0 - A Filmosound Projector

Author: sgeorge, Posted on: 10 June 2021 07:58

Whats another project or two between friends?

Today we picked up a Bell and Howell Filmosound Specialist projector, Model 399AV.

To start with, the amp inside the 399 is the same as the amp in the Model 385, so that is what everyone knows it as, if you want to start googling it.. 385..

The goal is to turn this into a neat little guitatr amp. The kicker is, I dont know what version of the tube amp is inside it.

(These photos are the sellers).

That is either, GREAT or FANTASTIC as there are two designs it could be.

So the very common GREAT option is a paired 6v6 tube model. This is what I expect.

The FANTASTIC option is the much rarer version that usees EL84 tubes, this is the more sought after one, but here in North America you usually only find them in Canada rather than the United States.

So I'd love it if it was an EL84 version, but the 6v6 version is what I am setting myself up for.

I specifically hunted down a 385 variant model because not all of these old Filmosound projectors can be easily used, some of them are known as Widow Makers because they have no isolated transformer, they just pump wall AC directly to the tubes, and if you plugged in a guitar, would have 120vac ac wall access right there on your strings. A Very Bad Idea!

Because we are going to repurpose an amp from the 1950's, there are several things that need to be done to it to 'bring it up to spec' so to speak.

  • Replace power with 3 prong IEC
  • Earth ground chasis
  • Replace output jacks with 1/4" jacks
  • Replace on/off switch + fuse to be inline with hot
  • Replace all capacitors
  • Remove unused parts (like the oscillator + projector lamp circuitry)
  • Bias new tubes
  • Trimpot the negative feedback loop
  • Convert to a head enclosure.

I've read the horror stories of the insides of these amps, being crazy cramped and a real pain to work on, so we will just have to take our time and tease it apart.

tags: Amp, Audio, Guitar


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