Radio Boulevard
Western Historic Radio Museum

the  hallicrafters  inc.
 

Skyrider Diversity - Model DD-1

History of Diversity Reception,   Development of the DD-1,

Amateur Radio Station XE1G,   The Production DD-1

Restoration of the Skyrider Diversity DD-1 Console Receiver

Schematic Errors and Engineering Upgrades,   DD-1 Performance Details,

Known DD-1 Serial Numbers,   DD-1 Collector's Photo Gallery

by: Henry Rogers WA7YBS - Western Historic Radio Museum

DD-1 SN: H-80596

 Skyrider Diversity - Model DD-1

History of Diversity Reception - Diversity receiving equipment utilizes two or more receivers connected together at the second detectors and AVC lines. The receiver inputs are from widely separated antennas. The goal of a diversity receiver is to greatly reduce or eliminate fading radio signals. Fading radio signals have always plagued shortwave reception and are encountered when the signals being received originate from a transmitting station located at a distance that requires the radio waves to propagate via skywave through the ionosphere. As signals fade down to the noise level much of the information being transmitted is lost until the signal level increases above the noise again. Sometimes deep fades will last for half a minute or more, causing program interruption or important messages to be lost. Besides fading, other phenomena occurs when radio waves are refracted through the ionosphere, such as selective sideband fading causing distortion on AM signals along with rotation of the radio waves causing polarization changes.

Beverage and Peterson first connected strip-chart recorders to a combination of three antennas and three receivers. The charts showed that not only was the same signal at different amplitudes at each antenna but, at any one instant, the signal at one antenna was also many times out of phase with that same signal on the other antennas. At first the engineers speculated that radio waves were being refracted in the ionosphere at different angles and therefore some waves would be intercepted by an antenna while other wave-angles would miss the antenna. A large multiple antenna should capture more wave angles and reduce fading. Actually, they found the opposite happened. Fading became worse with larger antenna arrays. The two men then theorized that over-the-horizon radio waves could be refracted simultaneously from different heights in the ionosphere, these waves would travel slightly longer or shorter paths and arrive at a single antenna at slightly different times. The delay of the longer path signals would sometimes cause multiple phases of the signal to occur on a single antenna. Sometimes the phase differences would add resulting in stronger signals and sometimes the phases would cancel causing a drop in signal strength. Since the ionosphere was nearly always in a changing state and since radio waves would frequently be simultaneously refracted at several different levels in the ionosphere, fading due to radio wave phase changes on a single antenna was always going to be present.

 The solution was to use separate antennas and separate receivers to provide the isolation necessary so each antenna and receiver would react to radio waves specific to its time and space relationship. As the signals passed through the receivers, the various phases at the RF frequency maintained their out of phase relationship until they were converted to audio signals at the second detector. The process of detection eliminated the RF out of phase nature of the signals since now the signal information was at an audio frequency. Each second detector output would be tied together with a common load, operating an AVC system that interconnected all the receivers, resulting in a single audio signal the amplitude of which was the result of the strongest received signal at any one time. Through experimentation, it was found that at least a full wavelength of antenna separation was necessary to have consistent difference in the phase of the signals.

Additional problems started to surface when it became necessary for the diversity receivers to operate on CW. The interaction of the receivers in maintaining a constant detector load output regardless of variations on the separate antenna-receiver inputs required the AVC to be operational. When a BFO was injected into the second detectors the strength of the BFO oscillator would capture the AVC and not allow it to follow the signal strength variations in that receiver. >>>

By the late twenties, RCA had 41 triple-diversity receivers installed at Riverhead in communications with 26 different countries. The outputs were routed to a main office in New York City where operators would copy the strip tapes, decoding the messages. By using filters and multiple tones, several signals could be routed simultaneously to the main office without interference. The associated antenna farm, with 1000 feet of separation between antennas, required acres of land. The installation was used for commercial sending and receiving world-wide radiograms.

As receiver design progressed, the diversity stations became more sophisticated. By the forties, RCA had introduced its AR-88 receiver which was adapted to the new triple-diversity receiver, the DR-89 (Navy designation RDM.) These seven foot tall racks contained three AR-88 receivers, a Tone Keyer with combined output meter, a Speaker Panel, a Meter Panel with S-meters for all three receivers, an antenna patch panel and a power supply. Even more complex was the military RCP and RBP-1, also built by RCA for the Navy during WWII. The RCP used double conversion receivers with multiple tuners installed in four, seven foot tall racks. The RBP-1 was a dual-triple diversity receiver that was essentially two RCPs side-by-side. Using six double conversion receivers in seven racks the entire setup weighed a mere one and a half tons! The RBP-1s were still in use as late as the 1970s.

The Signal Corps also used diversity in many of their teletype installations. The system used was "frequency diversity" which used one frequency and receiver for "mark" and another frequency and receiver for "space." The theory was that each frequency would fade differently and rarely would both frequencies fade together. Only either a mark or a space was needed to decode the teletype, (if it isn't a mark - it must be a space.) The popular receivers used were the Collins R-388, R-390 and the R-390A.

Another form of diversity was to use a vertical oriented antenna in combination with a horizontal antenna. The theory was that the radio waves many times rotated as they were refracted through the ionosphere and therefore good diversity action could be achieved with both vertical and horizontal polarization. This form was called "polar diversity" and was generally used when a full wavelength of antenna separation wasn't practical. In the early forties, a QST article featured a novel way to experience a diversity action using only a single receiver. The writer used a high speed antenna switch, running at 400Hz, to switch between two antennas. The average of the signal strength of each antenna was more or less what the receiver responded to supposedly giving some relief to fading. Additionally, the 400Hz switching gave a sort of modulation to the signals so CW was easy to copy without a BFO. 

Amateur interest in diversity reception waned as WWII loomed in the near future. The expense, the complexity, the space required for antennas all made the results not worth the effort. With less expensive equipment most hams could get the same results. So what if the 'phone stations needed to repeat some of their transmission. On CW, there was no obvious benefit to diversity and, in the pre-WWII days, most hams were on CW. After WWII, there is hardly any mention of diversity in any ham magazines. The commercial stations and the military had always been and were to remain the primary users of diversity reception. As technology progressed into satellite communications by the late 70s and other more reliable forms of communication came into use, the need for large, expensive diversity receiving installations all but vanished. Most of the equipment has been scraped or sold into surplus.

