SSE UL question

[ChetJettison]

I've just finished soldering all the components on to my SSE PCB. Next I'll be performing a bench test before building a chassis.
But I have a question (probably more than one, eventually) before I proceed.
It's about UL mode.
I ordered some Toroidy output transformers that have a UL tap.
What are the benefits of UL? Should I set my SSE up with UL by default, or should I install a switch? If I wanted to switch UL only, how would I wire that up? I've seen the diagrams on the tubelab site, but they seem to show UL switch AND CFB switch, and I'm not sure I'd need both. I don't really know what CFB does, and as a matter of fact I'm not entirely clear on UL either.

By my limited understanding, I gather that UL allow more power delivery to the speakers. I'll probably be using this amp with Bozak Rhapsody speakers, of unknown sensitivity, but probably not TOO efficient, I'm guessing. So would a default UL configuration make sense? Or should it be switched?

Can someone help explain UL for me?

 

[rayma]

Ultralinear in a local feedback loop in the output stage, performance being between
pentode and triode operation.
Ultra-linear - Wikipedia

 

[ChetJettison]

Based on the wiki page description, I'm thinking that UL might be desirable.

 

[rayma]

An old school speaker would likely benefit from a low source impedance.

 

[ChetJettison]

An old school speaker would likely benefit from a low source impedance.

Which is what UL would offer me?

 

[rayma]

Pentode mode has the highest Rout, UL mode medium Rout, and triode mode lowest Rout.

 

[ChetJettison]

Hmm so I guess I’m still not clear on which option to choose. Is triode mode the default configuration? Is UL still the best choice?

 

[rayma]

Try both, and then decide. It depends on the speaker system and its impedance curve.

I would first set any tweeter or midrange level controls on the speaker to flat,
(using for example white noise from an FM tuner) while using a ss amplifier.
On older speakers, a setting marked as flat can still be dull sounding (like AR, etc.)

 

[OldHector]

I suppose if you have a mono source with a balance control, it should be possible to have both options set up, and switch between them, to do some side by side testing?