Two questions about this; 1. Are there any safety implications with removing and changing preamp tubes myself? (The booklet about tubes, which came with the amp, warns about high voltage discharges from tubes, but is that only from power tubes)? 2. The original 12AX7's in my amp have some kind of silver paint on the outside of the glass, where it fits into the drilled metal bracket. My new 12AX7's don't have this external coating. Is it important? Does it help to eliminate vibration, or soak up heat, or what is it for? Any ideas? Any other tips on changing SVT-4 preamp tubes, or which brands and models are best, would be much appreciated.