300B Tubes - Which is Best?

The Western Electric 300B is THE class act in this arena.
They have a rated life of 40,000 hours (the 6550 in my ARC VT-100 Mk-III are reated for 2000 hours/2 years).
The designers took something like five years (from project genesis) before they reissued this classic.

I thought Cary used the 300B up to a threshold (10-12 watts?) then the "big gun" (845/211) kicks in up to the rated maximum (50 watts?).

O.K. What does that mean?

ED_SAWYER: You are right. The following taken from Stereophile Archives:

"The following circuit description is based on information provided by Dennis Had. The input signal is DC-coupled to the grid of a 6SL7 dual-triode operated in parallel as a single voltage-gain amplifier. The 6SL7's plate is AC-coupled to the control grid of an EL34 pentode wired as a triode (footnote 4). The EL34 dissipates about 19W of class-A power and produces 4W of audio power to drive the grid of the 211 through an inter-stage transformer of air-gap design. The 211 is cathode-biased, and the output stage is operated in class-A1 (no grid current) up to 25W output. As the drive to the 211's grid is further increased, operation shifts to class-A2. The 211's grid goes positive (and starts to draw current) while the output power with increased efficiency reaches about 50W. The ability to drive a 211's grid positive is made possible by the use of the inter-stage transformer coupling between the EL34 and 211."

The Cary 805 does shift gears but only within the 845/211 output tube.
BTW, the previous info is from the "B" version of the 805 amp so substitute "300B" for "EL34" and "845" for "211".

Regards, Ken