What speakers for 300B S.E.T ??

Any of the Klipsch Heritage series from the late 70's / Early 80's. In your price, LaScala for sure, Cornwall's, or Heresy's if wanting to keep the investment lower (though you will miss some bass authority here you should still get a very good sense of the SET/Horn experience).

If you are wanting to go the single-driver, purist route you could look for a used pair of Cain & Cain Abby's. I have not heard them myself, but reports I've read indicate they'd be a good match too. If your expectations are around the single-driver kind of sound (though the Academy uses two drivers) this may come closer to the sound you heard with the Lowther speakers. Used Abby's usually go for about a grand.

Nothing better than SET with horns to my ears so far.

Marco

If interested in monitor (bookshelf) speakers, check out the Omega line. Have no experince with, but look very interesting. He uses a bass-reflex design to save money on complex backloaded horn enclosures.

I have an 8 wpc tube amp & use with 87db/w/m monitors. As long as you keep the volume reasonable, tube amps are fine. It should be noted I live in small apartment & listen about 87db max.

Don't be BSd into believing you are limited to speakers above 8 ohm impedance. What do you think 4 ohm taps are for. Just stay away from speakers with wild impedance swings. However, my research leads me to believe tube amps DON'T like impedances below 4 ohms very much.

I was not crazy about the Loth-X horns, or the newer Klipsch variety. But hey, that's just me. If you are going the Klipsch route, go for the earlier models. As mentioned, the Cornwall (around $800 used) is also a great choice. If nothing else, I would recommend trying the SET/horn combo before jumping into a monitor. My wife said it best, I think. When we paired our SET amp with our $6500 floorstanders, she said, "It sounds commercial, whereas the horns make it sound real."

Let us know what you end up getting.
All the best,
Howard

The horn shoppe: Aside from bass cut off around 50 Hz, it should have a good tonal balance over all. However, placement and matching amps is tricky.
Loth-X: Have not heard their high end models but entry level ones were quite a disappointment.

Only recommend using 4 Ohm speakers if your SET output transformers are lower than 3K or else you might complain about lack of low frequency response. Keep in mind, most of the commercial version are 5K. The damping factor is very different from speakers to speakers. That's why matching amps is quite important. There is no BS like Beavis mentioned, it is all about science behind speaker and amp design.

I've tried a few things in the SET area, regarding speakers.

The first thing is that nothing replaces high efficiency/sensitivity when you go to low power amps. You need to get as high sensitivity speakers as you can. This gives you more headroom, and reaches deeper into the detail.

Regarding the Hornshoppe speakers, they are nice and made pretty well, and sound pretty good. But I have used FE103 drivers in a few designs, and they just don't get into the bass very well, and what bass they do produce is restricted by the very small amount of air that a small driver like that can move. You will find that they lack in the bass.

When I switched from FE103 based speakers to Lowther EX3 based speakers(Voigt Pipes), the difference was staggering. Better all around sound, much more headroom, gobs more bass, way more detail, just way more everything.

I'd agree that the Cain and Cain Abbey speakers would be a good try for your under $1k budget. They are a Voigt Pipe design, and have the single-driver advantage that mates well with SET amps. However, the Fostex drivers will not sound like a Lowther, and although they are good, the Lowther drivers are way better. I made my Voigt Pipes myself(very easy to do), and spent my $1k on the Lowther drivers. I made a few custom changes to mine, and drive them with my Berning 45 SET-ZOTL(2 watts per channel) and an analog front end. Very awesome results down to about 40Hz on the bottom end. Max SPL peaks at around 106db.I really don't notice any "lack of bass" with this system. It is so good at doing 40Hz and up, that the few things that actually occur below 40Hz don't make a difference in my enjoyment. Of course if you are a pipe-organ fan or something, you'll need a sub. I did make some mods to my cabinet which overcomes the baffle-step losses which are typical in this type of system, so my bass is better than other Voigt Pipe designs.

Regarding your comment that Lowthers are too expensive to experiment with, you can just build an easy cabinet like a Voigt Pipe, and you can be good-to-go for under $1500/pr complete with Lowther EX3 drivers.

The down-side is that they are pretty large, and may be a bit taller than your size requirement dictates.