I've had my new Fender Rumble 75 for exactly a week now, and yes I am still digging it muchly.
I've found out through Fender's customer service that the power section is a class 'F' amplifier. The 75 watt rating is in continuous "pre-distortion" watts. Clean Power. The number of absolute peak watts is not published. Fender's claim that their power ratings are on the conservative side ring true to my ears.
I wanted a real world test of this lovely little bass amp. With no input signal, and the tone controls set flat, I dialed up the power (volume) to 10.
There will always be some high end hiss, and so there is, but not much. Even with the high mid & treble controls maxed out the amount of hiss was negligible. I also listened for any "crackles" or other unexplained noises. I didn't hear any.
Turning the volume all the way down, I returned the tone controls to flat, and plugged in my Fender Precision Bass Guitar. While plucking the open 'A' string, I began turning up the volume slowly. I was listening for: a) any rattles in the cabinet, b) any speaker breakup/distortion, and lastly c) any amplifier distortion. At half volume I paused and just played for a bit. Nice clean sound with tons of top end, and clear punchy bottom. I continued to turn up the volume to 7. This is very loud! Still clean and clear sound without any audible distortion or speaker breakup. Even digging into the low E didn't phase this amp. Talk about punchy attack! I am still amazed at what this little amp can do. I went ahead and dialed the volume all the way up to 10, and played for a few minutes. Still distortion free, and yes, very loud! Loud enough to play with a drummer? Maybe. I've got a jam session set up with a drummer this comming Saturday.