The Red Roo guitar amplifier's standard configuration is for push-pull Class-AB operation giving about 20 Watts RMS of power. However, it can also be configured for single-ended Class-A operation which will give about 8 Watts RMS output.

Single-ended operation requires a different type of output transformer, different output tubes (2x 6V6), and some changes to wire links on the PC board. So, why would you want to do that?

Most low-power guitar amplifiers are single-ended. i.e. they have a single output tube or several tubes connected in parallel. They operate in Class-A where all output tubes are conducting throughout the entire signal-voltage cycle. 

Guitarists might opt for single-ended tube amplifiers for various reasons, as they offer distinct characteristics and tonal qualities that may suit certain playing styles or preferences.

Single-ended tube amps often produce a warmer, more harmonically rich, and organic sound. They tend to distort more easily at lower volumes, producing a sweet, compressed, and saturated tone that many guitarists find appealing, particularly in blues, jazz, or classic rock genres.

However, it's important to note that single-ended tube amps might not be suitable for all genres or performance needs. They generally lack the headroom and volume required for larger stages and simple designs (not the Red Roo) do not deliver the high-gain distortion preferred in heavy metal or hard rock. Additionally, they might not have the clean headroom necessary for genres that demand pristine, undistorted tones at higher volumes.

Ultimately, the choice of an amplifier, whether push-pull or single-ended, comes down to the individual guitarist's preferences, playing style, the specific sound they're seeking, and the contexts in which they'll be using the amplifier.

We suggest you start with the standard push-pull configuration and experiment later on.