The 10 uses a single 6AG7 in the output. I recall tht the 6AG7 has 11 watts
plate dissipation and the stage runs class A. Class A runs about 33%
efficiency - and the circuit is poorly laid out and resistors are across the
coils to prevent parasitics. I measured 3 watts output with my 10A.

Although the power output ought to be able to drive a pair of 6146 tubes, I
do not think that was the way they did it.

Hopefully the manual for the adapter will answer the question.

73, Colin K7FM