Both have 100 watt maximum plate dissipation. The 7241 has a maximum DC plate current of 1.2 amperes and the 7242, 0.9 amperes. So you are thinking about OTL (output-transformer-less) circuits, huh? Do not let anyone fool you, both of these tubes are pigs. Both take nearly 48 watts of filament power (6.3 volts @ 7.5 amps) and they both require very well designed drivers, as the maximum allowable grid resistance for fixed bias is only 50,000 for the 7241 and 20,000 for the ’42.. On the other hand, they are beautiful beyond belief, and have plate resistances of only 67 and 82 ohm respectively. The basing is JEDEC #A7-17 and they mate with the increasingly hard to find Johnson 122-237 – the same socket that is used for the 813B. The 7242’s transconductance is 110,000 micro-mhos. Oh, do I have your attention now?