Build your own Van de Graaff Generator using these high quality collector spheres.
The general rule of thumb for voltage output is 70,000x sphere radius. For the spheres above: 490,000 volts for 14" and 595,000 volts for 17". Actual voltage output depends on a variety of factors, but this estimate is fairly accurate. Both collector spheres have a 3.5" hole in the bottom -curved inward to prevent high voltage corona losses. Fabricated from highly polished Stainless Steel (far more durable and dent-resistant than aluminum). The mirror polish eliminates parasite corona discharges and increases voltage capacity by 4%