Patent ID: 7692384

Claim:
An electron tube comprising: an envelope formed with a photo cathode in a predetermined part of an internal surface thereof, the envelope comprising: a cylindrical base; and a main body having a first main body and a second main body that connects the first main body and the base, the main body having substantially a spherical shape; an electron-bombarded semiconductor device provided on the main body side relative to an intersection between an axis of the cylindrical base and an imaginary-extended-curved-surface of the second main body that is located inside the cylindrical base; and a supporting member that faces photocathode and supports the electron-bombarded semiconductor device, at least part of the supporting member being provided on a main body side relative to the intersection, the supporting member being conductive, and an insulating tube that has one end and another end, the another end being connected to the envelope and the one end protruding inside the envelope, the supporting member being disposed on the one end of the insulating tube, the insulating tube being located on the cylindrical base side with respect to the imaginary-extended-curved-surface, the semiconductor device detecting photoelectrons emitted from the photocathode in response to an incident light thereon, wherein the supporting member comprises: a conductive portion; and an inner stem connected to the one end of the insulating tube via the conductive portion, wherein the electron tube further comprises a conductive member provided on the one end of the insulating tube and protruding outside the insulating tube to reduce the field intensity in the vicinity of the one end of the insulating tube, and wherein the semiconductor device is disposed on the inner stem.