Picked this little guy up for a dirt cheap $10 Replacing the electrolytic capacitor with spare Panasonic 47uf/200v ones i had left over from a previous project. it's a 3-tube unit! The 4th glow is the pilot light which lights up after the tubes light up. Cold chassis (thankfully). After figuring out which were the input terminals and testing for stray voltages, wired in a 3.5mm jack cable, works like a charm as an external speaker.