Are most tube preamps ‘ultra linear’?

Is ultra linear prefered ?

hard to discern this designation when reviewing specs. 
...the ultra-linear’ power doubles. no change in volume when you change back and forth, just a discernible different sound...
If you are learning about tubes, this is not remedial. Throw in 4 and 8 ohms taps and I am really lost! :-)

I read this thread because I am new to tubes.  Now I know a little about what ultra linear refers to.  The condescension in this forum is at times amazing.  Big fish in a shallow pond, I suppose.
One thing That is good to look for is a preamplifier operating in pure class A . I find their purity very appealing 
a  DHT is the purest single ended But it lets you hear everything 
not all speakers and amplifiers are a ideal match . I have owned 
several hand built models from Vacuum tube Guru Radu Tarta 
exceptional build and sound quality.
@audioman58 : All tube preamps operate in Class A! They have a single tube connected to the output straight - or through a cathode follower or a transformer!