Bell & Howell Filmosound Find

Discussion:

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Scott McKnight

2004-04-19 16:25:28 UTC

Last Friday I found a Bell & Howell Filmosound audio amp in a pile of
trash beside the road. I know that these amps were discussed in AGA
back in early 2003. In that thread there was a mention of Bernard
("Bernie") Raunig and the fact that he had been converting a bunch of
these for folks including Colin Cripps. I'm wondering what might be
involved in getting this one up and running as a guitar amp. I'd be
interested in hearing the function of some of the more oddball (to me)
tubes on this thing. Here's a whole mess of digital pics:

Loading Image...

Loading Image...

-Scott McKnight

Phil Symonds

2004-04-20 02:09:14 UTC

Permalink

Post by Scott McKnight
Last Friday I found a Bell & Howell Filmosound audio amp in a pile of
trash beside the road. I know that these amps were discussed in AGA
back in early 2003. In that thread there was a mention of Bernard
("Bernie") Raunig and the fact that he had been converting a bunch of
these for folks including Colin Cripps. I'm wondering what might be
involved in getting this one up and running as a guitar amp. I'd be
interested in hearing the function of some of the more oddball (to me)
http://www.scottmcknight.com/FOSX1.JPG
http://www.scottmcknight.com/FOSX2.JPG
http://www.scottmcknight.com/FOSX3.JPG
http://www.scottmcknight.com/FOSX4.JPG
http://www.scottmcknight.com/FOSX5.JPG
http://www.scottmcknight.com/FOSX6.JPG
http://www.scottmcknight.com/FOSX7.JPG
http://www.scottmcknight.com/FOSX8.JPG
http://www.scottmcknight.com/FOSX9.JPG
http://www.scottmcknight.com/FOSX10.JPG
http://www.scottmcknight.com/FOSX11.JPG
http://www.scottmcknight.com/FOSX12.JPG
http://www.scottmcknight.com/FOSX13.JPG
-Scott McKnight

Scott,
No pix of the innards? My knee jerk (provided the iron is good) reaction is
to gut and rebuild using some of the more common tubes like 12A?7. Looks to
me like you've got a tube recitfier, a diode (kinda like a choke maybe?)
some preamp tubes with octal bases, maybe one with a nine pin base? Any
sense of what the OT is looking for in ohms? A two 6V6 amp could be killer.
I'm jealous. This is a good project for someone.
Phil

Phil Symonds

2004-04-20 13:10:31 UTC

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Post by Phil Symonds

And one more thought, if you decide it's not the project for you, I'd be
happy to discuss taking it off your hands. ;~}
Phil

Scott McKnight

2004-04-20 17:28:34 UTC

Permalink

On Tue, 20 Apr 2004 09:10:31 -0400, "Phil Symonds"

Post by Phil Symonds

Scott,
No pix of the innards? My knee jerk (provided the iron is good) reaction

Post by Phil Symonds
to gut and rebuild using some of the more common tubes like 12A?7. Looks

Post by Phil Symonds
me like you've got a tube recitfier, a diode (kinda like a choke maybe?)
some preamp tubes with octal bases, maybe one with a nine pin base?

I've since confirmed that some of those tubes aren't for the audio amp
portion. I think what we see that's audio amp is two 6V6s for power,
a 5Y3GT rectifier, an octal pre tube and maybe something else.

Post by Phil Symonds

Post by Phil Symonds
Any sense of what the OT is looking for in ohms?

I'll guess 8 ohms. Back when I had someone working on another
projector amp I found we guessed that A) the thing was meant for one
speaker only and B) speakers are mostly commonly 8ohm, therefore it
was 8ohm. I can think of amps that defy that logic. When the tech
did some output tests he did find that 8ohms was correct.

Post by Phil Symonds
A two 6V6 amp could be
killer.

Post by Phil Symonds
I'm jealous. This is a good project for someone.
Phil

And one more thought, if you decide it's not the project for you, I'd be
happy to discuss taking it off your hands. ;~}
Phil

Yeah, I have to figure out what I'm going to do with it. I could try
to learn to do it myself, pay someone else to do it, or sell it. I
should probably do option 1, though that would require more time,
space and tools (and brain cells) than I have these days.

-Scott

Who's Drivin?

2004-04-21 01:37:26 UTC

Permalink

Post by Scott McKnight
On Tue, 20 Apr 2004 09:10:31 -0400, "Phil Symonds"

Post by Phil Symonds

Scott,
No pix of the innards? My knee jerk (provided the iron is good) reaction

Post by Phil Symonds
to gut and rebuild using some of the more common tubes like 12A?7.

Looks

Post by Scott McKnight

Post by Phil Symonds
to

Post by Phil Symonds
me like you've got a tube recitfier, a diode (kinda like a choke maybe?)
some preamp tubes with octal bases, maybe one with a nine pin base?

Post by Phil Symonds

Post by Phil Symonds
Any sense of what the OT is looking for in ohms?

Post by Phil Symonds
A two 6V6 amp could be
killer.

