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WSHU Chief Engineer Paul Litwinovich explores aspects of vintage radio, from the radio sets themselves to the people and technology that made it all possible.

Zenith Trans-Oceanic, The "Royalty of Radios"

P. Litwinovich collection.

Last month, we took a look at the beginnings of what would be the age of connectivity on the go, the battery portable radio. This month I'll feature a line of battery powered tube radios that brought the technology to its pinnacle. The Zenith Trans-Oceanic series of shortwave portables would stretch from 1941 through 1982, with tube models produced until 1963. The radios performed so well, and became so popular, that they earned the nickname "The Royalty of Radios."

Credit U.S. navy file photo
Lt. Commander Eugene McDonald as a naval officer.

One of the sets that I featured last month was the Zenith Model 5G401, the beginnings of a long line of such sets. The Zenith Corporation was founded in 1918 by amateur radio operators Ralph Matthews and Karl Hassel in Chicago as Chicago Radio Labs. They produced and sold amateur radio equipment. In 1921 they were joined by Eugene F. McDonald, who had served as a lieutenant commander in the U.S. Navy in WWI. Under McDonald, the company incorporated in 1923 as the Zenith Radio Corporation. By 1924, the company began marketing consumer radios and in 1926 began the mass production of its first AC powered radio. McDonald remained a naval reservist until 1939, but was never recalled to active service. He did however, become an avid yachtsman.

Zenith was a significant player in the 1920s radio market, but, prior to the Great Depression, did not hold the same market share as Atwater Kent or RCA. The closing of the Atwater Kent factory in 1936 and RCA's decision to make the greater part of their income from licensing their patents rather than be a major producer of radios at this time, opened the door for Zenith to become the leading manufacturer of mid-grade to high-end radios. With the development of tubes in the late 1930s to support portability, McDonald came up with the concept of a portable shortwave radio that he could use while at sea on his yacht. Although the series of radios was inspired by his yachting experience, Mr. McDonald correctly assumed that consumers were hungry for portables that could receive international shortwave broadcasts. By this time, the popularity of international shortwave broadcasts was growing rapidly.

Using the circuit developed for the Model 5G401, Zenith first refitted it to a larger chassis and cabinet resulting the Model 6G601 shown below. The larger chassis would allow for the addition of the components required to receive shortwave. The AM only radio became known as "The Clipper" because it had the image of a sailboat on its grill.

The greatest challenge facing the Zenith engineering team, lead by Chief Engineer Gilbert E. Gustafson, would be to design a tuning assembly that would result in stabile operation and still be able to fit into the 6G601's cabinet. Starting in 1939, and continuing through the remainder of that year, no less than 20 prototypes were submitted to CEO McDonald for his approval. All but versions 19 and 20 were rejected for one reason or another. (Trans-Oceanic, The Royalty of Radios, John H. Bryant and Harold N.Cones, Schiffer Publishing Co., 2008) The final version consisted of a six button band selector from which the user could select between the AM broadcast band, and five shortwave bands ranging up to 16 MHz. The components used in the tuning unit were of the highest quality to ensure stability in the often rough environment that a portable radio might be operated in. The outward appearance of the radio was the work of Robert Davol Budlong, and industrial designer who was a graduate of Grinnell College in Iowa. He was also well known for designing other appliances, such as Sunbeam toasters, shavers, and mixers, all featuring a modernistic appearance. He chose to make the radios look like radios, a trend away from attempts to make them look like furniture or other objects.

Credit P. Litwinovich collection.
The AM broadcast receiver preceding the Trans-Oceanic line of short wave portables.

The first version of Zenith Trans-Oceanic line of portable shortwave radios, the 7G605, pictured at the beginning of this article, was released less than two months before the Pearl Harbor attack. It bore the sailboat image, and continued to be known as the "Clipper." It sold for $75, and was an instant success. It was just the beginning, though, of the series' long and colorful history. Zenith planned to heavily promote the radio for the coming holiday season. Then, the surprise attack on Pearl Harbor came. Most manufacturers halted production of consumer goods for the war effort. Zenith had other plans for their new radio, though. They changed the image on the grill from that of a sailboat to the likeness of the B-17 bomber. The change was implemented in such a hurry, that collectors have reported finding the bomber grill inserted over the top of the sailboat grill. Such radios fetch a premium on the collector's market. It is not documented as to how many sets shipped this way.  As the original radios were called Clippers, collectors often refer to these as "Bombers."  Zenith continued to produce the radio based on parts that it had ordered and received prior to the start of the war. On April 22, 1942, Zenith was forced to discontinue all consumer production by the government decree known as the "war planning board federal edict" ordering all manufacturing efforts to be directed to the war effort. By then, 35,000 sets had been made. At the time, it left approximately 100,000 orders unfulfilled. (Trans-Oceanic, The Royalty of Radios, John H. Bryant and Harold N.Cones, Schiffer Publishing Co., 2008)

Credit Unknown (posted to collector's listserve)
The dial of a Trans-Oceanic Presentation Radio.

Government edict or no, and despite a ceremony in front of the press celebrating the "last" 7G605 to roll off of the assembly line, the company did produce a limited number of additional sets, rumored to be about 1000 (some sources have Zenith sitting aside 1000 sets from the final run). These were retained and used as presentation pieces given to Zenith executives, dignitaries, war heroes, and celebrities such as movie stars who promoted war bonds. The radio would have the recipient's name silk screened on the face plate. When I was trying to acquire a 7G605 for my collection, I was outbid on one such presentation radio, bearing the name of a Zenith vice president. The 7G605 in Clipper or Bomber form is the rarest of the civilian series, and is highly sought after by collectors.

