Radio Boulevard
Western Historic Radio Museum



Classic Pre-WWII Ham Gear

Part 1 - 1928 to 1935

(Part 2 - 1936 to 1941)



photo right: Station W1AVJ of Robt. Byron of Concord, NH
in 1932. The receivers on the desk are a Pilot AC Super Wasp
and a National AC-SW-3. The homebrew transmitter is a MOPA
using a 210 oscillator and the PA is a 211. Antenna is a Zepp.
The device with the two National vernier dials is the antenna tuner.
Note that the wire feed line runs across the wall on insulator standoffs.
Also note the WAC (Worked All Continents) award on the wall. Difficult to do in 1932.

Classic Pre-WWII Ham Gear -  Part 1 - 1928 to 1935

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 Co., Pilot Radio & Tube Corp. - "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 most "Super-Wasp" receivers found today will have some 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! When examining vintage QSL cards that date from about 1930 up to about 1934, it's surprising how many times the Pilot Super Wasp is listed as the station receiver. In fact, the header photo showing station W1AVJ has a Pilot AC Super Wasp on the desk. The AC Super Wasp is profiled next,...    


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 K-112 power pack can also work with the A.C. Super-Wasp even though it was for a receiver that used 45 tubes (just don't use the +HV and ground the B-/CT return to power up the A.C. Super-Wasp.) The lower right-hand switch was wired back to the K-111 to provide an "on-off" switch at the receiver (other power packs provided the same option.) 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 Model" SW-5 available and a special "Low Drain Battery Model" that used 2-volt tubes that ran on an air-cell battery that was supplied with the receiver. There was also a "Special Broadcast Model" that had P-P 45 tubes in the audio output. Early SW-5 receivers may have been available as a kit similar to the Pilot Wasp sets. Some 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. 

Go to "Military and Commercial Communications Gear Part 1" to see and read about the U.S. Navy RAD-2, a National SW-5 built for shipboard use in 1932.


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 - the 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. The superheterodyne manufacturing license had just become available from RCA in early-1930 giving Hammarlund sufficient time to engineer their new receiver. Before the Comet was introduced however, Hammarlund had offered a three-tube shortwave receiver as a kit. It was patterned after the Pilot Wasp and its sales most likely gave Hammarlund an interest in entering the shortwave receiver market. With the Comet's 1931 introduction, Hammarlund decided to offer a real improvement to the typical shortwave receiver of the day. At the time, the majority of hams and many professionals considered the regenerative detector (with TRF stages proceeding it and AF stages following 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 would be easier to operate and provide more consistent reception results thus reducing the skill that was required to obtain the same performance results using a regenerative detector receiver. 

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. 


National Company, Inc.

  RHM, AGS, "Single Signal"AGS-X

The very rare (but equally famous) National Company's AGS receiver had its origins with their Department of Commerce Airways Receiver, the RHM, that was designed to supply "state of the art" receivers for airports in 1932. At the time, airports and air navigation were both growing and developing. Communications between pilots, Airway stations and Airport towers required the best equipment and air navigation, including the various Airways remote beacon stations, also needed improved communications equipment. National was given the contract for the ground receivers, General Electric was given the contract for the ground transmitters and Aircraft Radio Corporation was given the contract for airborne communications equipment. National was going to build their first superheterodyne to fulfill this contract. It seems likely that Herbert Hoover Jr. and his West Coast design team would be involved in some of the electronic engineering work of the RHM. National provided the mechanical engineering and the ability to produce the receivers in the quantity required. The RHM used nine tubes and tuned from 2.3mc up to 15mc. Most airport communication RHM installations also included a Type 58-C Monitor Receiver that allowed receiving two separate signals simultaneously. The RHM rack also included a dual power supply, panel rack holder for the spare coils and a rack mounted loudspeaker.

As mentioned, 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 receiver for commercial and ham use and dubbed it the AGS. It was an expensive receiver selling for $265 (with all accessories) in 1933. Frequency coverage was improved to allow better coverage of the ham bands, 1.5mc up to 20mc. The RHM had used first class materials and components throughout and the AGS was built to the same specifications resulting in the same high performance and reliability that the RHM had. National's advertising implies that after the initial DOC contract was fulfilled with RHM receivers, National continued to supply AGS receivers to airports and other commercial users from late-1932 up to the introduction of the HRO receiver in October 1934 (first deliveries were in early 1935.)

photo left: AGS-X sn: F-151 from 1934. This receiver has its complete set of 27 coils. 15 general coverage coils for five ranges from 1.5mc to 20mc and its complete bandspread coil set for 160M, 80M, 40M and 20M coverage (12 coils.) The second coil holder is mounted on top of the rack. The Lamb crystal filter uses a 500kc crystal (as does the FBX receiver) to match the IF. The AGS-X also moved the BFO frequency control from inside the receiver to the front panel. AGS-X  F-151 has the air-trimmers for its IF adjustments indicating it's a late-production receiver (it's from the last production run and 151 receivers into that run would indicate it's one of the last AGS-X receivers built.) I constructed the metal frame rack. It's based on a table top rack pictured in a ham station photo (with AGS-X receiver) in a 1934 QST magazine. The material used is .75" square mild steel tubing with welded joints.

There were several variations throughout the AGS' short, two-year production life, mostly involving tube types and calibration procedures. The most significant improvement was the "Single Signal" AGS-X that was designed specifically for the affluent ham market (not heavily populated during the Depression.) The installation of the Lamb Crystal Filter allowed the operator to narrow the receiver IF passband considerably to improve copy in the congested ham bands. Also at this time, National started to offer ham bandspread coils for the AGS that allowed tuning the 160M, 80M, 40M and 20M ham bands spread between "20" and "120" (100 divisions) on the Type N dial (scaled 0 to 150 with 270º rotation.) Air trimmers replaced the old compression types used in the IF transformers by mid-1934. By late-1934, even 10 meter coils were being offered for the AGS.

