Troubleshooting Marshall JVM and Bias points explaination

Hey guys, I ran into some trouble with my power tubes. FS6 blew on my circuit board and I read on the JVM forum that its most likely my power tubes. After runing my serial number I found that the amp was made in 2008 and still had the original tubes. I played a show last night and the amp worked awesome.
The brand new tube set made a big difference.