I need a quiet tube amp

300b with Proacs??

I agree with Marakanetz. What are you doing making a 300b work so hard. You should be looking at something with more like 100 watts/channel. Much of your noise is from having the volume so high. I'll bet these amps are silent on a 94db speaker??????????
Borrow some high powered amps and check it out.
@87db:
1 watt = 87db
2 watts = 90db
4 watts = 93db
8 watts = 96db
16 watts = 99db
I know your amps can't put out more than this!
To get to THX levels with 87db speakers would take over 220 watts for 110db-your poor 300b's :( Wanna trade for my 120 mono's?

There are two things you need to keep in mind to match speakers and amp: sensitivity and impedance. The impedance dip are often overlooked.
x x x x x x x x x x
I prefer the Mac Mc240 driving the ProAc 2.5s. This is just my taste.

See my last entry. The 2.5s are an extremely easy load especially in a small room like mine (see my entry above!) although the 2A3 monos I owned a few years ago failed miserably. However, my Air Tight has more drive power than any other 300B amp I know and does great in my room with most types of music. However, I do hear buzzing/hum coming from speakers when being within 3-4 ft of them. I think it does have to do with some sort of grounding problem and am in process of checking things out through pre-amp company.

Also, phase angle also is very meaningful when choosing a partnering amp. I'm not real knowledgable about this fact but was able to find out the 2.5s have a begnin one and many speakers don't.

One thing, my experience with SETs (having owned four) is that the more efficient the speaker, the louder any noise in the system will be. I took my 2A3 monos to a friends house maybe three years ago and his Corner Horns were far noiser than any other one tried - they were the most efficient. By the way, I'm getting music as loud as I want with the volume control less than half engaged. Yes, when it's turned up beyond what I ever want to listen to (remember my small room) the amp's limitations become evident. However, this combo is the best I've used at home an that includes everything from another 300B amp (mono-blocks), 20wt 572 SET, 25wt OTL, 25wt S/S, 100wt S/S, and a 135wt P/P tube.

Elevick, thanks for the offer but this is the best SET I've ever heard and I'm keeping it even if something replaces it.

Tomyran,
You have probably explored this option, but on my Wright Mono 10's I used a 3-into-2 prong adapter, and the hum disappeared almost entirely. With his 3.5 SET amp monoblocks, I found that the hum through the speakers had mostly to do with the quality of the 2A3 tube I was using. When I found an excellent NOS tube, the hum was reduced dramatically.

If those suggestions--and the ground loop check--don't work, I would take the amps to a tech and have them checked out. If there is no issue with the amps, it may be a problem worsened by the 2A3's being used.

Hope my amateur advice helps.

All the best,
Howard