Ed Murlatt & Associates, Inc.
RF Services for the Broadcast Industry
IOT Grid Out Gassing

                                                           ESCIOT5130W OUTGASSING PROCEDURE
The instructions in black font below were provided by E2V, and are published here unedited, with the following observations:
Prior to taking the tube off-air for service, reduce its output power to less than 50% so it won't be coming back at an excessive
power. 
Once power is removed and while making the grid connections detailed below, verify the heater voltage meter calibration.
I recommend keeping a log of your outgassing for future reference.  You can download the Excel Spreadsheet I use here
Keep a close watch on the ion current while increasing the grid voltage.  You may not always be able to increase by 2 volts
without exceeding the 10 µA ion current limitation.  Be aware the ion current can increase a little after you have set the
voltage.  Also, be aware the voltage versus power increase is non-linear, because the current is constantly increasing. 
Therefore you need to calculate power as you increase the voltage to be sure you do not exceed the maximum grid
dissipation. 
Mindful of the 10 µA maximum, but regardless of any lack of ion current, I allow at least 10 minutes after each voltage step. 
Never outgas longer than 24 consecutive hours.
Once the outgas has completed, I allow the gun to set cold for at least 10 minutes then proceed with a slow startup.  I allow the
tube to set at idle current for at least 10 minutes while monitoring the grid and ion currents.  Assuming everything is normal, I
adjust the idle current if necessary, then begin applying RF drive.  
If you have been doing heater management (operating below the original heater voltage), be sure to keep an eye on the grid
current as you return the IOT to service.  I've seen several cases of positive grid current immediately following an outgas.  The
effect is usually temporary, but positive grid currents in excess of 10 mA should be addressed.  Typically a small increase in
heater voltage will reduce the positive grid current.  I remove high drive and high voltage before making changes to the heater
voltage so I can monitor the gun voltage at the IOT and not rely on the transmitter metering.  I increase the heater in 0.1 volt
increments until the grid current drops below 10 mA with the RF output at 80%.  Normally, the heater can be returned to its
lower voltage within a few days.  Heater management is recommended to maintain the maximum interval between out-
gassings.  Do not exceed the manufacturer's recommended minimum or maximum heater voltage. 
You should not tune the IOT until the grid has stabilized.  Allow 24 hours after outgassing before tuning. 
        
                  If you have ANY questions, please call for clarification before you start!

The objective of this procedure is to reduce excessive grid emission in an ESCIOT-normally recommended if emissive grid current
exceeds 50 mA.  The grid temperature is elevated above normal until evolved gas has been removed.  The procedure will take 1 hour.
1. Ensure high voltage is off and isolated from the tube.
2. Disconnect the umbilical grid wire from its supply.
3. Connect a DC power supply (40 V, 5 A): positive terminal to the grid umbilical wire, negative terminal to the cathode wire.
4. Turn on the cavity blower, heater voltage and ion pump voltage (transmitter=’standby’); allow 5 minutes for warm-up
5. Slowly increase the external DC supply voltage until grid current rises and normally an ESCIOT will have very little ion current.  To
avert damage, grid dissipation must not exceed 90 W; ion pump current must not exceed 10 µA.
6. Increase grid dissipation to the 20W range and then slowly increase the dissipation over a period of 1 hour normally in 2V
increments.  Please note, an ESCIOT will only show very little ion current and may not have any ion current.
7. After outgassing, remove the power supply and reconnect the grid wire
8. Restore the transmitter to standby operation (beam off).  After gun temperature has stabilized (10 minutes if not cold) measure
heater voltage; if necessary, adjust to recommended setting.  Make note of heater voltage and grid current meter readings.
9. Adjust grid voltage for recommended quiescent cathode current.
10. Operate the transmitter at no more than 80% of the station’s power output requirement for 1 day before restoring to full power.  This
is to allow for gain change during and immediately after out-gassing.

Caution:
Only qualified engineers should attempt the above procedures. Good engineering practices must be adopted when working with High
voltage circuits. If clarification of any of the above instructions or any safety related point is required, please contact your transmitter
supplier or E2V Technologies Inc for guidance.

Contact E2V Technologies Inc at:
1-800-342-5338 [Monday -Friday 9.00am-5.00pm EST] or
1-914-592-6050 [Monday -Friday 9.00am-5.00pm EST] or
Our 24-hour technical support line 1-888-433-8852 [outside of normal business hours]
                                                             End of ESCIOT Outgas Procedure
                             IOT OUTGASSING PROCEDURE (Conventional Collector Tubes)
The instructions in black font below were provided by E2V, and are published here with my edits in blue italic. 
In addition to the edits, I make the following observations:
Prior to taking the tube off-air for service, reduce its output power to less than 50% so it won't be coming back at an excessive
power. 
Once power is removed and while making the grid connections detailed below, verify the heater voltage meter calibration.
I recommend keeping a log of your outgassing for future reference.  You can download the Excel Spreadsheet I use here. 
Once the outgas has completed, I allow the gun to set cold for at least 10 minutes then proceed with a slow startup.  I allow the
tube to set at idle current for at least 10 minutes while monitoring the grid and ion currents.  Assuming everything is normal, I
adjust the idle current if necessary, then begin applying RF drive.  Never outgas longer than 24 consecutive hours.
If you have been doing heater management (operating below the original heater voltage), be sure to keep an eye on the grid
current as you return the IOT to service.  I've seen several cases of positive grid current immediately following an outgas.  The
effect is usually temporary, but positive grid currents in excess of 10 mA should be addressed.  Typically a small increase in
heater voltage will reduce the positive grid current.  I remove high drive and high voltage before making changes to the heater
voltage so I can monitor the gun voltage at the IOT and not rely on the transmitter metering.  I increase the heater in 0.1 volt
increments until the grid current drops below 10 mA with the RF output at 80%.  Normally, the heater can be returned to its
lower voltage within a few days.  This is recommended to maintain the maximum interval between out-gassings.  Do not
exceed the manufacturer's recommended minimum or maximum heater voltage.          
Not all ion pumps are created equal.  The pumps in Axcera transmitters fold back somwhere between 20 µamps and 25 µamps,
so I recommend you keep the ion current below 20 µamps when using the internal ion pump in an Axcera transmitter.  The
third party ion pump used in Thales DCX millenium transmitters with plug in IOTs do not provide an appropriate current meter
range to allow for monitoring the ion currents specified.  I use another ion pump when working with these transmitters.
                     If you have ANY questions, please call for clarification before you start!

