The output impedance of your cartridge is 6 ohms. You've no doubt run across the "25 times" rule regarding a theoretical optimum load of 25 x the cart impedance = (in your case) 150 ohms. The actual best loading in your system will fall in a range of 50% higher to 50% lower than that optimum point, in otherwords, 75 ohms to 225 ohms.
It's best to start lower, say 100 ohms, and then move up slowly: 120, 140, 160, etc. until the bass tightens up and stops being muddy/boomy (but without thinning out or losing strength) and you'll be at just the right place.
It's best to start lower, say 100 ohms, and then move up slowly: 120, 140, 160, etc. until the bass tightens up and stops being muddy/boomy (but without thinning out or losing strength) and you'll be at just the right place.