Frederick E. Barrett beamed as he looked over the table where the sleek back turner box sat last night -- next to a pre-amplifier, an ampifier and a stereo -- issuing clear notes of classical music. A haze of bluish-green light flashed erratically in amoeboid shape on the tuner face.

"It's a labor of love," he said. "Somethimes I don't know why we get paid for it."

But Barett, who heads the Barrett Group, including the Sequerra Co. which specializes in music-equipment, does get paid for it.

In fact, he was one prime example of very successful black business, which was basically the theme of last night's dinner given by the National Association of Black Manufacturers at the Hyatt Regency Hotel.

Barrett's Sequerra Tuner Model I, on display last night as well as in use during the cocktail hour under a gigantic banner proclaiming SEQUERRA, was given the "State of the Art" award by Stereo Sound, the largest audio magazine in Japan. The award -- which was also on display last night -- is given to the top product in categories of hi-fi equipment.

"Can you imagine that?" said one businessman, studying the trophy award. "A Japanese giving a black an award -- in technology, at that?"

Elsewhere in the room, businessmen -- most were men, not all were manufactures -- traded business news, compared notes, apprised each other of who was available for consulting, and generally brainstormed.

"For black businessmen, this is our country club," said Jim Hansley, head of Vanguard Investment Co., a venture capital firm in Winston-Salem, N.C. "This gives us a chance to relax and do a little reflecting."

It was billed as a "Tribute to the Growth of Minority Business Dinner," and it was the third annual one the association put on. The honorees were Johnson Products head George E. Johnson, Johnson Publishing company head John H. Johnson, Essence magazine publisher Edward Lewis, and Floyd McKissick, president of Soul City Co. and founder of Soul City, N.C.

Neither John H. Johnson nor George E. Johnson (no relation) was there.

"I feel they're the future leaders of American society," said McKissick about the organization as he waited to be introduced on stage.

And President Carter sent his greetings by way of his special assistant Jack Watson. Watson met yesterday morning with many of the same people to discuss how to better implement a year-old federal law requiring federal agencies to make provisions for doing a certain amount of business with small and minority businesses. "Th president wants to get this law working better. He wants to get agencies working faster," said Watson, punctuating his statement with the snap of his fingers.

"Minority contractors can and do produce," said William Dougherty, a white program analyst from the Federal Aviation Administration, last night. "The truth is we have a lot of majority contractors who can't produce a goddamn thing in five years.

The association's president, Eugene Baker, struck a somber note when he closed his opening remarks with, "We have to seriously ask ourselves some questions. If not now, when? If not us, who? Welcome."