Break in period for tube amp. How long?

Can you please share your experience on break in time and initial sound of new tube amps. Mine are sounding awful out of the box (NAGRA VPA).
I would recommend letting then run at least 100 hours before doing any series listening..They will probably even improve a little more after about 150 to 200 hours or more.. I would run CD player ect. on repeat at low volume levels and let run a few days straight to break in a little quicker..
Good luck,
Musicslug is correct, they should not sound aweful though, i would check other possiblities out that can cause this possibly..
Breaking in the capacitors, especially if is a common capacitor coupled design (rather than interstage tranny), is very critical. Takes hundreds of hours for the caps to be broken in fully.
Please define "awful". And what was your previous amp? Are you still using the same speakers...what are they?
Thank you everyone for your kind input.
I went from ARC VT100 MKIII to a used pair of NAGRA VPA's.
Well, I was so impressed with the improvement (dynamics,air, soundstage, placement ambience etc.) that I upgrade to the current new VPA model. With the new unbroken in model, however, the sound seems congested and harsh........i.e.awful. I'll try to break them in to 100 hrs as suggested. So far I have about 10 hrs break in time.