientific results are interesting. If anyone here has ever read one of the Journal of Irreproducible Results issues, well… you get the idea!
Terms used:
Clarity: used to describe definition present in low, mid, and high EQ ranges.
Flat Response: my term here means the 3 EQ ranges are even and may sound somewhat compressed.
I do not use this term to mean the sound is flat sounding or lifeless.
The 10 Tubes I tested so far:
Stock used JJ 12AX7s (3)
All 3 JJ’s are used to an unknown degree. They all sounded different from each other. One had great clarity overall, and the other two seemed somewhat more mushy.
1956 Long Plate Mullard 12AX7
One of the Holy Grail tubes in a guitar amp and the best sounding preamp tube I have for guitar. For bass it had less high end and clarity and was not an outstanding tube.
Short Plate Mullard 12AX7
Another Holy Grail guitar tube. This tube had a flat and even response in all 3 EQ ranges. It had more clarity that the long plate Mullard and sounded better on bass.
Mid 60’s Amperex Bugle Boy 12AX7
Flat consistent response. Not outstanding in any way for bass.
Telefunkin 12AX7 year etc. unknown (info rubbed off)
Very good overall, somewhat less highs, solid sounding tube for bass
West German 12AX7 of unknown origin
Less high end and very good mids and bass response. A flat response overall (no spiky tones)
Mitsushita Japan vintage 12AX7. These are supposed to be “Japanese Mullards” made on Mullard equipment. Don’t ask me if this is true.
Good overall response and clarity. Good tube.
Pretty new Tung Sol, Russian made with gold plated pins. I don’t know if this is a typical tube or a special one from them.
I did not expect great things of this tube, having pulled many failed Russia made Tung Sol tubes out of newer guitar amps I have worked on. However, I was very surprised to find it had fine clarity and response for bass, with nice lows. A good tube!
I also have many USA made 12AX7’s that I might test someday, like RCA, Sylvania, Westinghouse, GE, etc.
Conclusions:
1) 1) Great guitar amp 12AX7’s do not necessarily make great bass preamp tubes.
2) 2) Check your tubes every so often. Even ones that seem to be working fine can be suffering from tone loss and other issues.
3) 3) The JJ’s that Alembic recommends are fine tubes, but like everything, they do get old. I suspect that they keep on soldiering on even after other tubes have bit the dust, but that their performance may drop of with time and hard use.
4) 4) Different tubes DO sound different!
