I have a Marshall JMP 2203 Master Model Lead 100w Mk2 from 1979 with two 65W speakers and on club gigs and at rehersals was way too loud. That kind off amps start to perform best at 3/4, i used to play at 1/4 or less. USED TO!!!
With SPL REDUCER i finally have true hot tube sound of this excellent amp even in my house. I have SPL for two days and as far i played with it I think its really minimal change of sound even at bedroom level. Check yourself some videos about SPL and you will see like i did. Its great it is pasive. It gets hot so have a beer and your fingers away and wait until tubes and SPL cool down.
It looks very cool, solid. Considering the impedance setting knob is at front panel near two other volume knobs, be carefull not to change them in the dark. Don't set impedance while operating!!! I put some tape across it for safety!
If lost i would buy another!!!