You must have one of the original hi-fi* Concordes, whose great beauty was that they were so light (6.3g) that they enabled high compliance styli to match perfectly with medium-weight tonearms like the Technics, with an ideal resonant frequency of around 10Hz. The problem was of course, that most tonearms couldn’t be balanced for an integrated plug-in headshell/cartridge combination that light, so they needed a much lighter counterweight, and one was supplied with each cartridge when new.
They came complete with special lightweight 70g Ortofon screw-fixed counterweights so that tonearms like the Technics one could be balanced. The counterweights supplied with the cartridge had 15mm holes, but if they didn’t suit your particular tonearm, Ortofon would exchange them free-of-charge for alternatives with 12mm or 18mm holes.
Seeing as how you don’t have the special light counterweights, another option is to buy another counterweight, which should be easy to find for Technics tonearms, and lighten it by drilling or cutting part of it off. Although drastic, that's a better alternative than making the cartridge heavier, because that defeats its major advantage - light weight, which enabled it to track even badly warped records spectacularly well on medium-weight tonearms.
* There are also now some DJ Concordes sold by Ortofon, which are much heavier (18g). Although the same shape similar to the aircraft, they really should have been given a different name, given that they’re not designed for high fidelity, and lack several of the originals’ great attributes, such as adjustable overhang and low mass.
