Radio Boulevard

Western Historic Radio Museum

 

WHRM Radio Photo Gallery
 

Classic Pre-WWII Ham Gear

1928 - 1941

 

 

 

photo: W6NXW - Gus Gram, Los Angeles, California, ca: 1937 - Rcvr: Breting 14  -  Xmtr:  HB

Classic Pre-WWII Ham Gear - 1928 to 1941

Pilot Electric Manufacturing Company  -  "Pilot Wasp" - Model K-101

Though Pilot's advertising claimed they had been in business since 1908 and the company had used several different names during that time, "Pilot Electric Manufacturing Company" was officially founded in 1922 by Isidor Goldberg in Brooklyn, New York. Pilot Electric Manufacturing Company also claimed to be "The World's Largest Radio Parts Plant" in the twenties and they did build all of the parts supplied with their kits. Some of the famous employees of Pilot were Robert Kruse, Alfred Ghirardi and John Geloso. David Grimes was a Contributing Editor for "Radio Design" - Pilot's magazine. Though not the first Shortwave receiver kit offered by Pilot, the three-tube "Wasp" was certainly their first really popular Shortwave receiver kit. In 1928 the selling price was $21.75 including the coils. The "Wasp" was designed by Robert Kruse and Milton B. Sleeper. The plug-in coils selected the tuning ranges that covered 500 meters to 17 meters or about 600kc up to 17.6mc. A complete coil set featured five coils each with color-coded handles for identification. The three tubes were usually 201-A and the circuit used a regenerative detector followed by two stages of transformer coupled AF amplification. The kit included detailed instructions along with an assembly drawing. Builders were warned to adhere to the wiring layout shown on the drawing or performance would suffer. The circuit was built on a bakelite board for the chassis and a mahogany colored bakelite panel. The "Wasp" was introduced just as Shortwave Broadcasting was beginning to grow and everyone wanted to tune in to stations located in foreign countries. The "Wasp" was very popular and soon spawned a newer, more sophisticated successor, the "Super-Wasp."  

 

Pilot Electric Manufacturing Company - "Super-Wasp"  Battery Model K-110

 The four-tube "Super-Wasp" kit was introduced in early-1929 and featured a screen-grid tube for an RF amplifier along with regenerative detector and two-stage AF amplifier. The "Super-Wasp" kit sold for $29.50 including the five pairs of plug-in coils providing tuning coverage from 500 meters to 14 meters or about 600kc up to about 21.5mc. Detailed instructions, including a full size blue print, made assembly  relatively easy and assured that each "Super-Wasp" could perform pretty much as expected. Since these were kits though, build quality was highly variable and dependent on the assembler's experience. Pilot's magazine "Radio Design" was always including updates along with suggestions for improving performance, consequently "Super-Wasp" receivers are sometimes found today having modifications or non-original parts. The stock circuit used a type 22 screen-grid tube as an RF amplifier, a 201-A as a regenerative detector and  a 201-A tube as the first AF amplifier and a UX-112A as the second AF amplifier. The user could substitute a 201A for the last audio stage and reduce the plate voltage and bias voltage if a UX-112A was not available. To the right of the K-110 is one of the modular units Pilot called "Redi-Blox."  This one is a single-stage transformer input audio amplifier using a type UX-112A tube. This module could be added for a third audio amplifier stage if the user thought it necessary. Pilot offered "Redi-Blox" assembled modules in the late twenties to enthusiasts to help ease the mechanical side of kit building. Around the time that the "Super-Wasp" was introduced, Pilot changed the name of the company to "Pilot Radio & Tube Corporation" (April, 1929.) "Super-Wasp" receivers were quite popular and sometimes were found in ham shacks of the late twenties and early thirties. By today's standards, the "Super-Wasp" is a very primitive shortwave/ham  receiver but performance can be surprisingly good if the operator has patience and is willing to put in a few nights learning how the "Super-Wasp" works. All controls interact with each other making tuning sometimes tedious and demodulating SSB or CW signals requires the detector to be oscillating which increases the instability. However, patience will be rewarded and it is fun to use a 1929 battery-operated receiver to monitor one of the many AM ham nets on 80 meters, especially when running the audio to a vintage horn speaker - talk about "broadcast quality audio" - well, 1929 style anyway!  

 

Pilot Radio & Tube Corporation - A.C. "Super-Wasp" Model K-115

The improved "Socket-Power" A.C. "Super-Wasp" kit was available by late 1929 and sold for $34.50. The tubes used were a type 24A cathode and screen grid tube for the RF amplifier, a cathode type 27 for the regenerative detector and two 27s for the AF amplifier. All of the tubes operated on 2.5vac at 7 amps for the heaters and the K-111 power pack supplied all of the A+ and B+ voltages required. The lower right-hand switch was wired back to the K-111 to provide an "on-off" switch at the receiver. The first AF amplifier was a resistance coupled amplifier while the second AF amplifier was transformer coupled along with an output transformer. There was a considerable design effort put into the A.C. Super-Wasp to eliminate hum since most operation was going to be using earphones. Hum reduction was one of the reasons for the RC coupled AF stage. Pilot also stipulated that only their own Pilotron tubes would perform correctly in the A.C. "Super-Wasp."  Pilot plug-in coils are used for five tuning ranges covering 600kc up to 21.5mc. Shown to the left of the K-115 is the K-120 Audio Booster Unit, another Pilot module (though it is not called "Redi-Blox") for builders, that could be used if loud speaker volume was desired. All of the Pilot "Wasp" and "Super-Wasp" receivers found today will vary greatly in the quality of workmanship. Since these receivers were kits, the assembler may have had little or no experience in soldering, wiring or mechanical building. As a result, don't be hasty to judge a poor performing set as a "bad design." Check the receiver over carefully. An inspection of the soldering will usually be a clue into the level of workmanship you will encounter in your receiver. When everything is correct, the Pilot "Wasp" and "Super-Wasp" receivers are fine performers considering their vintage and a lot fun to use.  

 

National Company, Inc. -  SW-5 "Thrill Box"

The National Co. started in business manufacturing toys and parts in 1914 (as the National Toy Co.) By the mid-twenties, National Co., Inc. had long ago dropped the "toy" from their name and was supplying parts for the Browning-Drake BC receiver kit and also started producing radio parts. Mechanical Engineer James Millen joined the company as General Manager and Chief Engineer in 1928. Millen was a Stevens Institute graduate and an enthusiastic ham so it was natural that he guided National into the ham/shortwave receiver market. This move happened to coincide with the new and developing shortwave broadcasting which was becoming popular with a new audience, the "shortwave listeners" or SWLs. National introduced the SW-5 "Thrill Box" in 1930. The name "Thrill Box" implied how exciting it was for the SWLs to receive foreign broadcasts direct from around the world. Though primarily designed for the SWL, the SW-5 could also be found in many ham shacks in the early 1930s. It was an expensive receiver with selling prices usually over $100 with the power supply. Robert Kruse, of the Pilot Wasp and Super Wasp fame, was involved in some of the design work in developing the SW-5 through his laboratory in Hartford, Connecticut and with several visits to National's lab. The circuit was a five tube receiver using a regenerative detector (24-A) with TRF stage (24-A,) audio driver (27) and P-P audio output (2-27.) The coil sets initially covered 1.5 to 30MC in five sets but eventually several other coil sets were added along with bandspread coil sets. The first coil sets were color coded for identification. The receiver was powered by a separate power supply that provided the 2.5vac filament voltage and approximately 180vdc B+. The tuning dial was illuminated and projected onto a frosted viewing screen. The left hand control is the regeneration and the right hand control is an antenna trimmer adjustment. There was a battery version SW-5 available and some early SW-5 receivers were sold as kits. Some early National receivers (SW-5 and SW-3 mainly) will have a decal or label stating that the unit was built at Jackson Research Laboratory, however this was a company that was solely owned by National and was located adjacent to the National plant. Labeling receivers as built at Jackson Labs was a form of product protection that was the result of a broad suit brought against all radio manufacturers by Cardwell sighting the use of their variable condenser patent. The suit was not successful but National kept the Jackson name around for a while afterwards.

 

National Company, Inc.  -  AC SW-3  (AC Version)

National introduced the three tube SW-3 in 1931. It was a regenerative detector with RF amp and AF amp utilizing plug-in coils. There was an AC model that ran off an accessory National power supply and a DC model that was operated with batteries. The DC model also had a switch under the lid to disconnect the A battery. James Millen and the National engineers put considerable effort into the SW-3 design to achieve maximum performance in a three-tube regenerative receiver. Shielding was carefully developed as was the coil design to allow both general coverage coil and amateur bandspread coils to be used. The end result was a little receiver that had amazing capabilities and was very stable at the point of oscillation. The SW-3 had a long production life and was produced in fairly large numbers. Coil sets were available for a wide range of frequencies from longwave to 30MC, along with the bandspread sets for the amateur bands. Later, the SW-3 became so popular as a stand-by receiver that National even offered it after WWII for a short time as the SW-3 "Universal" using three octal tubes. Parts and coils were available from National up well into the fifties. Probably the best testament to the SW-3 performance is in a photograph that is in a mid-thirites QST showing a ham station that used a full-size rack Collins built transmitter along with the station receiver - an SW-3 - certainly not typical but it says something about the SW-3 performance capabilities.

