S. O. 765244 INSTALLATION
Subject: Date November 18, 1935
AND
Reduction of “Wows” Number 7.6B
SERVICE DIVISION
MODEL D 22-1 Classification
Rejecting
RCA Manufacturing Company, Inc and
NATIONAL OFFICE Inspection.
Camden, N. J.
INSTRUCTIONS AND INFORMATION
"Wows" may originate in the worm or worm gear of the motor clue to unevenness of either
part or manufacturing variations. It is extremely difficult in the field to correct for
these conditions even if the two are lapped in. Furthermore, lapping in is a difficult
job in the field and whether an improvement would result is questionable.
The end thrust of the rotor is adjustable. This adjustment is fairly critical and, in
general should not be tampered with in the field. It has been found possible, however,
to reduce “wows" considerably by proper adjustment of this end thrust provided the
setting was poor in the first place. This is a possible source of "wow" which should be
tampered with last.
A very important source of "wows” is located in the top spindle bearing of the motor.
This bearing is housed in a die casting which fits very closely in an opening in the top
of the motor casting. This die-casting is held in place by two screws which serve to
clamp it in position. It has been found possible to reduce "wows" by 50% by proper
alignment of this bearing. Both screws are accessible from the top of the motorboard
after the turntable has been removed. Particular care should be taken, however, that
the main gear of the automatic mechanism is not damaged during adjustment of one of
those clamping screws. In making the adjustment, use either a constant frequency record
at approximately 1,000 cycles or a musical selection having sustained notes in which the
"wow” can be noticed. After having determined that "wows" are present, the two clamping
screws should be loosened and the turntable placed back in position and another
listening test made. During both these tests care should be taken that the record is
properly centered, otherwise eccentricity of the record groove with respect to the
spind1e will give misloading resu1ts. Also, the listening test should not be based upon
one position of the record on the turntable since none of our recordings are "wowless"
but have around .3% speed variation in themselves. It can be seen from this that if the
small percentage "wow" in the record adds to the "wow" in the turntable, a much greater
speed variation is obtained than when the two are in opposition.
After having made the latter test and provided no change in "wows" is noticed after two
or three trials with record positions, the top bearing casting should be rotated part of
a revolution and the clamping screws again tightened. With this condition repeat the
tests just given and note the results. As a further check it would probably be
desirable to make another test with the clamping screws loosened. By doing this it
should be possible to reduce the "wow" content by as much as 50% in practically all
cases unless by chance the original adjustment was the best one possible.