The objective of this procedure is to reduce excessive grid emission in an IOT-normally recommended if emissive grid current exceeds
50 mA.  For tubes with chronic grid emission issues, I recommend outgassing well before the -50mA mark is reached.  This
reduces the potential for extended outgas time.  The grid temperature is elevated above normal until evolved gas has been removed. 
The procedure can take several hours.
1. Ensure high voltage is off and isolated from the tube.
2. Disconnect the umbilical grid wire from its supply.  Verify the heater voltage meter calibration.
3. Connect a DC power supply (40 V, 5 A): positive terminal to the grid umbilical wire, negative terminal to the cathode wire.
4. Turn on the cavity blower, heater voltage and ion pump voltage (transmitter=’standby’); allow 5 minutes for warm-up
5. Slowly increase the external DC supply voltage until grid current rises, followed by a rise in ion pump current.  Mindful of the 70
µA ion current maximum, I recommend stopping at 26 - 28 watts of grid dissipation initially, and allowing the grid to settle
in for about 10 minutes.  You will likely see a burst of ion current between 30 W and 40 W of grid dissipation.  To avert
damage, grid dissipation must not exceed 100 W; ion pump current must not exceed 100 µA.
6. Increase grid dissipation in the 30 W to 90 W range as needed to maintain ion pump current in the 30 µA to 70 µA range until it
decreases significantly within several minutes-usually to below 5 µA.  I recommend taking it a little slower than this particular
instruction might indicate.  I suggest you limit your increases to a maximum of 2 volts (mindful not to exceed 70 µA ion
current or 90 Watts grid dissipation), and wait for 10 minutes after each increase, or until a substanial reduction in ion
current occurs, whichever is the LONGER period.  Also, be aware the voltage versus power increase is non-linear, because
the current is constantly increasing.  Therefore you need to calculate power as you increase the voltage to be sure you do
not exceed the maximum grid dissipation.  After the ion current drops below 5 µA at greater than 90 watts dissipation, I
maintain the power on the grid for an additional 30 minutes.
7. After outgassing, remove the power supply and reconnect the grid wire.  See comments above for additional information
regarding tube restart.
8. Restore the transmitter to standby operation (beam off).  After gun temperature has stabilized (10 minutes if not cold) measure
heater voltage; if necessary, adjust to recommended setting.  Make note of heater voltage and grid current meter readings.
9. Adjust grid voltage for recommended quiescent cathode current.
10. Operate the transmitter at no more than 80% of the station’s power output requirement for 1 day before restoring to full power.  This
is to allow for gain change during and immediately after out-gassing.  Do NOT tune the IOT until the IOT has stabilized.

Caution:
Only qualified engineers should attempt the above procedures. Good engineering practices must be adopted when working with High
voltage circuits. If clarification of any of the above instructions or any safety related point is required, please contact your transmitter
supplier or E2V Technologies Inc for guidance.

Contact E2V Technologies Inc at:
1-800-342-5338 [Monday -Friday 9.00am-5.00pm EST] or
1-914-592-6050 [Monday -Friday 9.00am-5.00pm EST] or
Our 24-hour technical support line 1-888-433-8852 [outside of normal business hours]
                                                  End of Conventional Collector IOT Outgassing Procedure
In some IOTs, the conductive material can migrate from the cathode to the grid causing the grid to become emissive.  When this occurs, the transmitter metering will indicate a negative grid current.  Up to about -50 mA, this is not a large problem.  Be advised that I am speaking about negative grid currents.  If you are experiencing positive grid current, please see the notes below on corrective action.  I should also note that some transmitters will have issues at lower negative grid currents, and I prefer to outgas the grid well before the current reaches negative 50 mA.

Depending on the IOT, its operating parameters and grid emission history, simple heater management may be all that is required to reduce grid emissions.  In the case of the E2V IOTD2100, heater management is the best course of action.  If you are attempting heater management BE SURE TO CHECK THE HEATER VOLTMETER CALIBRATION before and after adjusting the heater voltage.  Some transmitter heater voltage meters do not maintain calibration and/or track heater voltage correctly.  If you are lowering heater voltage, you want to be certain you don't accidentally go too low.  Also, check the heater supply for presence of AC on the heater.  I have found upwards of 3 volts of AC atop the measured DC voltage.  The additional heating can result in excessive grid emission. 

When heater management doesn't fully address grid emissions in E2V IOTs, outgassing is recommended by the manufacturer. 
Due to the potential for personnel to be exposed to lethal voltages, outgassing should only be attempted by qualified engineers.  In very rare instances even when the IOT is outgassed correctly, damage to the IOT can occur.  Improper outgassing increases the likelihood of tube damage.  Therefore, regardless of skill level, experienced assistance for the first outgas or two is recommended.  The information provide here is for qualified enginners, and only qualified engineers should follow the appropriate ESCIOT Outgas Instructions or Conventional Collector IOT Outgas Instructions (further down the page).