This follows on from the work of my testatika small machine testbed 1. In fact, it is the same machine but with many parts replaced with new ones in an effort to elmininate the wobble of the disk.

Testbed 2 with wobble.

Testbed 2 without wobble. The top waveform has interference added from household wiring otherwise it would be flat like the bottom one.

How the above measurements were made.

Specifically I've done the following:

• New disk - The thick acrlyic disk with guitar wire wires was replaced with a CD with wires taken from stripped insulated solid 30 mil electrical wire. The change in disk was to ensure that I had a flat one. The change in wire was to use one what could be pressed flatter against the disk face.
• New support structure for front grids - I needed a structure that allowed me to adjust the position of each grid individually.
• Better support for the drive shaft - Another bearing was added to hold the shaft. It was found that some of the wobble was introduced by the imprecise motor itself. Using two supporting bearings took care of this.
• Better positioning of the motor - The position of the support that the motor was sitting on was made adjustable for better lining up with the shaft bearings.
• Position adjustable front, center grids

The following pictures illustrate the above new testbed.

Testing

• August 10-11, 2005 - Initial testing:
  With almost all wobble gone, previously unseen periodic spikes are seen but nothing else that would seem to be coming from the rotation of the disk. The spikes were found to be due to the motor and not the disk. The motor was one component that was replaced since testbed 1. As this left nothing useful is coming from the disk itself, we're back to the drawing board.
• August 12-22, 2005 - Variable capacitor testing:
  Having a more stable machine, measurements were made to learn the interaction and purpose of all the grids. The main finding, though, is that the purpose of this disk arrangement is just to be a variable capacitor providing alternating voltage for other components.
• April 1, 2008 - Vinyl backing testing:
  Wanting considerable higher voltage oscillations from the antenna keys, I added vinyl sheets on the back.