Subclass 1/20: Details of amplifiers with only discharge tubes, only semiconductor devices or only unspecified devices as amplifying elements Modifications of amplifiers to reduce detrimental influences of internal impedances of amplifying elements (wide-band amplifiers with inter-stage coupling networks incorporating these impedances H03F 1/42; eliminating transit-time effects in vacuum tubes H01J 21/34) by use of distributed coupling in discharge-tube amplifiers