Kosst, not to belabor a minor point, but a "passive" electronic device would usually be considered to be one having no "active" components (e.g., transistors or tubes), at least in its signal path. A device which provides zero voltage gain but amplifies current and power is not a passive amplifier, in the sense that George was using the term and per what seems to be generally accepted terminology.
Regards,
-- Al
Regards,
-- Al