The Bass brothers, the prominent Ft. Worth...

The Bass brothers, the prominent Ft. Worth investors, have increased their stake in Avantek Inc., a Santa Clara maker of radio frequency and microwave components, from 5.5% to 6.5%, according to filings with the SEC . . . A federal judge refused to dismiss claims that one of Genentech Inc.’s major products, an anti-heart attack drug, violated a rival firm’s patent . . . Gap Inc. said it ended discussions with Retail Ventures Inc. and Natco Industries Inc. that were aimed at the Gap’s acquiring American Eagle Outfitters Stores . . . IPM Technology Inc., a Los Angeles company that earned $54 million in fiscal 1988 providing refueling services and aircraft ground support, said it has extended the deadline for submission of proposals to acquire the company to Friday . . . National Medical Enterprises Inc. said it will issue $300 million of convertible subordinated debentures in a private placement with the proceeds to be used to retire debt . . . The number of working oil and gas rigs declined by 18 this week to total 743, Houston-based Baker Hughes Inc. reported. A year ago, the rig count was 946 . . . The Federal Reserve reported that the average yield for one-year T-bills, the most popular index for making changes in adjustable-rate home mortgages, fell to 9.39% last week after averaging 9.40% the week before.