H.H. Scott applications that use the 7591-A beam power  pentode:

HHSCOTT TYPES:	7591-A
208 233 299-C 299-D 340-A 340-B 345 380 830 LK-72-A LK-72-B	BEAM POWER PENTODE Tube Data provided by Duncan Amplification Glass octal type used in the output stage of audio amplifying equipment. Requires octal socket. This tube, like other power handling tubes, should be adequately ventilated. Download Duncan's utilities and tube database software.