"It was shocking - it was like nothing else," says the Swiss organist, librarian and ondist with the kind of enthusiasm that is instantly infectious.
Three years later Geneva's Orchestre de la Suisse Romande gave a performance of Olivier Messiaen's Turangalila Symphony - a vast, ecstatic orchestral love song that features piano and ondes Martenot as its central couple - and Tchamkerten was mesmerised.
When Messiaen came to Geneva to give a lecture not long after, the young organist seized his chance and introduced himself to the composer's sister-in-law Jeanne Loriod, finest ondiste of her generation. Loriod invited him to Paris for a lesson; he took up the offer and before long he was hooked.
The ondes Martenot is like that: it hooks people, enchants and intrigues them. I have come to meet Tchamkerten in the Royal Scottish National Orchestra's rehearsal hall - he performs Turangalila with the orchestra this weekend - and a small crowd of musicians has gathered around the instrument to take a closer look. Up close it is wonderfully dinky: just a petite six-octave keyboard and three neat little speakers lined up along the floor. But hear its violent shrieks in Turangalila and the impact is far from cute.
The ondes was invented in 1928 by a French cellist, Maurice Martenot, who had worked as a radio telegrapher during the First World War and saw the potential of using oscillating radio tubes to create sound waves via electronic pulses. It was one of the first electronic instruments to be used alongside acoustic instruments by French experimentalists such as Edgard Varese, but its sweet, swoopy voice did not sit well with mid-century modernists and it fell out of fashion after the Second World War.
"The ondes had a period of purgatory," says Tchamkerten with a doleful shake of the head. "Pierre Boulez was an ondist at the Folies-Bergere at the start of his career, but he denounced the instrument: it was too expressive, too sensuous for him." Even the great Loriod had trouble finding enough work as an ondiste in the 1960s and had to take a job in a laundry for five years to pay the rent.
But Messiaen always had a soft spot for the instrument. He wrote rapturous music for ondes ensembles (Fete des belles eaux), for ondes and voices (Trois petites liturgies de la presence divine) and included three ondes in the orchestration of his opera, Saint François d'Assise.
As classical performance styles evolved through the 20th century, so too with the ondes. "At the beginning it was Martenot's sister Ginette who was the main ondiste," Tchamkerten explains. "She played with huge amounts of vibrato, extravagant glissandi and so on. Many composers hated the sound - Francis Poulenc, for example. When Loriod took over she found a much more subtle way of playing. But Messiaen loved it always. He had un petit mauvais gout - a taste for the kitsch. His taste in paintings was very strange too, always over-saturated with colours."
Turangalila is rare among Messiaen's works for taking its inspiration not from religious but romantic love, based on the legend of Tristan and Isolde. "Maybe the piano represents the man and the ondes the woman," Tchamkerten suggests. "The piano writing is massive and full of arabesque detail, whereas the ondes is the expressive voice that sings the sensitive melodies and the terrifying glissandi."
So why don't we hear more of this magnificently expressive, lyrical instrument? Partly it is an access thing: there simply are not enough of the rare beasts to go around. Numerous adjustments were made to the design over the decades (Messiaen wrote mostly for an instrument that dates from around 1937). Martenot himself died in 1980 and production stopped altogether in the 1990s, making an original ondes a pricey purchase nowadays. There have been attempts at new models, but these are not cheap either - a new replica will set you back around £10,000.
Neither is it an easy instrument to learn. Tchamkerten estimates a study period of 10 years to master it properly, and without much repertoire there are not many chances to perform. At a travel weight of about 14 stones (90kg) with plenty of obsolete fiddly electronics to go wrong, the ondes does not really lend itself to touring, either.
I suggest, as a joke, that maybe Tchamkerten should just play a theremin instead: after all, it is cheaper and packs up much smaller - it was even invented in the very same year. He looks hurt.
"Mais non," he says. "The theremin can never do what the ondes does. Monsieur Martenot was a musician; Theremin was an inventor. The theremin was often used in Hollywood; there are many theremins in the world. But for precision, contact, lyricism, for real expressive feeling, there is nothing that can match the ondes."
The RSNO perform Messiaen's Turangalila Symphony at the Usher Hall tonight and Glasgow Royal Concert Hall tomorrow