AR 8300TP8G12 Service manual

Operating and
Service Manual
8300TP8G12
Model
10031734
Part Number
Serial Number
160 School House Road, Souderton, PA 18964 • 215-723-8181 • Fax [phone] • www.arworld.us

EC Declaration of Conformity
We: Amplifier Research
160 School House Road
Souderton, PA. 18964
declare that our product(s);
the Model 8300TP8G12 series RF amplifiers
to which this declaration relates is in compliance with the following European directives:
Low Voltage Directive: 2014/35/EU
EMC Directive: 2014/30/EU
Supplementary Information:
Safety : EN 60215-1:1989
EN 61010-1:2010
EMC: EN 61000-6-2:2005, EN61000-6-4:2007
Year Mark Applied: 2016
I, the undersigned, hereby declare that the equipment specified above conforms to the above Directives and
Standards.
Authorized officer of the company:
James M. Maginn
President

Instructions for European EMC Conformity
WARNING
It is the responsibility of the user of this equipment to provide electromagnetic shielding, filtering and isolation
which is necessary for EMC compliance to Directive 2014/30/EU. The equipment must therefore be operated in
a shielded area which provides a sufficient level of attenuation to meet the radiated emissions and immunity
specifications. The following minimum levels are suggested for use in accordance with the rated power of the
equipment.
Rated Power
Minimum shielding attenuation
100 watts
50 dB
101 - 1000 watts
60 dB
1001 - 10,000 watts
70 dB
Since this equipment is designed to generate high levels of Radio Frequency energy, it is also essential that the
user read and follow the “Instructions for Safe Operation” in this manual. If other equipment is operated in the
shielded room it may be disturbed by the amplifier.
ACHTUNG
Der Benutzer dieses Gerätes ist dafür verantwortlich, daß die elektromagnetische Abschirmung und Filterung
gewährleistet ist, welche gemäß Richtlinie 2014/30/EU notwendig ist. Das Gerät muß deshalb in einem
geschirmten Raum betrieben werden, welcher eine ausreichenden Schirmung bietet, um die Emissions- und
Störfestigkeitsspezifkation einzuhalten. Es werden folgenden Minimalwerte der Schirmdämpfung und Filterung
in den unterschiedlichen Leistungsklassen empfohlen.
Hochfrequenzleistung
min. Schirmdämpfung
100 Watt
50 dB
101-1000 Watt
60 dB
1001-10.000 Watt
70 dB
Falls andere elektrische oder elektronische Geräte gleichzeitig mit dem Gerät betrieben werden, kann es zu
Beeinflussungen kommen. Da das Gerät zur Erzeugung von Hochfrequenzenergie dient ist es daher auch
unbedingt notwendig, daß der Benutzer die Sicherheitsvorschriften in der Bedienungsanleitung liest und einhält.
AVERTISSEMENT
Il est de la responsabilité de l'utilisateur de cet équipement d'assurer la protection électromagnétique, le filtrage
et l'isolation nécessaires, afin de se conformer à la directive 2014/30/EU concernant la C.E.M. Par conséquent,
cet équipement doit être mis en fonctionnement dans une enceinte d'atténuation suffisante pour satisfaire aux
spécifications d'émissivité et de susceptibilité. Pour une utilisation conforme, les niveaux d'atténuation
minimums suivants sont suggérés en fonction de la puissance de sortie de l'équipement:
Puissance de sortie
Atténuation minimum de l'enceinte
100 Watts
50 dB
101 à 1.000 Watts
60 dB
1.001 à 10.000 Watts
70 dB
Puisque cet équipement est destiné à générer de forts niveaux R.F., il est essentiel que l'utilisateur se conforme
aux instructions de sécurité indiquées dans ce manuel. Tout autre équipement en fonctionnement dans la cage de
Faraday peut-être perturbé par 1'amplificateur.