Not all airport users were satisfied with the RHM-AGS with some airlines complaining that the receiver was not advanced enough. In response, National provided an improved RHQ-AGU version with all three coils ganged together to allow easier band changing. Frequency coverage on the RHQ-AGU was reduced to 2.5mc to 6.5mc and only two coil sets were supplied with the receiver. The RIO-AGL version was a medium wave and low frequency receiver that tuned from 160kc up to 630kc in two band switched tuning ranges. The circuit was a TRF receiver with tracking BFO. All of these versions were produced in 1933 through 1934 (go to "Commercial & Military Radio Gear" for more info on RHQ, RIO, RHM receivers.)

Although some AGS receivers were sold to amateurs, National obviously was aware that the receiver was just too expensive for amateurs during an economic depression. National reworked, simplified and cost-reduced the AGS design and came up with the FB-7 receiver that was priced so most hams could afford it. The AGS receivers are so seldom encountered today, it's estimated that probably no more than 300 or 400 were built from 1932 up to 1934. All of the DOC-Airways versions probably account for about another 100 receivers.

The HRO receiver was in the design-phase in the late-summer and fall of 1934 and, with its introduction in October 1934 (and availability by March 1935,) the AGS receivers became obsolete commercially. The AGS-X was available from Leeds at this time (early 1935) for only $123. Although the AGS-X was a great receiver in 1933, the HRO receiver's outstanding performance had antiquated the AGS-X in a little more than one year's time.


Radio Manufacturing Engineers, Inc.  -  RME-9D

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 was designed in 1932 and was on the market by 1933. The RME-9 was a nine tube receiver with a single airplane-type tuning dial and an R-meter for measuring relative signal strength. The RME-9 featured a tuned-RF stage, two stages of IF amplification and a built-in power supply. The receiver was compactly-built onto a stout chassis made out of aluminum extrusion with the overall size of the receiver being quite small (19"W x 9"H x 10.5"D.) After some months of production and about 100 receivers produced, RME revamped the "9" and introduced the improved RME-9D. The RME-9D incorporated electrical bandspread and thus used two airplane-type dials with the R-meter between the two dials. Nine tubes were still used since the basic design remained unchanged. Five tuning ranges were provided with frequency coverage from .54mc up to 23mc. The tubes used were 58 (4), 57 (1), 2B7 (1), 2A5 (1), 24A (1) and 80 (1.) . Selling price was usually around $112 from discount houses.

The RME-9D was produced from late-1933 up to the introduction of the RME-69 in November 1935. There are some minor variations that are encountered with different types of knob sets being the most common. This especially relates to the tuning knobs with the large "RME-69" type tuning knobs often found on late versions of the 9D. Like many "Depression Era" receivers, it is common to find examples of the RME-9D with modifications added. The tuning and bandspread dials are relatively small and the nomenclature is miniscule and difficult to read but the dial illumination does help. For its time, the RME-9D was a first-class receiver that introduced what became the "basic necessities" for amateur radio receivers - built-in TRF stage, Carrier Level meter, panel operated BFO, Crystal Filter and Bandspread tuning. Although not necessarily the first receiver to incorporate any of these individual features, the RME-9D was the first receiver to use all of the features together as "standard equipment" and with no external assemblies necessary other than the loudspeaker. This rapidly became more-or-less "the standard" for all communications receivers for the next two decades.

The RME-9D shown in the photo is an all-original, late production version with a serial number of "431." RME receivers had a paper label on the bottom of the cabinet with the calibration date hand-written on it. The date on this receiver's tag is 9-12-1935. This is about two months before the introduction of the RME-69. Since this receiver is very late in the RME-9D production and has a serial number of 431 one can infer that the total number of RME-9D receivers built is probably around 500. The scant number of RME-9D receivers encountered today seems to confirm that production levels were very low.

RME-9D Speaker - The RME speaker housing was an unusual trapezoid shape that allowed for a bench corner location to be used for the speaker and then rectangular equipment cabinets could butt against the speaker cabinet sides. The speaker utilized was an eight-inch Rola PM speaker with a large "wrap-around" magnet support structure. The transformer is a matching transformer that provides a 4000Z for the receiver output transformer impedance and an eight ohm impedance for the speaker voice coil. This same style of speaker housing was supplied for the RME-69 receiver although the Rola speaker was a more modern configuration with a much smaller magnet assembly. Luckily, a date is ink-stamped on the speaker frame - JUL 9 1935 - indicating that this speaker was probably purchased with the RME-9D.


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 six general coverage coil sets available and identified by the prefix "FB" and the letters AA, A, B, C, D and E (AA was the 10M coil set covering 18mc to 34mc.) Or, the ham could purchase a bandspread set of coils (ID prefix "AB") for 160, 80, 40 and 20 meter coverage. The FBX Single Signal 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. The IF was 500kc for the FB-7 and approximately 495kc for the FBX depending on the particular crystal used in the Crystal Filter. The BFO frequency control is a knob on top of the BFO coil can and is accessed under the lid.

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 RF 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 as evidenced by the examination of 1930s QSL cards.


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

Emmitt Patterson started Patterson Electric Co. in 1920 but renamed the company in the mid-twenties as Patterson Radio Company and began selling radios as a dealer. Around 1930, Patterson began building his own All Wave entertainment radios at the Gilfillan plant in Los Angeles. Patterson decided to enter the short wave amateur communications receiver market in 1933. Introduced in May 1933, the PR-10 was designed by Engineer 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 was very good (especially for 1933-34) but by adding the PR-10 Pre-selector, with its two RF amplifiers, one could have a first class receiver. The initial models were slightly different and were designated as the "ALL-WAVE 10." The AW-10 didn't have a chrome plated chassis or the Manual Gain control (the AVC was always on - like a broadcast radio.) The AW-10 was probably produced for a few months before it was replaced with the redesigned version designated the "PR-10." The updates included the ability to disable the AVC allowing control the front end gain manually. This was particularly necessary for good CW reception and, at the time, virtually all ham communication was by CW. Other upgrades that were incorporated by 1934 were the reduction of the BFO coupling capacitor value to allow more sensitivity for CW reception and changes in the AVC time constant capacitor. With the designation PR-10, the chassis was then chrome plated. The PR-10 Pre-selector didn't change during production although there are some variations in coil diameter and under chassis component placement depending on early or late production. Like other West Coast radio builders, Patterson's documentation was never updated therefore the "one and only" schematic has several errors when compared to the actual production models.

