Posted this at beans last night, nothing more to add...
Hundred dollar challenge at Wattkins, could they do a tube amp using new off the shelf parts, except for the obsolete tubes and sockets, for less then $100. Evolved into the 'Savage Croaker' (their name) which uses a 6u8 Triode/pentode preamp and a 6aq5 (mini 6v6) power amp.
Started this four years ago at the same time i started it's 'civil' twin, an Octal One with 6aq5, uses the same power supply i contrived as well as the same component values around the 6aq5. Did the eyelet/tube board in 2011, the PCB's were done in early 2012, painting the chassis took years of stops and starts. Many bad ideas and corners to squeeze out of.
Much louder then the Octal One. Power supply voltage doubles the 120v secondary of the HV transformer then splits to a power scaled circuit for the power amp and 230v regulator for the preamp which has seperate feeds for the triode and pentode sections of the 6u8. Tried something different for the heaters, uhave same current demand so put them in series and
current regulated the dc heater supply with an LM317 to 350mA.
Cut the top stencil from frisket film, tried black on black first, no good, redone with white, legending done with dilute gouache paint and a lining/ruling pen. Sprayed with the waterbased sanding sealer, counterpoint to the lacquer i use and it turned the chassis milky/hazy and crazed. After hiding the belt sander packed things away for awhile to breath and wait for my first inclination to pass. Figured i had one chance at redemption, painted the steciled letters with liquid frisket, loaded the lining pen with the liquid frisket and traced over the legending. Reshot with as much black as i could and still be able to see the silver checkerboard... belt sander can stay packed, it worked ok.
Extremely quiet, much louder then the Octal One, great crunch, haven't found the clean yet, few quibbles to sort out but pretty decent and another project off the backlog that has to be eliminated before moving on to something new.
Mostly power supply not much for the actual amp. Mode is a rotary switch that controls the tone stack and a gain cap on a preamp stage- neither/either or both.
Cheers
dave
