Amateur Radio Station W1UJR

A very special transmitter arrived at my shack in early June 2008, and although it has no nomenclature tags, via the effort of some ham friends, I have narrowed it down to the Gross CB-25.  The Gross CB-25 seems to have first marketed in the March 1934 ARRL publication QST, and was labeled the "CB-25". The "C" stood for CW, the "B" for class B fone modulation, and "25" for the 25 watt RF output. The QST advertisement from 1934 is listed on the menu to the left, along with other Gross information and advertisements.

This particular Gross Radio transmitter was originally owned by Bill Orr W6SAI, and given to my friend John Rollins W1FPZ SK to restore. The deal, as I understand it, was John could keep it if he would restore it for Bill. Parker W1YG, drove all the way to California and back to pick up the unit for John.

With John's passing the unit came from his estate to my care. Overall, the transmitter is in remarkable condition thanks to John's restoration efforts, but I'd like to find out a little more about it. Unfortunately W6SAI is now a silent key, so this may be a story left untold.


The CW/CB-25 Transmitters
Perhaps the best know Gross product of the day was the CW-25 “Beginner's Transmitter. Offered as both a kit, one set of band coils, for $13.95, and fully wired and tested for $14.95, the CW-25 was a simple way for the radio newcomer to get on the air. While $13 sounds cheap today, in 1931 it was a far stretch for the average radio amateur. Bill Orr W6SAI writes “In those dark days of the depression, however, this sum was equal to a week’s wages to some and was only a theoretical concept to the many unemployed.”

Still, the CW-25 was a great bargain to the average ham, offering 50 watts input, with about half that power output on the 160 and 80 meters band, lowering a bit on 40 and 20 meters. Think about it, a four band transmitter, with what was considered good power output for its day, in one compact chassis, must have certainly been pretty tempting for the new ham. Gross also offered a power supply kit for the CW-25 for $8.75, 50 cents additional if wired, and plug in coils at 75 cents per coil. The Gross used three coils per band, so for the total cost of $27, one had a full four band set, complete with power supply.

Functionally the CW-25 and its fone cousin the CB-25, are quite identical on the RF decks, its only in the power supply and modulator that the two depart. We’ll start with the RF deck first as its common to both variants, and discuss the CB-25 later.

The CB-25, the “B” standing for class B fone operation, was offered for the princely price of $66, wired and tested units cost an additional $10. For this additional cost, the proud owner received a small desktop rack to hold the chassis, a power supply deck with modulator circuit, and a metering panel. One could apparently buy all of these parts separately, but Gross offered both a kit and assembled version. In the Gross design, the rack stood about 24 inches tall, with the RF deck located at the of the rack, and the power supply below. A metering panel, with two large Weston panel mounted meters, was located directly below the RF deck.

Bill Orr W6SAI
Bill Orr W6SAI, the author of the famous “West Coast Handbook”, held high praise for the Gross, writing about it in at least two articles in CQ magazine. In these pieces Bill shared his joy of visiting “Jerry’s Place”, drooling over the various designs, and then heading home to build his own. At some point in later life, Bill became the proud owner of at least Gross transmitter, a story he shares so well in his February 1977 CQ article. Bill relates that in 1976, while browsing a flea market, he came across a mint CW-25, reigniting his childhood love of the sets. I’ll not spoil by attempting to relate Bill’s experiences here, suffice to say that Bill enjoyed the Gross so much that he rounded up yet another Gross set, this one making its way to Maine, and this is where our story really begins.

John Rollins W1FPZ
A short time after I became a ham back in the mid 1990’s, my interest turned to the older 1930s sets. I joined the Antique Wireless Association, a group dedicated to collecting, documenting and restoring old equipment. Being involved with the AWA I became aware of a man named John Rollins W1FPZ who lived on the Maine coast. John was quite renowned for his building abilities, and had at that time just taken over one of the AWA’s on air contests from an ailing Bruce Kelly W2ICE.

At this time I didn't know much about John, but I was soon to find out a great deal more!
In 2001 I moved to Maine, and later up the Maine coast, just a short drive from John’s home. John, aside from his wonderful building skills, was a most generous person with his time and materials. He was always willing to help out the radio newcomer, often building and giving away his creations. For me, John was a source of inspiration and knowledge. He was always ready and able to answer a question, assist with a part for my latest restoration, or demonstrate his home brewed marvels.