Development of the Skyrider Diversity

Amateurs became familiar with the principals of diversity reception by reading various books and magazine articles throughout the twenties and thirties. QST published an article by Chester W. Rice in the August 1927 issue about shortwave uses that mentioned diversity theory and reception. For the avid 'phone operator, having the equipment to eliminate fading signals and the associated distortion, must have seemed like a virtual necessity. To the CW op though, diversity seemed to not be worth the effort, after all, CW copy was not that seriously affected by fading. However, James Lamb, Technical Editor for QST, and engineer James McLaughlin decided that diversity was worth a try and began their research into some kind of practical amateur receiver that would incorporate diversity. With the financial help of Dr. James M.B. Hard XE1G, the first amateur dual diversity receiver was built in the Spring of 1936.

The XE1G Receiver - The First Amateur Dual Diversity Receiver

James Lamb and James McLaughlin had been experimenting with diversity reception as early as 1931. At that time, the two engineers used two shortwave converters connected to two identical TRF receivers used as IF amplifiers. Both TRF receivers had been modified to have amplified AVC. The performance was satisfactory enough for each to continue their research and designs. For the next few years, each pursued their own careers but decided to have an informal meeting in the spring of 1935. The purpose of the meeting was to discuss each others thoughts on what technical advances might be used to create a practical amateur diversity receiver. At about the same time, well-known amateur operator Dr. James M. B. Hard,  XE1G from Cuernavaca, Morelos, Mexico, let it be known he was ready to finance the construction of a dual-diversity receiver of Lamb's and McLaughlin's design.

Both Lamb and McLaughlin thought that the tuning of commercial diversity receivers was too cumbersome. In commercial installations, where usually only a few frequencies were used, tuning each of the receivers to a specific frequency was a task only performed once or twice a day. In an amateur station, the ability to tune though each amateur band easily and switch from band to band quickly was an obvious necessity. The XE1G receiver uses a single Local Oscillator between the two receiver front-ends to provide "single dial" tuning. Other circuits incorporated in the XE1G receiver were chain-drive for the band switch, separate pre-selector tuning (not ganged to the main tuning,) three power supplies, separate audio amplifier using a modified Collins 7C audio amplifier, tuning coverage from 1.7MC to 30MC in four tuning ranges, amplified AVC and a separate Jensen speaker with an add-on tweeter unit. The completed receiver was delivered to Dr. Hard in the Spring of 1936.

Photo left shows the XE1G receiver as it appeared in the May 1936 issue of QST along with an article describing the receiver in detail. The rack contains the dual receivers, pre-selectors and multiple power supplies. Shown on top of the speaker is the modified Collins 7C audio amplifier. The speaker cabinet contains a Jensen speaker with an add-on tweeter unit.

The First Prototype DD-1

The Prototype DD-1 built by James McLaughlin and Karl Miles in 1937

Photo QST, Dec. 1937

Shortly after the QST article about the XE1G receiver was published, Hallicrafters became interested in building a Dual Diversity receiver for the amateur market. Karl W. Miles, Hallicrafters' chief engineer, was given the task of developing the working prototype. Working directly with James McLaughlin, Karl Miles was to build a dual diversity receiver, based on the XE1G receiver, that was within the capabilities of the company to manufacture.

The first prototype was given ample space in the December, 1937 issue of QST.  The simplified schematic shows that the prototype now has the preselector stage ganged to the second RF and Mixer stages. The Diversity Meters are now in a small cabinet that can be placed near the receiver. The Infinite-Rejection system is now incorporated into the IF amplifier. Separate Power Supply and Amplifier are now in much smaller cases which can be placed on each side of the receiver but they are not shown in the schematic. Obvious in the photo of the prototype are the many Hallicrafters parts utilized in the construction.

By the time McLaughlin and Miles started work on their new prototype, the XE1G receiver had logged in 5000 hours of reliable operation. Dr. Hard was still enthusiastic about his receiver and stated that many times, with poor conditions, only it could be relied upon for intelligible reception. He mainly operated on 20 meters with two antennas spaced at 50 feet, not the ideal spacing but sufficient to provide usable diversity action. With improvements that had been developed since mid-1936, mainly in mechanical design, IF amplifier improvements and the Infinite-Rejection system, Miles' and McLaughlin's new version would cover .54 to 36 MC in five bands, have a simpler band switch system and be housed in a smaller cabinet. The article concluded with a rather vague statement about how the audio modulation for CW is not really working satisfactory and there were still "bugs" to be worked out. >>>

The Production Skyrider Diversity DD-1

The new Diversity Receiver's advertising had been carefully nurtured and the publicity was going to be more important to Hallicrafters' reputation than any profits derived from sales of the receiver. Following their tradition of naming receivers, the DD-1 was dubbed the "Skyrider Diversity" and the June 1938 issue of QST features no less than 10 pages of ads devoted to the new receiver. All of the major component suppliers, such as Mallory-Yaxley, Crowe, Aerovox, Jensen, Stancor, Aladdin and Raytheon weighed-in with their own ads plugging themselves along with the DD-1. It was the largest ad campaign for a new receiver up to that time and this was just QST! Advertising for the DD-1 was everywhere.

The advertising campaign for the DD-1 didn't last very long - only about six months. Bill Halligan and probably everyone involved with the DD-1 project knew that the Skyrider Diversity was not going to be a major seller. With initial prices between $300.00 and $500.00, depending on options, the diversity receiver was just not in most enthusiasts' budget. The base price for the receiver was to be $300.00, with the Power Supply adding another $40.00 and the Audio Amplifier adding another $50.00. The Diversity Action Meters sold for an extra $20.00 and the 12" Jensen table speaker sold for $12.00. The total for the receiver with the standard accessories was $422.00. If the purchaser wanted the ultimate, he could spend a full $500.00 for the Skyrider Diversity Console DD-1. That price included the Diversity Action Meters installed in a matching wooden top. The huge machine-age style speaker cabinet has shelves in the rear (right side) to house the Power Supply and the Audio Amplifier. The 15" Jensen Ortho-dynamic speaker is mounted in a Bass Reflex enclosure that takes up most of the center and left side of the cabinet (as viewed from the front.) A small table is provided as an arm rest for fine tuning the DD-1 or it could be used as a small writing table for logs or whatever. The speaker has a 5000 ohm to 8 ohm matching transformer mounted on it. The fabulous cabinet design was the work of Auther Haggstrom, who had also designed cabinets for Jensen, E.H.Scott and McMurdo Silver. When one looks for a price comparison to get a feel for what could be purchased for $500 in 1938, look at the Chevrolet coupe, selling for $550 in 1938 - essentially, the Skyrider Diversity Console DD-1 was the price of a new car! >>>

>>> The initial prices might seem high but after the first advertising campaign was over the prices were increased,...substantially. Certainly the second production run of about 20 to 30 receivers cost the prospective buyer dearly. The prices listed in the 1940 ARRL Handbook ad for the DD-1 are $450 for the receiver, $135 for the amp and power supply and another $135 for the 15" speaker in the Haggstrom cabinet. Total cost for the DD-1 console was $720! The price of the DD-1 table version with diversity meters and speaker was $627!  

