Its not bad at all, you dont have to get a pro Its bit scary the first time opening up the amp but its simple. Power and Pre amp valves just pull out on the DSL100 should be the same on the 50. there are metal clamps holding them in tight but you just pull them apart a little, i got someone to hold it whilst pulling it out its was easier Then you just push the new one back in, there are pins on the bottom that can only slot in one way, it should be the same as mine, oh also got told not to touch the glass of the valve so use a cloth or tissue to push it back in. was a bit of a bastard as just after replaced my Poweramp Valves the Pre-amp valves blew a week later bastard ! was 80 for all 8 valves!