OK -- That is adding insult to injury as well. This is not to in any way disparage the control that Mark sells. His control is correct relative to total resistance value, where the loudness tap is placed within the total resistance, and the type of power switch installed. His control is also of a general "audio" taper as well, which is the type that volume controls employ. But the taper is not exactly the same as that offered by original Fisher control. As a result, while the volume control's taper has nothing to do with the ultimate total gain of the unit, it does determine how quickly the available gain is brought into play with rotation. In comparison with the original control, Mark's control initially brings the gain up somewhat faster than the original one did during the first half of rotation. Couple that with today's hot FM signal, and you can end up with a receiver having the volume control operating "down in the weeds" when any FM function is selected, making the unit appear to have excessive gain (i.e., a hair trigger) when listening to FM.
It is certainly possible to install attenuators to reduce how hot the FM signal appears -- but while doing so makes the aftermarket volume controls operate much more manageably, they can also potentially limits the unit from being able to produce full power output on FM if the attenuators attenuate the signal to less than that required to achieve that.
I worked with one client to install attenuators on his 500B, as he was very frustrated with how fast the (likely) Oppat provided control installed in his unit brought up the FM sound. Of course, the amount of attenuation desired is subjective, since each person's perception is different, as are the sensitivities of the speakers they use. And, you need a total of three attenuator networks -- two matched ones for the stereo channels, and one separate one of different values to tame the FM Mono signal taken directly off of the Ratio Detector transformer. But again, this does nothing to add any gain for the weak audio output from your digital devices -- it can only bring the apparent FM signal level down to that of the digital devices.
Dave