Crawls Backward (When Alarmed)

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What's the Sound of a Filmosound?

We welcome to the workbench yet another old amp destined to (maybe) get a second life. I now have a small collection of amps like these, so it's probably about time I start in doing something with them other than taking a quick look-see, yes?

This one is way cool. It's a Bell & Howell "Filmosound" amp. You may know Bell & Howell from the film projector business. If you went to public school in the US during the late 40s through the 70s, you may recall classes in which you were shown films. Films on virtually any topic imagineable. I remember some history and science films, and even some in shop class. Usually the teacher wheeled in a projector on a cart and set the thing up and started it running. If your teacher wasn't real technical, some lucky dude (ahem) might have even gotten to Run The Projector.

Some schools even had an "Audio-Visual" or "A-V" person or department. Those folks were responsible for the setup and maintenance of projectors, record players, tape recorders, etc.

As I recall, quite a few of these films were 16mm. Films as shown in theaters were 35mm, and 16mm was for the serious amateur, or education. A number of feature films, it turns out, were also printed on 16mm film for use by smaller theatres or the semi-wealthy homeowner for his or her own use.

Which brings us to my amp. Not that I have a small theatre or am a semi-wealthy homeowner.

This amp came out of a 16mm Bell & Howell 'Filmosound' Model (I think) 179 projector. The whole projector was for sale, but it was missing some major bits and the seller said "make me an offer if you just want the amp," so I did and here it is.

Dig that way cool logo. It's hard to tell in the pictures, but the nameplate is a sort of greyish-blue. Totally rockin' also.

B&H made a whole line of 'Filmosound' projectors from the 1930s through the early 80s as far as I can tell. The early ones were tube, and the late 60s-onward models were solid state. The easiest way to tell the tube models from the later ones is by the model number. The tube models are three digit (1xx, 2xx, 3xx) and the transistor ones are four digit.

Naturally, we only care about the tube ones. Heh heh heh.

This one has push-pull 6V6 output tubes and a 6J7 input. The rectifier is a 5Y3. There is also a photocell circuit with another 6V6 and a 988 (I's not in front of me right now as I write this). I'll ditch that part when I get it going.

The EIA date code on the volume pot is "304504." The 304 means it was made by Stackpole. The 504 translates to the last digit of the year - 1955 - and the 04 is the 4th week of that year.

I'd think with those output tubes it would be around 10 watts or so output. Fairly healthy, and it could easily drive a couple of efficient speakers to pretty high levels.

I wanted to do a quick run-through to see if it even worked. I didn't see anything burned or otherwise wrecked so I thought it would be reasonably safe to turn it on.

It is, however, missing the cap for the fuse holder, and of course the fuse itself. Hopefully this is not a sign that something major is wrong and someone ditched the cap in hopes that no one would just plug it in.

The missing cap is no big deal, I have a bunch of vintage fuse holders just waiting to be reused in New Amps I May Build. Having a bunch of these on hand is either nuts or is really thinking ahead, depending on your outlook.

There also is no power cord - there is a 2-prong male jack on the chassis that a proprietary cord connected to. I just took an AC cord I have that terminates in 2 bare wires and hooked it up with jumper cables for testing. Put a fuse in it (I used 1.5 amps) and connect it up to the Variac.

On the front end we have my little Walkman FM radio going to the input.

I gradually brought the amp up on the Variac while watching the ammeter to see if it starts to draw a lot of current - which would mean something is shorted or worse. At about 80 volts, I got a lot of hum (filter caps are bad) and a squeal that varied with the position of the volume control. At that point, I shut it off.

The good news is it doesn't seem to have any major issues, but it will need a rebuild. Looking at the bottom of the chassis gave me a headache - it's very compact and some components will be a pain to get to. But it should make a cool amp when I get around to working on it. For now, onto the Shelf Of To-Do Projects.


Post a Comment 5 comments:

  • Unknown said...
    June 21, 2016 at 10:59 AM
    wow very nasty amp! I would like to know how this babe sound with a smokey blues guitar!
    Did you find a schematic of this anywhere? I could be very interested in! Let me know.
  • Yr Fthfl Blggr said...
    June 22, 2016 at 7:11 PM
    Hi -
    I didn't find a schematic for that specific model.

    To be honest, the amp is way back in the project queue. Whenever I do get to it, I'll probably convert it to a Fender-style circuit but keep the Filmosound transformers.
  • Anonymous said...
    July 21, 2016 at 6:49 PM
    Thank you very much for your answer dude!
    Actually I've found the schematic after a lot of research! It's seems very interesting...It can be modified to sound better with a guitar...but I suggest you to do not upset too much the original schematic because the vibe is hidden in its architecture! If you will turn it in a Fender will just sound like many other amp!
    If you are interested in the schematic let me know your email somehow...I can send it to you! ;)

    Cheers mate,
  • ian vandenberg said...
    June 15, 2017 at 3:43 PM
    its a filmosound 179 i believe
  • Yr Fthfl Blggr said...
    June 18, 2017 at 10:02 AM
    Thanks for confirming, that's what I thought it was.

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