OPERATING

INSTRUCTIONS

HIGH-POWER

CW TWTs

OIHPCWTWT Rev. B

ECO No. MPP621637 ECO Date: 03/01/21

INTRODUCTION

These Operating Instructions provide basic information for

installing and operating CPI MPP’s 6200 Series, 6300 Series,

and VTC-6164H4 high-power CW helix vacuum electron

devices (traditionally known as helix traveling-wave tubes, or

TWTs). Supplementary information is given in the individual

Test Performance Sheet, Product Specification, and the

product outline drawing. The Test Performance Sheet, which

is shipped with the product, contains characteristics and

operating values for the individual unit. Inquiries for

additional information and requests for copies of these

publications should be made to:

Manager, Marketing

Communications & Power Industries, Inc. (CPI)

MICROWAVE POWER PRODUCTS DIVISION

811 Hansen Way

Palo Alto, CA 94303

Telephone: (650) 846-3900

For more detailed product operating procedures in specific

equipment, consult the applicable equipment manuals and

equipment performance standards. Additional information

may be obtained from the equipment manufacturer. Some

operational details specified by the equipment manufacturer

may vary from those given herein.

WARNING

SERIOUS HAZARDS EXIST IN THE OPERATION OF

MICROWAVE DEVICES. BEFORE ATTEMPTING ANY

PRODUCT OPERATION, CAREFULLY READ AND

UNDERSTAND THE “OPERATING HAZARDS” SECTION

FOLLOWING THESE OPERATING INSTRUCTIONS, AS

WELL AS THESE INSTALLATION AND OPERATING

INSTRUCTIONS. A COPY OF “OPERATING HAZARDS” IS

ALSO SHIPPED WITH EACH PRODUCT.

SPECIFIC HAZARDS

CPI as a component supplier can assume no responsibility for

any damage or injury resulting from operation of CPI

products. These devices must be used with equipment

designed to protect personnel against all operating hazards.

Installation and operating precautions should be observed,

and ratings given in the Test Performance Sheet must not be

exceeded.

High Voltage — Normal operating voltages are deadly. The

equipment must be designed so the operator cannot come into

contact with high voltages. High-voltage circuits and

terminals must be enclosed, and interlocking switch circuits

must be maintained so they open the primary circuits of the

power supply and discharge high-voltage capacitors when

access is required.

RF Radiation — Exposure to rf radiation generated by this

device during operation may cause serious bodily injury,

possibly resulting in blindness or death. Cardiac pacemakers

may be affected. Exposure of the human body to microwave

radiation in excess of 10 milliwatts per square centimeter can

be harmful. For this reason, rf energy must be contained by

the waveguides and shielding. If voltages are to be applied

when the device is not connected into a waveguide system,

the rf input and output flanges should be closed tightly with

shielded terminations.

Beryllium Oxide (BeO) — Some of these product types

utilize beryllium-oxide parts. The dust and fumes from

beryllium oxide are highly toxic and can cause serious injury

or death. Those devices containing beryllium oxide are so

labeled.

Elevated Temperatures — External surfaces of those

product types that are conduction cooled will attain

temperatures in the 100–200C range during operation,

notably in the collector region. Avoid physical contact for a

sufficient period after operation is terminated to permit

adequate cooling. The water used to cool the collector reaches

scalding temperatures. Touching or rupture of the cooling

system can cause serious burns.

These hazards are specifically described in the Operating

Hazards section immediately following these operating

instructions. Equipment using these devices must be designed

to minimize risk to personnel from these hazards. Equipment

manufacturers and users must develop and institute

procedures suitable for the particular equipment and specific

use to guard against all hazards not eliminated through

equipment design.

HANDLING

The product is shipped in an approved package that will

protect it from moderate handling abuse. If the outer

container shows evidence of being dropped or is punctured,

open the package and inspect the unit for damage. Inspect the

product when it is removed from the container. If any obvious

defects appear, a report should be sent to the factory at once.

Any damage during shipment should be reported to the

carrier. Handle the device with care during unpacking and

installation. Exercise particular caution to prevent any

damage to the mounting surface of conduction-cooled

devices, since such damage may restrict heat transfer during

operation.

