Many of us have seen the great info by @robrob on building a bucking transformer to drop B+ to at or near vintage levels. A nice 1998 article by R.G. Keen on the "Vintage Voltage Adapter" explains how it works and shows a couple of options and useful schematics. I've thought about this for a long time, since I've built three tweeds, a brownface, and two blackface-era amps that were not born to run on 120+VAC, and even with lowered-HT power transformers I was often higher than schematic on my B+. Rob very helpfully shows how to build one in a 3-gang plastic switch box, which is handy since you really want a duplex outlet cover -- and I couldn't figure out how I'd do that if I used say a Hammond chassis. As suggested by Rob and Mr. Keen, I wanted a duplex outlet with wall voltage on one receptacle and switchable, reduced voltages on the other. As Rob advises, I used a Hammond 166N12B (12 volt 4 amp) transformer. The hardest thing was actually finding a 3-gang wall plate laid out blank/blank/duplex. Even if I could find one, the standard plastic wall plates are very brittle, and I wanted a power switch *and* voltage selector switch *and* power indicator light, and it would be handiest if they were on the front/top, and drilling holes in a brittle plastic switchplate would be both difficult and pointless. Top tip -- an outfit called Mulberry Metal Products makes steel wall plates in blank/blank/duplex. The only problem is sourcing one. I finally found a retail source, but they took three weeks to ship, so I'm not recommending them. Being metal, and having the switches and lamp mounted on it, I decide I'd better have a ground anchor on the wall plate. Luckily, it turned out to be nice and rigid, yet easy enough to drill. Drilled 1 x 11/64" for the ground anchor, 1 x ¼" for the mini-toggle, and 2 x ½" holes (light and power switch) -- the latter are easier with a step drill. Note clamp... The plastic boxes often come with 'nailing ears' to mount on studs, but those're super easy to cut off with a hacksaw. I suggest you compare boxes for total cubic inches -- a bit deeper and roomier makes this project easier. Recall a standard Heyco strain relief doesn't require a 'double-D' hole -- they also fit in a 5/8" round hole. That's an extra great reason for a step drill, which also makes the hole both tidy and easy. Note blue tape 'depth guide.' I used a beefy SJT cable which even more than SVT really rewards your imitation Heyco strain relief pliers... Also drilled a few 11/64" holes for #8 mounting bolts. The transformer takes up a surprising amount of space in the box, but arranging the primary and secondary leads just right let it sit flush on the floor between the Romex wiring 'doors.' I was going to use a Fender style fuse holder, but found there was room for the inboard kind instead. And this one on Amazon came with screw-down wire clamps -- Rob points out we're doing wall-style wiring here, and I decided less soldering was in order. With a 4A transformer, Rob notes you should use a 4A slo-blo fuse.