Is 5 Watts enough for Horns ?

How much power is enough to drive a 107dB sensitivity Avantgarde ?
Is 5 Watts from A 300B SET enough?
Consider that the Subwoofer of the Avantgarde has its own high power amplifier (each woofer 500 Watts)so the work in the bass department is largely taken up by the subwoofer amp.
I have seen McIntosh MC501 power amps connected to 107dB sensitivity Avantgardes and seldom did hit the 5 Watt mark on the meters when cranking the volume up to hurting levels.
0.5 Watts was what the meters show at normal listening levels.
Horns are made to use with low powered amps, You could use a SET with the 45 output tube around 1.5 watts and be in pretty good shape. I have not seen horns used with amps above 20 watts I sure you could but I have not seen it done.
5 watts is plenty of power to drive a 107dB sensitivity Avantgarde providing the room isn't huge. If the room is huge, you might not get the volume you desire.
What's the size of your room?
I have 6 watts on mine and am never wanting more..... I had a very reputable reviewer tell me I needed more with AVG.... don't know what planet that guy is on. The Art Audio PX25 amp I have is pretty darn sweet, IMHO.

The room is 400 sq.ft.
The volume can be cranked up to where the bass moves objects on the shelves and the. I did that with a pair of Klimos 300B SET monos.
But I also did read somewhere on this forum that 5 watts is not enough. That's why I am asking.
CMO , Chris
Sweet System !! The Art Audio and the Avantgarde's must be a nice match. I have heard people say that 8 watts of that amp can drive you out of the room. Plenty of power.

Give what you have a try and if you think you need more go to a dealer and barrow a more powerful amp and give it a try. I think you will be fine though.
300B amps are fine on Duos. I've since switched to 18 watt "behemoths" (Lamm ML2), but for sonic reasons, not lack of volume capability.
At 107 dB, I would guess that that is more than enough power.
The David Berning headphone amp only put out about 1 watt is plenty of power for my avantgarde horn..but I prefer the 300B amp for my horn..
5 watts will work out fine for your size room.
Assuming the doubling of effective power per every 3db sensitivity increase (assuming both sensitivity and power are measured correctly), 5 watts at 107db is the same as 320 watts at 89db. For most 89db sensitive speakers, 320 watts would be considered fine and another 20% (5 to 6) would probably enough overhead.

I don't see a problem with 5 watts...
As long as it is tube watts and the speakers are efficient maybe 95 db and above, yours are extremely efficient at 107 db. From what I gather, 5 tube watts per channel are equal to about 15 watts of solid state power. I had a tube amp (push/pull) that was 8 watts per channel and my speakers have an efficiency of 110 db. I could drive my speakers to almost concert hall levels.
It should be enough in my opinion. I am running Welborne Labs SET 2A3 Moondogs-3.5 watts with a pair of 98.5db efficient 1981 Klipsch Cornwalls with upraded crossovers using Auricap capacitors.
The Moondogs will play plenty loud for me. Though I am not a metal headbanger.
my buddy is using a 6 watt chip amp (forgot name of that amp) on his Omega DUOs and even in his small room I hear this thing sounds strained and clips quite fast.
I'm using a tact digital amp which putts out around 75 watts into the DUOs 16 ohm impedance and I love the headroom.
Sure I won't ever use all the watts but a more powerful amp is much more at ease when the going get tough compared to a 6 watts amp. JUST IMHO of course.
Lonestarblues: no doubt, 3,5W sound OK on yr COrnwalls. BUT, try 20W capability and listen to orchestral music -- and I think you'll be surprised.

You've modded those Cornwalls I assume (nice spkrs)?
Hello Gregm. I have 4 systems-2 SETs & SS/tube hybrid amp with tube preamp & Mcintosh SS. I am a Klipsch Heritage speaker fan. I have liked the Heritage speakers since I was a teenager and could not afford them. All Ears a stero shop when I was young carried Klipsch Heritage, Advent & EPI/Epicure speakers. I bought one pair of walnut Advent 1's in 1979 & walnut New Advents back in 1980. The Advent 1's have the same drivers as the New Advent in a slighly smaller cabinet.

You can pick up used Klipsch Heritage speakers for not a lot of money. Change out the crossover network with a new upgraded crossover using the caps of your choice and have a high performance horn loaded speaker with excellent sonics to my ears. Klipsch Heritage speakers are not everyone's sonic cup of tea. But I like them very much.

