Pure Class-A Amp under $2000 (USED)

soix Some valid points, most I would agree with, some you’re off the mark by taking points out of context.

You’ll note for DK8586’s benefit (+ others), I used the term "relatively" inefficient/power hungry speakers,

(S/F Venere: Nominal Impedance 6Ω, Sensitivity 88dB). Now for the sake of correlating lets use an apples to apples example, (ProAc D2: Nominal Impedance 8Ω, Sensitivity 88.5db). (Focal Sopra N°1, Nominal impedance 8Ω, Sensitivity 89dB). Now the (Coincident Triumph Extreme II, Impedance Flat 8Ω, Sensitivity 94dB)!

So as you can see yourself soix the S/F Venere’s are "relatively" hard to drive. Now that’s cleared up lets move on.

Your quote "a Class A amp, which out of the box affects how many Watts are required as they mostly double power into 4 Ohms". Where are you at on this comment soix? Mind you lets not be over critical.

1st of all, regardless if it’s an A/B amp or a pure Class A amp, any good quality amplifier doubles in power when it’s impedance is halved. Eg: 100W into 8Ω, 200W into 4Ω, it is not what defines a Class A amp.

2ndly 50watts is 50watts, regardless if it’s an A/B amp or a pure Class A amp. There are no magic watts for Class A amps. They sound different because they run flat out, making them faster and ...... warmer?

Now I’ve got to give you credit on two points. One, the recognition of Nominal Impedance. Two, the observation of higher than rated impedances at certain frequencies. The term Nominal Impedance recognizes that values fluctuate with dynamics, so a speaker that’s rated at 6Ω may drop down to 3.45Ω when reproducing low octive notes and/or sustained crescendos. (How Israel Blume over at Coincident gets a dynamic speaker to operate at 8ohms FLAT is by me). The second point, that impedances at certain frequencies rise, is new to me! So I’ve learned something. Thx.

Reading further into your text, unwittingly you seemed to have reinforced my point. "Further, I had the 2.5 in my system and will attest they were not hard to drive at all, and my 100Wpc Class A/B amp drove them to very loud levels without even nearly breaking a sweat". Well of course you didn’t have any trouble driving you Venere’s soix, when the impedance drops your A/B amp was pulling close to 200watts.

Now you say "And I’d have actually NO reservation saying a 50Wpc Class A amp would be more than sufficient to drive the Venere 2.5, which is why I recommended the Clayton S50 would be a great choice here". Well where’s the correlation between your 100Wpc A/B amp & an S50 Clayton soix?

If I may, let me share my experience with 6Ω speakers & Class A amps. Class A amps run hard, that’s why they’re hot, that’s part of their charm/ethos. Back in the 80’s-90’s a company called Sumo made a fantastic Class A amp that in my area got paired up a lot with low impedance Infinities. (Not implying the Venere’s are in the same boat). They often went up in smoke. Conversely, Mark Levinson made ML-2’s mono blocks that could drive a bus all day and not break a sweat. How an S50 Clayton holds up I would not presume, but Class A amps can be dodgy.

I used a Classe’ Audio DR3, 25Wpc, to run a pair of SB-E 100’s (37Hz to 22kHz. Impedance 6Ω. Sensitivity 95dB). They were used in a 15x25x7.5 room. The DR3 was the sweetest sounding amp you could imagine, and even though the SB-E 100’s were vastly more efficient than Venere’s, it did not have the power to fill a room of that size with the necessary SPL’s I was after, so it had to go. My point is this.

The lesson I learned is that all things being equal, it’s better to have power in reserve than not enough.

Unfortunately, used $2k Plinius SA100 amps aren’t around any more. I believe people are hanging onto them. 100 watts 8 ohm, I believe 200 watts into 4. And flip the front panel switch to listen in A/B mode. 
 

They would drive anything.
 

These amps were some of the best available in 1999. Commonly available used everywhere for $2k. Their Mark III version was the finest Class A amp I’ve ever owned. But sadly today, those amps are gone. If you didn’t sample one in 1999, you truly missed out. 

An amplifier that runs in pure class A operation does exist regardless of what some may say. There are some amps that switch to A/B when pushed in volume but there were amps designed to run class A always.  A killer and very inexpensive class A amplifier is the Forte Model Four.  50 watts per channel and a killer of an amplifier. Sold by Nelson Pass under the Threshold company but the amp was designed by a Swedish Engineer who worked for Nelson during that time. The Forte Four was the 1st amplifier I purchased 35 yrs ago with a Conrad Johnson tubed preamp when I first entered this hobby. I picked it up in a Stereo store in Manhattan NYC. I sold it 1 year later and moved in the direction of tube amplifiers. I’ve owned since about 50 amplifiers, all extremely good and now listen mostly to single ended tube amps. Never forgot how good the Forte sounded. After 30 yrs, I’m so happy to be he owner of the Forte again. I own 2 now with all the Jon Soderberg upgrades. If 50 watts per channel will be enough, the Forte Four is not just a good amplifier, it’s a killer amp. If you need more power, Vintage Threshold has a good line of amps. Krell KSA series was great as well, KSA 100 Mk 2. Good Luck.

I'm a big fan of the SONY TA-A1Es integrated amp,   Built like a tank and sounds amazing, can't believe how good it sounds for the price.  I thought Sony did a terrible job of marketing this amp, it should be far more well known than what it is.  

$2000 is a tough budget for a good Class A amp. Your choices will be limited to older amps like the Krell KSA or the Plinius. The KSA are great amps but old which means you will be sitting on a time bomb. Rebuilding those amps will be expensive.  If you can wait and up your budget, the Pass XA25 is the current model and should drive your speakers just fine
 

Are you a DIY type? Nelson Pass has provided many amplifier designs to the DIY community. Anything from 5 W/ch up to 100 W/ch, all biased into Class A. I have built the Aleph-J (25 W/ch) which is based on the original Aleph series of amplifiers with J-FET inputs instead of MOSFETs. A very popular design is the F5 (25 W/ch) and the F5 turbo (50 W/ch). Both the Aleph-J and F5 were sold under the First Watt brand as well, but can be hard to find on the used market.

Rogue ST100, with first 25w class A.

Belles SA30