PR-10 Pre-selector SN: 1473  and  PR-10 Receiver SN: 6361


PR-10 Pre-selector SN: 1247  and  PR-10 Receiver SN: 6102  in Umber-Gray Wrinkle Finish


The Patterson PR-10, along with the RME-9D, was one of the first communication receivers to offer a carrier level meter, band spread tuning, band switching (rather than plug-in coils,) stand by switch and built-in power supply. The only "standards" lacking were a crystal filter, a front panel frequency control on the BFO (the frequency control was under the lid) and a tuned RF amplifier. The latter was available if the Pre-selector was used. Overall, the PR-10 was an excellent performer that was reasonably priced and was found fairly often in ham shacks during the thirties, especially in the west.

The PR-10 listed for about $120, though most dealers sold the PR-10 for $70. According to Patterson, total production was around 50,000 to 70,000 receivers - an incredible and dubious claim. Supposedly, the majority of production was sent overseas to Asia which then accounts for the relative scarceness of the PR-10 today. But, who in Asia (in 1934) would be buying thousands of Patterson receivers? The reported serial numbers seem to indicate a different story however. A more believable production quantity is around 4500 receivers. If the Patterson All-Wave 10 production is added, the total might be around 5000 receivers. But, even that level of production is not reflected in the serial numbers collected.

All Patterson receivers were built at the Gilfillan Bros.,Inc. in Los Angeles, since Patterson did not have an RCA superhet license (see the next section below for the history of RCA, the superhet patent and Gilfillan.)

The first communications receiver I owned (in 1965) was an old PR-10. Unfortunately, I decided to replace the 58 and 57 tubes with metal octal tubes, hoping for better sensitivity. The end result was a receiver that was basically non-functional! In 1985, I obtained another PR-10 and this one I restored correctly. It appears in Ray Moore's "Communications Receivers" Fourth Edition. The PR-10 shown in the photo above is the third one I've owned having purchased it from a visitor to the museum in 2005. It's had a long, well-preserved life having spent all of its time in Nevada. I fully restored this third PR-10 and the Pre-selector in 2016 in order to write a comprehensive web-article on Patterson Radio Company and the PR-10. The most recent (fourth) find is shown in the photo to the left - a Patterson PR-10 and Pre-selector finished in umber-gray wrinkle paint with nickel-plated escutcheons. Although the original PR-10 finish was black wrinkle, there was a chrome cabinet deluxe version available but gray wasn't an offered option. This umber-gray version was a professional repaint accomplished in the 1940s at a US Navy depot. The R-meter bezel was also nickel-plated. Note that the Pre-selector has the earlier style "rosette" knobs.

For the ultimate information source on the Patterson PR-10 and matching PR-10 Pre-selector, including LA Radio Manufacturing history, Patterson Radio Co. history, PR-10 circuit and schematic analysis, serial number analysis, restoration and performance data, go to:

"Patterson Radio Company - PR-10 Communication Receiver and PR-10 Pre-selector" - Link in Home/Index


The Creation of Radio Corporation of America, Superheterodyne Licensing and Gilfillan Bros., Inc.

In 1919, GE was working on a sale of their important wireless patents, including the Alexanderson Alternator, to the British Marconi Company (known as Marconi's Wireless Telegraph Company Ltd. in England) When the U.S. Navy "got wind" of this intended sale, they were livid. Especially since the information had come to them through "ordinary trade channels." The Navy had just spent the past few years (WWI) securing and protecting US wireless stations along with protecting the transatlantic communication cables which were the sole communications between the US and Britain during WWI*. Developing reliable U.S. maritime radio communications was a top priority for the Navy and, here was GE, ready to sell their major wireless licenses and patents to the Brits.

The Navy sent their top brass, headed by Commander Stanford Hooper and Rear-Admiral William H.G. Bullard, to GE to persuade them to not sell USA wireless patents to a foreign nation, even if they were a longtime ally. The Navy wanted GE to create a "radio company" that would "do everything in radio." That would include building equipment for the Navy, operating and maintaining commercial wireless stations, building and selling radios and parts and, generally, be the exclusive manufacturer of "all things radio" for the United States and especially for the Navy.

Admiral Bullard, who was the newly appointed Director of  Naval Communications for the Navy Department, was able to convince GE's chief console and vice-president Owen Young that this "radio company" was not only a patriotic response to British Marconi's intent to purchase the USA wireless technology but that such a "radio company" could be a very lucrative arrangement for the GE. Owen Young convinced the other GE board members that the sale to British Marconi should be cancelled. In October 1919, GE set up the preliminary version of "the Radio Corporation" using just their own assets. This didn't seem to be enough since no manufacturing facilities were included, especially for the type of company the Navy (and now GE) had in mind.

GE knew that the American Marconi Company had long been concerned that the majority of their ownership was in British hands. Ed Nally Jr, vice-president of American Marconi and A. G. Davis (of GE) were sent to Britain to first, cancel the GE-British Marconi deal and to second, negotiate a new deal to buy American Marconi. Davis and Nally were successful and were able to have GE buy the entire American Marconi company, including their manufacturing plant in Adelaide, New Jersey. >>>

photo right: Owen Young (left) vice president of GE and board member of RCA, Guglielmo Marconi (center) of Marconi's Wireless Telegraph Company Ltd. and Ed Nally Jr. (right) the first president of RCA. Aboard Marconi's yacht, Elettra, in 1922.      Photo from: "Radio Journal" Sept, 1922

>>>  In November 1919, RCA was officially formed and announced to the wireless world. Ed Nally Jr. was the new president of RCA with Owen Young becoming a powerful RCA board member. The RCA formation seemed set to launch the "Radio Corporation" into the wireless business, but, at the last moment, General Electric decided that too much strategic manufacturing power would be in the hands of RCA and that GE would have little control of RCA operations. To have and maintain control over RCA, GE retained the American Marconi plant for themselves and essentially took all of RCA's ability to function as a manufacturer away from them. RCA became what was essentially a sales agent for all of the members of the "Radio Group,"  an unofficial name for the patent-sharing and cross-licensed radio companies headed by GE. These companies were RCA, AT&T, United Fruit Company and Westinghouse. RCA sold radios and parts built by these companies (but, in most cases, with the RCA name on them) through most of the twenties.

