Hydro-Aire and MarVelco

Copyright Mark P D Burgess 2012 

Hydro-Aire was founded in 1943 in Burbank, California and began by making soldering irons and electric wall heaters. But it quickly moved into high technology products in support of the war effort:  Hydraulics, pumps and valves for aviation. It was acquired by the Crane Company in 1951. After joining the Crane Company Hydro-Aire established an electronics division to manufacture and market semiconductors at its San Fernando plant. In the 1960s Hydro-Aire supplied coolant pumps for the Apollo programme including the lunar landing module. [Watson 2005]

The Crane Company was founded in 1855 by R T Crane. It was one of the first 35 companies that paid $25,000 for a license to Western Electric for the rights to make transistors under its patents and was one of the attendees at its industry Transistor Technology Symposium in April 1952. Its semiconductor interests were vested in Hydro-Aire.

Armed with the knowledge acquired over the eight days of the Symposium and the Proceedings issued in September that year, Hydro-Aire made good progress and previewed a hermetically

sealed point contact transistor in its February 1953 edition of HYDRO-AIREings. [Hydro-Aire 1953 courtesy Jack Ward, Transistor Museum]

But four month’s later the transistors were not available. In June Hydro-Aire announced that it would soon be producing “new point-contact transistors in large quantities for immediate delivery.” The new transistors would be hermetically sealed in an unusual pentagonal can and featured “a unique arrangement of the contact wires.” [Picture from Electronics 1953.]

In October 1953 Hydro-Aire hosted Aviation Week for a photo shoot of their point-contact transistor production line. This showed the process starting from germanium dioxide through to a finished transistor.


Transistor production from a soft white powder called germanium dioxide to a thumb-nail size unit (above) is a difficult, complicated process involving metallurgy, microscopes and exception manual dexterity. Close checking must be continued throughout the process. This unusual series of photos taken at Hydro-Aire, Burbank, California, details important steps in manufacture of a point-contact transistor.

Baking the essential ingredient, germanium dioxide, in a hydrogen atmosphere is the first step in the life of a transistor. This stage of the process produces the required germanium ingot.


A growing furnace converts the ingot into a single crystalline structure. A helium atmosphere is also maintained in this furnace to insure exclusion of undesirable impurities.


Slicing the crystal into sections approximately 0.020 inch thick is done (above) after a purity check, made by measuring the crystal’s resistivity. Purity must be in order of one part in ten million of germanium.

Following cross-cutting, diced germanium creates particles approximately 0.040 inch square. Each of these will become a transistor. Next, particles are etched and cleaned.

Assembly of the germanium particle and wire “cat’s whiskers” is done with tweezers under a microscope. Wire spacing (approximately 0.001 inch) has a critical effect on performance.

A hermetic seal encloses the transistor elements after preliminary testing and adjustments. Hydro-Aire was one of the first firms to produce hermetically sealed units.

A final test measures the unit’s amplification (alpha) over a range of input signal frequencies. Laboratory-type techniques needed indicate why transistors presently are expensive and difficult to make. [Aviation Week 1953]

A remarkable recruit into Hydro-Aire was Dr Hans Erich Hollmann who joined the engineering staff of the Electronics Division, Hydro- Aire in 1954. Hollmann is popularly known as the “Father of Radar” due to his work in the 1930s in Germany. He was one of the many Operation Paper Clip scientists that were repatriated to the USA after World War II. His position at Hydro-Aire was his first industry job after he concluded his post war work at the US Point Mugu Naval Air Missile Test Center in California.

By 1954 Hydro-Aire had a range of five point-contact transistors all in the pentagonal can. They are shown in the following table.





RF Point-contact type

Cut-off 4.5 MHz


RF Point-contact type

Cut-off 3.0 MHz


IF Point-contact type

Cut-off 1.5 MHz


AF Point-contact type

Cut-off 0.5 MHz


Fast switching Point-contact type

Turn-off < 2µ Sec


Medium switching Point-contact type

Turn-off < 6µ Sec

Source: Turner 1954

Hydro-Aire promoted its transistors to the radio amateur or ham community advertising in the Radio Amateur’s Handbook and QST. Soon after its point-contact transistors were available it suggested in the 1954 Handbook “Every Ham and Radio Hobbyist should know about transistors. The time to investigate is now!” Hydro-Aire offered free instructions for building a broadcast band receiver using its transistors.

Around this time assembly of point-contact transistors was manual and on a small scale. This is illustrated in the following picture (courtesy of Jack Ward, Transistor Museum):

By 1955 Hydro-Aire supplemented their point-contact range with a modest selection of PNP junction transistors. These are listed in the table below. In common with other producers Hydro-Aire branded low specification transistors for the Hobby market including its favourite niche: ham operators. For them it promoted the CQ-1. Amateurs of the day would have immediately appreciated its link to the early days of radio.

Picture: Reverse side of a CQ-1 Courtesy Andrew Wylie        

In support of the CQ-1 Hydro-Aire produced a booklet entitled “The Transistor and You” featuring cartoons encouraging the amateur fraternity to embrace the  modern world of transistors. [Hydro-Aire 1955] Picture left from QST 1955.

