I just picked up an old USA HRD for $200....it's stock, in good shape, and it sounds OK, I guess...comparing it to my Mesa Lonestar it falls short of that amp, as you would expect. The clean channel sounds good, if not a little pedestrian. The OD channel is a bit cheezy but I don't care about that so much... Iv'e read about guys replacing the speaker, using 12AT7 tubes, and a reverb mod (clip one of the wires?) to improve the sound of this amp. So my question is will any of these changes make a noticeable difference? The amp is what it is, and I'd hate to disappointed by spending another $100 to find out it wasn't worth it. So give it a shot, sell it, or just live with it?