Of course, Hallicrafters realized they weren't going to sell very many DD-1 receivers. The price, the size and the usability was just not what the average ham could justify. Hallicrafters probably estimated that somewhere around 100 to 150* receivers would fill all of the orders besides all of the publicity donations that might be needed. The major benefit to Hallicrafters was to their reputation. They now had proven that they were capable of successfully engineering and building a complex, dual-diversity receiver.
 

*For the past several years, I have been collecting serial numbers of known DD-1 receivers in an effort to estimate production accurately. It now (2014) seems likely that a production quantity of 200 units is far too high. This estimate was originally based on Halligan's 1980 statement regarding DD-1 production. It appears from the reported serial numbers that an initial run was made that was probably for 100 receivers and used serial numbers in the H-80500 to H-80600 range. A few months later a very small production run was made, probably to use up the remaining DD-1 parts inventory and this run accounted for a few receivers up to maybe 20 or less receivers. Only three DD-1 receivers have been reported with serial numbers in this later range, H-85617, H-85629 and H-85648. The current information leads me to believe that only about 120 to perhaps 150 DD-1 receivers were produced and that total quantity came in two production runs of approximately 100 units and later approximately 20 to perhaps as high as 50 units. See "Estimated DD-1 Production" section below for more details.

The DD-1 Advertising Images

Shown to the right is an enlargement of the artwork that was used for most of the DD-1 advertising by Hallicrafters. It is artwork - not a photograph. Most advertising at the time used detailed drawings for their images and though the Hallicrafters DD-1 artwork is detailed, it is not a photograph. Whether it was based on an actual prototype or if it was a "mock-up" is not known but the receiver is different from the standard production DD-1. Obvious is the lack of the Heterodyne Oscillator implying that the BFO was a last-minute addition. Also, individual RF Gain controls on the far right panel with a "Master RF Gain" control (large knob) differs from the production DD-1. The tuning and BS dial logging scales are different and if there is any scaling on the tuning dial it is too light to see in the finished artwork. The four smaller panels are plain with no decorative border. Additionally, the toggle switches are mounted lower than center of the panels while the production DD-1 has these switches mounted center of the panel. The location of the larger knob on each lower panel is different than the production units. The standard production DD-1 used 21 tubes in the receiver, four tubes in the Power Amplifier and one tube in the Power Supply, bringing the total to 26 tubes.

More on photos right - The Skyrider Diversity Console DD-1 is shown in the shack of W6LYY, Barney Boyd of San Diego, California. Boyd's shack was to be the state-side link for communications to the Archbold New Guinea Expedition. The table version DD-1 that was delivered to New Guinea for the Archbold Expedition. This set-up featured a special, 15" Jensen speaker mounted in the familiar Hallicrafters speaker cabinet.

Photos - QST, Jan.1939

DD-1 Receiver Electronic Restoration Details

Before Restoration Photos and Assessment

DD-1 H-80596 was acquired in August 2006. It was basically complete except for the top and bottom covers for the Power Supply and missing interconnect cables. Minor condition problems were present, mostly in the form of surface rust. The most significant rust damage had occurred to the tuning condenser at the rear-most gang that didn't have a ground on the rotor shaft now. Also, surface rust on the back of the power supply case and the front of the power amplifier case was fairly extensive. As for the receiver cabinet, some minor rust was present on the case mounting lips but the most serious rust was located in the RF coil section of the chassis. Most of the electrolytics had been replaced over the years, a coaxial cable was installed to replace a shielded cable in Receiver B, the Master RF Gain and Audio Gain controls had been replaced along with a handful of other resistors and capacitors but the essentially the receiver was complete and no modifications had be installed - just repairs. The plastic dial scales were yellowed and warped - typical of certain plastics at that time (probably cellulose-acetate, a popular clear plastic in the late-thirties.)

The finish on the wooden top and on the speaker console was original. There were some small veneer chips at the bottom of the console. Also, some indications that the very bottom of the console had gotten wet and delaminated the plywood sides. The grille cloth was original. The 15" Jensen speaker was original. There was obvious wear to the finish on each side of the speaker console just below each of the control panel knobs showing that the DD-1 was used extensively at one time. All wooden parts to the cabinet were present including the rear cover. 

The chassis photo (below right) was taken before restoration. The box-type shield cover has been removed to show the Mallory-Yaxley Push-Button Band Switch assembly and the associated coils. Note the brass threaded rod and nuts that runs through all of the coil dividers. This, along with the shields, help support the push button switch assembly. The round cans on each of the outer chassis are the Infinite-Rejection tuning condensers while the rectangular cans are the IF transformers. The large transformer on the center chassis in front is for the tube heaters. One can see the three chassis that make up the construction of the DD-1. Also, obvious are the spots of surface corrosion on the chassis and some components. This is fairly typical of the cad-plated chassis of that time period. The most serious rust was encountered at the rear-left of the RF shield box area. Not only was the chassis involved but the shield also had a rust problem.
 

Photo left: A seldom seen sight,...two DD-1s on one workbench. In front is H-80596. To the rear is a second receiver with many missing parts including the bandswitch shield cover that had the SN tag attached to it.

Starting the Restoration

H-80596 in 2006 before restoration

Chassis before restoration

Touch-up Painting -  The inside of the cabinet is matte black finish and was touched up using artist's acrylic Mars Black mixed with a little water. I first cleaned any rusty areas with a wire brush and wiped the area with a cleaner - I used Glass Plus (no ammonia.) When the area was dry I brush painted the black acrylic. The acrylic paint matches the matte finish very closely. Artist's acrylic can also be used for small areas in the wrinkle finish that are missing, such as scratches or scrapes. I don't thin the acrylic when touching up wrinkle since the paint has some body and can be textured a little with brush strokes.

