For 20 years, Bob Ralston was known as the guy who played the electronic organ on "The Lawrence Welk Show." But this Sunday, Ralston shows what he can do alone when he pulls the plug and plays a "Mighty Wurlitzer" during his one-man show at the Weinberg Center for the Arts in Frederick.

Built in 1926, the Wurlitzer, Maryland's only remaining theater pipe organ, once provided background music for silent pictures. Only about 150 such organs still exist in the United States, says Ralston, though more than a thousand were once in use.

Unlike a church organ, theater pipe organs mimic the sounds of an orchestra. "There are whistles, bells, drums, xylophones and trumpets," says Ralston, "and you can play more than 10 notes at a time." For example, the ranks or sets of pipes produce the sounds of wind instruments and the stops those of the percussion instruments including bass and snare drums and chimes.

At the Weinberg Center, Ralston will perform light classics, show tunes and old standards. He often reserves the last quarter of his show for requests.

The Weinberg Center for the Arts is at 20 West Patrick St. Tickets for the 3 p.m. performance are available by reservation only at (301) 694-8585, and are $8 for adults and $6 for children and senior citizens. If the performance is sold out, another may be scheduled for 7 p.m.