What was going on when I was born?

The Seventh Regiment Armory on Park Avenue will be turned into a do- it-yourselfer's paradise Friday when the second annual Big Apple Fix-Up opens for a three-day run. More than 150 exhibitors will display and demonstrate products for renovating, remodeling and repairing houses and apartments.

MADISON AVENUE, which once was to advertising what Broadway is to show business and Central Park West to psychoanalysis, is no longer the same. The ad men are going and the bankers are coming. Not just coming, in fact - they are already there. In less than four years, more than two dozen banks from all over the world and this country have opened offices on Madison Avenue between 42d and 57th Streets. According to Andrew Roos, a vice president of Williams Real Estate Company, there are more than 50 banking offices within two blocks of the corner of Madison and 55th Street. The immediate reason for this particular surge of midtown money-changing, real-estate specialists and bankers say, is a lack of attractively priced space on Park Avenue. But a more fundamental explanation is the considerable increase in financial activity in New York City since the creation here two years ago of a free-trade zone in international banking.

HE is a big man with a full beard who might look intimidating if it weren't for the smile on his face and his gentle nature. He once played for the Los Angeles Rams and was part of a defensive line that was called the Fearsome Foursome. But now, Merlin Olsen can be seen on television extolling the virtue of flowers. In the past five years, Olsen estimated that he has turned down 10 major advertising campaigns and ''big dollars'' waiting for one that he felt was suited to his nature and tastes. ''What I like about this one,'' Olsen said, of the new Florists' Transworld Delivery Association (FTD) ads, ''is that in only one of the commercials is there any reference to me as a football player. And what I also like is that the commercial shows you don't have to be a softie to give or receive flowers. Too often, the people in advertising are not creative enough to get away from stereotypes.'' In recent years, television commercials have afforded a number of athletes the opportunity to move gracefully from the playing field to an alternative career. The money boom in professional sports and the growing awareness of physical fitness have been credited by those in advertising with giving many athletes the kind of visibility that only a few had enjoyed previously and which had been primarily associated with Hollywood stars.

The most conspicuous and, for the moment, most emotional political conflict being waged in South Africa is not the fundamental, gradually sharpening struggle between white nationalists and black nationalists. It is white versus white. More specifically, it is Afrikaner versus Afrikaner. The cleavage in the dominant white group - no more than 2.8 million people who are scarcely 8 percent of the 32 million people inside the country's traditional borders - results from a bold attempt by Prime Minister P. W. Botha to broaden its political base. His new constitution, which has been adopted by the white Parliament and is awaiting approval by the white electorate in a referendum on Nov. 2, seeks to do this by extending limited political rights to brown, but not black, South Africans.

Columbus House, a slim 18- story condominium apartment building nearing completion on the west side of Columbus Avenue between 78th and 79th Streets, looms over its low-rise neighbors, but it makes a design gesture to the American Musuem of Natural History, the massive landmark complex sitting just across the avenue. A search was made for a curtain-wall brick that would closely resemble in tone and texture the museum's rough- cut limestone facade.

PHILADELPHIA For nearly half a century, the Philadelphia Orchestra has been known as much for its sound as for its music. The word ''Philadelphia'' connoted a string texture at once soft, rich and powerful. It was an unmatched quality, one cultivated during Leopold Stokowski's many years with the orchestra and then pruned, enriched and perfected by Eugene Ormandy who took over the Philadelphia in 1936 and did not leave until he became conductor laureate in 1980. This beautiful quality lay often like a great oppressive weight over the vast repertory of music Mr. Ormandy seemed happy to apply it to. One orchestra violinist, recalling his first rehearsal under Mr. Ormandy many years ago, remembers the pressure on the bows all around him: ''I actually couldn't hear myself play.'' ''From Mozart to Sibelius,'' remembers another, ''it all tended to be the same.'' Riccardo Muti, who brings the Philadelphia Orchestra to Carnegie Hall on Tuesday, is entering his fourth season as heir to this grandly luxuriant, but obstinately uniform, way of making music; and, as the orchestra's music director, Mr. Muti's task has been to create many styles where previously there was one. ''There is no 'Philadelphia sound,' '' he says in his quiet, laconic way. ''There is a Mozart sound, a Brahms sound, a Mahler sound.''