@tritube Looking at the impedance curve that @hilde45 provided, its obvious to me an SET will not do the job.
You need an amplifier with a low output impedance, otherwise your system will have colorations. SETs have a high output impedance. If you really want that 'artist in the room' imaging, look elsewhere.
The efficiency is also an issue for an SET. You need more power than they can provide on a budget! Since you are looking for budget tube power, I think you are better off looking in the used market, possibly for a refurbished Dynaco ST70, which can make 35 Watts/channel.
Now if you are open to replacing the speakers as well, if you really want an SET, the speaker has to be more efficient than most internet posters will have you believe. SETs really only make about 20-25% usable power; above that distortion becomes so high that the amp takes on a 'dynamic' quality and at higher power levels tends to sound loud or shouty. This latter bit is why so many SET users think their 7 Watt amp is enough power- it isn't! If they had clean power they would figure out that they are playing much higher volume levels without the system sounding loud. IOW distortion is what makes SETs sound loud.
High efficiency speakers don't tend to be inexpensive since the magnet motor requires considerably more precision to execute and that costs money. You also sacrifice bass unless you really have a large budget or can afford subs.
That is why I think a refurbished older amp is your best bet.