Hi everyone,. I have just bought a new PF500 head I have 3 questions to answer please. 1..Have most of the reliabilty issues been sorted now with these amps? 2.. The serial number is..PF500EUCPJC0008, Can someone tell me in which year it was made and if it comes into the (hopefully) modified and sorted era. 3. Will it run cooler into an 8ohm cab or a 4 ohm cab?