A common mod several years back (advocated by a kit vendor) involved tearing out the filters, which I do not recommend after seeing the results on a scope. Otherwise, you can play with the resistor values at the back end of the mono stage and the MPX subchassis to nominally brighten up the top end. I recall posting in detail about the particulars and all the pitfalls some time ago. It should be somewhere in the archives.
But considering the magnitude of the result, correcting the de-emphasis is not usually worth the effort. A tweak of a tone control, or even a different audio output amp tube will yield a much greater result if you feel the tuner presents a rolled off top end. The effects of varying compression levels are more audibly significant than the de-emphasis error at this point.
