Magnetic coupling by parallel-wire grids and soldered cross-lateral grids in disc-seal triodes

The parallel-wire grids frequently used in disc-seal triodes exhibit a perceptible magnetic coupling of the grid which neutralizes the anodecathode capacitance within the range of application of the tubes (self-neutralization). Detailed investigations show that the magnetic coupling is considerably less with a new type of grid¿the soldered cross-lateral grid, where the self-neutralization frequency lies above the range of application of disc-seal triodes. Comparison measurements performed on parallel-wire grids and soldered cross-lateral grids with the aid of a measuring circuit that is described in detail showed a good approximation to curves computed for a triode as a passive four-pole with the aid of an equivalent circuit diagram. An indication is given of the significance of this problem to valves.