 

Hammarlund Mfg. Co., Inc.  -  Comet Pro with Crystal Filter
Eastern Radio Specialty Company - PEAK P-11 Pre-selector

Oscar Hammarlund immigrated from Sweden in 1882 to work for the Elgin Watch Company. In 1886, he became Superintendent of Western Electric's Chicago plant. Six years later, Hammarlund started working for the Gray National Company. His main project there was the Teleautograph machine. In 1910, Hammarlund founded his own company, The Hammarlund Manufacturing Company. Initially, the company built gadget-type devices but soon became involved with Western Union call boxes. An interest in wireless led the company into the radio component business and their variable condenser designs became an industry standard. In the mid-1920s, Hammarlund formed a partnership called Hammarlund-Roberts Co. specifically to offer kits for AM Broadcast radios using Hammarlund parts. By 1930, home radio technology had evolved to the point where kits were no longer practical or popular and Hammarlund-Roberts went out of business. That didn't affect Hammarlund Mfg. Co., Inc. since they were ready to enter into the shortwave receiver market with the introduction of their new Comet All Wave Receiver, a superheterodyne receiver, in 1931. At the time, the majority of hams and many professionals considered the regenerative detector (with TRF stages proceeding it) to be the most sensitive type of receiver. It had a very low noise figure and with the proper antenna and operator skill, reception results could be amazing. The superheterodyne on the other hand, while fine for broadcast reception, was considered too noisy and not sensitive enough for acceptable shortwave performance. Hammarlund hoped to prove that with careful design and quality construction a shortwave superhet could easily outperform the regenerative receivers in every comparison. 

Arguably, the Comet and its later successor, the Comet Pro, changed how SWLs, Hams and Professionals listened to shortwave signals. It was the first successful commercially-built shortwave superheterodyne offered to the communications receiver market (ham or professional.) Hammarlund advertised the Comet Pro as "The World's Finest Shortwave Receiver" and it certainly was built with high quality parts and high quality mechanical assemblies. Performance for the time was superb. The first versions of the Comet Pro (actually the Comet All Wave Receiver) used 24A, 35, 27 and 47 type tubes in an eight tube circuit that had no RF amplifier and utilized two unshielded plug-in coils - WL = Wave Length (mixer) and OSC = Oscillator - to change tuning ranges. The receiver was sometimes installed in a console cabinet. The receiver had a built-in power supply (with type 80 rectifier,) used a field coil speaker and came with a set of four pairs of coils covering 250M to 16M. An optional AM BC band (240-550M) coil set was available. The plug-in coils were wound on ceramic forms and had wooden handles for easy removal. Early table top cabinets were made of wood (painted black) with a metal front panel. In 1932, the audio output 47 was changed to a 27 and the field coil speaker connection eliminated. An earphone jack was provided in parallel with the audio output that was a direct plate connection. This implies that an audio output transformer would still be used at the loud speaker or that an input transformer would be used for the sometimes required external audio amplifier. Individual shields for each plug-in coil were added to this version. The OSC coil wiring was changed at this time. Additionally, "Pro" was added to the Comet name, implying that the receiver had evolved into a "professional level" of quality and performance and, by January 1933, the Comet Pro was fully a shortwave communications receiver. The tubes had been changed to type 57 and 58 types along with the addition of an audio output transformer to couple the 2A5 audio output to a 4000 ohm Z load - usually a loud speaker with matching transformer. The new audio output transformer also had a tapped winding for the earphone output. The antenna input was changed to allow a dipole feed line to be used and the WL coil's wiring was changed to accommodate the new antenna connections. The standard cabinet had been changed to an all-metal construction, however the wooden table top cabinet was still available on request. Later in 1933, a crystal filter option was added, then a 10M coil set option and finally, in Sept.1933, an Amplified AVC option was offered requiring the addition of a 2B7 tube to the circuit bringing the tube count up to nine. The "arc" dials set the WL and OSC condensers and then bandspread (the vertical dial) is used to tune in stations around the general settings of the WL and OSC condensers. The bandspread dial is illuminated and projected onto a frosted viewing window. The BFO adjustment is a "swing-arm" lever accessed under the lid of the cabinet. The Comet Pro listed for $150 not including tubes but usually sold for around $115 complete from discount dealers like Leeds. The usual sales procedure was to offer the Comet Pro chassis and then add options like the metal cabinet, Crystal Filter, AVC and tubes which then pushed the selling price up to around $150. Production continued up to early 1936. Hammarlund referred to the Comet Pro as a "Professional Receiver" and it was indeed used by many professionals, both military and commercial. It was also taken on several expeditions to the Arctic and Antarctic. The Comet Pro was also popular with amateurs and could be found in many ham shacks in the thirties. For its time, the Comet Pro was a first-class superheterodyne receiver that was well-built and performed quite well when compared to its early competition that was mostly composed of homebrew regenerative TRF receivers.

Eastern Radio Specialty Company was located in New York City and built many different kinds of ham accessories during the mid-1930s. Their brand name was "PEAK" and the P-11 Pre-selector was probably their most successful product. The P-11 used two type 58 tubes as TRF amplifiers. The tuning range was from 200 meters down to 14 meters (1.5 to 21.5MC) in three tuning ranges using built in coils. The P-11 had a built-in 2.5vac transformer to supply the tube heaters and the dial lamp with power but B+ had to come from the receiver. This was usually easy to tap into and the current draw of two RF amplifiers was going to be minimal. The circuit used electron coupled variable regeneration for its gain control (left knob.) The power on switch (right knob) also controls the routing of the station antenna as either bypassing the P-11 in OFF or through the P-11 when ON. The PEAK P-11 listed for $33.00 but, if the purchaser was a licensed ham he was automatically given a 40% discount from Eastern Radio Specialty, net price was then $19.80. The P-11 was first advertised in December 1934 QST. 

 


1932 - RHM Airport Receiver

National Company, Inc.  -  RHM, AGS, AGS-X 

The very rare (but equally famous) National AGS receiver had its origins with National's RHM receiver (shown in photo above) The RHM was designed to fulfill a Department of Commerce contract to supply modern receivers for airports in 1932. It seems likely that Herbert Hoover Jr. and his West Coast design team were involved in some of the electronic engineering work of the RHM. The RHM was National's first superhet but only a handful were built. To take advantage of the prestige the Government contract had given them (and to profit through additional sales to the general public,) National adapted the RHM for ham use and dubbed it AGS. It was an expensive receiver selling for $265 in 1933. Both the RHM and the AGS used first class materials and components throughout resulting in performance and reliability that was incredible for the time. There were several variations throughout its short production life, mostly involving tube types and calibration procedures. The most significant variation was the Single Signal AGS-X which was designed specifically for the ham market. Also at this time, National started to offer ham bandspread coils for the AGS. Frequency coverage changed as the AGS evolved. The RHM version only tunes up to 15mc while the later AGS tunes up to 20mc. By 1934, even 10 meter coils were being offered for the AGS. However, the list price of nearly $300 was beyond most ham budgets of the time. Actually, if the ham waited until the introduction of the HRO in early 1935, he could then pick up a new AGS for about $123.00 (from Leeds.) Uses nine tubes (10 with PS rectifier), a separate power supply and plug-in coils.

I have owned the RHM shown since 1990. It is all original and has its complete original coil set (15 coils) in the rack mounted coil holder. In March 1933, Radio News published an article by James Millen titled "Testing a Modern Superhet" that described National's procedure for testing and aligning the AGS receiver. In the article there was a photo of the Radio News' AGS set-up that showed they were using a National Dog House power supply and a set of Hi-Z 'phones for the audio output. I've been running my RHM in this fashion also, using a National 5886 PS (6.3vac Filament and +180vdc B+) and then listening on a pair of Type-C Navy Baldwin 'phones. This has given me the best results, although if I don't want to use the "Baldies," I can connect up a Hi-Z magnetic cone speaker like a Radiola 100A which then eliminates the need for an audio output transformer and provides ample volume. The RHM functions quite well with 75 year old components - every part was the best that was available at the time. Today, the RHM performance seems antiquated and crude but in 1932 it was "state-of -the-art" and the fact that the receiver is still operating and is still accurate in its dial readout is testament to National's build quality and Herbert Hoover Jr. and James Millen's design capabilities. This same design team again worked together in 1934, producing the famous HRO receiver.

For more information on the RHM-AGS and its role in the development of the HRO receiver, go to "National Co., Inc. HRO Receivers - The Cream of the Crop" - navigation link at the bottom of this page.

 

National Company, Inc.   -  FB-7, FBX, FBX-A 

In March 1933, National introduced the FB-7, a seven tube scaled-down and economically-built version of the AGS, offered so hams could buy a superheterodyne at a realistic price, (about $65 with accessories.) The FB-7 eliminated the RF amplifier and the AVC circuit of the AGS. Additionally, the 6.3 volt tubes of the AGS were replaced with 2.5 volt tubes in the FB-7. The extensive use of aluminum found in the AGS was replaced with sheet metal chassis and cabinet in the FB-7. The receiver used plug-in coils that are similar to the AGS coils. There were general coverage coils available and the ham could purchase a bandspread set of coils for 160, 80, 40 and 20 meter coverage. The BFO frequency control is a knob on top of the BFO coil can and is accessed under the lid. The FBX model added a crystal filter to the receiver with the controls accessible on the right side of the receiver cabinet. The FBX came out after James Lamb's article in QST about Single Signal receivers and crystal filters. A matching National pre-selector was available, the model PSK, that added a TRF stage to reduce the image problems but it required its own set of plug-in coils. The PSK was usually bolted to the right side of the FB-7 using standoffs - long standoffs if it was an FBX so the operator could have access to the crystal filter controls. Though many hams preferred using earphones, the FB-7 would drive a loud speaker quite well with the proper power supply. At least three different models of AC power supply were offered that could operate any of the FB-7 receivers but the 5897AB was recommended since it provided sufficient B+ voltage to allow the type 59 audio output tube to develop sufficient power to drive a loud speaker - about +240vdc. Most of the 5897AB power supplies that were sold with FB-7 receivers have a tag on top stating the the 5897AB was "designed especially for the FB-7." An "A" suffix to the FB-7 or FBX designation denotes the use of National's improved IF transformers that utilized air-spaced trimmers rather than compression trimmers. The receiver shown is an FBX-A from 1934. The FB-7 and its variations were very popular and found in many ham shacks in the mid-thirties.

