Cinerama Servo amplifier

[Bill Ryan]

Can anyone please help I am looking for the circuit diagram for the Servo amplifier that controls
the differential drive. This was a valve amplifier that sat in the control rack next to each machine. These were used only on the early installations, that is with Century D projectors.
Cheers Bill.

[Mark Gulbrandsen]

Probably your only chance at getting those is to look up the Cinerama Patents on line and then see if that is among them. The three locations that I have been in here in the States.. Salt Lake City, Chicago, and the set up that was in Dayton, all used 3-phase motors driven off a master 3 phase generator. I honestly never heard of them using any sort of servo - differential drive.

[Bill Ryan]

Hi Mark,
thanks for your reply, from what I know only
the early installations used the servo control.
Attached is the block diagram of the system
I am talking about. Hope that this helps. Only
about the first 30 installations used servo control
the later installs used selsyns as you described.
I have had a look through the patents but I have
not found any information about the servo amps.
Cheers,
Bill.

[John Eickhof]

it appears that due to the number of selsyns the amplifers were used to boost phase lock strength, the early selsyns had a 120v secondary, later selsyns had a 55v secondary and would hold lock easier, also, the early selsyns were 1800 rpm, later it was found that they would hold lock better at 1200 rpm or less thus the need for amplifiers was eliminated w/ gear or drive reduction of the later set ups, just like sound dubbers and other studio synch equipment. the servo amplifier would probably compare to western electric phase control that was used on the early 1A universal base, it took 1ph and made a 3ph signal and supply voltage to the dive motor and by phase shift it gave variable speed. Like nark says, I have seen three different cinerama setups here in the us and all were later selsyn drives w/ selsyn speed of 1200 rpm and timing belt drives.

[Jim Cassedy]

That early drive arrangement with the servo amplifiers John describes sounds very interesting.
I'd sure be curious to see the original drive amp circuitry if schematics ever turns up. I've only
seen a couple of partial Cinerama set-ups back in the mid 1970's, that were still in place at
an old theater, but were being cannibalized for parts, so they were incomplete. But these
systems appeared to have Selsyn motors that were chain-drive-linked to the main drive motors
and more or less kept all 3 machines, & the mag sound racks, in sync more or less by brute force.

There actually happens to be a Cinerama™ projector, complete with lens, big lamphouse
& oversize reel magazines that's been listed on e-bay for some time. Here's some pix:
CineramaProj_1.jpg

The machine appears to be missing the main drive motor, but
this is similar to the machines the old machines I described,
which had a drive motor to run the projector, which was held
in sync by a separate Selsyn motor with a chain drive that
kept all 4 machines in sync by mechanical 'brute force'

CineramaProj_2.jpg

It's even got the little CINERAMA logo on the door.
CineramaProj_3.jpg

BONUS PICTURE:
Just for fun- - if you're looking for a Cinerama screen there's
also one listed on e-bay. . . . sort of- - it seems to be several
hundred strips of Cinerama screen material- 1"wide by 18' long.
You'll just have to untangle the mess & come up with a frame!
CineramaScrnStrips.jpg
(the shipping charges listed on this are actually more than the
seller is charging for the "screen"

[Bill Ryan]

Hi all,
In the original system all 3 machines and the reproducer/rubber were driven by 3 phase sync
motors this drove a differential gearbox which enabled the operator (manually), the console operator (remotely) or the differential drive motor (automatically) to advance or retard the projectors
relative to the sound reproducer. I will attach a picture of the differential gearbox with the differential drive motor sitting on top. This drive motor is driven from the servo amplifier. This system worked very well and everything was normally in sync when the machines were up to speed. Please note that this machine also has a selsyn attached from the flywheel in the bottom of this picture.

[John Eickhof]

very interesting, obviously the differential reduces output speed to a good selsyn lock range, i assume to lower unit is the drive motor? where does the belt from the projector go? i like the 'lathe' hand wheel! i would suppose for inching and frame setting...sure wouldnt want OSHA or the electrical inspector to see that set up! later selsyns could be operated in parallel by the dozens because of the x-y-z secondary, i still have some selsyn synch meters that monitored the phase legs and would indicate any phase shift, they are for 120v selsyns with 55v secondaries though. we used them in permanent 3D set ups. they measured any slight lotage variations between phases.

[Bill Ryan]

Hi John,
The hand wheel is the advance/retard control which is I turn driven by the differential servo motor above it. The interesting thing about this is
when the hand wheel/ servo is not turning the drive is one to one. The drive ratio is only advanced or retarded whilst it is turning.
Refering to the block diagram the error signal
is sent from the selsyn transformer as a two
wire signal, to the amplifier and then to the servo
motor to advance or retard the machine.

[Jim Cassedy]

the error signal is sent from the selsyn transformer as a two wire signal,
to the amplifier and then to the servo motor to advance or retard the machine.

Ahhh! Now I I see, and that all makes alotta sense!

[Mark Gulbrandsen]

All this was for was to remotely frame the projectors from the control console that resided in the auditorium down stairs for the first 30 or so systems as Bill mentions. Cinerama did have issues with keeping the framing, and hence horizon, the same on all three projectors due to the extreme angle the system could see. This framing job was later turned over to the projectionists to control it right from the booth. All the Cinerama 35mm heads I have had either had the standard framing knob, or a lever affair that stuck out on the operators side so the operator did not have to reach around the front. All three of the 35mm Cinerama heads I had were converted for a new 3-D system Chris Condon of Stereovision was working on. Also note that 70mm Cinerama heads had all 70mm only sprockets.

[Mark Gulbrandsen]

The best 3-strip system was still Cinemiracle. It did not require any gigolos. They blended the image joins at the by using micrometer adjustable mirrors, and just let the light fall off the edge of the mirror. The three in the picture were for sale a few years ago, but are likely gone by now. A guy I used to work with father was head of engineering for Cinemiracle.

[Bill Ryan]

I will put up some more photos of Cinerama
equipment if people are interested. Just let me know what you would like to see. Here is a
Couple pictures of the jiggle-o.

[Jim Cassedy]

I like the under-slung feed magazine, Mark. The projectionists didn't have to risk pulling a back
or shoulder muscle slinging those big reels up to a feed spindle on top of the projectors. I Wish
I'd had something like that for the 70mm "Licorice PIzza" run last year!
(My feed spindles here are 7ft above floor level. Reel 4 (over 60lbs) was really a b-tch! )

BigReelPic.jpg/

[Bill Ryan]

Hi everyone, AA32D152-9566-4120-BA37-93F8387469FD.jpg C073DA7D-B4CD-4DC5-9A6A-6212DF95249A.jpg
these are a couple of pictures of the jiggle-o’s in a
3 strip head. This is a D series machine (based on
a C series Century machine). The picture that Mark has posted is of a later machine based on an (A series Century machine).

[Bill Ryan]

Cinerama actually made a device for lifting spools
but required removal of magazine doors. CD9C7923-0ACE-46D0-93EF-9170667C2604.jpg