However, many of the old American Marconi responsibilities became new RCA duties. The old Marconi Institute for training radiomen became the RCA Institute performing the same function. Many of the commercial wireless stations had to be maintained by RCA and, in some cases, operated by RCA. This was how RCA operated through the early-1920s. However, RCA was determined to become more than just a sales-agent for the Radio Group and throughout the 1920s was slowly purchasing various patents, developing the radio business and growing into what the Navy had first envisioned. It would take a decade of time and the Federal Government to make it happen, though.

photo left:  Rear-Admiral William H.G. Bullard was Director of Communications for the Navy Department. Bullard was instrumental in convincing GE to form RCA.      
Photo from: "Keeping the Stars and Stripes in the Ether" - "Radio Broadcast" -  June, 1922

* During WWI, Britain had laws in-place that prevented using wireless for wartime transatlantic communications therefore all of these important communications between Britain and the US went by wire telegraph over the transatlantic cable. The US Navy feared German submarines could have the ability to destroy these cables and seriously delay wartime communications. Thus the Navy spent considerable effort to defend these cables against attack.

RCA during the 1920s - Through most of the 1920s, almost all consumer-entertainment radio manufacturing business for RCA was controlled by GE and to a certain extent by Westinghouse. These two companies continued to build all of the consumer radios that RCA sold during the twenties. RCA, though, continued to buy other radio interests, radio patents and create other businesses related to radio. In 1923, RCA bought Wireless Specialty Apparatus Company from the United Fruit Company. This company specialized in marine radio gear and continued to build that gear for RCA to sell. Since this wasn't infringing on the lucrative broadcast radio market, the Radio Group (minus United Fruit Co.) didn't object. In 1925, RCA bought a New York radio station and from that created the first network broadcasting entity, National Broadcasting Company, or NBC. In 1927, RCA was able to purchase the TRF patent (not the Neutrodyne TRF,...that belonged to Hazeltine and the Independent Radio Manufacturers.) Additionally in 1927, RCA purchased Independent Wireless Co. and combined it with Wireless Specialty Apparatus and created Radiomarine Corporation of America, which became a subsidiary of RCA handling all of the marine radio business. In 1928, RCA got involved in the movie industry as part of RKO. RCA's first president Ed Nally Jr. was president from November 1919 up to late-1922, at which time he retired. Looking at the photo above (taken aboard Marconi's yacht) one would think that Nally died but he lived on quite a long time after retiring from RCA and died well-into his nineties (in the early 1950s).

RCA's second president was a retired military man, James G. Harbord. He ran RCA from late-1922 up until he retired in January 1930. Harbord viewed radio as a powerful medium that was destined to grow and become an essential resource for the business world and for daily human life. Most of his "radio predictions" did become reality.

David Sarnoff becomes RCA President - January 1930

Harbord's retirement was to allow general manager David Sarnoff, age 39, to become president of RCA. David Sarnoff had been with American Marconi before it became RCA and had worked his way up through the company. He was head of RCA up into the 1960s. Sarnoff is usually credited with starting NBC and with developing the idea of broadcasting via networks of radio stations.

Photo left shows James Harbord (left) and David Sarnoff (right) apparently depicting Harbord handing Sarnoff the "RCA reins."    

photo from:

  RCA-Victor Beginnings and the 1930 Anti-Trust Suit  - Around 1927, RCA was approached by the owners of the Victor Talking Machine Company. It seemed that VTM Co's CEO Eldridge Johnson had been in declining health and had sold his Victor interests to a banking syndicate in 1926. The bankers now needed someone to run the failing Victor company, or to buy it outright. RCA initially took over operation of VTM Co manufacturing and began to incorporate GE or Westinghouse-built radios into elaborate combinations with Victor phonographs. VTM Co. under Eldridge Johnson had viewed radio as a competitor but now Victor created a few radios using the RCA held TRF patent. These became the Victor Microsynchronous Radios found in many VTM Radiola-Electrolas. These machines were moderately successful but RCA really needed to "own" VTM Co to expand and develop their radio business and become independent of GE. To purchase VTM Co was going to require a substantial amount of cash - $15 million along with an additional $15 million to convert Victor, essentially an old "victrola" manufacturer, into a modern, up-to-date radio manufacturing company. Amazingly, RCA made a deal with General Electric and Westinghouse to have them supply the needed cash "up front" in trade for RCA stock to be transferred later down the road. Sarnoff was running RCA at this time because James Harbord had taken a leave-of-absence through most of 1928 to campaign for Herbert Hoover in the presidential elections of 1928. Harbord retired in January 1930 to allow 39 year old David Sarnoff to then become president of RCA.

The Victor factory in Camden, New Jersey was converted to a radio factory by late-1929. RCA created a couple of small companies, "Radio-Victor" and "Audio-Vision Appliance" to operate VTM Co. This cumbersome arrangement was quickly changed to one company called "The Victor Division of Radio Corporation of America" better known as "RCA-Victor." Almost immediately, the federal government stepped in and served up an Anti-trust suit against everyone that was left in the old "Radio Group." At the time the suit was filed, that included GE, Westinghouse, RCA and AT&T. The government singled-out GE and Westinghouse for punishment. RCA was singled-out for rewards.

