The Pengelly - Stringer universal electrical cylinder replay machine

by Joe Pengelly, 1998

I commissioned a cylinder replay machine to be built to my specification which stated that the machine should be designed so that during the replay process the machine should be sympathetic to the cylinder, i.e. it would not be possible to damage the cylinder in any way, that the machine should be able to cope with all the dimensional variables encountered between individual cylinders, to be able to accomodate the largest known cylinders and that the machine should be made to the highest accuracy possible.

Mike Stringer of the Mechanical Engineering Department of Plymouth University undertook the design and manufacture of the machine which, in essence, is similar to Edison's original concept of traversing the rotating mandrel. Edison used a single "motor" but the new design incorporates independent drives to both the mandrel and the feedscrew to facilitate control over speed of mandrel rotation and the traverse feed rate.

The rotational speed range of the mandrel is 0 to 230 R.P.M.; to compliment this it was necessary for the feed range to be between 0.1 to 3.25 inches/minute to cater for a 200 grooves/inch cylinder to be played at the slowest practical speed and for a 100 grooves/inch cylinder to be played at the highest speed.

To achieve the design specification speeds of rotation of the mandrel and the feed rates to compliment them it was necessary to reduce the speed of the drive motors. This was achieved by employing a flat belt pulley train (not gears which would produce "flutter") to produce a 5:1 reduction for the mandrel drive motor and a 3:1 reduction for the feedscrew drive.

The mandrel, drive motor, speed reduction box assembly is mounted on a carriage which is supported on two slideways, the feedscrew is positioned between the slideways and the feed is engaged and disengaged by operating a halfnut with a lever (similar to the feed engagement mechanism on a lathe).

Both the mandrel and the feedscrew are driven by D.C. printed armature motors with integral tacho-generators and have separate servo-amplifiers, which employ the feedback from the tacho-generators, which enables the rotational speed of the mandrel, and its direction, and the feed rate, and its direction, to be controlled independently to suit a particular cylinder while the machine is running.

The servo amplifiers, the power supply and the speed control of both motors are housed in a separate box.

The mandrel is much longer than the "standard" Edison to cater for standard cylinders, i.e. Blue Amberol, that have shrunk or have become deformed due to age. Larger cylinders such as the Kinetophone and the Celeste etc., can be played by fitting suitable secondary mandrels onto the standard mandrel. If such a beast exists, the largest cylinder the machine can accommodate is 6.5 inches diameter by 8.7 inches long (165.1 m.m. diameter by 221 m.m. long). As an additional reverse play facility the mandrel can be reversed on its shaft.

Both I and Mr. Stringer are of the opinion that using a fixed or driven stylus is foolhardy when replaying cylinders of any type as irreparable damage may occur in the event of a mismatch between "feed" and "speed" or a failure of one of the drives.

This is just one of the resaons why a free standing pivoted straight arm with a Shure M44C cartridge is employed and by using styli of differing radii the stylus can reach parts of the groove that other styli cannot. Further, the inclination and angle of incidence of the pickup arm relative to a cylinder and mandrel can be varied over a wide arc to achieve the best stylus/groove relationship. Also, the flexibility of the pickup arm is enhanced by the facility to vary the playing weight by adjustment of its counterbalance weights. This can both maximise performance and minimise wear.