Re: Pye, Black Box Mk1 1954, cartridge.
The volume control (actually a loudness one) on the BB is right up front so you can't overdrive the amplifier unless you turn it up too far. Adding a few hundred k of series resistance might increase the relative bass level with the added advantage of losing some excess signal voltage.
If you know the nominal outputs of the original vs new cartridges, a starting point would be the resistor which scales the voltage at the top of the volume control to leave the same as the original cartridge's.
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