The 773 is geared with a much different ratio than its contemporaries and has a much slower speed.
To clarify, what JohnsGG1 said is true. All of the 700-series Hudsons, beginning in the 2nd year of production (1939) right up through the Vision model are geared at 18:1. Even with those large wheels, the top speed is muted compared to other Postwar steam locos AND IT'S A BEAUTIFUL THING! Unlike the smaller locos, these were aimed at adult modelers from the very beginning.
Another key point is that the motor is rated for 20 volts. A small transformer, or an older ZW in need of reconditioning won't cut it.
Dennis Waldron (JustTrains) has published some tune-up tips for the Hudsons, but yours seems to run very well, so I would tread carefully:
Before you begin, please note that nothing will turn it into a speed demon. If that's what you want, I'll gladly trade you my 2046 straight across You have a great runner on your hands. Enjoy it!!