Microwave Amplifier & Oscillator Tubes

Magnetron tubes are high power microwave oscillators, best known for their role as the heart of centimetric radar and the defining component of microwave ovens. Magnetrons have a pulsed- or constant-current hot cathode, which emits a stream of electrons into a circular chamber lined with cylindrical cavities. An external permanent magnet applies a perpendicular magnetic force, causing the electrons to spiral outward and past the cavities. The cavities induce bunching in the electron stream, creating a high frequency signal which then passes to the anode.

The magnetron was invented by Albert Hull at the General Electric Research Laboratory (GERL) in 1920. By 1925, GERL achieved the successful operation of a 15kW magnetron at a frequency of 20kHz. Unlike a conventional magnetron, the Hull magnetron uses an external stator coil instead of a permanent magnet, and does not achieve the microwave frequencies usually associated with magnetrons. High frequency cavity magnetrons arrived in 1940, developed at Birmingham University by John Randall and Harry Boot. The cavity magnetron revolutionized the effectiveness of radar, offering much more power than the early klystron-based US and German centimetric radar systems.

The klystron was invented at Stanford University by Russell and Sigurd Varian in 1937. Klystrons rely on the internal geometry of one or more resonant cavities to generate oscillations in an electron beam, which is then velocity-modulated by a weak external RF signal. The velocity modulation creates electron bunching, generating an RF current within the beam which is then passed magnetically to an output waveguide or pickup. Because of their extremely critical dimensional requirements, klystrons must be individually hand-built, and tuned much like a musical instrument.

Early klystrons were low-power devices, surpassed by cavity magnetrons for high power applications such as radar. However, the highly stable output frequency of the klystron makes it an inherently more versatile device than the frequency-drifting magnetron. As more powerful klystrons have been developed, the magnetron has been made obsolete in virtually every instance. Klystrons are still widely used in radar, communications and high energy physics applications. The magnetron's last remaining widespread use is in microwave heating, where its low cost and high power-to-size ratio surpass the klystron. Precision frequency output is not required in such devices.

Federal Telephone & Radio 5J29
 Federal Telephone & Radio 5J29

The 5J29 is an unusual device, a water-cooled split anode magnetron, used primarily in the AN/APT-4 radar jammer. Unlike a conventional multicavity magnetron, the 5J29 is effectively a miniature cyclotron accelerator. The 5J29 is best known as a GE product; the second-source FTR version is much rarer. The 5J29 operates at frequencies between 350 and 770MHz.

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Microwave Associates 6229
 Microwave Associates 6229

The 6229 is a cavity resonator-type magnetron used in the Nike I missile guidance unit. The 6229 employs a grounded anode and a negatively pulsed cathode to generate 0.25-microsecond 700W pulses of RF energy. The average power output of the magnetron is 0.35W. The 6229 is tunable from 8.9 to 9.4 GHz by means of a tuner shaft that varies the cavity dimensions.

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OKI 17V10
 OKI 17V10

In the 1950s, the Japanese corporation OKI collaborated with Raytheon to produce their own versions of the WWII-era 2K33 K-band oscillator klystron. The OKI 17V10 is an example of this development. Note the similar construction to the related Raytheon QK291 pictured below.

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OKI 35V11
 OKI 35V11

A typical example of OKI's air-cooled envelope type, the 35V11 is a 150mW mechanically tuned reflex klystron operating in the 37.5GHz range.

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Raytheon 2K28
 Raytheon 2K28

The 2K28, an improved version of Raytheon's earlier 707 series devices, is a small external cavity klystron with an octal base. The 2K28 operates in the 1.2-3.75GHz range, 125mW output.

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Raytheon 2K45
 Raytheon 2K45

The 2K45 is a thermally tuned reflex klystron which operates in the 8.5-9.66 GHz range. It has an average power output of 30 mW.

Raytheon 2K45 Datasheet

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Raytheon 2K48
 Raytheon 2K48

The Raytheon 2K48 is an unusual external cavity reflex klystron with a long waveguide adapter. The 2K48 operates between 4.2 and 10.75GHz, 5-20mW output.

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Raytheon QK291
 Raytheon QK291

The Raytheon QK291 is a small two-cavity Ka-band klystron, mechanically tunable from 33.52GHz to 36.25GHz. The QK291 is a low-power device, with an 18mW average power output.

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Raytheon RK2K25
 Raytheon RK2K25

The RK2K25 is a small, mechanically tuned reflex klystron which operates between 8500 and 9660MHz.

Philips 2K25 Datasheet

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Raytheon RK5609
 Raytheon RK5609

The Raytheon RK5609 200W fixed frequency continuous wave magnetron is believed to be the first magnetron built to operate in the 2.45GHz heating band. Unlike cheaply constructed oven magnetrons, the RK5609 bears a close resemblance to WWII-era radar jammer magnetrons, such as the QK59.

