Just had my power tubes replaced due to wear and a microphonic issue in my AD200B. Being my first tube amp (and first set of tubes), I was talked into going the cheaper route with a quad of JJ 6550's (what the shop had available) instead of the Winged C's that were previously in it. Sparking up my amp back from repair - I noticed a slight tonal difference, obviously expected from different tubes, that wasn't bad, just different. After 15 minutes of warmup time - my amp goes to sh*t. No headroom, unwanted distortion, lack of punch and clarity. It also seemed it was running hotter than the previous set of tubes. It's going to go back to shop for diagnostic (to make sure one of the tubes didn't fail on me right away or that a preamp tube coincidentally burned out). All-in-all it was a bummer. I know this could be a symptom of biasing or possibly of more failed tubes - but my question to TB is this: • Does anyone have experience with the JJ's? Were they a bad choice for a bass amp, or this amp in particular? • Should I just replace them with a matched quad of the Winged C's and try to make up my losses by selling the JJ's somehow? • Any other tube experience on a decent (not ridiculously priced) set? Also, how does everyone deal with consistency issues and tube replacement? Is it just a sad truth to tube amp operation, or do I need to get to know my amp tech better for him to dial it in for me?