Parallel SET with sufficient power

@georgehifi , there’s more to it than that... generally speaking, SETs behave as power sources rather than voltage sources (which might be your typical solid state amp). The reason to go this route is to avoid the brightness and harshness often associated with loop negative feedback (harshness and brightness is after all a coloration and not one that is particularly pleasant).

Because no feedback is used, you can’t rely on the Voltage Paradigm for flat frequency response, and the 4 ohm tap may or may not help (likely won’t, as the speaker may be looking for +3db worth of power in the woofer section, and merely moving to the 4 ohm tap won’t get you that).

There are speakers that are designed to work with amps of higher output impedance (and no feedback): Merlins, Coincident, Audiokinesis, Quad 57 and Quad63, Classic Audio Loudspeakers, Rogers LS35A, Lowthers, PHY, Festerex, most horn speakers and many more.

Sorry Ralph I was talking about driving the OP’s speakers with two low 3ohm impedances around 50hz and 150hz, my experiences and measurements on the same amp a 4 ohm tap output tap has a better chance of driving a speaker that dips to 3ohms in the bass as the OP’s do at 50hz and 150hz, than an 8ohm tap on that same amp.
Also if on that same amp the global feedback is increased, it will drive it even better again as it lowers the output impedance even more. But may not sound as "euphonic".
Sure there are spl limits with a 45w set/ or push pull just as there are with a 45w solid state

Cheers George

George, are you sure that TubeGuru amp actually has a 4 ohm tap?  I couldn't find a rear panel photo, but I would interpret this photo, which is one of those shown for that amp at the TubeGuru site, as suggesting that it may have only a single output tap.  Also, the website description states "Output Impedance: 4-16 OHM," which could very conceivably mean that there is only a single output tap, with those numbers being the limits of the range of speaker impedances that tap is recommended for use with.

Regards,
-- Al
    

George, are you sure that TubeGuru amp actually has a 4 ohm tap?

Hi Al, yes when I Googled those amps one of the forum/reviews? said to use the 4ohm tap for hard to drive speakers. And the feedback is adjustable from 0 to some 30db That’s what led me to think so.

I did the same on my 805 sets and zero fb had soft ill defined bass, nice mids/and not much sparkle on the highs of the Monolithiths. Max 35db fb tightened the bass considerably and gave more (still not enough)sparkle in the highs (1ohm load) ouch!!.
In the end I went big bi-amp solid state, as 50w set was not enough for loud level transients, but then the Monoliths are only around 86db where the OP’s Kefs are a touch higher and not as bad loading, as the Monoliths have far worse negative phase angles at 3 points with low impedance’s.

BTW: Edgar Kramer (reviewer) of Australian HiFi/ 6Moons/ and Audio Esoterica had a pair of (Elson Silva) Cymer Southern Star SE35, 35w single 13E1, set monoblocks and his drove his Wilson Watt 8’s comfortably, but in the end weren’t enough when the crew came around and wanted it turned up more than he does.
http://www.6moons.com/audioreviews/cymer/3.html

Cheers George

Correction, they were Wilson W/P Sasha, even harder to drive than the WP 8's.

Cheers George