For areas where about .5" to 2" were missing the wrinkle finish I used Krylon Wrinkle Finish Black. I spray a small amount into a small cup and then paint that on with a brush. Make sure the area to be touched up is clean and has been wiped down with lacquer thinner. Paint a "heavy coat" on with a brush and when finished apply heat using a 100W reflector lamp placed close to the surface (about six inches away is good.) For trouble spots that are slow to wrinkle (more than 10 minutes) I use a heat gun on low temperature to get the paint hot enough to start wrinkling and then stop. Too much heat will cause the paint to "gloss" more than normal and not match the rest of the original paint. Krylon's wrinkle finish paint is a pretty good match for the color and texture - but nothing is perfect since the original paint was a two part process requiring a nitrocellulose lacquer base with a catalyst applied after the base was dry. The two part wrinkle then had to be baked to activate the process. There were several different formulae that resulted in the slightly different wrinkle patterns that we encounter today.

The chassis rust spots were wire brushed and then a brush-on silver paint applied. This can be dulled to match the chassis with an acid brush or similar mild abrasive. The transformer covers were touched up using this same technique.

Power Supply and Power Amplifier

Certainly the rust damage on the power supply and power amplifier looks pretty bad. However, careful cleaning and rust removal followed by a new wrinkle finish paint job and the two units looked great. I did have to remove the damaged perf metal on the power amp and replace it. When painted the new piece was undetectable from the original. 

All capacitors were re-stuffed in these units. Luckily, all of the transformers in both units were original and in good operable condition. In addition to the rebuild of these units, two interconnect cables had to be made. I had some old battery set, cloth covered cable that looked very close to the original brown cables used by Hallicrafters. The AC connection is also via an interconnect cable plugged into the rear of the receiver. This was a rubber cable about 8 feet long. I installed a dual fused plug since the DD-1 originally has no fuses on the AC line. Hallicrafters assigned the amplifiers a four digit serial number that is on a paper label on the bottom of the unit.

The missing top and bottom covers for the power supply had to be replicated at a local sheet metal shop. The shop used the original top and bottom covers from the power amplifier as models since the covers are identical for both units. It was a long wait for the completed parts as most shops consider this type of work just for "fill in" unless you want to pay "full rate." I got both covers made for $60 each. The top cover is an exact replica except the perf metal holes are slightly smaller in diameter. The bottom cover is also an exact replica except that it is made out of stainless steel so it wouldn't have to be chromed. 

When the top covers were painted wrinkle finish black, it was difficult to tell which cover was the reproduction. The same for the bottom cover when installed - only the original has a few rust pits that show. The square rubber feet install on the two welded pieces that span across the front and back corners.  

Shown on the left are the finished Power Supply and Power Amplifier. The Amp has its original top and bottom covers while the Power Supply (on the right) has the reproduction top and bottom covers installed. Although they can't be seen at this angle, the square rubber feet are installed on both units. While the Power Supply and  Power Amplifier normally can't be seen with the DD-1 Console model, since they stow on shelves located in the rear part of the DD-1 Speaker Console, it is nice to finally have them both units complete and looking correct.

Re-stuffing Paper-wax Capacitors

Since nearly all of the 49 paper-wax capacitors in my DD-1 were the original Aerovox caps, re-stuffing the old paper shells with new capacitors was a practical idea that would result in an original under chassis appearance. One potential problem with any serious rework of the DD-1 is the polystyrene tube sockets. These sockets will not tolerate any over heating and therefore unsoldering should be avoided. It is possible to use "hook" splices for joints and if carefully done and kept very short they will not be apparent. This avoids overheating damage to the plastic sockets and to other components.

Since I was re-stuffing original shells I had to use "yellow-jacket" type, film capacitors. To re-stuff a paper-wax capacitor I use a heat gun to melt the old end seals on the original capacitor. Some caps will almost fall out of the shell when hot but not Aerovox caps. I had to use two needle-nose pliers on each wire lead end and pull the cap apart to remove it from the paper shell. While the shell is still hot from the heat gun I wipe the shell off with a paper towel to clean it up. The new cap is then inserted inside the old shell. I orient the new caps all the same way - it doesn't really matter with film type caps but it is just habit to do so. The new cap is held in place with hot-melt glue. When the glue has set-up, I fill the ends with brown sealing wax. The resulting capacitor is new inside and appears to be the original since we are using the old paper shell. It takes about 10 minutes to re-stuff each capacitor. Be sure to install the re-stuffed cap in the correct orientation - this is for appearance only. Also, there was a .01uf capacitor inside the BFO can that needed to be re-stuffed.

Photo: The completed under chassis restoration showing the re-stuffed paper-wax capacitors and re-stuffed electrolytic capacitors. The orange electrolytics are Beaver brand and are original shells. These caps were engineering upgrades in production that are not shown on the schematic. The end result of this restoration method is a fully functional DD-1 - plus, a reference that shows how the DD-1 looked as it came from the factory.

Non-Original Parts

Metal can electrolytic capacitors installed for 8 mfd screen filter caps. These had mounting clips that were soldered to the chassis. The clips were removed as was the solder residue and the correct value, style and brand (Beaver) rebuilt electrolytics were installed.

Coax cable connecting Receiver B Mixer to Receiver B IF amp. I installed new coax with tinned copper shield and removed the outer jacket so that the appearance was the same as original.

Master RF Gain control was defective and non-original. Replaced with correct style and value part.

Audio Gain control replacement part that was wrong value and style. Installed correct style and value part.

R20 wrong value - 1K installed should be 4K. Installed correct value and style part.

R2 wrong value - 10K parallel with 5K - should be 10K. Installed correct value and style part.

R26 Rcvr B JAN type 1K installed. Installed correct style and value part.

R27 Rcvr A JAN 100K installed. Installed correct style and value part.

C100 BCB Oscillator shunt is two series caps, should be single 6pf NPO style cap. Installed correct style and value part.

Defective or Missing parts
 

Tuning condenser was rust-damaged on the rear-most gang. I transplanted a good condition original from the "parts set" DD-1.

