Latest amp build--in a Maestro cab

[rfgordon]

I delivered this Saturday. My apologies for no gut shots, but it kind of came together quickly so I could get it to the client. He went from my house to a recording studio with this beast.

He brought me the cab and the original chassis and a bag of parts that he had gotten "years ago from a friend of my dad's who tinkered with electronics." The chassis had been semi-gutted already. The pots dated it to mid 1961, but the layout of the amp was nothing like any Maestro/Gibson/Epiphone schematic out there. I'm guessing it was a "transitional" model.

My buds at the sheet metal/roofing shop did a great job of duplicating the chassis. In this cab the left and right edges slide into grooves cut into the wood. The right side, however, (looking at the back) was broken off, so the chassis couldn't stay put. The guys fabricated a little metal brace that screwed right up in there to create a new groove. Most excellent!

I was able to use the PT, but I chose an 8 watt prototype OT I'd gotten from Matt at Musical Power Supplies. This turned into sort of a 5F2 with a choked power supply, though with some subtle but significant differences.

First off, the Rk for both gain stages is unbypassed 2k2. Coupling cap into the volume pot is 0.0048 white Mallory, and the cap into the 6V6 is a 0.022 yellow M150, with a 10k grid stopper on the 6V6. V1b has a 220k grid stopper. V2 Rk is 250 ohms w/ 100mF bypass cap. 100 plate R on both 12AX7 sides.

The B+ is only 275 on this beast, so it's very "brown." It's designed to be dimed--and boy does it shine there!! Thick, rich, creamy overdrive that is magical and truly addictive to play.

All into one of the new Weber Chicago Vintage 10" speakers with the chemically aged cone. Sounds gorgeous right out of the box.

The layout was a bit awkward, since he wanted to keep the bell cover. I enlarged the baffle hole from 8" size to suit the 10" speaker. Everthing did fit, and it sounded wonderful, once I figured out the 6V6 in there first was bad sounding.

He didn't want to spend any money on aesthetics for the face plate, but I did find some nice knobs from a 1961 Harmon Kardon PA amp for it.