Communications & Power Industries (CPI)

Varian Associates is remembered as the first company in Stanford Research Park and later as a maker of cancer treatment machines. But it started by building klystrons, the microwave tubes Russell and Sigurd Varian invented at Stanford in 1937. That tube business outlived the company that launched it. In 1995 Varian sold it. It became Communications & Power Industries, or CPI, headquartered on Hansen Way in Palo Alto.

CPI went through several owners and eventually moved its headquarters out of state. This profile covers how CPI came out of Varian, what it made in Palo Alto and where its pieces ended up. For the parent company, see our Varian profile.

The Varian tube business

CPI tells its own history as a continuation of Varian's. Its history page notes that Varian Associates started in 1948 with $22,000 of capital and six full time employees. The klystron was its first commercial product. In 1953 the company moved its headquarters to what is now Stanford Research Park. Our page on the Varian brothers covers the invention itself.

Varian's tube operations grew through the 1950s and 1960s. CPI's history lists several steps that later became CPI divisions:

• 1954. At the Canadian government's request, Varian set up Varian Associates of Canada in Georgetown, Ontario, to make microwave tubes locally.
• 1959 to 1964. Varian bought Bomac Laboratories, helped launch S-F-D Laboratories and bought LEL, Inc., combining them into one operation in Beverly, Massachusetts.
• 1960s. Varian bought General Electric's traveling wave tube business in Palo Alto.
• 1965. Varian acquired Eitel-McCullough, or Eimac, a tube maker founded in 1934 whose tubes powered Allied radars in World War II.

Later the Eimac division won an Emmy award for technical achievement for the Klystrode inductive output tube, an energy efficient tube for UHF television transmitters.

Spinning out in 1995

By the 1990s Varian wanted to focus on medical systems. CPI's 2004 annual report says the company was formed in 1995 when it acquired the Electron Devices Business from Varian Associates. Before August 11, 1995, its operations were part of that business. CPI's history page says the buyers were Leonard Green & Partners, a private equity fund, together with members of management.

The Palo Alto setup stayed close to Varian. CPI gave its principal executive offices as 811 Hansen Way, Palo Alto, California 94303. The 2004 filing said CPI subleased a portion of the larger Varian Palo Alto campus. Varian Associates itself split in 1999. Its medical business, Varian Medical Systems, kept the Hansen Way campus at 3100 Hansen Way.

What CPI made

In its 2004 annual report CPI described itself as a provider of vacuum electron devices, satellite communications amplifiers, medical x-ray generators and related products. It operated four manufacturing plants in North America and employed more than 200 scientists and engineers. Its main product families included:

CPI also rebuilt used tubes through its Econco operation, a rebuilder of power grid tubes founded in 1968.

Why tubes still matter

Most electronics switched from vacuum tubes to transistors decades ago. High power microwave work is the exception. A klystron sends a beam of electrons through a series of hollow metal cavities. A weak microwave signal in the first cavity makes the electrons bunch up. The bunched beam then hands much more energy to the signal in the last cavity. A traveling wave tube works on a similar idea along a long helix instead of separate cavities. Solid state devices can match tubes at low power, but at the very high power levels used in radar, satellite uplinks and particle accelerators, tubes often still win.

That is why a 1937 invention was still in production on Hansen Way in the 2000s. It is also why the business was valuable enough for TransDigm to pay more than a billion dollars for it in 2024.

A string of owners

CPI changed hands several times after 1995:

1. April 2006. CPI International, the parent company, went public on Nasdaq under the symbol CPII.
2. February 2011. An affiliate of Veritas Capital bought CPI for about $525 million and took it private.
3. July 2017. Odyssey Investment Partners acquired CPI.
4. October 2022. An affiliate of The Resolute Fund V, managed by The Jordan Company (TJC), acquired CPI.

Along the way CPI bought antenna, radome and amplifier makers including Malibu Research Associates, Radant Technologies, MCL and the satellite antenna business of General Dynamics. The company's center of gravity shifted from tubes toward large satellite antennas and defense systems.

The 2024 split

In November 2023 TJC announced the sale of CPI's Electron Device Business to TransDigm Group for about $1.385 billion in cash. The business, the direct descendant of Varian's tube operations, was described as a leading supplier of high power microwave components. It was spun out in June 2024 as CPI Electron Device Business and acquired by TransDigm. According to its own site it is headquartered in Beverly, Massachusetts. It employs about 500 people, mainly in the United States and the United Kingdom.

The rest of CPI kept the name. Its website now describes a communications and defense technology company focused on large aperture antennas, with about 1,400 employees. It lists its corporate headquarters at 1000 Klein Road, Plano, Texas. No Palo Alto location appears on its locations page. We could not confirm from official sources when CPI left Hansen Way or whether any CPI Electron Device Business work remains in Palo Alto.

Timeline

Why CPI matters to Palo Alto

CPI is the clearest example of how a Palo Alto invention outlived its inventors' company. Klystrons were first built in a Stanford physics basement, then produced on Hansen Way for more than half a century. They powered radar, satellite links and the accelerator at SLAC, which our research labs guide covers. For the people behind the tube, see our Varian brothers page and the Silicon Valley history.

Hansen Way is a short street in Stanford Research Park. The buildings are private and there is no marker. The best public reminder of what klystrons made possible is SLAC, which offers free public tours; see our SLAC visitor guide.

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