 

Patterson Radio Co.  -  All Wave, PR-10 All Wave & PR-10 Pre-selector

Emmitt Patterson started Patterson Electric Co. in 1919 but renamed the company in the twenties as Patterson Radio Company. By the mid-twenties, he began selling radios as a dealer. Around 1930, Patterson began building his own broadcast radios at the Gilfillan plant in Los Angeles. Patterson entered the communications receiver market in 1933. The PR-10 was designed by Ray Gudie and featured a 10 tube circuit with R-meter, IF gain control (no RF amp), single 59 audio output built onto a chrome plated chassis. Performance is very good (for 1934) but by adding the PR-10 Pre-selector, with its two RF amplifiers, one had a first class receiver. The first models were dubbed "ALL-WAVE" and didn't have a chrome plated chassis but soon that was replaced with the designation "PR-10" and the fancy chassis. The PR-10 Pre-selector also has variations in coil diameter and under chassis construction depending on early or late production. All Patterson receivers were built at the Gilfillan Bros.,Inc. in Los Angeles, since Patterson did not have an RCA superhet license*, (see note at bottom of page regarding Gilfillan and their licensing relationship with RCA.) The PR-10 listed for about $120, though some dealers sold the PR-10 for as little as $70. According to Patterson, total production was around 70,000 receivers - an incredible claim. Supposedly, the majority of production was sent overseas to Asia which could account for the relative scarceness of the PR-10 today. The first communications receiver I owned (in 1965) was an old PR-10. Unfortunately, I modified that poor receiver to the point of non-functionability! The PR-10 shown is the third one I have owned. It has had a long, well-preserved life having spent all of its time in Nevada. It is in original condition, unmodified and functions quite well.

 

W7FM - Homebrew Transmitter-Receiver (TX-RX)

Some homebrew ham equipment was so well-engineered and so well-built that in some cases it's difficult to image that the gear isn't commercially built. It's extremely fortunate that some former owners have had the foresight to save and preserve these superior examples of amateur engineering. The W7FM Transmitter-Receiver is an amazing example of efficient packaging and shows the creativeness that was necessary during the Depression to build quality, compact, useable gear. W7FM, Don Thorton of Spokane, Washington, decided to build a two-tube regenerative receiver and a four tube (crystal controlled oscillator, buffer and parallel power amplifier) CW transmitter both with their own individual AC power supplies. Not particularly unusual in the early thirties. But how about installing everything into a 1927 Kemper Radio Company K-5-2 cabinet. The original Kemper K-5-2 was a portable five tube battery operated TRF radio in a leatherette covered wooden box that featured a removable front cover and removable back cover. W7FM built the two AC power supplies into the lower section of the K-5-2 cabinet where originally a folded horn speaker and battery storage was located. In the upper section of the cabinet as viewed from the rear (shielding removed for photo) on the right is the two tube receiver and to the left is the four tube transmitter. What is amazing about the packaging is that full shielding was accomplished by building the entire TX-RX into a metal box that fits exactly into the Kemper K-5-2 cabinet. The entire receiver and each section of the transmitter are contained in shielded compartments. Looking deceptively light-weight, this TX-RX runs the scales up to an incredible 70 pounds! Full metering is provided with three panel meters. Six plug-in coils are required with two needed for the receiver and four for the transmitter. There are two complete sets of coils that were built for the TX-RX. Behind the speaker grille (with the "W7FM" embroidery) is an armature-pin speaker for receiver output. Separate receiver and transmitter antenna inputs are used. The receiver uses a type 27 for the regenerative detector and a type 47 for the audio output. The transmitter uses a 59 crystal oscillator, a 46 buffer stage and a pair of 45s in parallel. A hand-drawn schematic of the transmitter shows parallel 10s but Don Thorton probably decided that the 7.5vac filament voltage required for the 10s was impractical and went with 45s to keep all of the filament voltage requirements at 2.5vac. An 83 is used for the transmitter power supply rectifier and a type 80 is used in the receiver power supply. Note that the receiver power supply is built from old RCA Radiola parts. Don Thorton became an SK around 1940 and his son, Doug, was too young to remember his father using this TX-RX. Doug himself tried it out when he was in high school. The receiver worked fine and a friend listening on another receiver in town "thought" he copied the signal from the transmitter. Doug didn't have a license, so he didn't perform more than just the one test. Since then, the TX-RX has not been powered-up. Doug Thorton donated his father's homebrew TX-RX to the WHRM in October, 2010. Stay tuned for updates on this unit's functionability as we'll attempt to have it running soon. 

 


1935 HRO sn: D-65 (First Production Run) Rack Mount Receiver

National Company, Inc.  -  HRO, HRO Senior, HRO Junior - (1935 up to 1941)

National announced the HRO receiver in October 1934 and began production in January 1935 with the first receiver deliveries happening about March 1935. James Millen (at National) headed the mechanical design team and Herbert Hoover Jr. (on the West Coast) was in charge of the electrical design team. Millen and Hoover believed the best receiver performance was obtained using plug-in coils thus eliminating the losses found in most bandswitch circuits of the day. The HRO design also used a separate power supply in order to keep heat and hum out of the receiver. The HRO also used only the necessary number of tubes and all stages are run at maximum efficiency which lowered thermal tube noise and increased the signal to noise ratio. Many hams regard the HRO as the best of the pre-WWII ham receiver designs because of its great sensitivity with low internal noise along with its tremendous bandspread capabilities available on 80M, 40M 20M and 10M. It was an expensive receiver selling for about $200 with power supply and four coils in 1936. The HRO used 10 tubes (nine in the receiver and one in the PS) and featured double pre-selection on all of the plug-in coil sets. Plug-in coils for several frequency ranges were available and either general coverage or amateur bandspread were selectable on the amateur coil sets by relocating  four "jumper screws" on top of the coil assembly.

The micrometer dial was based on a Sperry Gyroscope design (National's version was successfully patented) and the National version was very smooth in its operation. The PW-D (National's term for the micrometer dial) had a scaled range of 0-500 that gave the user the equivalent of a linear dial twelve feet long. The precision nature of the PW-D readout allowed for extremely accurate reset capabilities. The PW-D numerical readout was correlated to frequency graphs that were mounted on the front of each plug-in coil set allowing the user to determine the receiver's tuned frequency. For hams, the dial readout vs. frequency graph allowed the operator to figure out where he was tuned and was probably as accurate as most direct readout dials of the day. Of course, most hams then were using crystal controlled transmitters and knew their operating frequency anyway.

The HRO was one of the first receivers produced to feature double pre-selection, that is two TRF amplifiers, which reduced images to a minimum. Many hams were using earlier-type receivers with a separate after-market pre-selection to achieve what the HRO was already equipped with. The band spread feature was based on what National had been offering with the FB-7 and AGS receivers. The HRO increased the band spread to the point where each of the 80M, 40M, 20M and 10M bands were covered in 400 divisions of the PW-D. This was equivalent to a linear dial that was nine and a half feet long.


                                 photo right:
1936 HRO sn: N-130 (10th production run) Table Top Receiver

There were several minor changes incorporated into the HRO from its 1935 introduction up to WWII. The HRO shown in the first photo is from the first production run and shows some of the earliest features of the initial run HRO receivers, that is, coil assemblies with white background graphs with black nomenclature, no pilot lamp, a nickel plated micrometer dial, black chassis, round IF cans, a "NC" on the dial pointer and a non-illuminated S-meter with a pearl-button push switch. The HRO shown in the next photo is serial number N-130, built in June 1936, showing many of the changes that had been incorporated by the 10th production run. The last photo shows how the HRO looked by 1940.

Initially, tubes used were 2.5v filaments if the AC power pack was used or 6.3v if battery operation was necessary but later either 2.5vac or 6.3vac tubes were optional. By the late thirties, only 6.3vac tubes were used. Millen believed that a lower noise figure was achieved using the 2.5vac tubes but later recanted this opinion as the 6.3vac tube quality improved. From the start, a rack mount version was also offered - it featured a crackle-finish, aluminum front panel (as D-65 shown in the header photo.)

 

photo left: 1936 HRO Junior sn: P-116 with original JD coil set installed - from the 11th production run

In 1936, the HRO Junior (third photo) was introduced as a reduced price version that eliminated the S-meter, the Crystal Filter and the bandspread coil feature (also, only one coil was included in the discount purchase price of $99.) With the introduction of the HRO Junior, the standard HRO became known as the "Senior." Also in 1936, the nickel plated tuning dial was changed to a black* painted lacquer version, chassis paint went from black to gray and the IF transformer shields were changed from round cans to square cans. In 1937, the S-meter became an illuminated unit and the following year the identification tag was added to the upper right corner of the panel.

The HRO shown in the last photo to the right is a 1940 HRO Senior (SN 463-K) with plug-in crystal. This version is how the HRO looked from 1938 up to about 1941. From this point up to the beginning of WWII, the HRO doesn't change except that some models will be found with a National "bar knob" for the Selectivity control rather than the round point knob.

For details on the WWII HRO versions go to "WWII Communications Equipment." For details on the post-WWII HRO receivers go to "Post-WWII Ham Gear." Navigation links are in the Index at the bottom of this page.

*The paint color on the PW-D varies from dark gunmetal gray to dark bronze. All dials appear black under normal room lighting and only show their true shades under intense light (like a photo flash.)


photo above: 1940 HRO Senior sn: 463-K

  For the ultimate in detailed information on all tube-type National HRO Series of receivers, including Production History, Serial Number Assignments, Performance and Restoration, click on
"National Co.,Inc. - HRO Communications Receivers - 'The Cream of the Crop"  in the index at the bottom of this webpage.

