This instrument was acquired in the early seventies, most likely
around 1971. It was an electromagnet system opeerating at 100 MHz
for proton using a 15 inch magnet. Originally only a CW instrument,
the FT system was added later. It was capable of doing proton, carbon,
phosphorus, fluorine, and boron NMR. It had both a deuterium lock
and an external Fluorine-19 lock. It was mainly used for proton and
phosphorus experiments. Some flourine but not much boron or carbon
due to the low sensitivity of the system.
The system was rather large and occupied about a third of a big lab
room. Above you see most of the system. Left to right:
computer, auxiliary console, teletype (not really visible, but below the
vertical conduit and light switch), main console, power supply (below the
red fire blanket cabinet), magnet, and sample prep table.
In the room through the door visible above the magnet was the heat
exchanger/chiller which kept the magnet and the power supply cool.
The computer was 16K ( I think, if not it was only 8K) made by Varian, and the program was loaded via the front panel switches and the paper tape reader on the teletype. We had only one copy of the tapes which would actually work. All attempts to copy the tapes failed to give reliable operation from the copies. A tape drive had been purchased prior to my association with the instrument, but they had never gotten it to work properly. We found out much later that they had gotten the wrong interface and it would not communicate with that particular model.
You can see the tape drive on top of the auxiliary console. The
aluminum sheet with the large yellow label is the plotter cover for the
main console.
Loading the software could take hours. First, you entered a number
of commands using the key switches on the front of the computer.
Next, you loaded the 'bootstrap' tape using the teletype. This at
least was a fairly short tape. Finally, you loaded the NMR program
tape which was quite long and took some time. If at any point something
went wrong you started over. Something usually went wrong and it
often took three or four tries to get the whole process completed.
With power failures, spring and summer could see considerable time and
effort going into the loading of the software. Now the process takes
only a few minutes to load what in comparison is huge amounts of programming
using a CD.
The auxiliary console shows the hooded oscilloscope used in locking the system, and the temperature control module( just above the plotter cover). I've forgotten what most of the other parts do as I haven't seen this system in about 15 years and I don't know where my notes from that time are stored.
The main console included the plotter, the shim potentiometers (one for each shim, 10 turn pots with vernier scaling), the rf selection and generation controls, decoupler controls, the lock sweep controls, and most of the other function controls for the system
The two small modules on top of the left side of the console are
a frequency counter and function generator used with the decoupler.
I don't remember exactly what they did as I didn't have to make adjustments
on them as a rule. The decoupler mode and frequency were set on the
second module from the left on the upper part of the console. I think
the middle module was involved with the observe channel parameters for
CW and the second from the right module was the nucleus selection
and more observe parameters. The right hand module is the lock module.
Immediately below it are the shimming pots, with the normal shims visible
and the non-spins below a sliding cover. The plotter controls are
to the left of the shim pots. The plotter was a single pen type using
either drafting pens or more often, felt tip pens using a modified holder
to avoid the mess from the fine line refillable drafting pens.
I don't remember what the Variac was used for but I seem to remember
it had to be on. The triple meter was used to monitor output, etc.
The light switch on the conduit hanging in the upper left allowed the
lights to be shut off when trying to shim using the oscilloscope.
The yellow conduit on the wall beside the clock was running to an indicator
light used to tell when the auxiliary pumps connected to the chiller system
were running. Due to water temperature and flow problems, the campus
chilled water system often caused downtime as the magnet was not stable
unless its chilled water system was well regulated. This let us know
when the flow was being boosted in order to heat exchange the water in
the unit next door.
The magnet was a real monster. It weighed about 8500 pounds when dry, and when it was removed, it had left a permanent impression in the tiles.
The magnet was sitting on a wood platform which apparently it had been
shipped in on. The probe is located in the center of the white area
between the two large dark gray plates and was removed for nucleus change,
etc. by pulling on the silver cross bar. Probe changes usually took
from 15 to 30 minutes with adjustments done to the observe and lock channels
and also the changing of a sample chamber quartz insert which held the
tuned coils. Once changed the probe was put back in and shimmed.
It's much nicer now to just reload the shims from the disk and only 'touch
up' the shim a bit or even have the computer do it for you. No gradient
shimmaps or computer autoshim back then! The white PVC plumbing is
the chilled water cooling system running to the magnet and the power supply.
It was filtered through a large, replaceable canister located on the right
side, behind the sample preparation table.
The small wooden structure on top held a meter used in optimizing the
magnet.
This instrument was a good steady workhorse which helped a lot of researchers obtain advanced degrees. While it suffered from age and on occasion from utility problems, it managed to stay in operation for what was probably well over its expected lifespan. Thanks to carefully scrounged and numerous spare parts, including a couple of complete main consoles, breakdowns weren't fatal even though parts from the manufacturer were likely unavailable.
Comparing this unit with the Varian 500 MHz system shows how far the science has come in the last fifteen to twenty years and the 500 is not really completely state of the art though it is very close. The newer systems use the same electronics and merely have larger magnets, slightly better computers, and more accessories we just didn't have the money to obtain.
