I had a VK 500 for a while. If I remember correctly it took about 50 hours for things to mellow down and loosen up a bit. At 100 hours it was really beginning to sing. Hang in there.
I used to have a vk 200 before I went to the BAT tube amps. You have a great amp. Say about 200 hours playing hard. I also used to leave mine on almost continuously. It seems to sound better after a hour of warm up...then another small notch after about 24 hours of being on...