Ampex 1200 / 1100/ 1000 erasure adjustments and checks

ERASURE ADJUSTMENTS for "Basic" Bias Cards
 (NOT purc bias cards...)

Please make sure to read the final notes section at the end !!

First you MUST have the machine correctly aligned in both Repro and Record.
It is essential that you have De-maged the machine very very well, and that 
you're going to use a "good" new-ish roll of tape for these tests and 
adjustments.  Make sure that the machine is nice and clean too !!


Note: Erasure adjustments should be made every time you change headstacks!

Next you need to put a blank reel of the same type of tape that you're 
going to use on the machine.  Feed an  1 kHz oscillator to all tracks 
of the recorder, and turn up the oscillator level so that you are peaking 
out all the machine's VU meters... say at +3 or +5 VU.   

Record this tone for about 4 minutes.

Rewind the tape, play back the beginning of the tone.  It should be 
pinning the meters.  

Stop the tape.   Now kill the 1 kHz oscillator tone.   Begin recording 
on ALL tracks.  Solo each individual track, one at a time, and listen 
for a background tone....  in a well performing machine, this tone will 
be either nonexistent, or way down into the noise level of the tape.
Make sure the machine is monitoring Repro while it's in Record !! 

If the tone is louder on some tracks, adjust the "Erase Peak" adjust 
trim-cap on the Bias Card, until you get the best erasure.  Remember 
you're erasing the tone and listening to the Repro mode...

Also listen for bias/erase related noises.  "Bias Gravel" is noise 
created as you record onto tape, due to slight inconstancies in the 
tape itself.  Your noise and "gravel" should be very low.  If not 
try adjusting the "Erase Peak" for the best over-all noise 
AND Erasure levels.

BIAS TRANSFORMER ADJUSTMENTS>>>>>

Now if all this doesn't get you very good erasure, you may have to 
adjust the 2 Bias Transformers located on the Bias Card....

You must get a PLASTIC ADJUSTMENT TOOL.  These can be bought at 
Radio Shack, and are often called "Slug tuners" or "Core Adjusters".  
They're plastic rods with Hex heads at the ends.

The transformers on this card adjust both the over-all Bias level 
and the distortion of the bias signal.  It's somewhat crucial that 
these are adjusted carefully and correctly.  These transformers 
must be set for the heads you're going to be using most often... 
24 or 16 track heads...


Always turn the machine OFF before pulling or installing cards!!!

First, if you have a Bias Extender Card, install the extender Card 
into the electronic bay, and install the Bias card into the Extender 
Card.  This will give you easy access to the 2 transformers.  If you 
don't have extender cards, you'll have to make slight adjustments and 
check everytime you've made an adjustment... a slow process.

Now Set the machine into Record, and select the "Bias" mode via the 
switch on the electronics bay.  Now adjust each transformer with your 
PLASTIC adjustment tool, until the VU meter reads it's maximum reading.  
Note that if the VU meter is either way too low (not around zero VU) or 
way too hot when reading Bias you should adjust the Bias Cal pot to 
bring the VU meter reading into a good area.

Adjust one, then the other transformer for maximum bias reading on 
the VU meter.  There is some interplay between transformers, so go 
back and forth and get the best reading.

Once this has been done, go back and redo the Erasure adjustment again.


Final Notes>>>>>>>

The bias frequency on most Ampex machines is 150 kHz  If you have 
major biasing problems check to make sure that the Master Bias 
frequency is correct.  If it's not, use the Plastic transformer 
adjustment tool and adjust the transformer on the Master Bias Card 
located in the Power Supply area.

Power Supply voltage is also important.  
              Check these and adjust if necessary.  

Most crucial of all is the correct alignment of the heads.  
If the tracks are ever so slightly mis-adjusted between the Erase head 
and the Record Head you are always going to have a portion of the track 
that will never erase.


The "Book" settings for the "Erasure Peak" level is an OK place to start.  
You should set the "Erase Peak" so that the VU meter reads maximum  
(in Bias Mode) for 16 track heads, and for 24 track heads, set it so the 
VU meter level has fell from the peak level by about 1.5 dB.  
Note that for 24 track heads you should see a "sudden" drop in the VU meter 
reading as you're adjusting the "Erase Peak" control clockwise.  
If this drop is more than 1.5 dB, you'll want to turn the adjustment 
counter-clockwise slowly to bring the VU meter reading back 
to the 1.5 dB area.


Some later series Bias cards have an additional adjustment pot on the 
card itself.  This is an adjustment that rarely needs to be adjusted, 
but it adjusts the noise level slightly .  Turn this pot one way then 
the other as you're checking erasure, and adjust for the lowest "Bias 
Gravel" noise... that is for the least amount to those small pops well 
into the background noise recording onto tape.


PURC BIAS CARDS >>>>>>>>>>>

The purc cards  are completely different, and do NOT adjust in exactly 
the same way as the normal bias cards.