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The following list is a recommended mainenance schedule for the care and feeding of your HPAs!

(Please note that these are my recommendations based on almost 20 years of experience and not necessarily the recommendation of the Transmitter Manufacturer)

Per Event

  • Verify incoming AC power prior to turning on HPAs or other equipment to avoid accidental damage due to incorrect voltage levels.
  • Power up HPAs before turning on the Air Conditioning in transportables to help prevent Condensation inside amplifiers.
  • Log: HPA m/n & s/n, Date, Location (if transportable), Operating Hours/Time, Metered Tube operating parameters, Metered RF operating parameters, Temperature & Humidity.
  • Note:  If you have any failures, try to log all of the above parameters as well as any fault indicators that appear prior to resetting the fault.  If your system has a fault log programmed into the controller, note the description listed in the log for that failure.

  • Verify Nominal operation of Equipment (make sure all the controls, indicators and metering work).
  • Check operation of Dual Path, Redundancy or Phase combined network and switching.


  • Check and Clean filters if needed.
  • Operate Amplifier for 2 hours to prevent the tube from gassing. Be sure Tube is conducting and Hot air is coming from the cooling exhaust.  RF output is not necessary.
  • Check for loose RF and interface connectors (transportables).
  • Check for loose intake and exhaust ducting.  Make sure there are no obstructions in cooling network (bird’s nests or leaves). Check that system is not recirculating heated exhaust air from HPA.


  • Listen for worn blower bearings during power up and down.
  • Using a Soft, Natural Hair, Paint Brush...dust around any switches and displays to remove excessive dust.
  • Wipe down front panels with soft cloth and mild cleaning agent to remove skin oils and dirt. (Caution!  Do not spray cleaning agents on front panel!  Spray cloth and then wipe!  Wipe only hard enough to clean off the dirt! Don’t scrub off the paint or silk screened labels!)



The Following Procedures Should ONLY be performed by Qualified Technicians or Engineers that have had the proper training to work around HIGH VOLTAGE!!!

See the Manufacturers Warnings about High Voltage in the System Manual!

See our Section on “High Voltage” Under “Technical Info”

Many of the following procedures may be life threatening or may create a life threatening condition if not done properly!


  • Follow Manufacturers Procedures to Remove power from HPA and discharge any High Voltage Potentials that may linger on capacitors.
  • Carefully Vacuum or Blow out interior of HPA.
  • Check for Leakage or Bulging on Electrolytic or Oil Filled Capacitors.
  • Check area around any PC Board mounted Fuse Holders, Diodes or Resistors for Heat Stress.
  • Check for Accumulation of Carbon and Dirt in High voltage areas and clean if possible with a soft brush and vacuum cleaner. Check for breakdown of any High Voltage Insulating Materials (discoloration of HV Wiring or cracks in potting material).


  • Do all Semiannual Checks
  • Check for loose connections/connectors or Printed Circuit Boards that are not properly seated in card cages or edge connectors.
  • Check all Wiring Harness Terminal Blocks for Loose Screws or compression contacts.  Check for Heat Stress around all terminal blocks and compression contact components.
  • Check Wiring Harness for cracks in the insulation, broken wires, pinched wires or indications of Heat Stress in any wiring (discoloration of wire insulation or Crimp Lug Insulators). Note:  Be sure to give any High Voltage Wiring extra attention as a small pin hole is enough to cause sometimes devastating problems.
  • Adjust Power Supply Voltages to Conform with Tube Manufacturer Requirements and HPA Manufacturer Requirements. *
  • Adjust all trip settings to conform with Tube Manufacturer or HPA Manufacturer Requirements *
  • Calibrate Metering to indicate correct Voltages, Currents, Trip Settings and RF Power measurements
  • Check High Voltage Connectors for proper seating or cracks (see notes on “Rowe” type connectors in “Connectors” under “Technical Info”)
  • Check Klystron Tuning (see “Tuning” Under “Klystrons” under “Technical Info”)
  • Adjust Phasing in Phase Combined Systems (see “Phasing” under “Technical Info”)

* Note:  Tube Manufacturer Requirements for voltages and trips Supercede HPA Manufacturer’s Requirements! Check Tube Specifications prior to installing and turning on a new TWT or Klystron. 

We at Green Satellite recommend all TWT Power Supply Voltages and Power Supply Sense Circuits and Trips be set up on a “Resistive Load.” Some HPA Manufacturers claim that New TWTs can be installed without a resistive load on their systems, however, all electronic equipment fails at some time or another! It’s a fact of life. Unless you know, absolutely, that the Power Supply Voltage Meter Calibrations and Trip Circuits are correct, why take a chance that you could turn a $10K-$20K tube into a “blown fuse!”

Think of it this you think the HPA manufacturers would install a tube in a new system without checking out the power supplies, the Fault Trips, and the metering if they thought there would be a chance that an expensive tube could be damaged?

Not Likely!

  If you did break a TWT because the voltages or trips were not correct, do you think they would give you another one for free to replace the damaged one?

Not Likely!

The manufacturers use “resistive loads” in the factory to set up the power supplies, the Fault Trips, and voltage metering prior to turning on a new TWT!  You should too!

We always use a “Resistive Load” to check our customer’s TWT Power Supply Voltages, Metering and Trips whether we are installing a TWT or doing Maintenance!

You may not HAVE to use a Resistive Load to maintain your system but it’s the SAFE thing to do!

2-6 Years

  • Check Thermal Conductivity between Heatsinks and TWTs or Power Supply Modules (see “Heat Sinking”)
  • Consider Replacing any Switching Duty Rated Electrolytic Capacitors in Switching Power Supplies that are more than 6 years old
  • Consider Budgeting for a New Tube for any HPA whos tube is more than 3 years old ( 2 years for Ku Klystrons) You DON’T have to Replace It!  Just Budget for the tube in case you have a failure.  Most Tubes Last Much Longer than that but the tube manufacturers have limits to their warranties for a reason...Nothing Lasts Forever!!!

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