The Orrr Rollins Connection
Sometime in the late 1990s, Bill Orr became aware of John also. Perhaps it was John’s article on restoring a Gross set in the 1998 AWA Old Timer’s Bulletin, or maybe it was just John’s reputation. In either case, Bill called John with a proposition, restore my old Gross transmitter, send me the photos, and you can keep the rig! Well for John this must have been irresistible, for it was his chance to get his hands on yet another Gross, John was likewise a fan of Jerry Gross’s creations, and a chance to bring a dead radio back to life.

John was not about to let a deal like that go through his hand, and was prepared to fly out in his private plane to pick up the rig from Bill in San Francisco, but a friend stepped in, and offered to drive out to California and retrieve the rig for John. Soon the rig arrived back in John’s workshop in Arrowsic, Maine where it underwent a full restoration, Rollins style. Any correspondence that passed between John and Bill seems to be lost with John’s passing earlier this year, but John never ceased to proudly point out the rig when showing a visitor his hamshack.

The CW/CB-25 Rig In Detail
The CW/CB-25 was quite robustly built as well, starting with the steel chassis, finished with the classic black crackle paint. The three air variable capacitors featured prominently on the front panel, were General Radio products, as were the dials, printed with the Gross lightening bolt logo. Such quality was surprising for a bargain kit of its day, for General Radio was well known as a manufacturer of very high quality parts and equipment. Underneath the layout is a very traditional design, with straight line heavy 12 gage tinned wire was used for the ground and RF bus, and 14 gage black insulated wire used elsewhere. A mixture of ceramic and fiber sockets are used for the coils, vacuum tubes and electrical connections. Two air variable capacitors, mounted on the rear of the top chassis, are used to neutralize the buffer and final stages.

The RF circuit of the CW/CB-25 was based on the then popular type “46” tube, and the design was often referred to as the “46 job”. Starting from right to left on the RF chassis, a type “47” tube was used as a crystal oscillator as it would run on 160, 80, or 40 meter crystals. The 47 was designed as an audio pentode, but would provide decent RF output at 300 volts in a crystal oscillator. Output of the 47 went to a type 46 used as a buffer stage, which was neutralized for a vertically mounted capacitor located almost directly behind the tube. The buffer output was then directed onto a pair of 46s in a class C amplifier arrangement. A plug in coil was used for each stage, hence the need for three sets of coils per band. The crystal holder was mounted on the right front of the top panel, and Gross sold both the crystal holder and blank, you ground your own crystal in those days, for one dollar each.

During the tune up process, one used either an external meter, plugged into the jacks on the front panel of the RF deck, or the tried and true light bulb with an inductive loop of wire. Each stage was loaded and tuned to resonance, with the one caveat that the phone jacks were live with plate voltage! The CW/CB-25, like most sets of the day, was designed for a high impedance balanced antenna, so the link coupled output, again via the plug in coil, went directly to a set of porcelain insulators.

The modulator circuit on the CB-25 is a classic design that appears to have been taken from the early ARRL handbooks. A type “57” was used as the first stage in the speech amp, driving a single type 46 tube. The output of the single 46 was then sent into a pair of type 46 tubes in push pull, which used as modulators. Gross had designed the set for use with a carbon microphone, so the resulting audio was anything but “hi-fi”. Still the set did work, and offered a moderately priced entry into the fone band. A pair of type “83” mercury vapor rectifiers completed the rest of the tube compliment on the power deck. Connection between the two chassis was via a cable running from the power supply to the jack on the rear of the RF deck. A set of “wander” leads were used on the front panel meters to switch in, measure and tune the various stages of the transmitter. A lower power meter on the right was used with the oscillator and buffer sections, with the higher power meter on the left measuring 46 amplifiers in push pull. Keying was made via the front panel jacks, and a set of insulated dummy plugs were used to block following sections when tuning.

Contrasted with the Collins 32B rig, selling at $125, the Gross was a bargain. Sadly it appears that few of the CB-25 variant survive today, its unknown if this was result of poor sales, or just the ravages of time.

73 Bruce W1UJR