 

 

Breting Radio Mfg.  -  Breting 12

Paul Breting started selling communications receivers in 1935. Ray Gudie, famous for the Patterson PR-10, was Breting's chief engineer. Gudie came over to Breting after a wage dispute with Emmitt Patterson. Gudie felt the success of the PR-10 should have warranted him a salary increase - Patterson disagreed in a manner that caused Gudie to resign and go to work for Paul Breting. The Breting 12 was Gudie's first major design for Breting and it was introduced in 1935 for just under $100. The circuit was a 12 tube superhet that featured a second RF Pre-amp above 7.0Mc, band-in-use dial scaling, xtal filter, two meters (R-meter & Volume meter) and P/P 42s - all on a chrome chassis. The ham owner could also use the receiver's audio section as a transmitter modulator pre-amp. The BFO adjustment is a knob located under the cabinet. The dial had "oak leaves & acorns" decor on the early models while later dials had "rays." Breting didn't have the necessary RCA Superhet license so his receivers were assembled at the Gilfillan plant in Los Angeles, California*. The published Breting schematics are fraught with errors and rarely agree with the receivers produced.

 

Patterson Radio Co.  -  PR-16C

Patterson introduced their 16 tube receiver in 1935. After engineer Ray Gudie left Patterson over a wage dispute, Emmitt Patterson tried engineering the new PR-12 but soon discovered he was completely out of his element. Patterson hired Karl Pierson to complete the PR-12 but Pierson took one look at it and scraped the whole project. Though the PR-12 appeared in a few advertisements in late 1934, it was never in production. Karl Pierson designed the PR-16 in just a few weeks as the "new" Patterson receiver. The PR-16 featured parallel RF amplifier tubes (2-6D6s) which, in theory, increased the gain and reduced thermal noise. It also allowed the receiver to be advertised as having two RF amplifiers, even though there was only one set of RF coils per band and the receiver is essentially a single preselection front-end. The incredible audio section has three stages of Push-Pull audio using a 6A6 dual triode, two 76 triodes and two 42 output tubes supplying 18 watts of low distortion audio power. The BFO adjustment is a "swing-arm" lever accessed under the cabinet lid. Chrome chassis, band-in-use dial masking, illuminated R-meter, crystal filter, two-speed tuning - all for the low price of $101.70, (1936 price.) Even though the parallel RF amplifiers are unconventional and no other manufacturers ever tried to market the configuration - the PR-16C is a good performer with good sensitivity, nice mechanical bandspread and powerhouse audio. Built at the Gilfillan plant.*  Karl Pierson left Patterson in 1937, purchasing all of Patterson's communications receiver manufacturing business. Pierson continued to build the Patterson PR-15 under the Pierson-Delane name. Emmitt Patterson went out of business in 1939. This PR-16C belonged to W6BBK, who bought it new in 1936, using part of his WWI veterans bonus to fund the purchase.

 


W6HLJ Xmtr with National FBX receiver

W6HLJ - 1935 Homebrew XMTR

Alvin Norberg, ex-W6HLJ, began building this professional looking transmitter in 1934 upon graduating from Manteca High School. He worked as a laborer for Spreckles Sugar Company to earn the money to buy the parts needed. A few years later he was graduating from UC Berkeley as a BSEE (1939.)

The transmitter construction is entirely made out of wood and masonite. Each section of the transmitter is built onto a wooden base (with the masonite front panel attached.) Each section slides into place on guides. The cabinet is made out of 1"x12" pine painted black. Al tried to duplicate the look of a Bell Labs rack out of wood. Symmetrical layout with matching meters, function ID tags, 4" diameter knobs and purf-metal viewing ports added to the professional appearance. Al baked the wrinkle finish paint inside his mother's wood stove oven. Al said,

"When the transmitter was keyed all of the meter needles swung together and the mercury rectifier tubes flashed their blue light. When the key was held closed the plate of the final amplifier Heintz & Kauffman HK-354 would glow red! WOW!"


photo above: 2 photos - The W6HLJ Xmtr as it looked in 1935. Note that it is not yet painted.
Inside the transmitter the circuit is a crystal-controlled 6L6G oscillator that can be front panel switched to three different plug-in crystals. The buffer stage uses a Western Electric 211-D and the final amplifier is a Heintz & Kauffman "Gammatron" HK-354. The transmitter is CW only and originally ran 1 KW input power or about 700 watts output power. The PA plate condenser is homemade and was built by a machinist (the father of a friend) who made a gift of the precision made condenser. The plate transformer was a salvaged "peg-pole" transformer that was used to provide around 4000vdc on the plate of the HK-354. Unfortunately later in the transmitter's life, the original plate transformer was removed to lighten the total weight for easier moving. I have found a very nice 3K-0-3K plate transformer that looks similar to the original transformer and can handle 500mA. This level of plate voltage should easily provide about 750 watts input power and about 500 watts output. Whether we will be able to actually have a 2X CW QSO will depend on the level of RFI we encounter considering that the transmitter has absolutely no shielding whatsoever. Stay tuned for further updates as this restoration project continues.

Update for July 2013: Al Norberg, at the age of 97, is still a registered EE with the state of California. He recently (June 2013) donated his Speed-X bug that can be seen in the B&W photos and also the National Type-N dial that can be seen on his homebrew three tube receiver that is in the B&W photo. Unfortunately, the receiver was "parted out" years ago but building a duplicate is a possibility. The transmitter has been moved and is now at our new QTH in Dayton, Nevada. The top half of the transmitter is restored but the power supply section is still awaiting rebuilding before a test transmission could be made. Go to our webpage "Telegraph Keys" to see a close-up photo of the W6HLJ Speed-X. Navigation link in the index at the bottom of this page. 

 

 The Hallicrafters, Inc.  -  SX-9 

Bill Halligan bought Silver-Marshall Mfg. to start The Hallicrafters, Inc. and began offering receivers in 1933 with the first receiver designs using TRF circuits. All of the early Hallicrafters receivers were built by contractor radio companies, like Howard Radio Company and other contractors, since S-M didn't have a  manufacturing plant or the RCA Superhet license. Halligan formed a partnership with Case Electric to use their license and plant in early 1936 and shortly thereafter purchased Echophone to acquire their RCA superhet license and manufacturing plant. The SX-9 was offered in late 1935 through early 1936 and featured a built-in speaker, nine metal-type tubes and Aladdin iron-core IF transformers in a superheterodyne circuit with bandspread. All SX-9 receivers were built by contractors and the serial number tag will have a manufacturer code number for identification. Though the SX-9 was a significant improvement over earlier TRF models and performance is quite good, it still retained a somewhat crude "amateur" appearance. Like most Hallicrafters receivers, the SX-9 was designed to be built from "purchased parts" supplied by various component companies. This design and manufacturing method allowed Hallicrafters to offer great performing receivers at reasonable prices.

 

The Hallicrafters, Inc.  -  Sky Buddy Series - 5 -T "SKY-BUDDY", S-19 & S-19R "Sky BUDDY"

Hallicrafters believed there should be a market for an inexpensive shortwave receiver that would perform well enough to inspire young enthusiasts to choose "RADIO" as a hobby or as a career. First, the youngster would become an SWL (Short Wave Listener,) then go on to become a ham and finally would make RADIO a career. The idea certainly appealed to the parents of technically talented kids and it was those parents that were the target market for "entry level receivers." Hallicrafters' goal was to be able to produce the receiver at a cost low enough for the Depression-era parents of 1935 to afford the set for one of their "radio-minded" youngsters. At $29, the 5-T Sky Buddy was certainly low priced (about $250 in 2013 dollars) and with 5 tubes the performance was adequate to inspire hoards of young users into becoming hams. Many hams remember that their first listening experience to shortwave reception was on an "entry level receiver." (Of course, today most older hams remember the Sky Buddy's post-WWII successor, the S-38, as providing their first SW reception. As a kid, my first successful shortwave listening was on a second-hand S-38B.)
To ensure that the purchasers knew who the intended users of the 5-T Sky Buddy were supposed to be, the first few production runs included a picture of a "young ham sending with a bug" on the dial. A close-up of the dial is shown in the photo to the left. The 5-T was successful and popular. So popular, in fact, that many adults were buying the receiver for their own use. In a short time, Hallicrafters removed the "boy dial" and just used a plain dial with "SKY BUDDY" written across the center. Maybe this was to make the receiver look less like a kid's toy and more like a serious ham receiver. Note in the close-up of the "boy dial" that the boy is depicted using a semi-automatic telegraph key (bug) and is listening using "phones" just like a "pro." Of course, the vest and tie help for that future job interview to get into professional RADIO!

The "no boy" model 5-T was produced up to around 1938. By then the airplane dial was becoming passť and Hallicrafters had been using an external metal dial on their larger receivers so the Sky Buddy was revamped with a new dial and a few tube changes. The model number changed to S-19 Sky Buddy. Later, in 1939, other improvements warranted another model number change to S-19R. The major features of the S-19R were the added band spread dial and another tube to the circuit bringing the total to six. The price was also increased to $39. The early S-19R receivers use toggle switches but the very late versions (just before WWII) replaced the toggle switches with slide switches.

After WWII, the Sky Buddy returned,... well, the concept of an "entry level receiver" returned. The new version was designated the S-38. The S-38 eliminated the AC power transformer used in the pre-war Sky Buddy and went with an AC-DC circuit. Six tubes were used in the first S-38s but soon that was changed to five tubes when the BFO became a gimmick in the IF to cause oscillation and the Noise Limiter circuit was dropped altogether. Still, many hams remember the S-38 as their first exposure to shortwave reception and the little receiver was an amazing performer given its obvious limitations. The S-38 went through a series of upgrades running from the S-38, S-38A, B, C, D and E. Also, a faux mahogany cabinet S-38EM along with a blonde finish cabinet S-38EB. 