INSTRUCTIONS FOR SAFE OPERATION
Revised 0517
Observe the following safety guidelines to help ensure your
own personal safety and to help protect your equipment and
working environment from potential damage.
INTENDED USE
This equipment is intended for general laboratory use in
generating, controlling, and measuring levels of
electromagnetic Radio Frequency (RF) energy. Ensure that the
device is operated in a location which will control the radiated
energy and will not cause injury or violate regulatory levels of
electromagnetic interference.
SAFETY SYMBOLS
These symbols may appear in your user manual or on
equipment.
This symbol is marked on the equipment when it
is necessary for the user to refer to the manual
for important safety information.
The caution symbol denotes a potential hazard.
Attention must be given to the statement to
prevent damage, destruction, or harm.
Dangerous voltages are present. Use extreme
care.
Indicates a terminal intended for connection to
an
external conductor for protection against
electrical shock in case of a fault, or the terminal
of a protective earth (ground) electrode.
Indicates invisible laser radiation–do not view
directly with optical instruments.
Indicates fra
me or chassis ground connection
terminal.
Indicates alternating current.
Indicates this product must not be disposed of
with your other household waste.
Indicates that the marked surface and adjacent
surfaces can attain temperatures that may be hot
to the touch.
EQUIPMENT SETUP PRECAUTIONS
Review the user manual and become familiar with
all safety markings and instructions. Protection
provided by the equipment may be impaired if
used in a manner not specified by AR RF/Microwave
Instrumentation (AR).
•Follow all lifting instructions specified in this document.
•Place the equipment on a hard, level surface.
•Do not use the equipment in a wet environment, for
example, near a sink, or in a wet basement.
•Position your equipment so that the power switch is easily
accessible.
•Leave 10.2 cm (4 in) minimum of clearance on all vented
sides of the equipment to permit the airflow required for
proper ventilation. Do not restrict airflow into the
equipment by blocking any vents or air intakes.
Restricting airflow can result in damage to the equipment,
intermittent shut-downs or safety hazards.
•Keep equipment away from extremely hot or cold
temperatures to ensure that it is used within the specified
operating range.
•While installing accessories such as antennas, directional
couplers and field probes, take care to avoid any exposure
to hazardous RF levels.
•Ensure that nothing rests on your equipment’s cables and
that the cables are not located where they can be stepped
on or tripped over.
•Move equipment with care; ensure that all casters and/or
cables are firmly connected to the system. Avoid sudden
stops and uneven surfaces.
BEFORE APPLYING POWER
Your AR equipment may have more than one power supply
cable. Use only approved power cable(s). If you have not been
provided with a power cable for the equipment or for any AC-
powered option intended for the equipment, purchase a power
cable that is approved for use in your country. The power
cable must be rated for the equipment and for the voltage and
current marked on the equipment’s electrical
ratings label.
Incorrectly installing or using an incompatible line
voltage may increase the risk of fire or other
hazards. To help prevent electric shock, plug the equipment
and peripheral power cables into properly grounded electrical
outlets. These cables are equipped with three-prong plugs to
help ensure proper grounding. Do not use adapter plugs or
remove the grounding prong from a cable.
Do not modify power cables or plugs. Consult a licensed
electrician or AR trained service technician for equipment
modifications. Always follow your local/national
wiring rules.
Do not operate the equipment if there is physical
damage, missing hardware, or missing panels.
SAFETY GROUND
This equipment is provided with a protective earth
terminal. The mains power source to the
equipment must supply an uninterrupted safety
ground of sufficient size to attach wiring terminals,
power cord, or supplied power cord set. DO NOT USE this
equipment if this protection is impaired.

