Fender Deluxe Style Amplifier - 15 Inch - 40+ Watts - Push-Pull 7591 With Fixed Bias

Last crawled date: 1 year, 10 months ago

Cabinet CNC router cut from 3/4 and 1 in. Purebond plywood (viewed from front the sides appear to be 1/2 in.), oak, and CNC plasma cut 0.075 in. cold rolled steel chassis. CAD files do not include clearances added latter in CAM unless noted in part name. Easy 90 deg. bends. Assembled with Titebond Supreme glue and 8 pocket hole screws (speaker baffle).

Update: 1 in. oak plywood top to better support the heavy amplifier chassis. Cabinet photos show speaker and amp chassis in place during test fit. Includes DXF with unfolded chassis. Added (probably unnecessary) glue blocks and supports.

Intentional material protrusions or interference that appear to be design errors require manual trim and/or sanding to match adjacent surface and (limits machining to 3 axis with few tool changes). 3.3 deg. sloped front and speaker baffle. Finger joints cut with 0.125 in. end mill with 0.0625 in. radius dog-ears for tight fit. Note different height front trim, which are visually equal (after cabinet is covered) due to the 1 in. top and 0.75 in. bottom panel thicknesses.

Amplifier uses parts from Hammond A0-63 chassis (B3, et. al.) including transformers, chokes, tube sockets/shields, etc. Photos don't show several shields (near chokes and rectifier) and an additional tube/socket that will be installed. AC power cord (shown in a temporary bracket) will move. Tube order was backwards when chassis was cut (but noise hasn't been an issue) and has since been fixed in the CAD file. Yeah, those are big transformers... The amp chassis does not require ends (in file) unless formed from thin metal.

Compact (but heavy) kick-ass amp with dual 7591 push-pull output (550V plates, 500V screens, and -50V to 0V adjustable fixed bias), 7247 (or 12AX7) cathodyne phase inverter/final pre-amp, 12AX7 preamps (one with cathode follower for tone/volume section) and tremolo oscillator, and single GZ34 rectifier. On bench it's output 38 to 51 watts with best THD if less than 40.

Schematic will be posted when created (designed as it was built). Circuits are nothing out of the ordinary except (Fender has done this at least once) tremolo targets a pre-amp stage instead of output tube bias.