Ultimately, the Sky Buddy name returned with the S-119 receiver (also available as a kit, S-199K.) Although the idea and goals of interesting youths in RADIO was still somewhat popular, times had changed with television encroaching into the domain of RADIO with the ham often viewed as a TVI nuisance to the neighborhood rather than the valuable emergency asset he could be. The S-119 Sky Buddy II never gained the popularity or memories of the original Sky Buddy or the S-38 Series. 

Nostalgia certainly drives the collector market for Sky Buddy series. The performance of these receivers is very limited with rampant images since no RF amplifier was used in any of the series. They are easy to restore and when operational hopefully will bring back memories of youthful excitement when receiving signals from foreign countries.

Go to our webpage "Post WWII Ham Gear" for more info on the Hallicrafters S-38 series. Navigation link below in the Index.
 

photo right: 1941 Sky BUDDY S-19R. Note that this version has Band Spread. On all of the pre-WWII versions of the Sky Buddy, the speaker grill is flocked with a mohair felt that is usually dark brown or olive-brown color. On nearly all examples found today the flocked felt has fallen off or has been rubbed off so that only the wire screen part of the grille is left. 

 

Radio Manufacturing Engineers, Inc.  -  RME-69, DB-20 Preselector

Radio Manufacturing Engineers, Inc. started in business in the early thirties, founded in Peoria, Illinois by two hams - E. Shalkhauser, W9CI and Russ Planck, W9RGH. Their first receiver, the RME-9 and RME-9D (built from 1932 to 1935,) incorporated all of the basic ham requirements into a nine-tube, bandswitching superhet with built-in power supply. For its time, the RME-9D was a first-class receiver that suffered with an archaic tuning and bandspread dial. The RME-69 was announced in November 1935. Using nine tubes, a stout chassis and a tight, compact layout, the RME-69 provided the user a receiver with lots of sensitivity along with great performance features and a tuning and bandspread dial system that was "velvet smooth" - even though the dial nomenclature was miniscule. The "Compensator" control (located between the two main tuning knobs) allows the operator to keep the RF and Mixer stages "peaked" for any frequency tuned. "Stand-by" is actuated by pulling the Audio Gain control knob. A terminal on the rear chassis allows the station transmitter's AM signal to be monitored through the receiver. The Carrier Level meter is calibrated in both "R" units and in db (with 48db equal to R-9.) The standard RME-69 covered .55 to 32MC and sold initially for $135 - the price was raised to $151 in 1937. Throughout production various improvements were incorporated into the design. The RME-69A was an AC or Battery operated version and the RME-69B was battery operation only. Late in production changes were made to the mounting of the BFO switch and headphone jack, the mounting of the two dial lamps and the Crystal Filter design. Another late offering was the Lamb Noise Silencer, designated as the LS-1 option (there was also an LS-2 variation for battery operation.) The LS-1 added two extra tubes to the circuit.

A popular RME accessory was the DB-20 Pre-selector, introduced in October 1936. It provided the user with two tuned RF stages ahead of the RME-69 with an advertised gain of 20 to 25 db along with reduction of images. When the RME-69 was used with a DB-20, three tuned RF amplifiers were in operation - sensitivity was incredible and images were no longer an issue. A VHF Converter was also available. RME also offered the DB-20 and the RME-69 installed into one very long cabinet. The matching speaker is mounted in an unusual trapezoid shaped cabinet. In 1939, the RME-70 was introduced and the RME-69 was slowly phased out of production. About 6500 RME-69s were built from 1935 up to about 1940. Shown in the photo above is our 1937 RME-69 SN 1931 with its matching speaker and matching DB-20 Pre-selector.

If you are aligning an RME-69 be aware that it has a decidedly different front-end with no trimmers to compensate for variations in the coil windings of the RF or Mixer sections. This was because the coils were all pre-tuned before assembly and all coils should be identical from receiver to receiver. Whether they have aged the same over the past 70 years is an unknown but most seem to have weathered time quite well. Since the alignment requires some special information, it is lucky that the quirky alignment procedure is in Rider's VOL. X. When aligning the RME-69, it will be noted that the adjustments for the LO are compression trimmer capacitors which are notorious for not "holding adjustment." RME, more than any other communications receiver company, believed that the "ham owners" of their receivers were "tinkerers" - the type that was always adjusting this or aligning that. The fact that the LO might need adjustment every few months didn't bother that sort of owner and apparently didn't bother RME either.

The RME-69 by itself is an average performer since it only has a single RF amplifier, however when rebuilt and aligned, the RME-69 used with the DB-20 preselector is an almost unbeatable vintage receiver. It will be noted that some of the components used in construction are somewhat on "the cheap side." Also, it appears that several parts are just AM BC radio parts that were purchased to construct the receiver. Although Hallicrafters made their reputation on using purchased parts to construct their receivers, RME didn't have that sort of reputation. This was probably due to the RME style of advertising that promoted the "engineering" side of design rather than the source or quality of the components. Still, the RME receivers do perform quite well when rebuilt and aligned correctly.

 


1936  "Super-Pro" SP-10 from WMI
 

Hammarlund Mfg. Co., Inc. - "Super-Pro" - SP-10 Series, SP-100 Series

Hammarlund spared no expense to build the very best communication receivers available from the mid-thirties through most of the 1940s. Uncompromising quality made the Super-Pro the choice of professionals, both military and commercial, along with the few well-to-do hams who could afford the $400 list price (though most discount dealers offered the Super-Pro with Crystal Filter for about $250.) Designing began as early as 1933 (when it was referred to as the "Comet Super-Pro") but the actual introduction wasn't until March 1936. The Super-Pro used several custom designed parts, including its variable-coupled air-tuned IF transformers, its silver-plated cam-operated bandswitch and its four-gang main tuning condenser and twelve-gang bandspread condenser. Using 16 tubes, the circuit featured double pre-selection on all bands with 25 individual laboratory tuned coils mounted on 20 Isolantite bases, frequency coverage from .54-20MC, amplified AVC, front panel adjustable BFO and 0.5% dial accuracy (incredible for the time.) The variable-coupled IF transformers allowed the user continuously adjustable IF bandwidth from 16KC down to 3KC. Separate RF Gain, IF Gain and Audio Gain controls were used and even a Tone Control was provided. A separate power supply was included in the purchase price (along with a speaker.) The power supply provided three levels of B+ voltage, -C bias voltage and tube heater voltage, all connected to the receiver via a five foot long, nine wire cable that had a special terminal strip type connector on each end. 

The first Super-Pro, the Model SP-10, used all glass tubes with vented shields on the all but the audio tubes. The audio section including triode connected P-P 42s driven by another triode connected 42 with potted audio transformers with an 8 ohm Z output. Some SP-10 receivers had a 600 ohm Z audio output that added resistors to the audio line output to achieve a 600 ohm Z while utilizing the standard 8 ohm Z transformer. The first, second and third IF transformers were variable-coupled and cam/lever controlled from the front panel Selectivity control. Additionally, the Input and Output IF transformers for the Second Detector and the Output transformer for the amplified AVC were also variable-coupled but adjustable via knurled nuts on threaded shafts that protrude out the top of each transformer housing. The front panel was .190" thick aluminum finished black wrinkle then engraved so the nomenclature would appear bright silver (when it was clean.) The separate power supply was designed to utilize the field coil on the standard 8"speaker (a 12" deluxe speaker was available at $25 extra.) The speaker was just that - a speaker, no cabinet was supplied. The Tuning Meter was not illuminated and had an arbitrary 0 to 5 scale (but with 50 divisions!) Since it measured total IF amplifier plate current, stronger carriers would increase the AVC voltage, reducing the IF gain thus resulting in a lower reading on the meter scale. When tuning in AM stations, one would tune for the lowest reading on the meter. Signal reports were based on the difference between the "no signal" meter reading versus the "signal' meter reading to calculate "db over noise." Bandspread was only operational on the upper three frequency ranges and used a 0-100 logging scale. The crystal filter option was designated with an "X" suffix added to the model type. In mid-1936, an "S" version was offered that had coverage from 1.2 to 40MC with bandspread on all five tuning ranges (identified with an "S" suffix.) This model was advertised extensively in ham magazines of the day. The SP-10 designation is a later identification addition, when new, the receiver was just advertised as the "Super-Pro." The SP-10 was in production for only nine months.


1937 "Super-Pro" SP-100X

The SP-100 series Super-Pro was introduced in January 1937. Changes included going to metal octal tubes in the RF front end and in the audio section - eight tubes in all were changed (2-6K7, 6L7, 6J7, 6C5, 3-6F6,) the other eight tubes remained large glass tubes, (3-6D6, 6C6, 2-6B7, 5Z3 and 80 - the 80 was a change from the 1-V tube used in the earlier supplies.) The separate RF and IF Gain controls of the SP-10 were combined into a single Sensitivity control on the SP-100. The "knurled nuts" adjustable-coupling Second Detector Input and Output IF transformers and the adjustable-coupling Amplified AVC Output transformer of the SP-10 were changed to fixed-coupling units on the SP-100. The front panel was still .190" thick aluminum, wrinkle finished then engraved and now reference scales were added to the BFO, Bandwidth, AF Gain and Sensitivity. The "unique" Tuning Meter remained unchanged but the audio transformers were changed to vertical mount, frame-types with 8 ohms Z audio output. Added to the rear chassis apron was a two input pin jack socket that provided a remote relay access to control the receiver B+ by paralleling the Stand By switch. Around the same time the size of the standard speaker was increased to 10 inches. The standard power supply still had field coil connections on all versions but chassis space was provided for the substitution of a filter choke to replace the speaker field coil which then allowed the use of a PM speaker. Although not mentioned in advertising, an "L" version was available that included longwave coverage 100-200KC and 200-400KC in place of the .54 to1.25MC and 1.25-2.5MC bands. The "L" model also featured a front panel "Phone" jack and a dual secondary winding on the audio output transformer. A special SP-100X was built for Swedish government use, the Markradiomottagare 5, or MRM-5. These receivers were standard SP-100X configuration except for the frequency coverage - 200KC to 400KC and .54MC to 10.0MC. The Swedish manuals are dated 1937.

