A group including two of the Bass...

A group including two of the Bass brothers from Ft. Worth has boosted its stake in Avantek Inc., the Santa Clara, Calif., maker of microwave amplifiers, to 7.5%, or 1.3 million common shares . . . Diagnostic Products Corp., Los Angeles, increased its quarterly dividend to 6 cents a share from 4 cents, payable Aug. 23 to shareholders of record Aug. 9. This represents a 50% increase from the previous dividend (adjusted for the May, 1989, 2-for-1 split).