Full tube amps? Affordable? He he, aren’t you funny!
I’ve been using this $3K+ Decware amp for 90% of my listening after receiving it late last year. I’m using my home built Bottlehead Crack OTL amp too, but it’s not remotely as capable as the Decware. Still, with a ~$500 build cost it performs magic with the the HD 6XX and Beyerdynamic DT880 600 ohm. It’s not technically capable of reaching the HD 800 S’s potential, and OTL doesn’t work with the Clear. I have a nice but now largely inactive RebelAmp Class A solid state. I still recommend it and do like it, but the Decware is on another level.
EDIT: More generally, there’s a thread on amp recommendations (and other amp threads too). As a rule, you can get a taste of “tube tone” with $500 hybrids such as the Schiit Lyr, and then there’s a price/quality jump up to $2K and above. My Lyr 3 is rarely used these days.