INSTRUCTIONS FOR SAFE OPERATION
Revised 0517
HAZARDOUS RF VOLTAGES
The RF voltages on the center pin of an RF output
connector can be hazardous. The RF output
connector should be connected to a load before AC
power is applied to the equipment. Do not come
into contact with the center pin of the RF output connector or
accessories connected to it. Place the equipment in a non-
operating condition before disconnecting or connecting the
load to the RF output connector.
ACOUSTIC LIMITATIONS
If equipment noise exceeds 80dB, ear protection is required.
MAINTENANCE CAUTION
Adjustment, maintenance, or repair of the equipment must be
performed only by qualified personnel. Hazardous energy may
be present while protective covers are removed from the
equipment even if disconnected from the power source.
Contact may result in personal injury. Replacement fuses are
required to be of specific type and current rating.
ENVIRONMENTAL CONDITIONS
Unless otherwise stated on the product specification sheet, this
equipment is designed to be safe under the following
environmental conditions:
•Indoor use
•Altitude up to 2000m
•Temperature of 5°C to 40°C
•Maximum relative humidity 80% for temperatures up to
31°C. Decreasing linearly to 50% at 40°C.
•Main supply voltage fluctuations not to exceed ± 10% of
the nominal voltage or minimum and maximum
autoranging values.
•Pollution degree 2: Normally non-conductive with
occasional condensation. While the equipment will not
cause hazardous condition over this environmental range,
its performance may vary.
EQUIPMENT CONTAINING LASERS
AR Field Probes (FL/PL Series) and Field Analyzers
(FA Series) are Class 1 laser products containing
embedded Class 4 lasers. Under normal use, the
laser radiation is completely contained within the
fiber optic cables and poses no threat of exposure. Safety
interlocks ensure that the laser is not activated unless the
cables are properly connected. Always exercise caution when
using or maintaining laser products. Do not view directly
with optical instruments.
RF ANTENNAS
•This equipment (antenna or antenna assembly) may be
heavy, requiring two persons to lift. Use caution when
installing or removing unit. Follow all equipment setup
and lifting instructions specified in this document.
•Ensure connectors are appropriate for intended operation.
Connectors are specified in the user manual and product
specification sheet.
•Do not exceed the maximum RF input level stated in the
specifications. Refer to the user manual and product
specification sheet to determine the applicable RF levels.
•Excessive RF input could damage the equipment or
connectors, causing safety hazards.
•When in operation, the RF voltages on the antenna
elements can be hazardous. Do not come into contact with
the antenna or elements when the RF input connector is
connected to a live RF source.
•To avoid injury to personnel and accidental damage to
power amplifier or antenna, disable the RF output of
power amplifier before connecting or disconnecting the
input connection to the antenna.
•Perform periodic inspections of antenna and field probe
systems to verify calibration due date, proper operation,
and overall condition of equipment.
RACK MOUNTED TWT MODELS
Some TWT models are supplied without the removable
enclosure offered for benchtop use. These rack-mountable
models may be supplied with either carry handles or slides
and front handles installed. Follow all lifting instructions
specified in this document and installation instructions
supplied in the TWT user manual.
LIFTING INSTRUCTIONS FOR AR EQUIPMENT
Because most products must be
handled during distribution,
assembly and use, the risk of serious
injury due to unsafe product handling
should be a fundamental
consideration of every user. An
authoritative guideline for eliminating unwarranted risk of
injury caused by lifting is provided by the NIOSH Work
Practices (Publication #94-110) available at:
https://www.cdc.gov/niosh/docs/94-110/pdfs/94-110.pdf.
In general, observe the following guidelines for lifting a
weight of 50 lb or more:
•Use lifting eye (for floor standing) or side handles (table
top) to lift unit only.
•Use equipment of adequate capacity to lift and support
unit.
•If using forklift to move unit, be sure forks are long
enough to extend beyond the side of the unit.
•For additional information, follow the link specified
above.