 Hammarlund always used "Series 100" in their advertising but model designations in their sales literature usually are SP-110 or SP-120 with 10 or 12 denoting the speaker size. Model designations also include suffixes that identify the tuning range and installation of a crystal filter - "no suffix" tunes .54 to 20MC, "S" tunes 1.2 to 40MC or "L" tunes 100-400KC and 2.5-20MC. The addition of  an "X" suffix denotes the installation of the crystal filter option. The serial number on all Super-Pro receivers is located on the rear apron of the chassis, stamped into the metal. Great sensitivity and fantastic audio with continuously variable selectivity make the pre-war Super-Pro receivers a natural for a vintage AM ham station today however they are seldom encountered. Probably because the early models are quite rare and the later 200 Series receivers are usually the military versions that are commonly found in an abused condition requiring extensive electronic and cosmetic restoration. When rebuilt and aligned, the Super-Pro is an incredible performing receiver with tremendous audio capabilities.

Shown in the top photo is our 1936 "Super-Pro" SP-10 SN:576 receiver that was used at WMI, a ship-to-shore radio station located in Lorain, Ohio. This receiver has been totally restored to original, "as delivered to WMI" condition and its performance is terrific with powerhouse audio. The lower photo is our 1937 SP-100X SN:3387 receiver that has also been totally restored to original. Performance is phenomenal and the receiver is pleasure to use. The SP-100X is used as the main receiver in our 1937 Vintage Ham Station paired along with a 1937 Utah UAT-1 transmitter.

More information on the "200 Series" Super-Pro further down this webpage.

For the ultimate source of detailed  information on the Pre-WWII Hammarlund Super-Pro receivers, including Product History, Estimated Production, Serial Number Assignments, Performance and Restoration, click on "Hammarlund Mfg. Co., Inc. - The Incredible Pre-War 'Super-Pro'" in the index at the bottom of this page.  

 

 The Hallicrafters, Inc.  -  SX-11 

The SX-11 was a major step forward for Hallicrafters. As a continuation of the design and manufacturing style that was used with contactors, Hallicrafters' engineers designed the SX-11 to be built from purchased parts that could be assembled into a first-rate communications receiver. The SX-10 and SX-11 were the first receivers that Hallicrafters built without the use of contractors. The SX-11 boasts several firsts for the company. It was Hallicrafters' first receiver with Push-Pull audio output, first with a tuning-eye tube, first to use a separate speaker. The 11 tube superheterodyne circuit also has such unusual features as variable injection BFO, 0-200 bandspread scaling, illuminated main dial, 6L6 tubes in the P/P audio output (14 Watts of audio) plus the fabulous styling that remained in the Hallicrafters line for the next several years. The SX-11 evolved during production with early versions sporting SX-9 type knobs and several circuit differences from the later versions. From the factory, the SX-11 was housed in a metal enclosure painted black wrinkle but the advertised SX-11 was also sometimes pictured in an after-market, shielded, solid-walnut cabinet. These wooden cabinets were not a Hallicrafters' product but were available from various "jobbers" during the thirties.

 

 
1936  NC-100  (SN 334D)

National Company, Inc.  -  NC-100 Series - "MOVING COIL" Receivers

The NC-100 was introduced in 1936 and was National's first successful receiver to not use plug-in coils. Though National's Chief Engineer and General Manager, James Millen, insisted that the best receiver performance was achieved using plug-in coils, National's mechanical engineers offered a solution with the NC-100 receiver, the first in a series of "Moving Coil" receivers. The "Moving Coil" system consisted of a movable cast metal coil box (sometimes called a "catacomb" by collectors) contained all of the coils mounted in individual shielded compartments with short contact pins mounted in molded insulators on top of the coil box. The band selector knob turned a rack and pinion gear mechanism that moved the coil box into place engaging the proper coil set pins into short, fixed contacts mounted under the tuning condenser. The mechanical action simulated plugging in a three coil set for each band with the ease of turning a knob while keeping all of the unused coils isolated and shielded.
 
The NC-100 was a general coverage receiver using 12 tubes including a cathode-ray tuning indicator that was included for AM reception. A crystal filter version was also offered - the NC-100X. In a short time a ham band only version, the NC-101X was introduced (it was within the second production run of NC-100 receivers.)  The later NC-101X receivers use an S-meter rather than the tuning eye tube. The photo to the left shows the early version of the NC-101X with the tuning eye tube indicator (SN:181-G.)

The Micrometer tuning dial, the PW-D, used on the early NC-100 is gray-blue with a red inner readout - very deco! All NC-100X versions seem to have a PW-D with a black inner ring and a gray outer dial. NC-101X receiver cabinets are all black wrinkle finish and generally use the same black PW-D dial as the HRO although early versions might be found with gray PW-D dials.

There was a "reduced cost" AC-DC version "Moving Coil" receiver that was available as either General Coverage or Ham Bands only, the NC-80X and the NC-81X. These receivers feature a slide rule-type, direct-read dial rather than the PW-D micrometer dial.  


photo left: 1937 National NC-101X  SN: 181-G

In 1937, the Department of Commerce, Bureau of Air Commerce contracted National to build rack mount NC-100 receivers that tuned 200kc to 400kc rather than tuning the AM-BC band. The first in the series was the RCD. The RCE that followed had several updates to improve the receiver for airport use. By 1938, the Civil Aeronautics Authority (CAA) was created and then that government body contracted for the remaining versions of the "Airport Receivers" built by National. The CAA versions start with the RCF. The use of National NC-100-based receivers at airports continued post-WWII when many of the earlier versions were professionally modified into the RCP and the RCQ versions.

In June 1938, the NC-100 was given a new, direct-reading dial with mechanically articulated dial pointer that indicated the band in use along with a standard S-meter that was mounted behind the panel and read through an opening in the panel. The new version was dubbed the NC-100A and soon all the NC-100 series receivers featured this dial. The Crystal Filter version was referred to as the NC-100XA. The ham band "A" version was available for a while in either configuration, PW-D dial - the NC-101X or the new, direct-reading dial version, the NC-101XA. By 1940, the NC-200 was introduced which combined both general coverage coils and ham band coils into one catacomb allowing the users both options in one receiver and thus eliminating the need for either the NC-100XA or the NC-101XA.
 

photo right: 1938 National RCF-2 CAA Airport Receiver

The introduction of the NC-200 (in 1940) wasn't the end of the NC-100A or NC-100XA receivers however. The military had been ordering versions of these receivers just before WWII began. With the USA entering into the war, both the Navy and the Army ordered thousands of National receivers. The Army designation was NC-100ASD and this receiver had the AM BC band replaced with a 200kc to 400kc band. The Navy had the RAO Series. The versions from RAO-2 and up to RAO-9 have two RF amplifier stages for maximum reduction of LO leakage to the antenna. The Navy also ordered the RBH receiver with better coverage of the medium wave bands due to its 1500kc IF. See "WWII Receivers and Post-War Ham Gear" webpage for more information on these WWII versions.

James Millen left National in May 1939, officially to form his own company, James Millen Mfg. Co. but it is thought that Millen was adamantly against National going "public" and selling stock in the company and that this may have influenced his decision to resign. Some of Millen's close friends relate a different story however. It seems that Millen had gone to Washington D.C. to discuss the use of the HRO receiver in the military. At the meeting, Millen represented himself as president of National. Somehow word got back to William Ready (the actual president of National Co.) who was livid. During the meeting at National (upon Millen's return) Millen was asked to resign, which he did. Though it seems like an over-reaction on Ready's part apparently there was more involved in Millen's resignation and perhaps the Washington incident was just the "final straw" in a situation that had been "brewing" for some time.

For the ultimate in detailed information on the NC-100 Series "Moving Coil" receivers, including Airport Receivers, Military Receiver versions, serial number analysis and restoration suggestions, go to our web-article "National NC-100 Series - Moving Coil Receivers" - navigation link below.

 

Sears-Roebuck - "Silvertone"  Model 5656A, (Howard Radio Co.) 

During the thirties, even Sears-Roebuck got into the communications receiver market by offering their Silvertone Model 5656A, built by Howard Radio Company in 1937. The receiver was an eight tube superhet with three tuning bands covering .55 to 18.0 MC. Also included was variable coupled IF for adjustable selectivity, an eight inch diameter tuning dial with multi-colored scales that somewhat compensated for the lack of a bandspread, an AVC switch with separate Sensitivity Control (IF Gain) and a built-in 8" Jensen speaker. It is likely that the screen-grille was originally flocked with some kind of mohair - this was typical of the screen grilles of the day. The BFO was built on a separate small chassis. The 5656A provided the basic ham necessities and performance was surprisingly good with sensitivity and stability that was hard to find - even in more expensive receivers. 

