Any US manufacturer of a 845 SET amplifier

This causes me pause as my 93db/6ohm speakers might be on the edge.

@decooney You are correct. In most rooms with speakers of that efficiency you’ll want more like 50 to 100 Watts. SETs, if zero feedback (and most are), have only about 20-25% usable power. Above that level, higher ordered harmonics show up on transients (where the music power is) and so causes the amp to sound ’dynamic’ since the ear uses higher ordered harmonics to tell how loud sounds are.

This is why so many people comment about the 'dynamics' of SETs. Its really distortion masquerading as 'dynamics'.

So if you are going to be successful with an SET, it really needs to be used on a speaker that is efficient enough that the amp never makes more power than that.

The other problem SETs have is making bandwidth. Typically about 7-8 Watts is the most power you can get out of an SET design before the bandwidth becomes limited. Because most SETs are used on higher efficiency loudspeakers (like horns) they often will compromise the bass response to get the highs right.

An additional problem limiting bass is an engineering problem; to operate correctly the power tube has to be placed in its most linear region of class A. There is something called a ’load line’ which helps the designer design the circuit that does that. The problem is most output transformers lack the inductance needed for them to make bass properly. This results in an elliptical load line at low frequencies- if you go low enough, its almost like the tube is driving a short, which can be very hard on it!

So for best operation, the SET really should not be exposed to low bass frequencies.

@danager thx those STL amps with OTL design look fun and intersting. That Dr D guy on YT is quite giddy about Alans creations it seems.

@mesch looks like you are set, literally, no pun intended LOL. I think id like that Transcend amp you have more than my prior Inspire Hot Rod.Will look it up.

@atmasphere Ypur kind response helps me, alot. Thank Ypu for your time explaining and writing that up. It is similar with "bandwidth" discussion I had with Luke Manley at VTL. Maybe I should appreciate what i have right now even more. 

Back to listening. Happy Holidays to all of you.

@danager I have a lower model STL hybrid that uses KT150 tubes, and I agree with your assessment, I'm using mine with apogee duetta 2 speakers and the bass is great. The hybrid amp doesn't have the power of my Krell amp, but the bass is more detailed and the midrange is better. 

@decooney My Transcend is an earlier model which I bought used. His later version has similar circuit topology with higher grade parts. Aric can build/modify to ones desire. A fine person and easy to work with. You will enjoy your conversation with him.

Thanks @mesch, I’ll be keeping an eye out for a 2nd smaller form factor stereo tube amp I can rotate in while leaving my pimary QS Mono 120s in place, saving these.

Contemplating with some reservations about selling off a good chunk of my vintage NOS tubes and my Pass/Forte’ Class A SS amp and preamp system I had Jon Soderberg upgrade for me. He’s 10m from me. Can’t seem to get myself to list it all.

This would help fund a nice EL34 amp I could rotate in so I can save the QS monos for a long time - they are extra amazing with the specific mundorf coupling cap, nichicon power cap, tube upgrades. Amp2 forthcoming. Will take a closer look.