ADDITIONAL WARNINGS & NOTES
WARNING:
This equipment operates at potentially lethal voltages. Only trained,
qualified personnel should operate, maintain, or service it.
Hazardous energy may be present while protective covers are removed
from the equipment even if disconnected from the power source. Contact
may result in personal injury.
CAUTION:
Only qualified personnel must perform adjustment, maintenance, or
repair of the equipment.
CAUTION:
Replacement fuses are required to be of specific type and current rating.
CAUTION:
The information in this document was obtained from reliable sources and
was believed to be accurate at the time of publication. Since subsequent
modifications to the machine may have been made, use this information
only as a guide. Carefully compare the unit's actual configuration and
operation to the descriptions in this manual before you undertake to
operate, service, or modify this machine. Any variance or modification
should be noted, dated, and initialed in the discrepant part of all manuals
on hand for future reference. If you have technical or editorial comments
you wish to make to the manufacturer, please write them on photocopies
of the relevant sheets.
NOTE: The contents of this document are the property of the manufacturer and this document is delivered on the express
condition that it not be disclosed, reproduced in whole or in part, or used for manufacture for anyone other than
the manufacturer without its written consent, and that no right is granted to disclose or so use any information in
this document.

TABLE OF CONTENTS
TABLE OF CONTENTS ..................................................................................................I
1. DESCRIPTION AND SPECIFICATIONS ....................................................... 1
1.1 TWTA Description ................................................................................................ 1
1.2 Suggested Applications.......................................................................................... 1
1.3 Specifications......................................................................................................... 1
1.4 Accessories ............................................................................................................ 1
1.5 Test Data Sheet...................................................................................................... 2
2. THEORY OF OPERATION .............................................................................. 5
2.1 Design of the Amplifier......................................................................................... 5
2.2 Description of the RF Subsystem .......................................................................... 5
2.3 Description of the Power Supply Subsystem......................................................... 6
2.4 Description of Electronic Crowbar........................................................................ 7
3. OPERATION....................................................................................................... 9
3.1 Warnings and Cautions.......................................................................................... 9
3.2 Installation ........................................................................................................... 10
3.2.1 Unpacking ..................................................................................................... 10
3.2.2 Mounting....................................................................................................... 10
3.2.3 Cooling Requirements................................................................................... 11
3.2.4 AC Line Power Connections......................................................................... 11
3.2.5 RF Connections............................................................................................. 12
3.2.6 External Interlock Connector ........................................................................ 13
3.3 Front Panel Features ............................................................................................ 15
3.4 Front Panel Display and Soft Keys...................................................................... 16
3.4.1 Overview....................................................................................................... 16
3.4.2 Menu Screens................................................................................................ 17
3.5 Rear panel features............................................................................................... 21
3.6 Initial Turn On and Warm-up Procedure............................................................. 22
3.6.1 Before Applying Power................................................................................. 22
3.7 Remote IEEE-488 Operation............................................................................... 23
3.8 TWTA General Considerations ........................................................................... 28
4. MAINTENANCE............................................................................................... 31
4.1 Safety Warning.................................................................................................... 31
4.2 Unauthorized Repairs .......................................................................................... 31
4.3 Preventive Maintenance....................................................................................... 31
4.4 Troubleshooting................................................................................................... 33
5. TECHNICAL DOCUMENTATION................................................................35
5.1 Schematics........................................................................................................... 35
5.2 Top Level Build Tree........................................................................................... 35
5.3 Sample Program for IEEE-488 Communication .................................................35

Rev B 1
1. DESCRIPTION AND SPECIFICATIONS
This manual provides operating, interfacing and selected service information pertinent to AR Model
8300TP8G12 Broadband Microwave Amplifier. The Model 8300TP8G12 is a 8300 watt pulsed X-band
traveling-wave tube amplifier (TWTA).
1.1 TWTA DESCRIPTION
The amplifier uses two traveling-wave tubes (TWTs) power combined to provide a 10,000 watt nominal
(+70.0dBm) output over the TWT amplifier's full bandwidth.
The amplifier is completely self-contained and packaged for standard 19-inch rack mounting or bench top
use. The front panel of the rack mountable amplifier is 15.75 inches high, and the overall unit is 30 inches
deep, excluding the rear-panel connectors.
Primary power is 190-260 volts 50-60 Hz., single phase. An efficient switching power supply design
provides minimum power consumption. A fast regulation control loop and a high degree of filtering ensure
performance within specifications over a wide range of operating conditions. The amplifier is fully enclosed,
and the upper and lower panels of the rack mountable amplifier are interlocked to reduce the likelihood of
accidental contact with high voltage.
1.2 SUGGESTED APPLICATIONS
•RF Susceptibility testing
•Antenna and component testing
•Equipment calibration
•General laboratory instrumentation
1.3 SPECIFICATIONS
Refer to the AR Data Sheet at the end of this section for detailed specifications.
1.4 ACCESSORIES
AR RF/Microwave Instrumentation offers a number of accessories for use with this amplifier including:
•Directional coupler
•Antenna
•Flexible transmission line
Refer to a current AR RF/Microwave Instrumentation catalog for Microwave Accessories.

