Testing of the various parts carrying ht has been given special attention. It pays off to spend some time in tracing possibile arcing paths. Serious damage can be avoided if it has been ensured that all voltages can be applied with an adequate margin.
This margin is necessary to allow for possible easier flash-over during periods of high humidity.
High voltage testing
The anode area is the most critical one. As a target a voltage of 10 kV has been set.
This picture shows the testing of the lecher. On the right hand side the 0 - 30 kV tester can be seen (switched to 0V for security reasons). On the left hand side are the tube and the lecher. Both the upper and lower lecher plate, insulated by a teflon layer, are mounted on the anode of the tube. The exact mechanical position of the lecher on the anode has been checked in the amplifier.
It was found out that at a voltage of 6.5 kV severe arcing occured from the extending ring around the cooling fins to the grounded lower lecher plate. The reason was a (still) too narrow air gap between this ring and the lecher plate. The diameter of the hole has been enlarged to 10.9 cm.
A closer look at the necessary gap between tube ring and lecher plate is given below.
The same test has been applied to the ht connector, ht feed through and ht capacitor in the anode compartment.
A voltage of 10 kV could be applied to all components.
During operation the rf voltage on the upper and lower lecher plate is always the same. Given the fact that the voltage of the lecher close to the anode is same as the voltage on the anode itself no additional rf voltage has to be taken into account for security reasons.