What interesting or unusual gear has passed though your system during your audio life?

Had a battery powered MC demagnetizer. Hooked it up a few times, never seemed to make any difference. Opened it up, pretty impressive looking circuit board, LEDs and everything. One day I thought, well if it's doing anything it would be generating a sweep tone or something. Hook it up to the phono stage and.... nothing. Nada. Not doing a damn thing. Did it ever? Was the whole purpose of the board to light up those LEDs? Dunno. 

Lots of cool stuff.

Maxell AE-320

No regrets, but I would not recommend it in 2021. I still have it. Box, instructions, small brush, cover/stand, mint condition.

In the similar tone, TDK HD-30 (red type). It did make sound and it did have a LED. It still looks and works as new. I mean, the LED still lights up and chirping sound is still there. I never noticed difference after using it.

An N.E.W. DCA-66 amplifier. It’s powered by four 18 Ah batteries. Didn’t sound too bad. It’s not in my system right now but I still have it. It was making some strange noises and I need to investigate the cause. Hopefully it’s a small issue.

@mkgus  I also had NEW DCA-66! Recently sold mine to a guy who was going to refurbish. I had issues with the charging system, can't recall the exact issue, want to think it was diode issue. Mine was making strange sounds when I had the issue, screeching sound if I recall correctly.