The settlement turned literally everything "radio" over to RCA. The superheterodyne patent that had been owned by Westinghouse was now RCA's. Additionally, all of RCA's debt to GE and Westinghouse (involving the VTM Co. deal) was cancelled. Also, GE and Westinghouse couldn't compete in radio with RCA for two years (they actually had to buy RCA-built radio chassis to install in their own cabinetry until 1933.) RCA came out of the settlement not powerful in radio,...they were OMNIPOTENT in radio. They owned or controlled almost all aspects of radio. All "legal" radio manufacturing in the US required a license from RCA. In essence, the government had stepped in and re-created RCA into the "all-powerful" entity that the U.S. Navy had wanted eleven years earlier.

Superheterodyne Licensing, Sub-contractors
 and the Gilfillan Bros.,Inc.

The anti-trust settlement also 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 royalties, certain rules to be followed and other conditions with having the license. By mid-1930, most of the major radio companies had their superhet licenses and were designing their new models for the 1931 sales year (Fall 1930 to Spring 1931.) However, some of the conditions required that the manufacturers 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 in the West (exclusive license-holder for 11 Western states.) This arrangement was the result of a 1928 "face to face" confrontation between S. W. Gilfillan and David Sarnoff, (who admired Gilfillan's determination.) At the time of the Sarnoff-Gilfillan meeting, James G. Harbord (RCA President from 1922 to 1930) had taken a leave of absence to campaign for presidential-candidate Herbert Hoover and that left general manager, David Sarnoff, in charge. The Sarnoff-Gilfillan arrangement was the offer of exclusive RCA licenses in exchange for closing all Gilfillan operations not in the Western States. Specifically, the Gilfillan plants in Kansas City and New York City were the apparent targets of the agreement. At the time, this licensing was mainly for TRF circuitry but, in 1930, the superheterodyne was added to Gilfillan's exclusive licensing.  >>>

>>>  Gilfillan allowed subcontractors to build their own chassis on the second floor of the Gilfillan plant. This included Los Angeles companies such as Patterson, Breting, Jackson-Bell, Packard-Bell, Kemper and Pierson-Delane along with dozens of other smaller companies, all in the Los Angeles area. During the early 1930s, the sub-contractor policy was not very strict and the complete radio didn't have to be totally assembled by the licensed company. Some sub-contractors only had the radio chassis and cabinets built and then completed assembly themselves. The subcontractor was protected because he was building the radio using a chassis supplied by the licensee and the building process was supervised by the licensee. Some companies (including Gilfillan) allowed sub-licensed companies to supply their own assemblers, set up their own production lines, utilizing plant stock and tools, using plant floor space at the license holder's company.

The sub-licensing policies allowed many small radio companies the start-up operations because the major expense, that is,  purchasing real estate, building a factory, purchasing equipment and production stock expenditures were eliminated. This left the new radio company/sub-contractor to only have to hire personnel and have a good design to build. During the Depression, this really was the only option for a small company to produce quality radios, be able to sell those radios and profit from that business. Also, those profits were shared by the licensed company (5% to Gilfillan which they split with RCA.) The subcontractor licensing allowed everyone involved to profit during the difficult economic times of the 1930s. There was the added benefit to the would-be purchasers that, because the subcontractor radio company's overhead was so low, the radio products could be sold for a much lower price and still net a profit for that subcontractor and for Gilfillan. On average, Breting and Patterson receivers sold about 40% to 50% less than a comparable National or Hammarlund product and about 30% to 40% less than a comparable Hallicrafters product.

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. However, Patterson had quit the radio business in 1939 and his major West Coast competition, Breting Radio Manufacturing, quit the radio business in 1940.


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. Thorton probably built his TX-RX around 1934 judging by the circuits and the parts used.

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. 


National Co. - HRO  SN: H103, fifth production run from Sept.1935

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 (A, B, C and D 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.

There were several minor changes incorporated into the HRO from its 1935 introduction up to WWII. Each production run of receivers were identified by the prefix of the serial number starting with "D" used on the first production run. The first three production runs had coil assemblies with white background graphs with black nomenclature, a nickel plated micrometer dial, black chassis, round IF cans, a "NC" on the dial pointer and a non-illuminated S-meter. The "pearl button" switch for the S-meter was on the first two runs (D and E.) The pilot lamp was installed on the third run (F.) Also with Run F, the 2nd detector wiring was slightly changed to reduce AF Gain adjustment noise. Run H was the last to use the plated PW-D. Run J saw the introduction of the lacquer painted PW-D. The subtle shading of the black only shows in flash photos*. In regular room lighting the PW-D paint appears black. 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.

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.

Early HRO Receiver Gallery

SN: D65

photo left:  First production run HRO sn: D65 from January 1935. This receiver is mostly original and hasn't been restored. It appears that it was sent back to National for minor upgrades early-on. The BSW remote standby was added, a pilot lamp was installed (later removed) and the second detector/1st AF amp and AF Gain circuits upgraded to third production run. This receiver has its four matching coil sets but doesn't have its original rack mount PS.

photo right:  Second production run HRO sn: E50 from Feb. 1935. This HRO spent most of its existence in Alaska. It was modified for use by the CAA in the 1940s. E50 was donated to WHRM in 2012 and its extensive restoration was completed in 2018. No original coil sets or power supply. The complete restoration write-up can be read in the web-article "National HRO - The Cream of the Crop" - use Home-Index below to navigate.

SN: E50

SN: F16

photo left: Third production run HRO sn: F16 from March 1935 had originally been a table model but sometime in its past it was converted to a rack mount. This receiver's chassis was rebuilt in the 1950s or 60s with plastic molded paper dielectric capacitors. Unbelievably it still does function very well. Restoration was mainly a clean-up and minor detailing. F16 has its original four matching coil sets plus correct vintage E and F coil sets but it didn't have its original PS.

photo right: 10th production run HRO Sr. sn:N130 from July 1936. This HRO receiver has nice cosmetics and is fairly original but under the chassis shows a "repair tech" approach to the rework. Some of the original components were replaced with modern equivalents,...ugh. No original coil sets or dog house PS.

