I did a search and couldn't find exactly what I am looking for. This thread is only about bass amps with tube power sections, and this thread is focusing on just the power output section. I have seen amps with four KT88s that are rated at 150 watts output power (example: Shaw B150), and I have seen amps with four KT88s that are rated at 300 watts output power (example: New Vintage Undertow). What's up with that? Is it simply a difference in the amount of THD in the output rating? In addition, I have seen amps with six 6550s that are rated at 300 watts output power (the Ampeg SVT). How can the SVT pump out 300 watts if 6550s are rated at 30 watts output each? (with six 6550s, that should add up to 180 watts, correct??) What am I missing? Is this another case of THD?