Several braided jumpers on the bandswitch assembly torn off. Replaced using pieces of "Solder Wick" as it was about the correct size and appearance.

ON/OFF switch cables insulation missing. Replaced cloth insulation.

C109 missing (AVC delay.) Installed correct style rebuilt capacitor.

C46 RCVR B missing (IF cathode bypass.) Installed correct style rebuilt capacitor.

C48 one end disconnected - RCVR B Diversity Meter Amp Grid coupling cap, 100pf. Reconnected.

C34 RCVR A missing (IF xmfr B+ bypass.) Installed correct style rebuilt capacitor.

After about 10 hours of operation R76, the 750 ohm 10W WW cathode resistor for the 2A3s opened. Replaced with 20W 750 ohm WW.

Schematic Errors

The DD-1 schematic and parts list contain several errors. This was probably due to the receiver's short production life. Hallicrafters would normally correct the documentation with the second issue of the manual or perhaps with an errata sheet. Since the DD-1 was only in production for a few months and only a hundred or so were built, when production halted, apparently everything else involved with the receiver also stopped. This included all updates to the flawed schematic and documentation of any engineering upgrades that were incorporated into the production units. Fortunately, most of the errors are not critical to repairing or restoring the DD-1 receivers. Some of the conflicts are actually engineering improvements and these should be left installed. Since I had two DD-1 receivers at the same time, I was able to compare the schematic to production conflicts and resolve what was correct for the receiver. Additionally, I had two other resources in fellow DD-1 restorers who were able to confirm that their receivers also had similar production upgrades. The following is a list of schematic errors and non-documented engineering upgrades to the DD-1 receiver.

Schematic vs Engineering Upgrades

Two 8 mfd electrolytic capacitors on the 250vdc B+ line for RCVR A & B on each 1st IF AMP tube screens - provides better filtering of the screen supply. Non-documented upgrade.

RCVR A & B IF Chassis 6J5 Diversity Meter Amp has .01 uf cap from plate to chassis not shown on schematic - upgrade? Provides RF filtering for meters

Oscillator plate load resistor shows 3.5K on schematic parts list but 10K is installed in most units - upgrade?

Schematic and Parts List Errors

R27 Rcvr A & B - schematic parts list shows 1K, production installed 100K in all units. Parts list error.

One .01ufd paper capacitor installed on plate to cathode of 6J5 Heterotone Oscillator not identified on schematic. Schematic error

Input IF transformer T-1 on Rcvr A and B has trimmer on secondary only - schematic shows T-1 is with both primary and secondary trimmers.

Output IF transformer T-3 on Rcvr A & B has two trimmers - schematic shows T-3 with one trimmer.  Schematic error in both cases.

Alignment instructions do not address the PHASE adjustments on the IF A and B chassis. This was thought to be a one time adjustment carried out at the factory but over time certainly someone probably moved the adjustments to see what happened. Instructions for proper adjustment are in November 1937 QST in an article on the Infinite Rejection IF by Karl Miles and James McLaughlin. The PHASE adjustments control the power factor on the IF transformers and therefore the depth of the rejection notch. Alignment instructions over-sight or it may have been a deliberate omission.

Several variations on values of resistors encountered - this was probably due to production supply, e.g. 20K on schematic parts list is actually 25K in receiver.

Diversity Meter B initially seems to be wired reverse but this is correct for the way the meters work mechanically. Div Meter A + is + and Div Meter B + is -

Bass Reflex Cabinet

The Machine Age styled cabinet was designed by Auther Haggstrom and features the Jensen Ortho-dynamic 15" High Fidelity speaker with bass reflex port. The cabinet also allows stowage of the power amplifier and power supply on the two shelves. The cabinet is in very nice original condition with original grille cloth and all of the various wooden covers intact. The finish is in good condition with some wear apparent, including the ubiquitous "water glass ring." This just allows the cabinet to "show its age." One can also infer from these wear marks that a former owner enjoyed this DD-1 for several years, spending many hours tuning in various shortwave broadcasts from around the world. There is some moisture damage at the very bottom sides and also some minor veneer damage.

Restoration Problems: A common problem with DD-1 speaker consoles is that the side veneer went all the way to the bottom with no protective bottom moldings. Originally, the console had small metal glides that kept the bottom of the console off the floor,...slightly. As long as the console sat on a hardwood or concrete floor, the glides provided enough clearance for the bottom veneer to not contact the floor. However, many DD-1s were later placed on carpet and that's where the problems began. Sliding the heavy DD-1 console on carpet with the glides sinking well into that carpet allowed the bottom edge of the console to drag along the carpet surface. Depending on the carpet and the direction of movement it was very easy to chip off pieces of the veneer. Most DD-1 speaker consoles will have some veneer chipping these days. Also, in very humid environments the carpet may have a certain amount of moisture, especially if in a storage area that isn't heated. If the bottom edges of the cabinet sides were contacting this type of carpet that could have allowed moisture to "wick" into the bottom of the plywood sides that would cause delaminating of the layers of wood. Most of the chipping and loosening of the veneer is easy to repair but it is a time-consuming job that requires quite a bit of "glue and clamp" type of work. Touch-up is easy since most of the damage is very close to the floor and not easily seen. Veneer patches are sometimes required but usually the chipping is small enough that Artist's Acrylic paint can be used for a good match to hide the chips.

Console Back Showing the shelves and the speaker back cover

Amp and PS installed and cover removed to show the 15" loudspeaker

H-80596 Chassis after restoration

Note the reproduction plastic scales over the tuning dial and the bandspread dial. These were made by K6DGH.

Also note the brown plastic handles on the switch levers. All DD-1 receivers had lever handles that are similar to the black band switch push-button knobs (except they are not recessed for the band indicator ID.) The brown lever handles were installed on my DD-1 when I got it. They are definitely not original but they are vintage, look really nice and they do all match,...so I've left them on the receiver.

On the Black Fill Paint on the Front Panel Engraving -  I've noticed that about half of the known DD-1s have the engraved lettering filled with black paint and the other half of the DD-1s don't have any fill in the engraving. I really don't know what was original. Some of the prototype artwork shows the engraving filled but the actual photos taken at Hallicrafters with Halligan at the controls surrounded by his engineers seem to show that the panel wasn't filled. It's impossible to know since the photo was obviously a publicity shot and that DD-1 might not have been a production line example. I think it's likely that some DD-1s left Hallicrafters with the engraving filled and probably some didn't. I suppose that for now, when doing your restoration, just choose what you think looks best.

