Filmosound amp-story

a long time ago i scored an amp from a Model 601 Gaumont-Bell & Howell 16mm movie projector. It took a while to discover exactly what it was. i thought it was a North American amp because the power supply was designed for 110vac. but it turned out to be British.

I took it to a technician to check over before using it...decided to convert it to 240vac (australian mains power), replaced some capacitors...removed a bunch of circuitry which related to amplifying the film soundtrack via a light-sensitive tube. these units are very crowded inside, so getting shut of the unnecessary parts was helpful.

the parts which came out of the amp were date-stamped July 1948

it uses a 5Z4 rectifier, an octal pre-amp tube (6J7), a 6SL7 phase inverter and 2 x 6V6 tubes in the power amp. i believe its puts out around 14w.

modified the tone circuit which was originally a treble roll-off. now has separate bass and treble, plus a custom circuit board which allows some additional shaping of the tone. essentially allows fine tuning of the tone across 6 separate frequency ranges, which are then controlled by the bass and treble pots.

made new panels for front and rear, and made an aluminium cowling to go over the top.

also put 2 inputs (hi and lo), a line out, provision for a footswitch and an fx loop. the new circuit board is isolated from the rest of the amp and runs off the 6v heater filament power supply

it also has 16 ohm and 8 ohm outputs

Photos:
http://www.dropbox.com/gallery/28259795/1/Filmosound?h=411ad5

i plan to run it into 2x8" weber speakers at 1st, in a 16ohm configuration, but i haven't got that together just yet, and the amp still needs a baseboard to make it safe...it runs about 590v on the live connections

but tested it today through an 8ohm 4x10 sovtek bass cab. the 1st time its been tested through a stage-type rig...although i think this bass cab is probably not ideal. plugged in my CM mic

i am pretty happy with the sound i think. obviously will still tweak a bit, but its plenty loud and sounds pretty musical.

BUT...i really didnt know what i was getting into with this...for the money this turned into, i could have imported a really nice harp-specific boutique amp like a HG double trouble. if you can do your own work, its probably more economical, but this has been a very long and expensive road. you get to a point where you have to decide to either accept the loss and quit, or see it through and hang the expense. i decided to go ahead because i figured i can always sell it if i need to. for this reason i resisted the urge to use my name on it anywhere. it is called "Harpman 15"

as it is, i think its gonna turn out to be a cool unit, and its a one-off. the finish will be important though.

oh...and the other thing is that there are now a lot of expensive and somewhat difficult-to-comply-with safety regulations for electronic equipment, which need to be taken seriously. these can particularly impact insurance coverage, especially if you want to use your custom amp in someone's venue for instance.