SN: N130

SN: P116

HRO Junior

In 1936, the HRO Junior (photo to the left) 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, for both the Junior and the Senior, the chassis paint went from black to gray and the IF transformer shields were changed from round cans to square cans. James Millen had interviewed hams both in person visits and via mail to find out what features they wanted to see in the HRO. Many wanted to know if the HRO could be purchased without the Crystal Filter and without the S-meter for a lesser price. Millen used these interviews to have the "Junior" put into production. The Junior wasn't a "cheap" HRO, it used the same components as the Senior. The reduced price was a result of removing the Crystal Filter, the S-meter and the band spread feature on the coil sets. Another option offered was that an owner of a Junior could return it to National and they would rebuild it into a Senior for a very reasonable price.



photo left: 1936 HRO Junior sn: P-116 with its original JD coil set installed - from the 11th production run (Aug 1936.) This receiver has all four correct vintage "Junior" coils sets and, as expected, only the JD is a matching SN. Other Jr. coil sets had to be purchased separately and these don't have serial numbers. No original dog house.

Later HRO Receivers

The HRO shown 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 and into the middle of WWII, the HRO doesn't change noticeably except that some late models will be found with a National "bar knob" for the Selectivity control rather than the round point knob. During WWII, there were subtle changes to the HRO throughout the early part of the war. The major change happened in 1945 when the HRO-5 and HRO-W were released. These receivers used octal tubes.

For details on the post-WWII HRO receivers go to "Post-WWII Ham Gear." Use the Home-Index link 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 subtle color differences under intense light (like a photo flash.)


photo right: 1940 HRO Senior sn: 463-K has eight correct vintage coil sets but only the "C" coil set is a matching SN coil set. No original dog house.

SN: 463K

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



W6HLJ's Homebrew One Kilowatt Transmitter - 1934

W6HLJ Xmtr with National FBX receiver

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!"

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.

photo above: 2 photos - The W6HLJ Xmtr as it looked in 1935. Note that it is not yet painted.

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. 


Breting 12 - SN: 28952

Breting Radio Manufacturing

"The Breting 12 - Scientifically Correct - D-X Radio"


Paul J. Breting started selling communications receivers in 1935. Breting Radio Manufacturing didn't have the necessary RCA Superheterodyne license so their receivers were assembled at the exclusive "RCA licensed" Gilfillan plant in Los Angeles, California with Breting operating as a "sub-contractor" protected by Gilfillan's license. Breting was able to take advantage of Gilfillan's production processes, stock inventory and tooling while building his receivers. Ray Gudie, who was famous for the Patterson PR-10 design, was Breting's chief engineer. Gudie came over to Breting after a wage dispute with Emmitt Patterson. Gudie felt the success of the Patterson PR-10 should have warranted him a salary increase. The PR-10 was quite a popular communications receiver that sold very well but Patterson disagreed that it warranted a pay raise for Gudie. Patterson's disagreeable manner in the matter caused Gudie to resign and go to work for Paul Breting (both Patterson and Breting were located at the Gilfillan plant, so Gudie didn't have to go very far to be hired by Breting,..probably just across the hall.) The Breting 12 was Gudie's first major design for Breting and it was introduced in 1935. The advertising hype for the Breting 12 used the impressive description "Scientifically Correct D-X Radio" but exactly what that meant is vague. The list pricing for the Breting 12 shows several options. The receiver chassis without cabinet, meters or crystal (this meant the entire crystal filter unit, not just the crystal for it) was $135. The crystal (filter) could be added but not the meters for just the chassis with no cabinet for $145. The cabinet version could be purchased without the crystal (filter) for $145. The complete receiver listed for $155 but if the purchaser was a ham or experimenter a 40% discount was offered that reduced the cash sale price for the complete receiver to only $93. Most dealers seemed to offer the complete Breting 12 for about the same discounted price with perhaps a slight markup but still less than $100. All options included a 12" speaker and all of the vacuum tubes. Prices are from the Breting 12 sales brochure and old QST magazines.
Circuit Description - Breting's 12-tube superhet circuit featured two RF amplifiers, sort of, five band tuned RF amplifier stage along with a second  TRF Pre-amp switched in only on band 4 which was 7.0Mc to 14.5mc coverage allowing the pre-amp to function on 40M and 20M (Gudie believed these two ham bands would benefit most from the pre-amp.) Also, band-in-use dial scaling featuring an articulated dial lamp and rear-projection red translucent dial pointer, illuminated logging scale with rear-projected red translucent pointer, xtal filter, tertiary-connected 432kc IF transformers, two meters (R-meter & Volume Indicator meter) and triode-connected P/P 42s driven by a triode-connected 42 - all on a chrome chassis. A phone jack is provided on the left side of the receiver and loudspeaker four-pin socket is on the rear chassis apron. An Antenna Trimmer (only connected into the circuit when Band 4 was selected) was located inside the Antenna Input coil can-shield and consisted of a screwdriver adjusted compression condenser accessed through the hole in the top of the can. Since the Antenna Trimmer was only for Band 4, this "set and forget" adjustment assumed that the ham operator would be using either 40M or 20M but not both (or use of a Z matching device on the antenna.)

The Breting 12 circuit also featured many familiar "Gudie favorites" in the design. Like the early version Patterson All-Wave (also designed by Ray Gudie,) the Breting 12's AVC cannot be switched "off." Rotating the Manual Gain (controls the RF/IF amplifier gain by varying the cathode resistance) from full CW will actuate a switch that only activates the BFO and further rotation CCW reduces the overall sensitivity of the receiver. By reducing the RF/IF gain, the ratio of received signal versus the BFO injection will allow CW reception since the AVC bias is reduced to the point where it doesn't control the sensitivity. Another "Gudie favorite" is the use of 432kc as the IF which he also used on the Patterson PR-10. The Beat Oscillator frequency adjustment is a knob located under the bottom of the cabinet. Since, in 1935, practically the only reason for the BFO was CW reception, this "set and forget" concept was fairly popular. Nowadays, tuning in SSB signals will require tilting the receiver back a little to access the BFO knob, setting it to close to the 432kc IF frequency and then tuning in the appropriate sideband for proper demodulation. Tuning a SSB signal will have to be accomplished solely by the Tuning dial with the Audio Gain advanced and the Manual Gain reduced to allow the proper ratio of BFO injection to received signal strength.

photo above: Reno Diedrich W7GPI Toppenish, WA. The receiver is a Breting 12 and the homebrew transmitter runs 200 watts input power. The W7GPI QSL was dated Jan.1939. Note the Breting 12 knobs and how they are the original smaller style knobs found on fairly early 12s.

