Watts! How many do we need?

@weatcoastaudiophile

Still don’t understand how you calculated your number from those specs but you were on the money. Here’s the response from Accuphase. 
 

The actual amount of Class A bias for the P-4600 is not a fixed amount and will vary depending on the load of the speaker.  For most speakers it should have around 8W – 10W of class A bias but that could be less for speakers if they have less than 4 ohm impedance.  The exact method for how Accuphase applies bias to its output transistors is considered proprietary information and they do not allow us to publish more than that.

@westcoastaudiophile

As a follow up I guess I’m mostly running in Class A since I have not been able push my meters pass 1 watt. 

@ifrmusic thanks for asking Accuphase support! being advanced analog circuit designer it’s not hard for me to estimate AB class amp linear (A class) range, sorry for not explaining to you all boring details of my calculation, which could be lengthy! 

The success of the Pass 25 and other small-bore tube amps Indicates that's plenty for most applications. But remember this - speakers are current driven devices and benefit greatly from amps acknowledging that fact.

Most modern speakers are less than 8 ohms and so are quite current hungry. Also, loudness is logarithmic, so twice the power is only 3dB louder - a just noticeable difference. To sound twice as loud requires 10X the power. Also remember the limits of your speakers. KEF LS50s 84dB @ 1W/1M and 100W limits means they are limited to 104dB maximum output. A big JBL 4367 is at least 10dB more efficient and will handle 200W peaks for a max output of 117dB.  The KEFs are meant for near field listening only a few feet away, the JBLs meant for a large room with the listener 10-15 feet away, so it all must be worked as a system, not just components in isolation. As for me, my 87dB Monitor Audio S300 7G and a solid 60W amp in my 12X16 room is plenty. In other systems, 200W was just adequate, and in another a 40W tube Mcintosh MC240 was fabulous. Lots of valid answers, just don't ignore physics.

My Speakers are Harbeth C7ES-XD at 86db sensitivity. They are rated at up to 150 watts. Their impedance is 6 ohms with the lowest at 5.8 ohms. So an easy drive. But I've been told they like power. The Accuphase P4600 is rated at 150 watts per channel at 8 ohms and 300 watts at 4 ohms and the amp is probably capable of delivering 225 watts per channel at 6 ohms. I have them positioned in a well furnished carpeted room about 7 feet apart and 30" out from the front wall very slightly toed in. I sit about 8-9 ft from them. I have the meters set to freeze at the highest output and they have never exceeded 1 watt so far. Now I don't listen at some of the levels some of you do. My sound pressure meter never exceeds 75 db and is mostly between 60 and 70 db. If the meters are accurate I'm in Class A all the time and the amp is not breaking a sweat.