Estimated DD-1 Production, Known Serial Number Log and Collector's DD-1 Photo Gallery 

Nearly all DD-1 serial numbers encountered so far are in the H-805XX range. One might infer from a single DD-1 serial number that perhaps more than 500 receivers were produced with the numbers starting at H-80,000. However, Hallicrafters assigned serial numbers sequentially as products left the production line and exclusive number blocks were not used or ever assigned to specific models. Therefore, serial numbers alone cannot provide the information necessary to determine an exact number of DD-1s produced. One can estimate a number based on the known examples (and perhaps include the small quantity that has appeared on eBay over the last several years.) That number is very small indeed, with a little over two dozen examples, including the few DD-1s that have been offered for sale. This leads one to conclude that the total number of DD-1 receivers produced was certainly far less than the "200" that Bill Halligan "recalled" that had been manufactured. Of course, the interview with Halligan was decades later but he always did seem to exaggerate some of the production figures, e.g., Halligan claimed 50,000 SX-28 receivers produced when a more accurate estimate is 28,000. As far as any archival records, when Hallicrafters was sold to Wilcox Instruments (aka Wilcox Electric,) a Division of Northrop, in the early 1970s, all of the production records along with all of Hallicrafters archives were destroyed by orders from Wilcox Instruments! Another identification problem is the location of the DD-1 serial number tag. Since it is riveted to the bandswitch-coil shield-cover, if this shield is missing so is the serial number. This was a problem found on two of the four DD-1s I have inspected. Also, the two out of the three "unknown" DD-1 serial numbers in the log are due to missing original shield boxes.

Does the DD-1 have a higher Survivability than other Radios?

One thing I've observed with the DD-1 is its amazing survivability. Where most radios seem to have about a 10% or less survivability, the DD-1 is at close to 25% survivability (probably more since I'm only considering reported DD-1s.) There are a couple of reasons that factor into why more DD-1s have made it to "octogenarian status" than most other radios. First, of course, would be its original selling price. It's unlikely that a radio that cost the original owner almost as much as a new car was going to be tossed out. It had been a special purchase and when no longer a radio that was used on a regular basis, it would probably have been put into storage somewhere until the original owner died. Maybe the heirs knew what it was, maybe not. Of course, all DD-1 survivors have had multiple owners over the decades which leads to the second factor. The sheer size and impressive Machine Age styling was sure to make anyone that came across a DD-1 "know" this was something special. Even a "non-collector" could recognize that the DD-1 wasn't just "an old radio." It was something rare and valuable. That's what has saved many DD-1s when they became a dealer's property. The dealer knew that his new find was worthy of research and maybe that might have resulted in a higher selling price but it did also assure survivability. I think these two factors, especially the second factor, are the main reasons that so many DD-1s are still here, mostly intact, surviving on the planet.  

DD-1 Serial Number Tag Location

The Serial Number Tag is located on the right side of the coil-bandswitch shield box. The tag is riveted to shield box towards the rear. With the top removed the tag is easily visible as shown in the photo to the left. Details of the tag are shown in the photo to the right. Absence of a serial number tag generally indicates that the shield box is a reproduction.

 DD-1 Enthusiast's Photo Gallery

WA2LTD  -  H-80510

Tom, WA2LTD, owns the earliest serial number DD-1 reported so far. It is a console model although the photo is only of the receiver. Tom has all of the components to this DD-1 including the power supply, audio amplifier, speaker console and the diversity action meters installed in the wooden top cover.

Note the black knobs on the switch levers - this is the standard type of knobs usually found on the lever switches on the DD-1 receivers. 

March Field Air Museum  -  H-80519

Here is a photo of  DD-1 sn H-80519. Frank WA6CJT has recently acquired this excellent receiver from well-known Hallicrafters collector, Chuck Dachis. Note the color-coded buttons on the band switch. More information to come.

This DD-1 SN: H-80519 has been donated to the March Field Air Museum in Riverside, California. Donation was made by Lyn Zizzo in 2021. The Moreno Valley Amateur Radio Association operates the radio station there and the DD-1 is on display in the radio station.

UEC Museum - Tokyo, Japan  -  H-80520

DD-1 H-80520 is a table model set that is now located in the UEC Museum in Tokyo, Japan. Originally owned by JA1BHR, Mr. Yasuda, the DD-1 was donated to UEC after JA1BHR became SK. The photograph to the left is shows JA1BHR on the cover of a Japanese ham magazine from 1975. Note the DD-1 upper right behind the globe. The magazine is part of the DD-1 display at UEC. Thanks to Hiroshi Ogawa from Tokyo for providing the information on the DD-1 and the photograph. Also, thanks to Skip Magnuson W7WGM for contacting both Electric Radio and Hiroshi Ogawa to obtain this DD-1 serial number.

K6DGH  -  H-80521

Peter has owned this console DD-1 for many years. He fully restored H-80521 about ten years ago. His restoration involved replacement of all resistors and all capacitors. Additionally, he repaired or replaced several of the IF transformers. A total rebuild of the Yaxley push button band switch assembly was also needed. The wooden top piece and speaker console were refinished along with replacement of the grille cloth. The metal plating and the black wrinkle finish is original.

Peter sold his DD-1 in 2017. I have yet to hear from the new owner.

photo by: K6DGH

KE5O  -  SN: H-80532
 

This is a photo of KE5O's DD-1 shown alongside his HT-4 transmitter with the matching Speech Amp. The HT-4 was the predecessor to the famous WWII Signal Corps transmitter, the BC-610. Steve says that his DD-1 is operational but still needs further restoration work if it were going to be brought back to original. It seems that during H-80532's past, it experienced a shorted transformer that lead to a creative modification of the audio system. A Wurlitzer jukebox amplifier and a 15" electrodynamic speaker were utilized in returning the DD-1 back to functional condition. The original amp and power supply were lost over the years. But, the Wurlitzer sounds like it would be very comparable to the original P-P 2A3 amp and the 15" jukebox speaker must really sound great.    

