On the Plexi 50W Nrml amp model there is no audible change when activating the bright cap, even with huge values. Checked using both the latest Axe-Edit and the front panel. You can change the values but no change in sound at all. I haven't played with this parameter on this amp for a while but I'm sure the bright cap had an effect in previous firmware revs (as that was the setting I used).
Now this model sounds different to the Plexi 50W Hi 1 model (which I assume is the 2nd channel/input from the same amp) when the latter's bright cap is off so you can't replicate the Nrml + bright cap with another model (i.e. if these 2 models were basically the same but one was with bright switch off & the other on).
Now this model sounds different to the Plexi 50W Hi 1 model (which I assume is the 2nd channel/input from the same amp) when the latter's bright cap is off so you can't replicate the Nrml + bright cap with another model (i.e. if these 2 models were basically the same but one was with bright switch off & the other on).