Bell & Howell Filmosound Conversion
After reviewing a Filmosound projector amplifier that Andy Drinkall of Oldamps converted for guitar use, I couldn’t resist trying to do one myself.
These amps are renowned for the sonic quality of their transformers and the cramped conditions inside the chassis, but it was well worth the effort.
Ready for action!
Whether you’d describe this as a rat’s nest or ‘point to point’ wiring probably depends on whether you’re buying or selling.
Space is very tight inside the chassis, tracing the circuit is far from easy and replacing components is even harder.
The component choice indicates this amp was assembled in the UK using a chassis and transformers that came from the US, so it runs at 110V.
The speaker connectors and power socket are archaic and will be replaced.
The value of the tubes arguably exceeded the purchase price of the amp itself, so it was well worth the risk.
Filmosounds contain a lot of circuitry that isn’t needed for guitar use and this brown capacitor and large inductor can be removed.
With the surplus components and wiring removed, it’s much easier to access the mains wiring and replace the Jones socket.
A new IEC socket has been installed, the switch and fuse have been moved over to the live side and the no-longer-required yellow transformer wire has been isolated.
The new speaker sockets will need to be labelled for 8 and 16 ohms and the IEC socket squeezes in between the 110V voltage label and fuse socket.
These silver capacitors in the tone circuit had to be temporarily removed for a pair of Jupiter caps to be installed.
Another Jupiter capacitor is used in the preamp and shifted to the side, where there’s more space.
A selection of the components and hardware that have been removed so far.
The old jack socket has been removed and the superfluous resistors and capacitors wired to the lamp socket are about to come out to create some space.
All the components are taken off the lamp socket and the shielded grid wire is soldered to a new muting input jack. The braided wire should be covered in heat shrink or you can use plastic insulated shielded cable.
Sometimes, amp restoration and upgrading is more about removing circuitry than adding to it.
The original cathode-bias capacitor is disconnected from the 6V6 sockets and a new one is soldered across the sockets in parallel with a 330R resistor.
These two yellow capacitors replace the originals and the tone control’s functionality improves dramatically.
This yellow 120pF capacitor wired across the volume control extends the Filmosound’s upper-frequency response at lower volume settings.
There’s just enough room inside to squeeze in an LED pilot light.
With its chrome bezel, the pilot looks the part and I can tell at a glance if the amp is switched on.