Frank Adams - SN: H-80534

Here is a photo of the DD-1, SN H-80534 owned by Frank Adams. This is the table top configuration with the power supply and amplifier flanking the DD-1 receiver. Also included are the optional Diversity Action Meters housed in the small cabinet to the right of the speaker. The speaker is homemade and contains a 12" speaker. This DD-1 was formerly owned by Skip Magnuson who did all of the rework to make it an operational DD-1 (all of the electrolytic capacitors replaced and some other minor repairs.) Skip sold his DD-1 to collector Frank Adams in October, 2016.

(photo by W7WGM)

W5CZ  -  SN: H-80584

For the past 50 years, Benito Serrano was the owner of this DD-1 receiver. The receiver was located in Bogata, Colombia and was owned by Benito's granddaughter, Diana. The DD-1 was recently purchased by Rod Perala, W5CZ who has fully restored it and is currently using it with an RCA ATC-40 transmitter "on the air." New photos coming soon.

WB5KLJ  -  SN: H-80589

This table top DD-1 is owned by Ron WB5KLJ of Goldfield, Nevada. It worked the last time Ron powered it up but that was several years ago. Ron is planning on starting the restoration of his DD-1 soon, so updates may be coming.

2012 photo

2022 photo

WA7YBS - SN: H-80596

This is the highest known serial number DD-1 from the first production run. I displayed this DD-1 at our Western Historic Radio Museum in Virginia City, Nevada from 2006 up to the closing of WHRM to the public in 2012. Photo above left shows the DD-1 in 2012 in its Dayton "upstairs" nook. The photo to the right shows H-80596 in 2022 at its new location downstairs.
 

UPDATE May 2022:  I've owned H-80596 since 2006. Here's how I found it,...I had a visitor to the museum in 2006, Bill Jungswirth AA6S, from Visalia, California. During our typical "ham visitor" conversation Bill asked me, "Have you ever heard of a Hallicrafters DD-1?" I replied that I had. "Would you like to own one?" I said something like, "Sure, that'd be nice." Well, nothing else was said, so I thought it was just a typical "ham-type conversation-type question." About three weeks later I got an e-mail that started out, "My friend Bill said you might be interested in this." The e-mail was from another Bill, also in Visalia (at the time) K6LK. We exchanged lots of e-mails and photos over the next month or so. It all cumulated in a trip down to Visalia during August 2006 to do the pick-up ,...and was it HOT! I visited AA6S afterwards and saw his fabulous collection. Overnighted in Visalia and came home the next day. I restored the DD-1 as described in this article and then it did six years on display at WHRM in Virginia City (until 2012.) For the past ten years, H-80596 was located in the upstairs landing-nook here in Dayton, Nevada. At the time, I thought this would be a nice place for the DD-1 since it provided something to see as one entered the upstairs ham shack. Well, as time went along, things began to "pile up" around the DD-1 and it became difficult to access it for cleaning, dusting or just about anything. Also, if any movement of the DD-1 was attempted, being that it was on carpet, risked the possible damage to the "already damaged" side veneer of the speaker console. Some 2022 downstairs redecorating allowed the possibility of incorporating the extreme Machine Age styling of the DD-1 into the decor and this meant the DD-1 could now be setting on a hardwood floor. I had to remove the metal glides and replace them with compressed felt glides that allow easy moving of the DD-1 on the hardwood floor without damaging the floor. Of course moving the DD-1 is difficult enough but stairs complicated the move. Disassembly was necessary to reduce the weight to a minimum. Even then, the speaker console by itself is still a very heavy unit (I don't know why, I suppose it's all of the hardwood pieces and the fact that I didn't dismount the 15" loudspeaker.) Since this move had to be accomplished "solo," I used a large-wheeled hand truck with straps (a "stair climber" might have been nice.) At any rate, only the console and the DD-1 receiver presented any real moving challenges that required the hand truck. Once downstairs, reassembly was routine. Hopefully, the DD-1 H-80596 might be seen more often now in its new location (as shown in the photo above-right.)   photo right: The rear view of H-80596 DD-1 Console with all of the cables connected (no connections to the antenna inputs though.)

WB9YIR - H-85629

This is a second production run DD-1. This receiver had spent some time in Europe where the original power transformer (a 115vac primary) was replaced with a transformer with a 240vac primary. Gary is in the process of restoring the PS for this DD-1 back to the original configuration to operate on 115vac. The receiver itself is in superb condition although some of the capacitors were replaced with modern components. Again, Gary is going to be returning the receiver back to an original under the chassis appearance as part of his restoration.

Formerly owned by NU6AM - SN: Unknown

Current Owner: Unknown

This is the restored DD-1 formerly owned by NU6AM. The receiver is completely rebuilt and functions quite well. Jim used his DD-1 on several AM QSOs on the 80 meter band. Jim had the replica cabinet and meter top built by an exacting woodworking cabinet shop that reproduced the original cabinet and meter top in amazing detail. The cabinet shop used the K6DGH DD-1 cabinet as a model. This stunning reproduction is difficult to distinguish from an original cabinet and should be seen "in person" to appreciate the detailed craftsmanship.

Interestingly, the front panel "SKYRIDER" is actually engraved as "SKYR DER" - the "I" was skipped although the space is there. Probably the engraver had set up the pantograph machine with the correct letter dies but skipped the "I" when performing the actual engraving which results in the correct space but no letter. Also, interesting that this panel made it through two inspections,...Hallicrafters' inspection process,...and, since it's very likely that the panels were actually made by Crowe Industries of Chicago for Hallicrafters,...through Crowe's inspection. Maybe it was a bad day in Chicago,...or maybe everyone involved were just "cleaning house" and this DD-1 was part of the last of the second production run. This DD-1 was also missing the original box shield and therefore the serial number is unknown. An exact reproduction of the shield box was made and installed. The plastic dial indexes are exact reproductions made by K6DGH.

Ham and Hi-Fi did sell this DD-1 for Jim but, unfortunately, the present owner of this DD-1 is unknown at this time.

photo courtesy of "Ham and Hi-Fi"

WQ9E - SN: H-85655

This DD-1 Console is currently being restored by Rodger, WQ9E. Overall, the DD-1 is complete and only is missing the back cover that encloses the speaker area and the dial indexes. The Power Amplifier and Power Supply were present as were the connecting cables. There were some chips in the veneer at the bottom of the console and the original grille cloth was ripped in several places. The internal shield the goes over the Yaxley push-button band switch was present. There didn't appear to be any rust on the metal parts. Overall, Rodger has a very nice and restorable DD-1.

This DD-1 has the highest reported serial number. It is from the second production run and is certainly among the final few DD-1s produced.

