Full Range Drivers and SET's, why is a classic combo?

Hello to all,

Thinking about go that route...

Wondering what are the main factors that makes this a classic synergetic combo?

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No crossover phase overlap issues from speaker or amp. 

Point source

low damping factor of SET amp doesn’t overdrive the wide band woofer

SET amp can tame the rising response of a wide band driver in the treble 

no or low negative feedback and no transistor distortion 

wide band drivers can sound dry with solid state amps

most simple amp and speaker type so less to get in the way of the music 
Nice! thanks for your explanation.
What are the main differences in sound between SET's with 300B tubes vs 211?

That depends upon the output transformer (the most important part of any tube amp - PP or SE). And the most costly and difficult to make! It is THE vital link between the output tube's anode (plate) and the speaker. And it's easier to build an OPT primary to match the RP (plate resistance) of the 300B than that of the 211 or similar transmitter tubes.
A 300B uses a plate voltage of about 400. The 211 and similar transmitter tubes use 1200 volts. It is difficult to build an OPT primary that can handle 1200 volts, compared to 400. The same for the power supply components!
The SE 300B can do about 7 watts at 1+ per cent distortion. The 211 and similar transmitter tubes can do about 15 watts SE. That is about a 3 db difference in drive capability for a whole lot more cost and complexity!
A good single-driver speaker for low-watt SE amps is an Altec 755. I had a pair. Put it in a one-cubic foot box and it will work from 60 hz to 12k hz with fairly flat response and enough sensitivity! Add a subwoofer for the bottom two octaves.
I own three SE tube amps: a 2A3, a 45 and a 6BG6. The best speakers in my collection for them are the venerable. Klipsch Heresy Mk1's (99 db sensitivity).
Thanks for the detailed explanations.

Any experience with  the current Heresy IIIs and SE tube amps? Are these different from the originals  (Mk1s?) in regards to ability to run well off SE tube amps?

If they are still available, the First Watt SIT-3 does a wonderful job with a horn and at 18 watts can easily drive most any horn.  Very tube like sound and a great price
Another possibility for better bass response with still a "SET" sound is a 6W6 Push-Pull Amp that has the screen voltage properly tuned--this will give amazing response.  The 6W6 is one of the most linear tubes made and very beautiful in this configuration with full range driver.  I have come to use this as my goto system--6W6 12W P-P driving a variety of full range speakers in both horn and bass reflex cabs.  Custom transformers from ElectroPrint.  The only SET I really preferred over this was a 71A design, and although the sound was to die for it was limited to about 800mW in a single tube configuration.  As you move up the SET family (71A, 45, 2A3, 300B, 211) the sound gets progressively less clean and a little of the sound stage disappears at each level IMHO.  Not that the entire family isn't amazing--just that the lower the power, the better the sound, again IMHO.
I use Heresy IIIs and a 12wpc (depending on output tube used) Dennis Had Inspire "Firebottle" SEP (pentode) power amp and it's an astonishingly good combo...loud and clear and a sub or two makes it really work.
Cube Nenuphar’s with Bakoon 13R 😜