A B747-400 Captain experienced multiple failures apparently related to electrical bus failure; elected to declare an emergency and returned to departure airport.

Narrative

Passing FL250 the crew heard a noise; and simultaneously lost the left radio; the Captain's radio panel; and received numerous EICAS and Status messages (about 20 of them); seemingly unrelated to each other. We elected to level off and trouble shoot. It seemed to be some sort of electrical bus failure; leading to multiple systems failure indications. Ultimately; we decided to return to departure airport. First Officer flew and coordinated with ATC; Captain consulted with Dispatch and Maintenance to determine what was wrong; and right; with the aircraft. No checklist really applied to the overall problem; although we did run several EICAS-driven checklists. Dispatcher declared emergency for flight; which we agreed with. Crew coordinated radar vectors to fully address the situation and landing considerations. We had Flight Control and Flight Operations run landing numbers for us to ensure we could return safely. Landed with anti-skid failure and brake limiter failure; Captain landed otherwise uneventfully.