Rodger also has this second DD-1 Table Model. It is does have the matching T-12 table speaker but the Diversity Action Meters were never ordered. Unfortunately, this DD-1 was in storage by a former owner for decades. Over the years the Power Supply and Power Amplifier units were lost. Also, lost over the years was the cover for the Yaxley push-button switch assembly that also carries the serial number tag,...so, no serial number for this DD-1.

DD-1 Installation at USN Station "J" at Jupiter, Florida - WWII

The USN installation was first associated with a lighthouse at Jupiter, Florida starting around 1890. As technology progressed, radio was added. In 1929, a "radio compass" (direction finder) was added to the equipment. At the beginning of WWII, the station provided intercept of enemy radio signals that were forwarded to Washington D.C. for decryption. During 1943, information provided by the Jupiter station (Station J) aided in the destruction of sixty-seven German U-boats that had been operating off the coast of Florida. In July 1945, with WWII winding down, the station was handed over to the U.S. Coast Guard then becoming NML.

The radio gear used at Jupiter in WWII was varied and consisted of many RBB and RBC receivers, at least one RBA receiver, several HRO receivers, an early Hallicrafters Skyrider (SX-16 or SX-17,) at least two Hammarlund Super Pro rack set ups and the two DD-1 receivers shown in the photo to the left. Note that these DD-1 receivers have the wooden console meter top section but not the speaker console. Note that the power supplies and the audio amplifiers are stowed under the table. The two loudspeakers are compatible Hallicrafters PM-23 types. The additional equipment consists of a CLOKEY Writer and Amplifier. The photograph is titled "DF RM."

Whether or not these DD-1 receivers were set-up for diversity reception isn't mentioned. Double-Dual Diversity isn't unheard-of, some of the WWII RCA diversity receivers were Double-Triple Diversity set-ups. Since a code writer is involved in this station, one would assume that Double-Dual Diversity was being used. The CLOKEY probably contains a Tone Keyer to allow the DD-1s to operate in AVC/Diversity and without the Heterodyne Oscillator and yet still "key" the printer. It's possible that these were "used" receivers when installed at Station Jupiter but this installation could have pre-dated WWII since the crypto work at Jupiter had actually started when WWII in Europe began in September, 1939.

More photos of Station Jupiter are at: www.stationhypo.com   when on "hypo" homepage, go to archive and select July 2021, then go to July 14, 2021 post which is the Jupiter station write-up and where this photo is from. Thanks to Andy KD6TKX for the info.

Conclusion and On-going Research

The DD-1 was to remain unique in receiver manufacturing as the only example of dual diversity circuitry designed for the ham market. Its lack of success was due to many factors that Hallicrafters should have anticipated - maybe they did and decided that the success was to their reputation and that was more valuable than profitable sales of the DD-1.

DD-1 survival rates seem to be much better than the average ham receiver or AM BC radio. This is expected since the selling price was nearly that of a new car and many of the original owners cherished their purchases for their entire lives. On the average, ten percent survival of total production is considered normal. I think the DD-1 is going to at least double that survival rate due to its uniqueness and the original expense of purchase

I have only been able to examine four DD-1 receivers in detail. 23 serial numbers have been collected so far. As with my article on the Hallicrafters SX-28, the information in this DD-1 article is always being updated to reflect new data that is supplied by Hallicrafters enthusiasts, collectors and interested hams. We need more serial numbers to more accurately estimate total quantity and the length of time the DD-1 was in production. Dated inspection tags are a great help as these tie the serial number to an exact production date. These are paper-wire tags that are usually attached to the line cord of each receiver. These tags sometimes have survived but I have never heard of one being found with a DD-1. Any dated tags that are in the SN H-80,000 to 86,000 range would help with more exact dating, regardless of what model the receiver it is.

If you have a DD-1 that has some differences from what I have listed in this article, please let me know. These variations (especially when tied to a serial number) can trace the engineering evolution or production upgrades of the DD-1. I will add these to the article for reference. Also, operational DD-1 performance appraisals would be interesting and would be included in this article if submitted (credit will be given.) E-mail me a photo of your DD-1, I'll add it to the DD-1 photo gallery.

Since all of the Hallicrafters archives and files were destroyed in the 1970s, collectors and enthusiasts now have to share our information in order to help renew our knowledge of this period of time in Hallicrafters' manufacturing history.
 

Send DD-1 info or photo to: WHRM  DD-1 SERIAL NUMBER or INFO

Thanks to all DD-1 enthusiasts that have sent in their serial numbers along with other information.

References:

1. QST May 1936, QST December 1937, QST June 1938, QST January 1939, QST March 1939 - all have articles or ads about diversity or the DD-1

2. Radio News, August 1933 - Diversity Reception by Murray G. Crosby - great article about H.H. Beverage and H.O. Peterson and the diversity station at Riverhead, NY. Murray Crosby worked for Harold Beverage at RCA.

3. Manuals - RCA DR-89 Triple Diversity Receiver, RCA-NAVY RDM Triple Diversity Receiver, RCA Diversity Receiving Equipment RBP-1 and RCP, Collins R-388/URR, Collins R-390A/URR (all contain sections about diversity reception)

4. Chuck Dachis' website - hallicrafterscollector.com - lots of info on all aspects of Hallicrafters

5. DD-1 Manual - from photomicrographics.com website - great source of DD-1 info!

6. Radio Shack - Boston, 1939 Catalog - from aade.com website - great source for original prices

7. 1939 ARRL Radio Amateur's Handbook - contains great ads about the DD-1

8. Riders VOL.X - schematic and alignment instructions - actually all the important information you need is in Riders VOL. X

9. Thanks to W7WGM, Skip Magnuson for his help in acquiring many of the DD-1 serial numbers listed in the serial number log

10. Thanks to Mike Greene for information on Auther Haggstrom

Copyright © Henry Rogers - September 2006/2022

Revised and new material added Sept. 2006, Nov. 2006, Dec. 2006, Mar. 2007, Apr. 2007, July 2008, Layout revised Dec 2009, new information Jan. 2010,
Layout revised with new material June 2010
Updates added August 2011
New price information - Sept 2018
New layout for two part article - Feb 2019
Updated NU6AM DD-1 - May 2021
Returned article to one part - Jan 2022
H-80596 20th Anniversary and Move - May 2022