I'll be honest about the yba100, it really did sound nice... sounded more like a bass amp than the yba1, deeper but not as saturated. I actually didn't play it out. The band I was in at the time was ampless, and the one time we decided to have an old school amplified rehearsal I had to help the frontman move all his (two amps, massive pedalboard and another smaller pedalboard, three guitars and his great dane) gear so I wanted to keep it simple. Ha, I remember now, I drive a regular cab and he was appalled that I was going to put his stuff in the box, he crammed as much as he could in the cab with him, he looked so put out. Get a car, guy. The yba1 through a 115 has always been plenty loud, and is naturally very mid heavy, so I took that instead of the yba100. I do regret that now, I wish I had a chance to hear it loud in the mix, but I dimed it at home and although it stayed clean and clear all the way up, I wouldn't do that with the yba1 without hearing protection, and have never needed to run it flat out, in fact, I almost never use it at full power (has variable attenuator) because at any volume I really like pillowy saturation. How's that for a run-on sentence.
If I was going to do an honest test of the yba100, I would bring a clean boost pedal along, and get the preamp nice and blooming before I brought it up to volume. Though the yba1 has no trouble pushing it's own power section into the sweet spot, that's what I think holds the yba100 back, and from what I understand the yba300 is similar, the preamp doesn't push the power section enough to really get it cooking. Does that sound about right to you @TTA ?
For a few years the YBA1 was my only real bass amp, aside from a SB115 that mostly does synth duty for my daughter now. One weekend I had two auditions and a jam, so I went into l&m to rent a YBA200, as the 300 was just a bit too much power for one of my cabs (edit - oh, I think the 300 needs a 4ohm load as well, so I would always need both of my cabs, 200 is fine at 8ohms). The actually cracked open a brand new one for me, and after that weekend I just couldn't give it back. All the saturation I want, if I want (and I want), but also the ability to keep it clean up to whatever level I need. Great amp, more than I need, but like guns and easy women, it's better to have one and not need it, than need one and not have it.
Sorry to hear about the poor filthy orphaned amp, @samcantjump , I guess good call if you don't want the hassle of problems and repairs, but if that was local to me I'd probably pay the 300$ just to give it a good home.
edit - add @Heavy Blue to the shout outs