And, on the BFO injection,...the BFO is electrostatically coupled with no direct connection to the IF or detector. This accounts for the very light BFO injection, however, the electrostatic coupling was necessary to keep the BFO from blocking the receiver since the AVC isn't turned off. Nowadays, for SSB, the BFO injection has to be at a much higher level and the only method available (without mods) is the reduce the Manual Gain until the signal demodulates correctly.

The Breting 12 had a "Communications Switch" on the front panel that (in the "Communicate" position) allowed the ham owner to use the receiver's 18 watt, almost high fidelity audio section, as a speech amplifier to drive a separate transmitter modulator (hi-Z Mike input and 300Z output.) It was also possible to use the Audio Input for a phonograph pickup and with a minor wiring change to the Comm Sw, use the Breting 12's audio section for playing records (wiring shown on schematic.) Normally, by switching the "Comm Switch" to the "Receive" position, the audio was routed thru the loudspeaker (2 ohm voice coil and 1500 ohm field coil doubling as a filter choke in the power supply.) The Volume Indicator meter used the diodes in the 6B7 RF Pre-amp tube to rectify the audio from the 300Z tap on the AF output transformer. A switch (labeled "Volume Indicator" on the schematic) located on the AF Gain control switched in a fixed 25K resistor (at full CCW) that would provide a "fixed" audio gain setting that would result in the Volume Indicator meter reading that would be relative to the received signal strength and sensitivity (or the level of the external audio input) rather the the audio gain. This provided a meter indication of relative signal strength for CW signals since the AVC bias and R-meter indication will be inactive when using Manual Gain. If the receiver is operated with AVC with the Audio Gain control somewhat advanced and a strong AM signal tuned in then the R-meter will indicate relative signal strength and the Volume meter will move around indicating relative audio output levels. If the audio amplifier section was being used as a speech amplifier then the Audio Gain control position would determine the transmitter modulation level and the Volume Indicator readings would show relative speech levels.

Breting 12 artwork from the sales brochure. Note that the later style "rays" dial mask is shown.

photo left: Early Breting 12 showing the original type of black wooden knobs. Also, note the "oak leaves & acorns" dial. (fredtrapock-ebay photo.)

Physical Description - Cabinet is 17" W x 11" H x 11" D. The receiver weighs approximately 60 pounds. The paint is black wrinkle finish however the wrinkle pattern is an extremely fine texture. The front panel is mounted to the chassis by way of four control bushing-nuts. The cabinet is mounted to the chassis with two sheet metal screws on each side. The front panel mounts to the cabinet using six sheet metal screws. The chassis mounts to the bottom plate by way of four threaded, metal covered, circular glides (feet.) The metal dial mask had "oak leaves & acorns" decor on the early models while later dial masks had vertical "rays" flanking the "12" on the dial. The cabinet on early versions only had side louvers while the later versions added several one inch diameter holes along the rear cabinet upper wall to provide better ventilation. There is evidence that Breting may have offered the "12" in a floor model cabinet. One known example has the "oak leaves and acorns" on the dial but in gold tone rather than silver. Also, it seems likely that the chassis was lacking the Crystal Filter since this was primarily for CW for the hams while an "All-Wave" floor model would appeal to the casual SWL.

RESTORATION NOTE REGARDING KNOBS: The Breting 12 brochure artwork shows the receiver equipped with five medium diameter knobs and two smaller knobs of the same style. The tuning knob has a small crank. These original style knobs were made of wood and painted black. However, every Breting 12 receiver that I've seen in person has had a bakelite knob set like the Breting 14. That would be three different sizes of black bakelite, fluted communications receiver type knobs installed as seen on SN: 28952. The photo to the left shows the original type knobs and it's the first photo I've seen of a 12 with the correct original knobs. Certainly, the early Breting 12s had these smaller knobs installed just as the Breting artwork shows. But why do so many 12s have the later bakelite knobs installed? I suppose it's possible that sometime during the 12's production, Breting changed to the bakelite knobs because the wooden knobs were no longer available (they probably were Gilfillan's stock anyway.) Why else would so many Breting 12s have the exact same type of bakelite of knobs installed? However, it's possible that some hams, to update their 12, replaced the old wooden knobs with the bakelite types like the newer Breting 14 was fitted with. But as to the "ran out of the wooden knobs scenario," SN: 28952 was found in a barn, where it had been stored since the 1950s, it had never been touched by a collector-restorer and it had the bakelite knobs installed (and those are the same knobs that are still installed on the receiver.)

Other Data - The "one and only" published Breting 12 schematic is fraught with errors and many schematic component values shown are actually different values in the receivers produced. In fact, almost any example of the Breting 12 chassis assembly will differ in several minor points from any other Breting 12 chassis examined. Most of the West Coast radio builders never updated or corrected their schematics, so normally only one version of the schematic was ever published. Production engineering sometimes had to cope with changing component suppliers or parts shortages and this might have required minor engineering changes that were usually done "on the assembly line" without stopping production. These types of changes were never documented. To compound the restoration problems, nearly all Breting receivers were owned by hams who seemed to have repaired and modified their receivers on a regular basis. It's rare to find any Breting receiver that's "all original" and this makes determining "what is original?" difficult. Some mods are obvious but many others were installed at a professional level and have now acquired the "patina of age." Additionally, typical Breting receiver construction is sometimes rather crude which makes the "original versus hamster" determination difficult. A big help for Breting 12 owners is that, several years ago, well-known Scott Radio authority Norm Brainwaite circulated a red-lined, corrected version of the Breting 12 schematic based on the "one and only" schematic that was published in Rider's. This schematic is "the most correct" data for most Breting 12 receivers. You might find minor differences but this schematic and notes should be a big help. Here's a link to the "corrected" schematic: BRETING 12 SCHEMATIC

