From day one, the loop has been terrible. Whenever I put a pedal in the loop, the amp's output is diminished, and noise and hum gets introduced. I've changed the effects loop tube, with no change. I also get a lot of RFI as soon as I put a pedal into the loop. None of this happens when I plug straight into the amp, or put pedals in front of the amp. It wasn't a big enough issue for me to send the amp back at the time, and honestly all I want to put in the loop is a reverb pedal.