Model 8300TP8G12
2 Rev B
1.5 TEST DATA SHEET
A Test Data Sheet for a specific unit is prepared at the time of manufacture and is included with the unit's
copy of this manual.

The rated power is developed by efficiently power
combining the outputs from two 5000 watts (nominal)
pulse TWTs that are factory matched in gain and
phase, resulting in an excellent combination of wide
instantaneous bandwidth with improved harmonic
levels.
Housed in a stylish contemporary cabinet, the amplifier
provides readily available pulsed RF power for a varie-
ty of applications in Test and Measurement, (including
EMC RF pulse susceptibility testing), Industrial and
University Research and Development, and Service
applications. AR also offers a broad range of amplifi-
ers for CW (Continuous Wave) applications.
See Model Configurations for alternative packaging
and prime power selection.
The export classification for this equipment is 3A999.d.
These commodities, technology or software are con-
trolled for export in accordance with the U.S. Export
Administration Regulations. Diversion contrary to U.S.
law is prohibited.
The Model 8300TP8G12 is a self contained, forced air
cooled, broadband traveling wave tube (TWT) micro-
wave amplifier system designed for pulse applications
at low to moderate duty factors where instantaneous
bandwidth and high gain are required. Reliable TWT
subsystems provide a conservative 8300 watts mini-
mum peak RF pulse power at the amplifier output
connector. Stated power specifications are at the fun-
damental frequency.
The amplifier's front panel digital display shows for-
ward and reflected average power output or forward
and reflected peak power, plus extensive system status
information accessed through a series of menus via
soft keys. Status indicators include power on, warm-up,
standby, operate, faults, excess average or peak re-
flected power warning and remote. Standard features
include a built-in IEEE-488 (GPIB) interface, 0dBm
input, TTL Gating, VSWR protection, gain control, RF
output sample ports, auto sleep, plus monitoring of
TWT helix current, cathode voltage, collector voltage,
heater current, heater voltage, baseplate temperature
and cabinet temperature. Modular design of the pow-
er supply and RF components allow for easy access
and repair. Use of switching mode power supplies
results in significant weight reduction.
Features
Specifications
8300TP8G12
 Pulse Amplifier
 M1–M12
 8300 Watts
 8GHz–12GHz
AR RF/Microwave
Instrumentation
160 School House Rd
Souderton, PA 18964
215-723-8181
For an applications engi-
neer call:800.933.8181
www.arworld.us

