the viva is a 15 watt amp, so the distortion is probably close to 5% with no feedback.
The 845 is a class A Modulator/amplifier, and actually works at lower distortion at
much higher power levels with much higher plate voltages. Can actually get down
to 1% at 50 watts.
Here are a few more entertaining numbers, asked by a person on an island off the
coast of spain.
Singlepower MPX3 with 6sn7 tubes... Actual measured distortion 5.4% into 300 ohms
at 2 volts...