Just want to wrap this up. After the Line Fuse was replaced and bias checked/adjusted on the tubes, the amp worked again perfectly and has continued to do so with no stutters. I have no idea why the fuse blew originally but I am thinking it might have been a "tube fart" (technical term) of some sort? At least I now have a complete set of fuses for all my L6 gear and know where to get those darn tube fuses for the DT25.
Lastly, this little experience made me get my SV212 MKII out again and I still enjoy that amp. It is a great backup to have and I have no inclination to sell it. However, my back goes into a panic attack every time I have to take it somewhere and "power lift" it up on the tailgate of my truck. My back really prefers the DT25 Head/Cab combination. I have actually tried running the two amps together (I have a A/B-Y switch) .... HUGE sound with 2 x DT25 112 cabs plus the open back 2 x 12 combo. I can be ONE LOUDER than anybody else in the band, which makes me king ... !~!~!~~
geppert's post in DT25 head dead was marked as the answer