Post by Phil Symonds
I'm jealous. This is a good project for someone.
Phil

And one more thought, if you decide it's not the project for you, I'd be
happy to discuss taking it off your hands. ;~}
Phil

You can do it Scott.
You may want to strip it, or put the iron in another chassis.
I said the other day in another forum, that you had whay you need for a
Champ clone. (I saw one 6V6)
Well you have what you need for more than that.
You could build a cool little amp out of what you got there.
Dave

Ether

2004-04-21 00:48:06 UTC

Permalink

Post by Scott McKnight
Last Friday I found a Bell & Howell Filmosound audio amp in a pile of
trash beside the road. [..snip..] I'm wondering what might be
involved in getting this one up and running as a guitar amp.

You'd be best off taking the transformers off and putting them onto a
chassis you can actually work in. If you look at the innards of this
B & H chassis, you'll see that it's the 1950's version of
miniaturization--everything is just crammed into the smallest possible
space. It's very difficult even to trace a single wire from one point
to the next.

Good luck trying to rewire it!

Also, the output transformer is tiny on these old B&H amps. If you
want any sort of volume out of it, you'll need bigger iron. The PT is
okay, as long as the insulation hasn't rotted off of the leads. The
capacitors on this thing are ancient, too, and most (if not all)
probably need replacing. The power tubes are probably worth re-using,
if they're still good.

Post by Scott McKnight
I'd be interested in hearing the function of some of the
more oddball (to me) tubes on this thing.

These amps typically have a 5Y3 rectifier, a 6-volt octal preamp tube
of some sort (6SL7 I believe), two 6V6 power output tubes, a 6V6 used
as an exciter oscillator, and an optical photosensor tube (used to
covert optical film coding back into sound--these were amps for a film
projector, after all). There ya go!

--E

Scott McKnight

2004-04-21 20:14:22 UTC

Permalink

Post by Ether

You'd be best off taking the transformers off and putting them onto a
chassis you can actually work in. If you look at the innards of this
B & H chassis, you'll see that it's the 1950's version of
miniaturization--everything is just crammed into the smallest possible
space. It's very difficult even to trace a single wire from one point
to the next.
Good luck trying to rewire it!
Also, the output transformer is tiny on these old B&H amps. If you
want any sort of volume out of it, you'll need bigger iron. The PT is
okay, as long as the insulation hasn't rotted off of the leads. The
capacitors on this thing are ancient, too, and most (if not all)
probably need replacing. The power tubes are probably worth re-using,
if they're still good.

Post by Scott McKnight
I'd be interested in hearing the function of some of the
more oddball (to me) tubes on this thing.

Thanks for the feedback. I kind of figured that part of the circuitry
and some of the tubes were not needed for a single channel amplifier.
I've also come to realize that the first step will be to strip the
thing. I've received pictures of the guts of one of the amps Bernie
Raunig made from a Filmosound. Once it's stripped and put back
together there's no where near as much stuff in there as there is
right now. Still you're probably right, it may be plenty of room for
an expert but not for me. You're correct about the tubes. Re: OT
size - I've heard a small combo made from a Filmosound (2XEL84
version) used on stage with a rock band in a 200-seat club and it
sounded mighty fine, and seemed to be sufficient for the guy playing
it, though it *did* require mic'ing.

Thanks again,
-Scott McKnight

Ether

2004-04-22 17:10:06 UTC

Permalink

Post by Scott McKnight
Thanks for the feedback.

No problem!

Post by Scott McKnight
I kind of figured that part of the circuitry and
some of the tubes were not needed for a single
channel amplifier.

Especially not the photosensor! But it would make a cool light
show...

Post by Scott McKnight
I've also come to realize that the first step will be to strip the
thing. I've received pictures of the guts of one of the amps Bernie
Raunig made from a Filmosound. Once it's stripped and put back
together there's no where near as much stuff in there as there is
right now. Still you're probably right, it may be plenty of room for
an expert but not for me.

The biggest problem will be mounting some sort of terminal strips in
there. I suppose you can use the ones that are already there, if
they're still solid enough. Also, make sure the tube sockets are
intact before you start--removing them later will be a massive
headache, since they're riveted and would require drilling out. It
also goes without saying, but...you should put some time into
designing your physical circuit layout beforehand, snce there's not
much room to correct any mistakes.

Post by Scott McKnight
You're correct about the tubes. Re: OT size - I've heard a
small combo made from a Filmosound (2XEL84 version) used on
stage with a rock band in a 200-seat club and it sounded
mighty fine,

Cool. EL84's are hard to make sound bad. But if the B&H EL84 OT is as
small as the B&H 6v6 OT's I've seen, I'd invest $20 or so in a larger
OT--it will really open up the sound.

Post by Scott McKnight
and seemed to be sufficient for the guy playing
it, though it *did* require mic'ing.

You won't find many 2 x 6V6 amps that *don't* require mic'ing! (In
anything larger than a living room, that is.) I just saw the Beach
Boys last weekend; one of their guitarists used a vintage Deluxe
Reverb (2 x 6V6), mic'ed of course, and it sounded great. You be
hard-pressed to fit an entire blackface Fender circuit into that B&H
chassis, though! (But I suppose it could be done--if you add some
9-pin tube sockets.)

--E