That first recording is a really good recording. Excellent fidelity and dynamics. When I played it through my PC speakers that were both shoved off to one side of the desk, it sounded like an amp was turning on next to me -- it didn't sound like a recording at all. Nice.
That second recording was harder to interpret -- I'm thinking that what you're referring to as the problem is the later half of the recording, where there is hiss and hum, not the wailing tone in the first half of the recording, right?
Here are my thoughts:
Your fan is too noisy. My SVT fans aren't that loud. The loudness could be a miking artifact, but if you think the fans are too loud then your fans are a problem. My fans are quiet.
Re-bias your amp. If you don't have good balance on the bias pots you'll get a lot of hum in the outputs. What' i'd do is bias one side of the push-pull circuit, setting it to the midpoint in the green range. Then bias the other side at that point in the green zone that minimizes hum.
As was suggested earlier, you need to have a supply of spare tubes on hand that are known to be good to do troubleshooting of tube-related problems. It's not at all uncommon for driver tubes to wear out in these amps before any other tubes.
In trying to help troubleshoot your problem, I'd like to review some terms that will make it easier to communicate with techs. "Noise" is a very non-specific term. It's sort of a wastebasket term that people use when they don't know how to describe what they're hearing. Techs tend to grimace when they hear people use the word "noise" to describe hum.
In terms of troubleshooting an amp, it's very helpful if you can separate in your mind the difference between hum and noise, and if you can categorize the artifact according to frequency.
Low frequency AC hum occurs at 60 cycles.
Rectified AC hum occurs at 120 cycles.
Depending on whether your hum is 60-cycle hum or 120-cycle hum tells you where in the amp to look for the problem.
What amp fixing guys call "Noise" occurs at higher frequencies, and it's often non-periodic in nature. To us, "noise" would include things like crackles, sputters, pops and hiss, and it wouldn't include 60 or 120 cycle hum. To find the fix for noise problems you have to look at other places in the amp.
If you're having hum problems on the DI out, have you tried lifting the ground?
