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Pocketmags Digital Magazines

HOW TO CONVERT A BELL & HOWELL FILMOSOUND AMP FOR GUITAR PART THREE

We return to our Filmosound projector ampli_ er-conversion project for a third instalment – and things suddenly take an unexpected twist…
Most of these components are not required for guitar-amp purposes and removing them inally solves the noise issue

Last time, I signed off with my Filmosound working and passing signal, but also squealing and producing a lot of unwanted noise. Having done some research, it transpires this is a known issue with Filmosound conversions, because the green signal-carrying grid wire emerges from the chassis and plugs onto the top of the EF37A pentode.

With the amp bolted into a metal projector chassis, the cable would effectively have been shielded. However, the standalone arrangement allows the wire to pick up interference and send it straight down the audio path to be ampliied along with the guitar signal.

A couple of weeks prior to getting back into this project, I received an email from Tony Teixeira of Tex Amps asking how the conversion was coming along. I explained the noise issues and he said that I should remove the green wire connected to the EF37A grid and replace it with a shielded cable. He also suggested replacing the 33K resistor on the grid connector with a 47R resistor.

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