Beginning with WWII, Zenith also pushed the idea of Trans-Oceanics being sold to soldiers not as military radios, but as a way for troops to keep in touch with what was going on back in the states. To this end, they frequently ran advertisements featuring pictures of the radios being used by soldiers in the field and included stories (presumably real) of the radios surviving nearby bomb blasts and even being dropped in salt water. I have my own doubts as to the radio's ability to function after immersion in salt water, but the radio did have performance specifications that make stories of it being used as a backup when a military radio was destroyed in battle quite credible. They were not able to sell this idea to the government until after the Korean War when, in 1956, they landed a small contract to supply 2,973 of the radios known as the R-520 to the army for such purpose. The R-520 was a militarized version of the civilian Model H500 shown above. It was ruggedized, damp- and fungus-proofed, had additional shielding, a set of spare tubes, and alignment tools included inside the cabinet. Extremely rare, it is identified by the army green vinyl covering stamped USA at one end, and the spare set of tubes clipped inside the rear cabinet door.

Left:the post-war Model 8G605., Right: the Model H500, circa early 1950s.

After the war, Zenith returned the radio to production in the form of the Model 8G605 and then a slightly improved Model G500 which, outwardly, looked the same as the 8G605. These were produced from 1946 through 1951. The sensitive, high performance portables remained a favorite amongst shortwave listeners and radio enthusiasts in general. In 1951, the H500 was introduced with an additional shortwave band, giving the user an additional band button to select. The H500 was the first model to use the new miniature tubes which had been developed as part of the war effort.

In 1954, the 600 Series went into production. It featured a "slide rule" dial, a departure from the traditional dials used by its predecessors. It was produced until 1962 and was the last portable vacuum tube radio produced in the United States.

Credit P. Litwinovich collection.
The 600 Series, the final vacuum tube version of the Tran-Oceanic radio.

All of the Trans-Oceanics featured Zeniths detachable "Wave Magnet" loop antennas. On the original 7G605, the antenna was taken to the extreme and made to look like a giant horseshoe magnet. It was toned down on subsequent models. The series also introduced the telescoping stick antenna that we are more familiar with today. The listener could switch between the two antennas to see which performed better under different conditions. The 7G605 came with a faux snakeskin covering. After WWII, almost all of the radios came in black leatherette-covered cabinets, with two exceptions. On later models a brown leatherette covering was offered as an option. I would not call these rare, but they are far less common than the black ones. The other exception being the very rare R-520 which was covered in either an army green vinyl covering or the brown leatherette, both stamped "USA" and bearing military insignias.

Credit P. Litwinovich collection.
The "Wave Magnet" antenna from the 7G605.

By now, the elegant high performance radios had earned the nickname "The Royalty of Radios," so when the first transistor version came out, overlapping the 600 series from 1958 on, it was named the Royal 1000. The line continued through several more solid state models ending with the Royal 7000, which remained in production until 1982. Just as the Model B600 was the last vacuum tube portable manufactured in the United States, Its descendent, the Royal 7000, was the last solid state portable radio to be made in the USA.

The Trans-Oceanic and the saga of the 1L6 tube

For those interested, read my June 2014 article about the heterodyne circuit for more on what a mixer tube does. Pictured below are three mixer tubes (left to right), the 1A7, used in the older model 5G401 radio, the 1LA6 used in the earlier Trans-Oceanics, and the miniature 1L6 used in the Trans-Oceanics starting with the H500. Zenith wanted to keep up with the latest technology and so they switched to the miniature tubes starting with the Model H500. This presented one major problem. The 1LA6 was a complex pentagrid converter which performed quite well at the higher shortwave bands. No one had yet created a miniature version of this tube. With few manufacturers building shortwave portables, most companies used the 1R5 mixer that worked just fine on the AM broadcast band and well enough on the lower shortwave bands to suffice.

Credit P. Litwinovich collection.
Progression of mixer tubes from the 1A7 through the 1L6.

It did not perform well at frequencies above 10 MHz, though. Zenith contracted several tube manufacturers to attempt to design a mini version of the 1LA6. Doing so was the equivalent of putting 5 lbs. of groceries in a 3 lb. bag. Zenith delayed the release of the H500, and was prepared to ship the radios with 1LA6 tubes if need be. Sylvania, the leader in battery powered tubes was, in the end, able to produce such a tube in the form of the 1L6. The tube was used almost exclusively by Zenith. By 1958, with the demise of tubes on the horizon, Zenith was again faced with the possibility of not being able to get the tube for the release of the R600. In the beginning, the chassis of the R600 was stamped to fit the older 1LA6 socket, and then, when they secured a source for 1L6 tubes, was fitted with an oversized socket for a 1L6. Today, finding 1L6 tubes is a challenge. Prices may range up to $120 for a new old stock 1L6, whereas you can purchase a 1LA6 for less than $7. Since I owned an R600 with a somewhat scruffy case and was not worried about keeping the radio completely original, I decided to try an experiment. I refitted the set with the larger 1LA6 tube and socket. The 1LA6 is electrically identical to the 1L6, and it even has slightly lower inter-electrode capacitance, which suggested that it might slightly outperform the smaller tube.

After retuning the H600 per factory procedure, I discovered that, indeed, the performance on the highest shortwave band was slightly better. If you are restoring a radio and need a 1L6, you can substitute a 1R5 and it will work on the AM broadcast band, but give poor performance on shortwave. There are also a few people selling solid state replacements made to look like the tube and directly replace it.

Paul was a design engineer and engineering manager in the broadcast industry for14 years before coming to WSHU in 1990. He holds an FCC commercial radio license, and an extra class Amateur radio license.