First foray into tube amps

The mcintosh  275 is 75 watts on stero.when you want more get a 2nd amp in the future 150 watts per channel in mono.that design has been around forever and just works.it will retain its value if you buy used version v1 or 6 is about 5k in your budget. Enjoy the hunt.

@elliottbnewcombjr Let's take another look at the OP's stated requirements and the room for them: "The room is 23x16x8 and is well treated.  I listen at low to moderate volumes, lots of vocals, blues, Argentine Tango, some classic rock."

As a former software engineer, I can tell you that requirements are everything...

Granted the terms "low to moderate" are somewhat subjective in nature, keeping in mind his self-powered subwoofers, I would think 75 to 100 WPC would be more than sufficient to drive the 8ohm Stirlings to pleasantly loud level without too much strain. 

Proceeding further here's a review of them:

Stirling Broadcast BBC LS3/6 loudspeaker | Stereophile.com

(Please note the wattages of the amplifiers used in the review.)

In closing, I would suggest that there are many reasonably priced tubed candidates for @treepmeyer to insert his system.

Happy listening.

@elliottbnewcombjr 

"We need double the power to make a +3db noticeable increment of more volume. Then double again for a bit more volume, +3db in each perceptible step up."

Elliot, you could also say that every 3 dB increase in a speaker's efficiency using hypothetically the same 20-watt amplifier is like doubling it's power output. Say, if you went from an 85 dB speaker to an 88 dB sensitive one it would give you a 3 dB increase in volume. Quite substantial from a headroom point of view.

@mark200mph 

I agree MC275 is a very good choice.

I often think starting with an amp that can be converted to mono makes a lot of sense, especially if liking low sensitivity speakers.

Reserves for Instantaneous Peaks is the concern.

I did discover, when converting to mono, often one of the impedance options/taps is no longer viable (they get converted).

For the OP, his chosen 8 ohm speakers, MC275 it’s irrelevant, for me, my Vintage speakers are 16 ohms, it matters.

in the MC275, the taps become half of their designation: 4 becomes 2; 8 becomes 4; 16 becomes 8 ohms (thus 16 ohm speakers would need to be connected to what became an 8 ohm tap,

not ’wrong’ in terms of danger, however frequency response will be slightly altered, there are articles to find, some guitarists purposely do this to get a slightly different sound out of their stage amps.

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https://www.mcintoshlabs.com/-/media/Files/mcintoshlabs/DocumentMaster/us/mc275bom01.pdf?rev=0c6db59bb1b141baac73dadb6b9c76b0&revision=0c6db59b-b1b1-41ba-ac73-dadb6b9c76b0

excerpt:

"Power Output Stereo Minimum sine wave continuous average power output per channel, both channels operating is: 75 watts into 4 ohm loads 75 watts into 8 ohm loads 75 watts into 16 ohm loads

Power Output Mono (Parallel) Minimum sine wave continuous average power output is: 150 watts into 2 ohm load 150 watts into 4 ohm load 150 watts into 8 ohm load

Output Load Impedance

4, 8 or 16 ohms (Stereo Mode)

2, 4 or 8 ohms (Mono Mode)"

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It does matter if OP chooses 8 ohm speakers and an amp that starts at 8 ohm (lacking a 16 ohm tap), and converts to Mono which converts that tap to 4 ohms.

Perhaps it only slightly matters.

 

@musicfan2349 

Reserves for Instantaneous Peaks is the concern.

We can select good or bad from any review, but generally:

regardless of sensitivity, there is no way I would use such a small speaker in such a large space as OP’s. I would not use my larger more efficient AR-2ax 3 way with a 10" woofer in a large space (even with subs).

Subs can extend the lows, but they are usually limited to 80 hz or lower, thus the little fellas are on their own it large spaces

A lot of good remarks in the review, and, for a small room, with enough reserve power, they certainly are a better choice than so many 2 way designs.

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I mentioned ’enough reserve power’ (in any room size), to selectively highlight my concerns for large rooms:

Excerpts of speaker review (some underline/bold/italics are mine)

 "SEAS, presumably to Stirling Broadcast’s specifications. The smaller and uppermost of the two tweeters has a 0.75" (19mm) Sonomex dome, while the larger has a 1" (27mm) coated-fabric dome; each has a ferrofluid-cooled voice-coil and a protective mesh outer cover. The 8.6" woofer has, as you’d expect, a polymer cone 6.5" in diameter

front-mounted reflex port

I also spotted two sets of miniature jumper switches, both marked "+0.6dB." Interesting.

19’ by 12’ room, the Stirlings sounded best when sited approximately 34" from their respective sidewalls and approximately 52" from the short wall behind them. (All dimensions are with respect to the center of the front baffle.) 

Aiming the enclosures more or less directly at the center of the listening area provided the best combination of good balance and spatial performance

regardless of which of my amplifiers were in use, the Stirlings played recorded music with what can be described only as exceptional clarity and openness.

although I wish the double bass had exhibited the depth, weight, snap, and temporal sharpness that I hear through my Altecs’ big, taut woofers).

The Stirlings also did a lovely job with the notably rich piano sound on that recording. With other, less decidedly rich piano recordings I heard a slight lack of power and volume in some left-hand notes

Yet expectedly—virtually unavoidably—the Stirlings compressed dynamic extremes far more than my Altec Valencias.

The floor tom in the opening of "7 Chinese Brothers," from R.E.M.’s Reckoning (LP, IRS SP70044), sounded more like a polite tap on the table than the forceful strike that it is, and the rhythm guitars throughout the Quintet of the Hot Club of France’s Hot Jazz collection (78rpm shellac, Victor HJ6) lacked the tactile quality heard through very efficient loudspeakers.

their overall sense of scale was smaller than I’m used to

sounded convincing without exaggeration (although, again, the whole of the thing sounds bigger through the DeVore Orangutan O/96s and Altec Valencias).

smoothness of response were at their best when my listening seat was just slightly farther from the speakers than the distance between the speakers.

In his room, the Harbeths played with greater bass extension and bass power than the Stirling Broadcast LS3/6s

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Measurements

Stirling specifies the LS3/6’s voltage sensitivity as 87dB/W/m; my estimate was significantly lower, at 84dB(B)/2.83V/m.

closer, therefore, to having a nominal impedance of 12 ohms, which will go some way to explaining the lower sensitivity, except when the impedance magnitude is high, the LS3/6 will also be an easy load for the partnering amplifier.

There is a discontinuity at 160Hz in the impedance traces. Investigating the vibrational behavior of the cabinet walls with a simple plastic-tape accelerometer, I did find a strong resonance at that frequency on the sidewalls (fig.2), as well as a mode at 145Hz on the rear panel. Art Dudley didn’t remark on any such coloration, but I do wonder if his feeling that double bass lacked the "snap and temporal sharpness" he is used to hearing from his reference Altec Valencias was related to these modes.

 behavior suggests that, to hear the flattest balance, the listener’s ears should be level with the Stirling’s lower, primary tweeter.