A kitchen table in the east end of Glasgow. Arranged upon it are objects required to tell a story: an old toy bus; three seven-inch singles each worth about £2,000; a yellowing newspaper with a bellowing headline, the tragic force of which has not faded these 50 years. Naturally, there is also a pot of tea.

“Milk?” says Stuart Cosgrove. “Sugar?”

Cosgrove is 64, that McCartneyish age, which I find hard to credit. The writer and media personality seems unchanged these last twenty years. His manner – erudition, lightly worn, mixed with pub banter, lightly sworn – has become familiar to the point that one might just consider him an institution. Yet it is difficult to see him ever becoming a grand old man of Scottish broadcasting; not in those gutties.

The youthful trainers and dress sense goes with the young family – a boy at five, just starting school – and it is Wee Jack we must thank for the fact that we are sitting in the kitchen. The plan had been to play some of Cosgrove’s precious collection of soul singles on the DJ-quality record decks in the living room, but his son, footering, had yanked some crucial wire and the thing was kaput. Plan B: the kitchen, to listen to the music online. “I believe,” croons John Gary Williams, via YouTube, “That the whole damn world is going crazy …”

That’s one of Cosgrove’s favourite songs. A Stax classic, Stax being the US record label that is the focus of his new book, Memphis 68. The follow up to the well regarded Detroit 67, it is the middle volume in a planned trilogy, each title weaving together the social and musical history of a particular city in a particular year. Subtitled The Tragedy Of Southern Soul, Memphis 68 is framed by the felling of two giants: the death of Otis Redding in a plane crash (Cosgrove has interviewed the only survivor) and the assassination of Martin Luther King Jr. Hence that newspaper lying on the table between us – The Commercial Appeal, the Memphis paper, dated April 5, 1968 – with its awful block capitals, DR KING IS SLAIN BY SNIPER.

In 1968, when all this was going on across the Atlantic, Cosgrove was 15 and living on the Letham housing estate in Perth, with his mother, Alice, and two sisters. What was he like in that year?

“I was quite a difficult child and teenager,” he says. “I was trying everything out, from drink to Mandrax. There used to be these brown pills called Do-Dos. They were for asthma, but they were actually a mild amphetamine, and you could buy them in Boots. My pals always used to say, ‘Cossy, you’ve got asthma, you go in and get the Do-Dos.’”

So, just as the shop was closing, the better to avoid any questions asked, the bold young Cosgrove would go up to the counter and, affecting a wheeze, make his pitch: “‘I’ve got an awfy tight chest. Do you have any of them Do-Dos, please?’ Then we’d share them out and buzz on them.” The pills were doled out in the Cutlog Vennel, one of the town’s many medieval closes. Afterwards, perhaps, there might be a trip to the Letham Community Centre, or the Perth City Soul Club, where he would hear his beloved Stax and Motown. Music was and remains much more important to him than the football with which he is more often associated. The fortunes of St Johnstone FC may have quickened his pulse, but that soul beat was his heartbeat, Cosgrove was, as he wrote in his semi-memoir Young Soul Rebels, “a stick-thin teenager from Scotland with atopic eczema and an insatiable appetite for the music of the American ghettos”.

As for him being difficult, was there a reason? That toy bus offers a clue. Blue and silver, its clockwork key resembling something that might open a can of sardines, it was a gift from Cosgrove’s father, brought back from a trip to Moscow in the 1950s. Jack Cosgrove was a lorry driver and trade unionist whose work took him to the Soviet Union. He was a giant in his son’s life, just as Redding and King were giants in the culture, and his sudden death in 1961, in a traffic accident, was as scarring for the boy as those other deaths were for an American generation.

“My dad had gone and I was a bit lost and angry,” Cosgrove recalls. “There was no money and we were a family just keeping our head above water. But teenage hormones made me impulsive, reckless. Nothing serious happened, but I was brought home by the police a few times and had successive bad reports from school. I was a worry to my mum. But she remained my greatest ally in life and quietly encouraged me to achieve.”

The Letham scheme was much like any big post-war housing estate. There was no central heating, no double glazing, the windows would rattle in a stiff breeze. Though it was hardly the ghetto, it gave Cosgrove lived experience of deprivation, and this empathy has informed Memphis 68. A brilliantly angry chapter on the deaths of two garbagemen crushed in their own truck, and the strikes and civil unrest that followed, would not have been quite so well done had it been written by someone other than the chippy son of a trade unionist who knows what poverty – and loss – feels like.