POWER (Fundamental), Peak Pulse, @ Output: Nomi-
nal, 10,000 watts; Minimum, 8300 watts
FLATNESS: ±10 dB maximum, ±5 dB at rated power
FREQUENCY RESPONSE: 8-12 GHz
INPUT FOR RATED OUTPUT: 1.0 milliwatt maximum
GAIN (at maximum setting): 69 dB minimum
GAIN ADJUSTMENT (continuous range): 35 dB mini-
mum
INPUT IMPEDANCE: 50 ohms, VSWR 2.5:1 maximum
OUTPUT IMPEDANCE: 50 ohms, VSWR 2.5:1 typical
MISMATCH TOLERANCE: Output pulse width foldback
protection at peak reflected power exceeding 4000
watts. Will operate without damage or oscillation with
any magnitude and phase of source and load imped-
ance. May oscillate with unshielded open due to cou-
pling to input. Should not be tested with connector off.
See S2M special option, if applicable.
NOISE POWER DENSITY:
(pulse on) Minus 70 dBm/Hz maximum;
Minus 73 dBm/Hz typical
(pulse off) Minus 140 dBm/Hz (typical)
HARMONIC DISTORTION: Minus 15 dBc maximum
PRIMARY POWER: See Model Configurations
PULSE CAPABILITY:
Pulse Width 0.2 – 50 microseconds.
Pulse Rate (PRF) 100 kHz maximum
Duty Cycle 4% maximum.
RF Rise and Fall 70 ns max (10% to 90%).
Delay 500 ns maximum from pulse
input to RF 90%
Pulse Width Distortion ±50 ns maximum (50% points
of output pulse width compared
to 50% points of input pulse
width)
Pulse Off Isolation 80 dB minimum, 90 dB typical
Pulse Input TTL level, 50 ohm nominal
termination
CONNECTORS (See S1C option, if available):
RF input: Type N precision female, rear panel.
RF output: Type WR90 waveguide flange, rear
panel
RF output forward and reflected sample ports:
Type N precision female, rear panel
Pulse input: Type BNC female, rear panel
GPIB: IEEE-488 female, rear panel
Interlock: DB-15 female, rear panel
COOLING: Forced air (self contained fans), air entry
and exit in rear.
SIZE (W x H x D): 50.3 x 43 x 84 cm, 19.8 x 17 x 33 in 
WEIGHT: 121 kg, 265 lbs
EXPORT CLASSIFICATION: 3A999.d
Page 2
Specifications
8300TP8G12
 Pulse Amplifier
 M1–M12
 8300 Watts
 8GHz–12GHz
EPackage Alternatives. May select an alternative
from the following [E1C or (E1C and E2S) and/
or E3H]:
E1C Cabinet: Without outer enclosure for rack
mounting, size (W x H x D) 49 x 40 (9U) x 81
cm, 19 x 15.75 (9U) x 32 in., Subtract approxi-
mately 16 kg, 35 lbs, for removal of outer
enclosure.
E2S Slides: slides installed, add approximately 5 kg,
10 lbs.
E3H Handles: Front pull handles installed.
PPrime Power: Must select one primary power
from the following [P1 or P2]
P1 208V, US: 208 VAC ± 10%, 3 phase, delta (4
wire) 50/60 Hz, 5 KVA maximum
P2 400V, Europe: 360-435 VAC, 3 phase, WYE (5
wire) 50/60 Hz, 5 KVA maximum. CE marked
to comply with EMC European Directive
89/336/EEC for operation inside a shielded
room.
P3 190-260VAC single phase, 50/60Hz, 5kVa
max
S Special Feature: May select a special feature
(extra cost) [S1C]:
S1C RF output on rear panel with all other connect-
ors on front panel. Interlock connector BNC.
RF output sample port 60dB coupling factor.
This option also removes reflected sample port.
Model Configurations
To order AR Products, call 215.723.8181. For an applications engineer call:800.933.8181. Direct to Service call: 215.723.0275 or
email: [email protected] For Faxing Orders:866.859.0582 (Orders Only Please) [email protected]
Approved for public release by AR RF/Microwave Instrumentation 021318
Model No.
Features
EPS
8300TP8G12 Base model P1 –
M1 E1C P1 –
M2 E3H P1 –
M3 E1C & E3H P1 –
M4 E1C & E2S P1 –
M5 E1C & E2S
& E3H P1 –
M6 –P3 –
M7 E1C P3 –
M8 E3H P3 –
M9 E1C & E3H P3 –
M10 E1C & E2S P3 –
M11 E1C & E2S
& E3H P3 –
M12 E1C & E3H P3 S1C
Model number example: Model 8300TP8G12M2
would have option E3H front pull handles installed.

