Behringer TU300 Chromatic Tuner
This is equivalent to the Boss TU-2 with bypass 1/4". Works with battery or 9vdc adapter. A tuner's a tuner - does all ranges all four, five or six string axes. I have two of these one as a back up but never need the backup.
Valve technology is the most elegant means by which music can be amplified to drive a speaker.