Funny you started this thread as I just spent an hour playing with tubes. Cleaning out the audio closet in the back of my church, I found two vintage 12AX7 tubes. The church has no tube gear of any kind, so I've no idea where these came from. One is a Sylvania and the other GE. These tubes have got to be at least 20 years old, and probably more like 30 based upon the other junk in the box I found them (I don't really know how to date the tubes themselves).
So I decided to compare them to the stock tubes (Ei) in my DI box, an ART Dual MP.
Testing gear was my '98
Gibson The Paul, direct into the ART box to
an Oz audio HR4 amp into Sony MDR-V600 cans. I set the tube gain on max, and reduced volume at the guitar to avoid clipping (I thought that the ART was supposed to bypass the tube if the input gain was at minimum, but testing a control without tube gain with the +20dB gain switch engaged still lit up the tube character LEDs. However, the sound in the control test was quite obviously lacking in tube character).
I haven't been terribly happy with the sound of the box, in fact I was thinking of selling it, so I figured nothing to lose. The Ei tubes are very soft, attack is reduced, sustain is OK, but the overtones are muddy. Not a winning combo on The Paul, but it works for Fenders.
The Sylvania tube had a similar attack & sustain, fewer muddy mids but still not materially different, just a little better.
The GE tube was a revelation. The attack was less suppressed, sustain was endless, and the overtones were rich and varied. It restored my faith in this box as a DI.
I don't know much about tube construction, but the internals of the three tubes are all notably different.
On
my Epiphone Viola bass (short-scale Beatle-type), none of the tubes really
sparkled. The Sylvania had the best controlled sound, the GE better highs (the Viola has a mean trebly growl). But the overtones on the neck pickup just sound like a big pile of poo no matter what tube I used. By comparison to a Fender Bassman 30 direct, the ART leaves a lot to be desired.
But I'm committed to an amp-free studio, so the search continues . . .