 

Breting Radio Mfg. - Breting 14 

Introduced in 1937, the Breting 14 offered the user spectacular styling with great performance. Some of the features were two RF amplifiers (although the first RF amp is an untuned pre-amp switched in above 7MC,) Crystal Filter and front panel adjustable BFO (although it is actually one of the small levers projecting from under the front panel.) There were also inputs allowing the ham owner to use the receiver's high fidelity audio section as a transmitter modulator pre-amp. Designed by Ray Gudie and selling for just over $100, that price also included a chrome-plated chassis and P/P audio with 6F6 driver and P-P 6F6 output tubes. The bandspread is accomplished mechanically using a slow-motion control coupled to the main tuning drive and operated using the knob on the lower right of the panel. The magnificent mirrored dial inside an art deco bezel also featured an edge-lighted translucent plastic tubular dial scale for band-in-use readout and a red pointer is backlit onto the logging scale. The "R" meter is also an edge-illuminated translucent scale. Certainly the dazzling dial illumination during operation gave the Breting 14 an impressive appearance that was matched by the receiver's great performance. In 1938, minor circuit modifications prompted a designation change to Breting 14AX. The most obvious of the AX differences are the two additional knobs on the front panel that replace the older levers that protruded through slots under the panel of the Breting 14. Some Breting 14AXs were painted gray. Paul J. Breting started selling receivers in 1935 but his receivers were assembled at the Gilfillan plant, in Los Angeles, since Breting didn't have the required RCA license.* Breting went out of business in 1940.

 

 The Hallicrafters, Inc. - Skyrider Diversity DD-1
 

In 1936, James Lamb and James McLaughlin custom-built an elaborate dual-diversity receiver for XE1G, Dr. James Hard, a wealthy and enthusiastic ham in Morelos, Mexico. In 1937, McLaughlin and Karl Miles, Chief Engineer for Hallicrafters, designed a version of the XE1G receiver for production. Hallicrafters began advertising the Dual Diversity DD-1 in June 1938. The dual diversity design utilized a shared local oscillator to provide single dial tuning which drove the seven-gang tuning condenser. Main tuning is accomplished with the left-side dial and bandspread uses the right-side dial. The massive Yaxley-built push-button switch assembly controlled AC power and bandswitching. The four meters monitored signal levels in each receiver, the signal balance between the two receivers and the common AVC line in S-units. 26 tubes are used in the DD-1, including the four VHF 1851 RF amplifier tubes which allowed the receiver to tune up above 40MC.

The table version was to sell for about $300 for the basic receiver without the Power Supply, Power Amplifier, Diversity Action Meters or speaker, (these accessories increased the basic price by $120.) The DD-1 Console version included the fabulous 15" Jensen Ortho-Dynamic High Fidelity Speaker in a Hagstrom-designed Deco-styled Bass Reflex cabinet along with a matching wooden top housing the diversity action meters. The DD-1 Power Supply and Power Amplifier chassis were stowed on shelves built into the rear of the speaker console. The DD-1 Console was priced at $500 - nearly the price of a new Chevy coupe in 1938.

Not surprisingly, the DD-1 was only advertised for about six months (last QST ad was 1/39) and total production is thought to be around 120 receivers. As a specialized receiver it confirmed that Hallicrafters' engineers were capable of sophisticated designs but this "over-the-top" creation certainly wasn't what the Hams of the late thirties would have purchased for their station receiver.

The DD-1 shown to the left is SN 80596, the highest known serial number from the initial production run. This DD-1 was on display in our Western Historic Radio Museum from 2002 until we closed the museum in 2012. It is shown as it now looks in its new nook located at our new QTH in Dayton, Nevada.
 

  For the ultimate information source on the Skyrider Diversity DD-1 including Estimated Production, Serial Number Assignments, Performance, Known DD-1 Serial Numbers, Photo Gallery of other DD-1 receivers, History of Diversity Reception plus many details on our Restoration of our DD-1 SN:H-80596.....click on "Hallicrafters DD-1 - Restoration and History of Diversity Reception" at the bottom of this page.   

 

  

 SP-200SX - 1.2MC to 40MC - Early version from 1939

Hammarlund Mfg. Co., Inc.  - "Super-Pro" - SP-200 Series  

Introduced in October 1939, the SP-200 series offered the same uncompromising quality of its predecessors while thoroughly updating the receiver to 1940 design specifications and reducing the cost of production so the receiver could list for about $315. Some of the changes from the earlier Super-Pro was the redesign of the IF amplifier section to use three stages followed by a conventional duplex diode detector tube, the 6H6. Additionally, the amplified AVC circuit was simplified with capacitive coupling pickup and reduction of the transformers to one unit. 16 metal octal tubes were used in the new receiver with two glass rectifiers in the power supply bringing the total to 18 tubes. The new Super-Pro still featured double preselection on all bands, variable coupled IFs (variable bandwidth) but added an improved Crystal Filter, a new illuminated S-meter with 0 to 9 scale that was connected to the AVC circuit so it worked normally (the early Super-Pro "Tuning Meter" measured total IF plate current and worked "backwards") and a brand new Noise Limiter circuit. The powerhouse audio still used triode connected P-P 6F6s w/ 6F6 driver and produced up to 14 watts of high-quality audio power. The suffix letters designate the frequency coverage with X (.54-20MC), SX (1.2-40MC) and LX (100-400KC and 2.5-20MC) models, (all SP-200 series receivers had a Crystal Filter and therefore the "X" option.) Early versions of the SP-200 feature a Speaker/Phone switch, standard vertical mount audio transformers with 8 ohm audio output Z and a wrinkle finished aluminum front panel. Later versions have a front panel phone jack, potted audio transformers with dual outputs (600 ohm speaker and hi-Z phones) and semi-gloss finished steel panel (the front was copper-nickel plated under the paint for corrosion protection.) The separate power supply was updated to eliminate the field coil requirement on most models. Some sales information will denote the speaker size by using variations in the model number, e.g. SP-210 (10" speaker) or SP-220 (12" speaker) however, Hammarlund always used "200 Series" in their advertising. By 1942, a matching speaker cabinet, model PSC, was listed separately at $5.10, which implies that the speaker was still being supplied without a housing. Hammarlund also indicated in their advertising their willingness to supply the Super-Pro in any special frequency requirement per customer request and special order. 

1941 SP-200LX - later version with a steel panel painted semi-gloss black

The most commonly heard complaints about the Super-Pro receiver involve limited frequency coverage. Though this is somewhat true, one should bare in mind that the Super-Pro was a commercial/military receiver that could also be used by hams. Hammarlund offered the "ham version" of the Super-Pro in the "SX" option - 160M to 10M coverage. Most of the limited frequency coverage complaints were from hams who wanted the SX version but could only find the X or L versions. Long warm-up time was another complaint with ~2 hrs. required for minimal drift - but most pre-war receivers won't quit drifting any sooner, if ever! Besides, the SP-200 was designed to be left on continuously which eliminated the drift issue. The non-calibrated 0-100 scaled bandspread dial brought more negative comments but since the Super-Pro was a commercial/military receiver also, it might be used anywhere in the frequency ranges so a calibrated bandspread wouldn't have been practical. Another common complaint was that high front-end tube noise limited the ability to copy very weak signals but this often-heard opinion was based on a popular modification article that appeared in CQ magazine, advocating replacing the front end tubes with miniature tubes (along with several other unnecessary modifications.) Actually, using a matched (or tuned) antenna would have been an easier solution. A matched antenna will help considerably in reducing noise and increasing signal strength. The Super-Pro does not have an antenna trim control and depended on the user to provide a matched antenna for best performance. Also, many users ran the receiver with entirely too much RF gain and too little AF gain resulting in high noise that tended to mask weak signals. The solution was to operate the receiver as a "communications receiver" and not as a "broadcast radio."

Today, the Series 200 Super-Pro is rarely encountered as the station receiver in a Vintage Ham Shack, probably from the many years of negative comments from hams who wanted to use this military/commercial receiver in their ham station and expected the receiver to have been designed exclusively for ham use, which it wasn't. The majority of SP-200 receivers encountered today are the WWII military versions and they have had years of hard use and probably a lot of abuse. Normally found in "rough" condition, the Series 200 Super-Pro will typically require total restoration to function at it design limits. When fully restored and aligned, the SP-200 series receivers are unbeatable performers. The military Super-Pro 200 Series receivers are generally identified with their Signal Corps designations of BC-779 (LX), BC-794 (SX) and BC-1004 (X.) These versions are more or less identical to their civilian counterparts. More information on the military Super-Pro receivers on the "WWII  Receivers and Post-War Ham Gear" webpage.

For the ultimate source of detailed  information on the Pre-WWII Hammarlund Super-Pro receivers, including Product History, Estimated Production, Serial Number Assignments, Performance and Restoration, click on "Hammarlund Mfg. Co., Inc. - The Incredible Pre-War 'Super-Pro' Receivers" in the index at the bottom of this page.

 

hq120xr.jpg (20424 bytes)        

Hammarlund Mfg. Co., Inc.  -  HQ-120X 

Hammarlund realized that the Super-Pro was far too expensive for the majority of hams and that it was really a commercial-professional receiver that wasn't specifically designed just for the ham market. So, Hammarlund designed and built a receiver that was designed just for the ham market, the 12 tube, HQ-120X, (introduced in 1939.)  To keep the selling price within the typical 1939 ham's budget, the circuit uses a converter tube, single pre-selection, single-ended audio and a built-in power supply but frequency coverage was .54 to 30MC and ham band calibration was provided on the bandspread dial (generally credited as the first ham band calibrated bandspread available.) Selling price listed at $230 but the receiver usually sold for around $190 (or less) from most dealers. The HQ-120X was popular and provided decent performance on shortwave and ham bands up to about 15 Mc. Beyond that, images and lack of sensitivity become a problem. Late in production, a special gray painted version was offered. The military also had versions built and designated as the RBG or CHC-46140, though the tube line-up is slightly different from the civilian HQ-120X. The HQ-120X was the first of a long line of "HQ" receivers built by Hammarlund specifically for the ham market. Shown in the left photo is a black finish HQ-120X with the unusual rack-mount option with an extended front panel and rear dust cover but with feet on the bottom to allow table-top use. The right photo shows the HQ-120X in the standard table cabinet with the later production gray finish option. By 1942, the gray finish had become standard and black finish was a special option.

