Most of our magnets have fielded many tube types, but our stockroom's
are supplied by these vendors:
Wilmad 77%
Norell 13%
Kontes 3%
New ERA 7% to the nearest %
one multi-vendor facility was cut in half
Insert scoring was more divisive with 20% believing, 20% disbelieving,
and 20% feeling that hot or long drying in ovens are the root of all
warped tube and insert problems. Wilmad recommends drying on a
perfectly flat tray at 125 deg C for 30 to 45 minutes,,,,,it may get
out of round and not fit in the spinner but not bent and ruin the probe.
The Wilmad concentricity tester (SD-5-7 for $7.00) which is a piece
of precision glass just big enough for a tube to slide through is
recommended as the best way to find tubes to throw out (if you can
convince a graduate student to toss an unbroken tube). Roundness
can also be tested by rotating a tube in a micrometer, with steady
resistance correlating to roundness.
............
comments (by vendor):
Wilmad:
528's ordered over a period of 4 years scoring inserts,
only one spot on the tube showed wear.
507's for everyday,,, 528's for important
507's are not good enough for water suppression.
507's work fine at 500MHz, but more often found at 300.
Do not break when freezing a sample in liquid nitrogen
for sealing, other tubes did.
Thrift tubes work well 99% of the time with no scoring observed.
Never had any problems with (common responce).
528 or better required at 300MHz and above.
528 or better required in all instruments.
Norell:
Spinning sidebands were a problem.
Avoid as much as possible.
Not Pyrex so don't try to seal to pyrex accessories.
Borosilicate glass doesn't warp as easily in a drying oven.
About 5% of the XR-55's give spinning artifacts which look like
coupling, but for $2.00 you can throw these out.
OK for general purpose work at 300MHz
most bang for the buck
508UP used (almost) exclusively
Kontes:
Overrates so you need to buy a better grade
Difficult to shim.
New ERA:
performance comparable to Wilmad for less money.
high quality
good experience.
Corning:
Good luck with (we had)
Throw Aways:
Increased rate of tube breakage in the probe.
............
The insert scoring boogey guy (this can be inclusive in the midwest) may be
disappearing. On a recent demo trip, none of the ap lab spectroscopists
routinely spun their samples. The mapped fields seem to make this
unnecessary,,,, will we still call them spinners?
...........
Entirely different topic:
We have 4 EM-360's which I would like to convert from cw to pulsed
for undergraduate teaching. Has anyone ever done this? Or if you know
of someone who has done this, please tell me so that I won't have to
either reinvent or make the same mistakes.
..........
Hope this has been useful,,,wish the tube vendors were on internet
to see if they agree with all of this,,
thanks again,
Robert D Scott
scott@iastate.edu
515-294-4057