In May 1955 Hydro-Aire advertised a new "bonded barrier" transistor, for high frequency applications. It had a frequency cut off of 5 MHz which made it suitable for oscillator/mixer applications for AM medium wave (broadcast band) applications.

It is not clear what the “bonded barrier” transistor was and definitions for it (“A transistor made by alloying the base with the alloying material on the end of a wire”) suggest it is simply an alloy junction transistor, possibly made in a variant of the conventional process.  Hydro-Aire’s advertising above mentioned that the new transistor was “ideally suited to large scale production” and that the Electronics Division of Hydro-Aire was expanding its production in order to meet the expected demand.

Picture from Electronics May 1955 showing “HA EC” marks on reverse side.


By 1955 its new transistors included:





PNP High gain audio type

150 mW gain 0.97


PNP Medium gain audio type

150 mW gain 0.94


PNP Low gain audio type

150 mW gain 0.90


PNP High gain audio type

100 mW gain 0.975


PNP Low gain audio type for Hobbyist/Ham use

150 mW gain 0.90





PNP Medium gain RF type

Cut-off 5 MHz


PNP Medium gain IF type

Cut-off 3 MHz





Point-contact switching type






PNP Medium power type

500 mW




Sources: Tele-Tech September 1955 and Electronics 1953


Left: Hydro-Aire Transistors HF-1 JP-1 and J-3 and rear side Right: showing “HA EC” marks. Courtesy Andrew Wylie

Hydo-Aire Becomes MarVelco

In 1955 the Electronics Division of Hydro-Aire changed hands and became part of Mar Vista Electronics Company. This was announced by Hydro-Aire’s President, Homer H Rhoads and Reagan C Stunkel,  head of the new firm. The PR around the announcement advised that in the future the brand name associated with the semiconductor product line would be “Marvelco.”

The parties to the deal noted that production would continue at the Hydro-Aire site at 3000 Winona Avenue, Burbank for “two months” but after that time the plant would move. [Western Aviation 1955]

By October thanks to further acquisitions by Stunkel, Mar Vista Electronics became a subsidiary of National Aircraft Corporation. [Aviation Daily 1955]

While still at Hydro-Aire, Hollmann had revealed that Hydro-Aire had developed experimental "tandem transistors" in connection with its work in free-power devices. These consisted of two transistors housed in a single container. [Aviation week 1955]

Hollmann followed the electronics division into the new Marvelco with publicity noting at the time: “The bonus: Dr. Hans E. Hollmann, Hydro-Aire's research scientist. Now NAC has appointed Hollmann director of research for its Marvelco Electronics Div., which will set about adding personnel for research into advanced techniques.”  [Control Engineering 1956]

Marvelco continuedthe Hydro-Aire range in their own livery as this J-2 type from the web site of Jack Ward shows. More information can be found here at the Semiconductor Museum.

By 1956 the Marvelco brand was established and launched the new MT-1 tandem transistor: featuring an integrated DC coupled design intended to provide better matching to the previous stage. Samples were available from January 1956 [Aviation Daily 1956] News of this new device also featured in Electronics for February 1956



Advertising for the MT-1 Tandem Transistor


New transistors available in 1956 are shown in the following table and which were now identified as “Marvelco.”






PNP Medium gain RF type

Cut-off 10 Mhz


PNP low gain IF type

Cut-off 3 MHz


PNP low gain IF type

Cut-off 3 MHz


PNP RF type for Hobbyist/Ham use

Cut-off 2.5 MHz


Tandem PNP type                      [Advertising]



PNP high gain AF type                [JEDEC 1758]



Source: Marrows H Transistor Engineering Reference Handbook J F Rider 1956

The only JEDEC registered transistor made by MarVelco was the 2N237 registered in 1956  shown below. [JEDEC 1758]


After 1956 MarVelco seems to have faded away as to date nothing more has been discovered about them.


Aero digest 1954 Dr. Hans Erich Hollman, one of German's early pioneers in the field of microwaves and transistors, has joined the engineering staff of the Electronics Division, Hydro- Aire  68-69

Aviation Daily Reagan C Stunkel, west coast aviation industrialist has acquired National Aircraft Corp   100 October  1955

Aviation Daily New Tandem Tranistor devlelped by MarVelco 102 January 1956

Aviation Week 1953 How a Transistor is Born October 26th 1953 74-7

Aviation Week 1955 Hollmann revealed that Hydro-Aire had developed experimental "tandem transistors" in connection with its work in free-power devices. 63

Control Engineering 1956 The bonus: Dr. Hans E. Hollmann, Hydro-Aire's research scientist. 3, Part 1

Electronics  June 1953 Hydro-Aire advertising p 257

Electronics 1956 Tandem transistor has high input resistance  29 2 (Feb)  354

Hydro-Aire 1953 HYDRO-AIREings 2, 3  Feburary 6th 1953

Hydro-Aire 1955 The Transistor and You

Marrows H 1956 Transistor Engineering Reference Handbook J F Rider

QST 1955 Hydro-Aire advertising 39 3 March 1955, p118

Turner R 1954 Transistors Theory and Practice Gernsback Library

Watson P 2005 Crane 150 Years Together (The Corporate History of Crane) Crane Company 2005

Western Aviation Magazine 1955 Hydro-Aire Section Becomes New Company