While the idea of a regulated DC filament supply is pretty superfluous to vintage amplifier designs such as that Tweed Bassman you're playing, in some high-gain amplifiers the implementation is not without merit. Mesa Boogie have used the idea with good results. If you like using a VariacTM with your vintage Marshall, a regulated filament supply is a worthwhile add-on. Of course, you'll need to add the DC filament power supply. This will mean drilling holes in that collectible amplifier, and finding a spot to add the power supply circuit board. Next, careful lead layout will have to be followed. Is it worth it? Not to me personally, but the article is presented for your consideration none the less.