At 16, going on 17, there came a change. Cosgrove “came alive to intelligent thought”. The catalyst was one of those life-altering teachers – in this case a Miss Campbell, who taught modern studies at Perth Academy. “She was the one that guided me towards studying Martin Luther King and all that. She opened up the tabernacle of knowledge. I got quite high on it.” He would be up after midnight and before breakfast, reading books about the Civil Rights movement. The music he loved – those three-minute symphonies of black yearning and joy – now had a political context. “So that was where it first started.”

He went to Hull University to study Theatre and English. At the orientation meeting, he was astonished to learn that the sixth floor of the library contained one of the world’s best collections of books on black music and history. “Whoosh! I was right up there! I remember walking up and down the shelves thinking, ‘F**k, I’ve got a lot to learn.’” This treasure had, it turned out, been assembled by the librarian, one Philip Larkin, using a generous budget to indulge his love of jazz and R&B. “He was quite an odd character. He reminded me of a gnomic intellectual insect. It was almost like he didn’t like the light. You’d see him down an aisle of books and he’d just scuttle away.”

As his obsession with American soul deepened, and as his leftist politics were increasingly shaped by his reading about the Black Panthers, Angela Davis and the Civil Rights struggle, it became increasingly important to him to visit the United States. In 1978, he won a three-year postgraduate scholarship which allowed him to study at Howard, a mainly black university in Washington DC, which he chose in no small part because they had awarded Stevie Wonder an honorary doctorate. Though excited about studying abroad, he also had a secret mission: to track down rare singles which he had heard played at Northern Soul nights around the north of England.

A tutor at Howard told him that if he really wanted to hook up with folks from the old soul scene, he should talk to a man known as Sir Clarence, a former record promoter rumoured to own every seven-inch every put out in DC. No full name, no address. It took some detective work, but Cosgrove tracked him down to the photographic store where he now worked. This tall figure shambled out from the back – thin with an arched back, mid-fifties, in the early stages of stomach cancer: Sir Clarence. Here Cosgrove pauses and reaches for two silver boxes of singles, hundreds in each. “That’s the Stax box,” he says. “And this is ultra-rare Northern.” He removes three records from the second box, and chucks them on to the table, rather cavalierly, considering their worth.

Sir Clarence invited him back to his home, a small wood-frame house off Georgia Avenue. They had some beers; talked old times, old songs. Eventually, out came a suitcase full of seven-inches and they struck a deal. Cosgrove would buy six records at $2 each. He still has them. That’s Ray Pollard’s This Time (I’m Going To Be True) lying on the kitchen table, the Shrine Records label a distinctive robin’s egg blue. It’s worth a couple of grand.

Walking back to his digs from Sir Clarence’s, Cosgrove felt a little guilty. “There was an element of triumph that I’d got the records. But there’s something slightly compromising about being with a man who says he’s never had a white person visit his house before, who considers you bringing him a tray of cheap beer a wonderful gesture, who talks for three or four hours about their life and memories, and then you walk away with records when they have no real understanding of the market value. I knew even then that the records were probably worth four or five hundred quid.”

That man’s whole life had been undervalued; Cosgrove understood this, and the sense of complicity is still with him. Still, he did not buy the records to sell, but to love, and he cherishes them as a symbol of an important and friendly encounter, a brief coming together of two men united by passion for a particular sound and spirit.

Stuart Cosgrove’s whole life has been shaped by soul; his friendships, politics, education, career – first as a music journalist and now as a chronicler of black American music’s social context. A blaxploitation movie poster on his living room wall, all pimp bling and smoking guns, hints at the forthcoming final book in his trilogy, Harlem 69: The Future Of Soul. Come November, he will be in New York, deep in research.

For now, though, time to listen to one more song: Look At That Girl by Otis Redding, that fallen giant. “Soul,” says Cosgrove, “is more than music, it is a spiritual calling” – and as this Memphis song blares and blasts and wails, rattling the tea cups in a Glasgow kitchen, it is easy to hear what he means.

Memphis 68: The Tragedy Of Southern Soul is published by Polygon on October 5, priced £16.99