Ampex Transport Alignment

Ampex 1200's and 1100's share a very good design philosophy on their transports: 
that you should be able to align the thing WITHOUT great technical expertise, 
and WITHOUT expensive tools.  That's very, very cool.  

So you should be able to make small adjustments or to fully align the transport 
without hiring a tech, and once you get to know how to align your own machine, 
you'll get to know when things aren't working as they should: 
   and that's the only time that you'll have to get a good tech in.

The purpose of this whole section is to teach both techs AND 
studio owners / engineers how to adjust the Ampex Tensions systems so the 
machines run at their best.  The adjustments are EASY to do, but 
I'd like you to know what you're doing...  

First I'll give a basic description of how the Transport System is 
designed to work. PLEASE READ THROUGH THE ENTIRE ARTICLE !!!   
I know you want to jump right in and start turning pots, 
but go get a cup o' joe, and learn something about your machine FIRST.
In fact I'm going to link the pages of this area together, 
so you have to read each page to get to the next!!


The Ampex 1100 and 1200 series recorders have just ONE servo system 
for the transport. (yes there's a Servo for the capstan too...)
What this means is that the whole Servo Control System  controls only 
ONE of the two reel motors at a time...

In Play, Stop and Fast Forward, it's the SUPPLY Motor. 
In Rewind it's the TAKE-UP Motor.  

Note that there are small differences between the MM 1100
Tension Control Card and the MM1200 Tension Control Card:
the MM1200 card engages the brakes in the STOP mode 
(eliminating any possible tape creep...this is good), 
while the MM1100 card uses just the tensions to stop the tape,
and if those tensions are not set correctly, you can get a 
bit of tape creeping in the stop mode, not a big problem.  
You can modify the 1100 card to work in 1200 units, and vice versa.

In all modes the NON-SERVO'D MOTOR is set to one given torque
for each mode of operation,and that's it, it ELECTRONICALLY 
does NOT change.. now of course if you remember your physics, 
the torque will change physically since the diameter of tape on 
the reel is changing...  more torque at small tape diameters, 
weaker torque when the reel is packed full of tape.


But the TENSION SERVO is controlling only ONE motor.... 
the TENSION of the SERVO'D Motor is changed as the diameter
of the tape on the reel changes, so in essence, the tension
of the SERVO'D Motor is ALWAYS THE SAME, regardless of the 
amount of tape on the reel.  That's what the whole thing is
about....  constant tension. 

When there's a full reel of tape on the Servo'd motor, 
the system electronically tells the motor to Increase the Tension, 
when there's little tape left on the reel the tension system tells 
the motor to supply less tension... the result is exactly the 
opposite of the physical tension changes due to the changing tape 
diameter, and this them means the Servo'd reel's ACTUAL tension 
remains the same regardless of the amount of tape on the servo'd reel. 


There's a Tension Bar on the Left Hand side of the tape path,
just before the Tape enters the headblock.  Underneith the 
bar is a mechicanical system that is attached to the bar.
In essence it's a small cut-out that allows light from a
bulb located under the bar to shine through onto a opto-sensor.
If the Bar moves in either direction, the sensor detects more 
or less light, and this sends a signal to the Tension Control
Card to increase or decrease the drive current to the Servo'd
Motor.

    Photo #1 : Tension Sensor (with cover removed)
     NOTE: The original and correct lamp is a # 376 lamp
You can use a more common # 327 lamp but you MUST realign the transport system !!!

Best is to purchase and only use the original #376 lamp...

Note that the WHOLE Tension SYSTEM RELYS ON THAT LIGHT BULB !!!!

If that light burns out (and it will) then your whole
servo system cannot work properly!!!  I can't tell you
how many times junior techs call me with pleas for help 
'cause they can't align the transport of a 1100 or a 1200 
recorder, and they've #1) never given a thought how the
Servo System works (they just start turning pots..) and
#2) they never check the light bulb!!!  duh...

Hey.. you can SEE IF THE BULB IS WORKING... 
                   there's light or none at all!!!