Tube Preamp: How many tubes does it take to .................

I have had many tube preamplifiers over the years. Ranging from only two tubes to many! The best that I have heard in my home, across multiple systems is the entry level Backert labs Rhumba 1.3. It uses only two tubes. It excels at detail, soundstage, clarity and more. I like the tonality. It is vivid and dynamic!. 

The Audio Research LS2B had a single tube. It was part of a system that was flat out phenomenal. I remember the session after 25 years.

1965 MX-110Z is hardly a maintenance nightmare……. an excellent engineer w ears…. paid heed to SOE ( safe operating envelope ) of ALL the components in circuits, including line voltage variability = legendary tube life and reliability…. so Gow and company understand this w the RCA tube design manuals as stone tablettes  ( yes that was intentional )… Of course further genius like Roger Modjeski….. used the envelope advantageously …..10 k hour tube life….in a power amp…

Maybe some engineers get paid by the part.

The Top Conrad-Johnson GAT2 preamp hand only two tubes.  One gain tube per channel.  A MOSFET at the output of each channel controlled and lowered the output impedance.  Their new unit uses four tubes.  A cathode follower on each channel replaces the the MOSFET transistor.