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RCA 1A5V4
 RCA 1A5V4

The RCA 1A5V4 is a traveling-wave tube of unknown specification. Traveling-wave tubes greatly amplify RF signals by using a high power electron beam which fires down the center of a helical coil, interacting with a parallel RF signal which is simultaneously being carried by the coil itself. This results in a velocity modulation feedback interaction between the RF signal and the electron beam, producing an amplified RF output. Traveling-wave tubes are considered broadband devices, with frequency ranges of up to three octaves.

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Sperry 2K35
 Sperry 2K35

The 2K35 is a multi-cavity, 25W klystron amplifier, tunable between 2.73 and 3.30GHz. Forced air cooling, 6.3V 1.6A filament.

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Sperry 2K36 / 416
 Sperry 2K36 / 416

The 2K36 / 416 is a klystron frequency multiplier, which up-converts a 300 MHz signal to 3 GHz. Coaxial inputs & outputs, octal base.

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Sperry 2K41
 Sperry 2K41

The Sperry 2K41 is a two-cavity mechanically tuned klystron used in various military radar and communications systems. This tube generates frequencies from 2660 to 3310MHz, with a filament voltage of 6V, beam voltage of 1200V, and a reflector voltage of 750V.

2K41 Datasheet

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Sperry 410R
 Sperry 410R

The 410R is a two-cavity, 3 GHz klystron tube with four threaded coaxial inputs/outputs; octal base. The 410R is a prototype of the 3K30.

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Sperry SRC8A
 Sperry SRC8A

The Sperry SRC8A is a fairly early C-band reflex klystron. This unit is a pre-production example, labeled as experimental.

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Sperry SRL-7F
 Sperry SRL-7F

The Sperry SRL-7F is a low power klystron oscillator, tunable from 1.7 to 1.9 GHz. Power output is variable, from 5.7 to 9.2 watts.

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Sylvania 6BL6 & 6BM6
 Sylvania 6BL6 & 6BM6

Devices included in this entry:

Sylvania 6BL6 (pictured in thumbnail)
Sylvania 6BM6


The Sylvania 6BL6 and 6BM6 are small glass-and-metal external cavity reflex klystron with an asymmetrically keyed four-pin 'peewee' style base. The 6BL6 is rated at 1.4-6.5GHz, 250mW, and the 6BM6 is rated at 0.55-3.8GHz, 175mW.

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Varian V-45
 Varian V-45

The Varian V-45 is a two-cavity 1:5 frequency multiplier klystron, designed to up-convert a L-band signal into a X-band signal. Output is 9.0-10.0MHz, 1W. Beam voltage is 650V.

Special thanks to Richard Hall K5GZR for donating this device.

Varian V-45 Test Data Sheet (PDF)

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Varian V-153
 Varian V-153

The Varian V-153 is a mechanically tuned 9500MHz low power reflex klystron.

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Varian VA-113
 Varian VA-113

The Varian VA-113 is a small reflex klystron, tunable from 5.925 to 6.575 GHz. The VA-113 has a mechanical tuning range of 650 MHz, and an electrical tuning range of 15MHz. Maximum beam power is 500VDC @ 80mA. 1964 date code.

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Varian VA-162P
 Varian VA-162P

Varian VA-162P backward wave oscillator. Specifications are currently unknown.

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Varian VA-220G & VA-221E
 Varian VA-220G & VA-221E

Devices included in this entry:

Varian VA-220G
Varian VA-221E (pictured in thumbnail)


The Varian VA-220G and VA-221E are two similar 1W microwave relay reflex klystrons with forced air cooling. The operating frequency range of the VA-220G is 6.425-6.575GHz; the frequency range of the VA-221E is currently unknown.

Klystrons of this type now suffer the attention of Dr. Who fans, due to their collective realization that a red VA-220 klystron performed the part of 'Etheric Beam Locator' in the 1975 episode Genesis of the Daleks. Consequently, the price of these $20 tubes temporarily spiked to well over $200.

VA-220A-G & VA-220Z Datasheet (PDF)

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Varian VA-806F
 Varian VA-806F

The Varian VA-806F is a four-cavity 8.2 GHz (X-band) water-cooled klystron tube with a 2kW output. The VA-806F was originally used in military satellite systems in the 1960s. Other members of the VA-806 series have seen modern use in plasma containment research.

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Varian VRX-7204A
 Varian VRX-7204A

The Varian VRX-7204A relay klystron is a functional replacement for the older Western Electric 457A klystron. The VRX-7204A is tunable from 10.7-11.7GHz, 100mw output.

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Western Electric 2K50
 Western Electric 2K50

The 2K50 is a thermally tuned reflex klystron which operates in the 23.5 to 24.5 GHz range. This particular example is an extremely rare pre-production Western Electric / Bell Labs variant.

Bendix 2K50 Datasheet

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Western Electric KS22469L1
 Western Electric KS22469L1

The Western Electric KS22469L1, manufactured by Varian Canada, is a large 25W X-band traveling wave tube. Little is known about this device.

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