Welborne Labs Moondogs & Welborne Labs Reveille 6SN7 tube preamp, 1981 Klipsch Cornwalls-with Deang type B crossovers using Auricaps. Deang a Klipsch Forum member makes & sells brand new upgraded crossovers-all parts are new. He sells them here on Audiogon. He is a great guy. The upgraded crossovers raise Klipsch Heritage speakers sonic performance to a much higher level than the old stock networks. I highly recommend them to anyone that owns Klipsch speakers.

deHavilland Aries SET 845 amps-25 watts x 2, deHavilland Verve 6SN7 tube preamp, 1983 Klipsch Cornwalls with Deang type B upgraded crossovers using aluminum Jensen PIO caps. The guy I bought the deHavilland gear from had the faceplates of the mono amps & preamp goldplated at a plating shop. He had an oversized volume knob machined at a machine shop. The volume knob & source selector
knob are also gold plated. As we say in Texas- they sure are purdy.

Llano Phoenix CAS 300/VA2 mosfet/tube hybrid amp-
300 watts x 2. The VA2 voltage section uses 6SN7,
6SL7 & 12SN7 tubes. Currently using a pair of RCA
12SX7 GT tubes. George Wright AU1000 12BH7 tube preamp with tone controls. 1989 Klipsch birch industrial LaScalas with Deang type AA upgraded crossovers using aluminum Jensen PIO caps.

Mcintosh MC7150 SS autoformer amp-150 watts x 2, Mcintosh C38 preamp, 1979 Advent 1's & 1980 Henry Kloss New Advents stacked with the top Advent 1's inverted.

The Mcintosh gear was bought used from two different Chicago area stereo dealers-my first purchase of separates. I have picked up the rest of the gear used from here on Audiogon. Audiogon has been very very good to me!
The guy I bought the deHavilland gear from had the faceplates of the mono amps & preamp goldplated at a plating shop. He had an oversized volume knob machined at a machine shop. The volume knob & source selector
knob are also gold plated
Now that's what anyone'd call a serious hobbyist!

Old Klipsch speakers had good quality Alnico drivers in them -- until the price of cobalt (or was it magnesium) shot up sky-hi.
The best amp I heard on the Avantgardes was a 1.56 watt 45 tube amp from Exemplar Audio. I think that a 300B SET would certainly be powerful enough. I presently have 93 db efficient speakers and 300B amps are not enough.
I have Trio 2.2 (8 ohms). I have used Viva Aurora (845 set)monos for three years. Mine has the transformer input. This is a must with horns, the tube input version is too noisy. Mine is dead quiet. Recently I tried a friends Wavac 300b. Enough power. The 845's are just totally more effortless though and better balanced (very extended at the extremes). I also have now a Yamamoto A-08s (45 set). It is ok sounding in comparison but not as good as the Viva. It is also enough power. With trios you have a speaker that is capable of effortless dynamics and presence. You will not get this from a 45 set. With the 45 set the trios aren't that much better sounding than dynamic speakers. I would go with a minimum of a 300b or maybe the Art Audio PX-25 I keep hearing so much about. My 845 IMO is much better than these and not just in power, all other areas too, very clean sounding. I have not heard the px-25 in my system though. 845 amps are very expensive to build and if one is chosen it must be of the best quality or I would chose something else. There are only a few manufacturers building to this quality. I have heard many comments saying the 845 tube is not an audio tube and can't compete with the lower powered tubes. Yes, for many lower priced 845 amps out there. But when it is built right, and top quality, IMO it is hard to compete with it.
I doubt if you are ever using over .5 watts on either the Duos or Trios. In my experience as well as in a test done at the old VSAC in Silverdale WA, the 45 tube in its old American made form is clearly the best sounding output tube, if your speakers are sufficiently efficient. The old 2A3 single plates are close.

There are many variations in amps using tube output stages and certainly power supplies, parts quality, and other design features can alter the impact of the output tubes.

I have no experience with the 845 tube, but I have found great differences among 211s. Again the old RCAs clearly outperform the new Chinese tubes. So in reality we are talking not only about comparing 45s, 300Bs, and 845 but also NOS versus newer production.

The simple answer to the original posting is that the 8 watts from a 300B SET is quite sufficient for 107 db efficient speakers in the normal listening room.