PROTECTIVE MEASURES

These devices must be used in equipment that provides

automatic protection as described below. In addition,

installation and operating precautions must be observed, and

ratings shown within the Test Performance Sheet must not be

exceeded. Failure to comply fully with the foregoing may

result in product failure, damage, or decreased operating life.

Any product damage or failure resulting from noncompliance

with these requirements or which, in CPI’s opinion, could

have been avoided by compliance with these requirements

will void the CPI warranty.

Heater Voltage — Either an ac or dc heater supply may be

used unless otherwise specified on the Test Performance

Sheet. In some cases, an ac heater voltage will damage the

device. If an ac heater supply is used, there is no limitation on

the frequency of the voltage. However, for minimum heater

modulation, a direct-current heater supply may be used. If a

dc heater supply is used, the yellow lead must connect to the

positive side of the heater supply (see Figure 1). Product life

will be greatly reduced if the heater polarity is reversed.

Moreover, heater surge current should never exceed

approximately two and one-half times the steady-state value.

TD3673

+–

HE LIX

SUPPLY

+–

INPUT

RED

BROWN

YELLOW

BLACK

HE ATE R

SUPPLY

+ –

OUTPUT

CO LLECTOR

SUPPLY

FIGURE 1.

TYPICAL POWER-SUPPLY CIRCUIT

Helix (Body) Current — An overcurrent relay (as depicted

in Figure 1) should be part of the power supply and should

remove the helix voltage (sometimes referred to as beam or

cathode voltage) in a fraction of a second if the TWT body

current exceeds the specified value. The relay trip level

should be adjusted to 130 percent of the maximum current

encountered in system operation or to a value just below the

absolute maximum rating, whichever is lower.

Power-Supply Insulation — Since the TWT body operates at

ground potential, the heater supply must be insulated to

withstand the full beam voltage.

Cathode Current Delay — Voltages that initiate cathode

current flow should never be applied to the device until the

cathode has reached full operating temperature. The cathode

is raised to operating temperature by applying heater voltage.

A time-delay relay in the power supply should prevent the

application of other voltages until the specified time after the

heater is turned on, or as defined by the individual Product

Specification. Refer to the “Operation” section of these

Operating Instructions.

Thermal Switch — Most of these devices are equipped with

an integral thermal switch that should be connected to the

power supply such that the device is turned off if the switch

activates. The designated operating (trip) temperature of these

switches is somewhat above the maximum continuous

operating temperature for each product type. Both normally

closed and normally open switches are used; see the specific

Product Specification. Because the thermal switch is intended

to protect the device in case of cooling-equipment failure,

absence of thermal-switch operation is not an indicator of

adequate cooling.

Cooling —

Conduction-Cooled Types. The most effective cooling for

these devices is provided by a liquid-cooled heat-exchanger

plate. Because conduction cooling is achieved through the

base plate, it must be tightly fastened to a heat sink whose

maximum temperature does not exceed the maximum

allowable temperature defined by the individual Product

Specification. A finned heat exchanger bolted to the base

plate can be used to cool these TWTs, but this method only

provides adequate cooling in limited applications (those

where the maximum inlet air temperature is not greater than

40C, the altitude is near sea level, and collector dissipation

is no greater than 1 kilowatt). Under these conditions, a

finned heat exchanger with high fin density (as in a brazed

assembly) is required. The exchanger must be compact and

placed directly under the TWT collector area. Heat

exchangers using extruded aluminum fins are generally

inadequate.

Air-Cooled Types. Air-cooled types have passageways within

the TWT package that allow air to be ducted from an external

blower. The blower chosen should be able to supply the air

flow in accordance with the requirements given in the

individual Product Specification at the total back-pressure of

the TWT, plus that of ducting and filters used with the

equipment.

Whether liquid or air cooled, the mounting surface of the heat

sink must be machined smooth and flat to ensure maximum

contact area with the TWT base plate. The heat transfer to

the heat sink is improved by using a thin layer of high-

conductivity grease, such as Wakefield Thermal Compound

No. 120-8, or equivalent. The amount of compound used