High Frequency Tubes

When operating in the realm of microwave and broadcast frequencies, electron tubes must take on unusual forms. The most common types of high frequency tubes are klystrons and magnetrons, which are used to generate microwave-level frequencies. Magnetrons are still widely used today, as the heat source in consumer microwave ovens. Klystrons still see use in broadcast transmitters for television and radio stations, as well as airborne and ground based radar installations.


Raytheon 2K33

The 2K33, made by Raytheon, is a mechanically tunable reflex klystron that operates in the 22 to 25 GHz band with a 40mW output. The tube is tuned by varying the length of the envelope through a flexible metal disk seal, a large mechanical lever arrangement on the top of the tube provides for this function. This unit lacks the bracket and tuning knob seen on some similar klystrons that is used for mechanical tuning, though the mounting flange is present and a knob could easily be installed.


Raytheon 2K33 Klystron Tube

The CV3615 is a small British klystron packaged in a glass tubular envelope with a 4 pin base. This tube can produce frequencies in in ranges between 500MHz and 3.5GHz, and can be electrically tuned within a 6MHz window. Unlike many larger klystrons, CV3615 tubes were designed to be used with an external cavity; a cylindrical brass and bakelite enclosure which would fit over the top of the tube and seal against the two brass rings in the tube envelope. The length of this cavity would set the 6MHz tuning window, a mechanical plunger attached to a rack and pinion assembly allowed the length of the cavity to be changed as needed. The CV3615 tube was first introduced in 1948.

Of note to collectors is that some versions of this valve were packed in metal canisters, though later versions came in normal tube cartons.


CV3615 Klystron Tube
English Electric Valve Company M558

This compact pulse magnetron, produced by the English Electric Valve Company, was designed for use in marine radar systems. Derived from the 2J42, the M558 operates in the X band and has a power output of 8 kilowatts. The M558 is designed to be mounted in an external cavity, which would include the large curved magnets necessary for the tube's operation. Interestingly, the tube's 6.3 volt filament is brought out to a standard bayonet lamp connection, similar to the type used on an ordinary flashlight bulb. In operation, this filament connection would poke out through a hole between the two curved magnets on the external cavity. The example shown here was still packed in its original carton, which includes a thermoformed Styrofoam clamshell to protect the tube during transit.

Special thanks to Antony Evans for providing this unusual part.


English Electric Valve Company M558 Magnetron Tube
Raytheon 2J56

The Raytheon 2J56 is a large 50kW pulse magnetron, one of a series of X-band magnetrons operating in the 9GHz range. Released in 1945, the 2J56 incorporates a pair of integrated magnets that are located on each side of the cavity. Versions of this tube were made with both opaque and transparent glass envelopes, the transparent version is shown here. The 2J56 was used by the US military in a number of airborne applications, and was a critical component of tail-gunner radar systems deployed on both the B-36 and B-47 strategic bombers.

The particular 2J56 shown here has a rather interesting history; it was removed from the fire control radar system for the Convair XB-46 medium bomber prototype. The Convair XB-46 was produced in 1947 under the request of the US government, and only a single prototype of the bomber was built before the project was canceled near the end of 1947. The XB-46 was subsequently dismantled and the cockpit section was sent to the United States Air Force Museum in Dayton Ohio for storage and eventual display. The remainder of the aircraft was scrapped and believed destroyed until 2015, when the fire control radar unit was discovered at an estate sale in Indiana. The whereabouts of the rest of the XB-46 prototype remain unknown.


Raytheon 2J56 Magnetron Tube
Sperry 2K46

The 2K46 is a tunable air cooled klystron frequency tripler, with an output of 8.1 to 10 Ghz. Tuning is accomplished mechanically; three pleated baffles can be adjusted by turning the threaded shafts located around the circumference of the tube. The heater voltage is 6.3 volts and the output is rated at 1.5kV. The inputs and outputs are coaxial, and exit from the sides of the tube instead of through the octal base.


Sperry 2K46 Klystron Tube
Sylvania 5789W

This device was somewhat difficult to identify, but research revealed that it is a magnetron. The copper portions of this device that are mounted on either side of the waveguide are slightly magnetic, suggesting that the device originally had much larger magnets attached. The output of this tube is a fixed 34 GHz and the power requirement is around 14 kV. According to the book Tube Lore, this is the first commercially available US magnetron for the Ka band, and was released in 1949.


Sylvania 5789W Magnetron Tube
Klystronics 7238

The Klystronics 7238 appears to be a fairly typical metal-enclosed reflex klystron, almost surely electronically tunable. This tube uses a modified octal base commonly seen in small klystrons, in which one pin is replaced with a long waveguide. Unfortunately data on this device is scarce, and the specifications are unknown.


Klystronics 7238 Klystron Tube
Western Electric 730A

The Western Electric 730A is a non-tunable magnetron with an oscillating frequency of 9.375GHz, +/-30MHz. The 730A was used in military radar equipment. Note that the wooden base is part of the tube's original packing material, not an installable component. This base would mate with a tongue-and-groove arrangement in the tube's packing carton to hold it firmly in place.


Western Electric 730A Magnetron Tube
General Electric ZP-597

The GE ZP-597 is a large liquid-cooled magnetron, built in the 1940s. Little is known about this tube, but it appears to be a mechanically tunable device; a threaded collar allows the length of the cavity to be varied without tools. The tube has two pairs of liquid cooling connections, one of which is a simple copper tube that circles the outside of the device.


General Electric ZP-597 Magnetron Tube
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. The two halves of the 2K41 are joined by a flexible metal accordion, which allows the dimensions of the internal cavity to be changed by turning the large knob on the right of the device.


Sperry 2K41 Klystron Tube
Raytheon 2J51

The 2J51 is a tunable air-cooled magnetron with a range of 8.5Ghz to 9.6Ghz. Unfortunately this sample is badly damaged and missing several components, including the large semicircular magnets that would be clamped to each side of the tube. An undamaged 2J51 can generate microwave pulses in excess of 40 kilowatts.


Raytheon 2J51 Magnetron Tube

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