SET Amp for Harbeth P7ES3

What size room are we talking here?

No experience with that exact combo, but that sounds a little low powered for the Harbeths...

I own a Mastersound 300B SE and also owned Harbeth SHL5's. It was a great combination. The 300B with 24 watts is the P version that utilizes 4 300B tubes, I think. Expensive to roll or replace the tubes, but an outstanding amp and very good with Harbeth speakers. Feel free to contact me for more opinions.
Scott

I drove Harbeth M-40.1's with a VAC 30/30 (32 wpc) with no problem. I'd be surprised if it did not work for you.

I'm using 30w class A tubes to drive your Harbeths. The Mastersound comes in 2 versions - the original is 15wpc, the newer one is 12wpc and the 'p' version is 24wpc.

I'd feel comfortable with the latter - the others might be iffy, especially if your room is large.

Mastersound is a great product.

Keep in mind, a single 300B tube puts out about 8 to 9 watts. So, two would put out about 16-18 watts. Some companies are rating them at 1kHZ only. I'm guessing this company is too.

Harbeth speakers will work well with lower-powered amps, but they ain't gonna play loud. That may or may not be important to you. From my experience with audiophiles, most like to listen at fairly high levels, although, like most things in this hobby, it's something that's often denied. As to Mastersound, I haven't heard the 300b amps, but I did have a Duo Trente. Excellent build quality, but it was, to my ears, very neutral sounding. Again, most audiophiles will claim to like neutral-sounding stuff (more of the great lie) so if you're among them, the Mastersound will be great. Also very quiet. Myself, I prefer something with a bit more of what people seem to want out of a tube amp, whether they admit it or not. Anyway, the Harbeths are excellent and my experience with Mastersound has been very positive, so I guess you'll be fine. Good luck