Rev B 5
2. THEORY OF OPERATION
2.1 DESIGN OF THE AMPLIFIER
The 8300TP8G12 TWT amplifier consists of two main subsystems. The power supply subsystem and the RF
subsystem, which are discussed in sections 2.2 and 2.3, respectively.
These two subsystems work in conjunction with the control system. The heart of the microprocessor control
system is the CPU board. The microprocessor control system supervises the power supply and RF gain
controls and processes operator input by enabling communication with a host computer over the IEEE-488
interface or local control through the front panel display and buttons.
Communication of operational status with the amplifier is via fiberoptic links to the HPA interface assembly.
The HPA interface assembly provides fault monitoring capabilities for discrete fault logic and analog
readbacks. This assembly also contains the digital to analog circuits for controlling the solid state pre-amp’s
(SSPA) gain adjustment.
2.2 DESCRIPTION OF THE RF SUBSYSTEM
The TWTA consists of two stages of RF amplification: a solid state pre-amp (SSPA) assembly with
adjustable gain and a traveling-wave tube amplifier.
The type N RF input connector is located on the rear panel. The RF input is fed to the input connector on the
solid state pre-amp. The solid state pre-amp's output is passed through a hybrid coupler which then connects
to the RF input of the TWTs. The RF output of the TWT is a WR-90 waveguide. The output of each TWT is
fed into a combiner to power combine the two TWTs. The combiner has 2 directional couplers that are used
for metering the forward and reflected power. The output of the combiner sticks out of the rear of the unit as a
WR-90 waveguide output.
The reflected port on the directional coupler is connected to a detector diode, whose output is used for VSWR
protection by the power supply logic & control module. It is also used on the machine interface board for
conversion from analog to digital for use by the control head to display reflected power.
The forward port on the directional coupler is likewise connected to a detector diode, whose output is used on
the machine interface board for conversion from analog to digital for use by the control head to display
forward power.
Both the forward and reflected ports are also sampled using a 10dB coupler and fed directly to the RF sample
ports on the rear panel.
Amplifier gain is determined by the adjustable gain solid state pre-amp (SSPA). The emergency bypass board
mounted behind the front panel is provided with a circuit for control head bypass in the event of a failure.

Model 8300TP8G12
6 Rev B
2.3 DESCRIPTION OF THE POWER SUPPLY SUBSYSTEM
The TWT power supply is of modular construction. All modules are connected through a motherboard, and
are very easy to replace. This makes maintenance fast and easy.
Low Voltage Module: AC/DC converter which generates the +15VDC/-15VDC/+5VDC needed for
housekeeping.
Logic and Control Module: This module controls the power supply, monitors all the voltages and currents
of the unit, and provides protection for the power supply and the TWT.
Power Factor Corrector Module: This switching module forces the line current waveform to follow the line
voltage waveform. This minimizes the line harmonics and maintains the power factor near unity. The output
of this module provides the 370VDC bus used by the high voltage switching power supply.
Phase & Post Power Converter: The post and phase module, consists of the following:
•Fixed frequency resonant regulator and converter
•A linear regulator (Post Regulator)
The resonant converter operates at fixed frequency of 66kHz, at a power level of 2500W. It converts the
incoming 370VDC into a sine wave, using a resonant tank. (resonant inductor and capacitor ). That
waveform, is driving the primary of the high voltage transformer which generates the cathode and collector
voltages. The cathode voltage is tightly regulated by the post regulator, which compensates for the output
capacitor droop during the pulse.
High Voltage Rectifier and XFMR Module, 8kW: This module contains the high voltage transformer and
the high voltage rectifiers. The voltage waveform at the transformer primary is amplified by the transformer,
and rectified by the diodes to generate the cathode and collector voltages.
8kW High Voltage Filter: This module contains the high voltage capacitors for the cathode and the
collector voltages. This module filters the ripple from the high voltage rectifiers, monitors the cathode and
collector voltages, and sends a feedback signal to the post regulator.
Tank Module: The tank module contains a resonant inductor. It works with resonant capacitor (in the post
and phase module) together to force the current from square wave to be sine wave, and drive it into the
primary of the high voltage transformer.
Storage Capacitor Assembly: This module contains high voltage capacitors, which store the energy needed
to keep the cathode voltage well-regulated during the pulse. Since the main regulator loop cannot respond
during the pulse, the energy is taken from the caps, and the post regulator compensates for the capacitors
droop, to keep the cathode tightly regulated.
The Heater Power Supply Module powers the TWT DC heater. It uses +15VDC input and provides isolated
-6.3 VDC at cathode potential.
The Grid Module controls whether the TWT is ON or OFF. It generates two floating voltages at cathode
potential (one positive with respect to cathode= TWT ON , and one negative with respect to cathode =TWT
OFF). It switches its output between those voltages, at a rate of up to 100kHz, controls by the TTL drive at its
input.