 

The Hallicrafters, Inc.  -  SX-28 & SX-28A

The masterpiece of pre-WWII Hallicrafters receivers. Introduced in July 1940, the SX-28 circuit boasted 15 tubes, covered .55 to 43MC in six bands, had P-P audio, ham band calibrated bandspread, Lamb Noise Silencer, Amplified AVC, on and on. Hallicrafters advertised that the SX-28 had been designed by 12 of their engineers based on 600 requested reports including input from the Government. The styling was beautiful and the performance incredible. Early versions of the SX-28 have gray panels but starting in 1941 the panel color was changed to black. About the same time the Lamb Noise Silencer was redesigned. A few months later the bandspread gearbox was replaced with a dial string drive. There were many engineering design changes throughout production. During WWII, Hallicrafters continued to redesign portions of the SX-28 and, in April 1944, a major redesign to the receiver's front-end prompted a designation change to SX-28A. The old front-end coils were replaced by smaller, Hi-Q Micro Set types that were mounted on removable chassis. The new coil design eliminated the majority of brass parts that were used in the early style coils. After WWII, Hallicrafters had nothing new to sell the hams as they had devoted all design and manufacturing to the war effort, so they offered the SX-28A as a 1946 model. The last 4000 SX-28As built have "SX-28A" indicated on the front panel (indications are that the "A" appeared around November, 1945.) Hallicrafters published that 50,000 SX-28s (and SX-28As) had been built by 1946, however the serial numbers seem to indicate a production figure of about half that amount, around 27,500 receivers. Nowadays, many SX-28s and SX-28As are still being used in vintage AM ham stations because of their fabulous audio quality and classic "good looks." Most ham AM operators find the sensitivity, selectivity and stability quite acceptable for communications on vintage AM nets today. The SX-28 (SN H-151197) shown above belonged to W3ON, John Ridgway (SK), who purchased it new in February 1942. In 1997, at age 85, John sold his receiver to me saying, "...it's so damn heavy, I can't even turn it on its side anymore." The W3ON SX-28 is in superb original condition and is an excellent example of how the pre-WWII SX-28 looked when new.

For the ultimate source in detailed information on the SX-28 and SX-28A history, production and engineering changes, dating by serial number information, competition comparisons click on "Hallicrafters SX-28, a Pre-war Masterpiece" at the bottom of this page 

The Hallicrafters, Inc. - SX-28 and R-12 Bass Reflex Speaker
 

During early production of the SX-28, three different speaker options were offered. The PM-23 was a 10" speaker in a table top, metal case. The R-8 was a small bass reflex cabinet with 8" speaker and the largest speaker offered was the Hallicrafters-Jensen Bass Reflex floor speaker, the R-12. Selling price was $29.50 and, together with the $159.50 that the SX-28 cost, represented quite a substantial investment in 1941. The R-12 uses a Jensen 12" PM speaker with 5000 ohm to 8 ohm transformer. The cabinet is constructed with panels made from solid lumber core with soft wood veneer. Paint was a dark silver color except for the decorative incised arch over the speaker opening that was filled with red paint. The cabinet panels are held together entirely with small internally mounted clamps. This method of assembly allowed the speaker to be shipped in a flat box. Originally, the wire screen grilles were flocked with a champagne colored mohair but most surviving examples have lost their flocking with years of use.

The SX-28 (SN H-130170) & R-12 combination shown to the left was purchased as a "set," new in mid-1941, by W6ANX, Theron "Woody" Woods. The combo was found in the basement of Wood's house in Auburn, California around 2004. The R-12 was in dismal condition with warped boards and missing veneer. The receiver functioned but not as it should have. Rebuilding the R-12 required total disassembly and straightening the panels. The straightening process involved wetting the panels and then clamping them to flat surfaces until thoroughly dry. After this, the soft-wood veneer pieces were glued and new pieces glued to replace the missing pieces. The paint was matched from the protected paint on the "h" grille. I didn't bother with the flocking of the grille screens since all of the R-12s I've seen don't have any flocking anymore. Also, it would have required mixing up a batch of special color felt that probably wouldn't have looked right anyway.

H-130170 was completely rebuilt. Only one strange problem was found. The slug of the third IF transformer had come loose and was at the bottom of the slug barrel. Since this transformer is a capacitive adjustment, the IF would peak but it was not really tuned. The output level was far below normal which was the clue that something was wrong. I replaced the transformer with a good one from a parts set. Both H-130170 and its matching R-12 sound incredible now with loads of bass response and great performance.
 

Want to build a replica R-12 speaker? I took this R-12 apart and photographed the interior in detail. I also measured all of the important dimensions and described the types of materials used in the original construction. Still interested? Phil Nelson of "Phil's Old Radios" has edited and hosts the article on his website. Here's a link to the article:  Build Your Own Hallicrafters R-12

 

 

*RCA Superheterodyne License and Gilfillan Bros., Inc.

In the 1920s, the "Radio Group" (an un-official name for the cross-licensed corporations -  General Electric, Westinghouse, AT&T, United Fruit Company and RCA) had control over most of the important radio patents and had excluded all non-licensed companies from building superheterodyne receivers by threats and law suits. RCA began licensing out TRF circuits (that had been purchased from Hazeltine) in the late twenties. Early in 1930, the government filed an anti-trust suit against the "Radio Group" essentially taking control (and patents) away from GE and Westinghouse. RCA gained full control of the Superheterodyne Patent at that time. As part of the settlement, it was stipulated that RCA would now have to license other manufacturers to build superhets. Every major radio company had to have the RCA Superheterodyne License in order to remain competitive even though there were royalities and other conditions with having the license. Some of the conditions required that license holders had to produce radio chassis in sufficient quantity and of high quality in order to qualify for the RCA license. This left many small companies unable to qualify for the license due to their limited market, small overhead and the expenses involved in producing high quantity and high quality chassis. Fortunately, for the small radio companies, there was a option in the RCA license rules and conditions that allowed a license holding company to build chassis for other un-licensed companies. Gilfillan Bros., Inc. in Los Angeles, California had the only RCA Superheterodyne license on the west coast (exclusive license holder for 11 western states.) This arrangement was due to a "face to face" confrontation between S. W. Gilfillan and David Sarnoff, (who admired Gilfillan's determination.) Gilfillan built chassis for Patterson, Breting, Jackson-Bell, Packard-Bell and Pierson-Delane along with dozens of other smaller companies in the Los Angeles area. During the early 1930s, the policy was not very strict and almost any part of a radio could be built by the licensed company and still protect the sub-licensed company. This policy was eventually changed to just the building of chassis or complete radios affording protection. Some companies (including Gilfillan) allowed sub-licensed companies to supply their own assemblers, set up their own production lines, using plant floor space at the license holder's company. The sub-licensing policies allowed many small radio companies to produce quality radios while at the same time allowed the licensed company to profit during the difficult economic times of the 1930s. In 1940, RCA decided that there was not enough quality control on the chassis produced for the smaller companies by the license holding companies and began to stop allowing the sub-licensing option. The RCA license structure was also changed at that time to allow most smaller companies to obtain their licenses direct from RCA.

References:

1. "Communications Receivers - The Vacuum Tube Era, 1932-1981"  by Raymond S. Moore - Undoubtedly the best reference book on tube-type superheterodyne communications receivers. History of receivers and the companies along with circuit description and photos of each receiver. Four editions have been printed.

2. "Shortwave Receivers Past & Present - Communications Receivers 1942-1997"  by Fred Osterman - Excellent reference book on later communications receivers. Includes many foreign makes. Circuit descriptions, photos, prices.

3. "Los Angeles Radio Manufacturing - The First Twenty Years" by Floyd Paul - Details the history of Gilfillan Bros., Inc and their licensing relationship with RCA. Many smaller LA companies are also covered.

4. QST, Radio News and Shortwave Craft magazines from 1928 up to 1948 - These vintage magazines are excellent sources for contemporary reviews of equipment and pre-production articles by the designers. Advertisments are invaluable for dating and development of the model line.

5. Operator's Instructions, Factory Manuals, Rider's Troubleshooting Manuals - Original manuals are excellent sources for circuit descriptions, design intentions and performance expectations. Many times the same information is included in the appropriate Rider's Troubleshooting Manual.

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National Co. - HRO Receiver
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"Moving Coil"  Receivers 
Comprehensive History, Serial Numbers, Restoration & More - Includes Civilian Versions, Military Versions & Airport Versions

Hallicrafters SX-28
"A Pre-war Masterpiece"

Comprehensive History, Serial Number Analysis, Restoration Details & More

Hallicrafters DD-1 "Skyrider Diversity"
Comprehensive History, Serial Numbers & Restoration Details

RCA's Legendary AR-60 Receiver
Comprehensive History, Serial Number Analysis, Restoration Details & More - including the AR-60 connection to Amelia Earhart's Disappearance.        

RCA's Amazing AR-88 Receivers
Comprehensive History, Restoration Info, How to do IF Sweep Alignments, Serial Numbers & More

 Hammarlund Mfg.Co.,Inc
The Incredible Pre-War 'Super-Pro'
Comprehensive History, Serial Number Analysis, Restoration Details. Includes info on the Hammarlund Comet Pro

Hallicrafters' "Super-Pro" R-274 Receiver
Comparison of the SP-600 to the R-274(SX-73) in detail, best features of each. VOTE for your favorite Super Pro

 

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Rebuilding the R-390A Receiver
Detailed Restoration Information for each module with Lots of Photos

Rebuilding the Hammarlund SP-600
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Rebuilding the ART-13 Transmitter
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Rebuilding the BC-348 Receiver
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     Rebuilding the Collins 51J Series Receivers
Detailed Restoration Information with Lots of Photos - Includes R-388 Receiver
Successfully Operating the BC-375 on the Ham Bands Today
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Rebuilding and Operating the AN/GRC-19
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Building an Authentic 1937 Ham Station
Utah Radio Products - UAT-1 Transmitter

 

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