Hey all. I've recently picked up a nice ltd Blues Junior (seafoam with creamback). I've been delighted with it so far - it's exceeded expectations. I wish I'd ignored the naysayers sooner; it's plenty loud enough, sounds much better than expected, and has behaved very well. Until... So something I'd always read about was the 'trick' of opening up the master volume on the BJ to release the tone and control it using the volume. After playing for half a year with both vol/master on 4, I thought I'd try a gig with the master maxed out, and the volume on 3ish. Definitely a different sound - I'd say fuller and more pleasing to my ears. So I did the same at the last gig and within a few minutes there was a bad squealing when played at any reasonable volume (not when idle, only playing). I replaced the three preamp tubes and output tubes in turn to find the culprit to no avail, tweaked anything that looked tweakable to a numbskull (ensured speaker/reverb were plugged in) before sending it back to Fender, as it's well within its warranty. Within two days it's been repaired and is on its way back to me with the fault report stating note 'shorted EL84 and open S.G. resistor replaced'. So even though the problem still existed with new valves, can I assume this is anything to do with the 'trick' of maxing the master volume? Or just a wild coincidence? I assume this is a widely used thing, so is it just left to chance? I have read all about the mods for this amp and had planned on getting a load including the bias mod. But even though I love the little guy, there's no way I'd contemplate mods with a BJ until the 2 year warranty had expired.