During the brief time I had a Harman Kardon A-500 integrated tube amp, I connected a Stromberg Carlson 445 tuner to it and the tuner sounded full with strong bass. The A-500 is sold (and I'm looking for a Sherwood S5000 II with 7159 output tubes). I now connect the 445 to my newer Harman Kardon HK-4390 receiver, and the 445's audio is now rather tinny. How could the sound be so dramatically different? I mean, would tubes have made that big a difference, or is this perhaps a line impedance issue? Thank you.