New old stock DM160 Philips made subminiature magic eye indicator tubes, typically used as level indicators in recording and receiving apparatus. The tube brightness varies with the signal.
DM160 is very small, runs on low voltage (anode ~ 50 volts), and has very low filament current (1 volt at 30 ma) so might be incorporated into phantom-powered preamps or tube guitar pedals.
For data please see: http://www.r-type.org/pdfs/dm160.pdf