Model 8300TP8G12
Rev B 7
Interconnects between the power supply modules are through a motherboard. It is installed in a finned heat
sink assembly to which the modules are bolted. The incoming cabinet air, boosted by a 400Hz fan, cools the
heat sink.
2.4 DESCRIPTION OF ELECTRONIC CROWBAR
Because the charge in the Cathode voltage capacitor storage module exceeds the maximum energy which can
be safely dissipated during a TWT tube arc, the 93PX is provided with an electronic crowbar which can shunt
the stored energy through a resistor network rather than through the TWT in the event of anomalous tube
behavior.
Two conditions cause the electronic crowbar to fire: an “unauthorized” pulse (a pulse that occurs in the
absence of a high on the pulse gate), or an “authorized” pulse accompanied by excessive helix current. An
unauthorized pulse may result from a number of abnormalities, including a TWT tube arc or a modulator
glitch. The high helix current condition may result from a high pulse top voltage, excessive RF drive, or a
tube arc within a pulse.
The electronic crowbar system consists of two subsystems, the Pulse Monitor Board and the Crowbar Driver
Board. The Pulse Monitor Board is responsible for making the decision to fire the crowbar, and the Crowbar
Driver Board contains the triggered spark gap switch and the trigger circuitry.
Pulse Monitor Board
The Pulse Monitor Board senses TWT pulses by means of a Hall Effect current sensor applied to the cathode
voltage (Ek) and heater (Ef) leads to the TWTs. Any beam current in excess of half an ampere or so results in
a detected pulse signal. In 3 to 5 microseconds this signal will cause a crowbar fire output from the board
unless it is masked by an “authorizing” pulse.
The “authorizing” pulse is created when all the following conditions prevail:
•The crowbar driver board is charged up and ready to fire
•A pulse gate signal is received
•High voltage power supply is turned on
•RF ON is selected
•No waveguide arc is detected
•Pulse gate is not over pulse width
•Pulse gate is not overduty
•Body current is within safe limits
When all the above conditions are met, the detected beam pulse is masked, and the crowbar will not fire
during the pulse.
If either over pulse width or overduty is detected, the pulse enable signal to the modulator is interrupted and a
warning is displayed on the front panel display.

Model 8300TP8G12
8 Rev B
Crowbar Driver Board
The Crowbar Driver Board contains the actual crowbar switch, which is a triggered gas gap between the
cathode supply and ground. The gap has a self-breakdown voltage of 20KV and will not fire when cathode
voltage is applied to it unless triggered by a high voltage pulse to its trigger electrode.
The driver board contains a 300 VDC supply which charges a storage capacitor. When this capacitor is fully
charged, the driver board signals the logic board that it is ready to fire the crowbar.
If a crowbar fire signal is received, a triac is turned on, dumping the charge in the storage capacitor into a
30:1 stepup trigger transformer. The transformer’s secondary is wired to the triggered gap trigger electrode.
When the spark gap fires, its series resistance is reduced to a few milliohms, and a large discharge current
quickly dumps the energy stored in the capacitor bank. The output resistors in the cathode supply have much
more impedance than the ignited spark gap, and as a result, most of the stored energy is dissipated by these
resistors. The actual energy dumped into the spark gap is low, so that the gap can fire repeatedly with no
significant deterioration.