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Tube manufacturers have a set of parameters that they send out with each tube. In addition, the basic operating parameters are listed on a label that is affixed to each tube. When replacing a Tube (either Klystron or TWT) it is necessary to supply the correct parameters as well as verify that the trip circuits and parameter metering circuits are indeed functioning before powering up a Tube. Tube Manufacturers spend a lot of time and money to create a Tube that will work for your application. Do not undermine them by trying to get a Tube to work using a different set of operating parameters. Some engineers believe that reducing Filament Heater Voltage will increase the life of the tube. The Tube manufacturers know of this trick and have implemented the use of Electron Guns that will last longer and give better performance using the Manufacturer's Specified Operating Parameters. Making changes on your own when changing out a Tube may convert a Tube to a very expensive “Blown Fuse.”
Klystrons: The klystron uses a magnetic field to focus the beam and is less subject to Beam Voltage Potentials that are specified. As a matter of fact, Tube Manufacturers claim that you can extend the life of a klystron by decreasing the Beam Voltage. Of course, you will also change the output capability and the gain of the device. Klystrons should be operated at the nominal voltage for several months prior to backing off the beam voltage. This may help to cure gassing problems during the Tube’s useful life.
TWTs: The Traveling Wave Tube uses the voltages that are applied as part of the focussing apparatus of the tube. The Magnets that surround the tube are very small and rely on these specified voltages to correctly focus the beam through the slow wave structure or the Helix. The Helix is a relatively “fragile” device and excessive energy applied to it in the form of an electron beam will rapidly do damage. Some Amplifier Manufacturers claim that their system needs no resistive load for checking out your HPA when replacing a TWT. This may be true if you can guarantee that the metering in the HPA will never get out of calibration and that trip settings will never drift and the power supply components will never fail. This is why we always use a Resistive Load when we change out a TWT for a customer. It’s a proven fact that you can’t damage a TWT with a power supply if it’s not hooked up! (Unless you drop the power supply on the TWT.) It’s better to catch a problem on a bank of relatively cheap resistors than on a $10,000.00 Plus Tube!
Note: If you damage a tube by applying the incorrect voltages or by not protecting it sufficiently, the tube manufacturer will know! If there is a warranty issue, the tube manufacturer will most likely NOT cover the warranty in the event of a failure due to such damage!
It is also necessary to verify the Tube’s environment. Make sure that the cooling system is working and is not blocked. If you are at a higher altitude, be sure your blowers are moving enough air for cooling.
Make sure that the waveguide flanges are concentrically aligned and parallel to each other BEFORE bolting them together.
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