Breting 12 SN: 28952
This late version Breting 12 (shown in the top photo and to the right) was found in a barn, outside of Genoa, Nevada. It had belonged to W7RPG, Rufus Adams, a longtime Nevada ham who had become SK in the late-1990s. Many "old-time" Carson Valley residents remember Adams' rural mailbox out on Foothill Rd that had "W7RPG ADAMS" painted on its side (I do.) The Breting 12 was in deplorable condition when obtained due to decades of barn-rodent activity. Fortunately, the vermin were never able to gain access inside the cabinet which left the chrome chassis and components in good condition (thanks to Nevada's Sierra East Slope dry climate.) The chrome chassis only needed cleaning with Glass Plus to have good luster so no polishing was done. There are minor pits but 98% of the chrome is in good shape. All of the polished aluminum tube shields and caps were present and cleaned up nicely. 

The cabinet however was a disaster and required a complete decontamination before restoration could even be started. The new black wrinkle finish paint job used VHT brand paint. The chassis was electronically restored and works well. Several modifications needed to be removed to return the chassis back to its original configuration. My older Breting 12 SN: 21685 was used as a model with the corrected schematic (link above) also used as a reference. The end result was a nice performing, mid-thirties vintage communication receiver that has good sensitivity, adequate selectivity and impressive audio when running into a large electrodynamic (field coil) speaker.

photo above:  SN: 28952 chassis after cleaning and reassembly. For the most part, the chrome is in pretty good condition (it hasn't been polished.) The Sprague filter capacitors appear to be vintage replacements. The shield-can with the red fiber washer and grommet is the access hole for the Antenna Trimmer adjustment that is only connected when Band 4 is selected. Also visible is the band-in-use mechanism that works off of the band switch shaft and places the correct dial scale in view within the dial mask opening.

Breting 12 SN: 21685 - I've owned the Breting 12 SN:21685 (shown to the left) for over twenty years. It's the early style with "oak leaves and acorns" on the dial. Unfortunately its chrome chassis is in absolutely horrible condition with lots and lots of rust spots and pitting (actually way more rust than chrome.) Despite the poor condition of the chrome, the chassis is complete with all parts and is nearly "all original" underneath. Only a couple of resistors and a few capacitors have been replaced over the years. The bottom plate was entirely missing when the receiver was acquired but I replicated a replacement using the bottom plate from a piece of old telephone test equipment. The cabinet is missing the left side lid stop so the lid sags a little on the left making it difficult lift the lid up once it's closed. Paint on the cabinet is only fair having been touched-up sometime in the past with over-sprayed flat black paint. Even the mounting screws were sprayed. I've never bothered to rebuild or restore this particular Breting 12 because of the terrible cosmetic condition of the chrome chassis. Luckily, that's preserved the actual originality of the chassis for future reference. However, this early Breting 12 could easily become a functional receiver. It's very likely that the knobs on this receiver are later "upgrades" to match the Breting 14 receiver. Early Breting 12 receivers had smaller knobs as shown above in the Breting 12 artwork and on W7GPI's QSL card. An additional reference that was sometimes used was the Breting 12 shown in Morgan McMahon's "Flick of the Switch" which showed the Breting 14 style knobs installed on the 12.


photo left: Breting 12 sn: 21685 showing the "oak leaves and acorns" dial mask decoration used on early versions

More Breting 12 Info - If you're planning on restoring a Breting 12 receiver, or, if you would like an interesting "read," then go to Gerry O'Hara's detailed article on his restoration of a Breting 12 receiver. Lots of photos, lots of information on problems that are common to these receivers. Gerry has included artwork for reproducing the paper capacitor labels for the Micamold brand capacitors used in most Breting 12 receivers. Also, artwork for the Sprague filter capacitor labels. Gerry's article is a pdf format on the SPARC website (Society for the Preservation of Antique Radios - Canada.) Here's a link to the article,...   Restoring a Breting 12 Communications Receiver


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 Communication Receiver himself but soon discovered he was completely out of his element. Though the PR-12 Communication Receiver appeared in a few advertisements in late 1934 it was never in production. A few prototype PR-12 Communication Receivers have turned up but they appear crude and not like a true production receiver. Also, Patterson did produce a 12 tube All Wave receiver that was generally housed in a floor model wooden console cabinet and this chassis is sometimes erroneously referred to as the PR-12. The PR-12 Communications Receiver was a different design that probably never went into regular production.

Patterson hired Karl Pierson to complete the PR-12 Communication Receiver but Pierson took one look at it and scraped the whole project. Karl Pierson then 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 (some early versions had P-P 6A3 tubes.) 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 - no other manufacturers ever tried to market the configuration - the PR-16C is a good performer with decent sensitivity, nice mechanical bandspread and powerhouse audio. The lack of visual appeal, a result of stodgy styling comprised of a bleak front panel with miniscule dial apertures and numerous large louvers placed on all sides of the cabinet, has relegated the PR-16 to collector's "least favorite" of the Patterson communication receivers. Patterson even offered the PR-16 in a floor console cabinet but not many were sold. At any rate, the PR-16 may be an "ugly" creation but its performance helps it to win favor,...eventually. Built at the Gilfillan plant. This PR-16C belonged to W6BBK, who bought it new in 1936, using part of his WWI veterans bonus to fund the purchase.


Doerle Globe Circler

In the 1930s, Walter C. Doerle of Oakland, California, came up with several types of regenerative detector receivers for the "homebrewer." Hugo Gernsback published a book (in 1935) that was titled "How to Build Four Doerle Short Wave Receivers" and it became a very popular publication. In fact, the Doerle-circuit receivers became so popular with "homebrewers" that some builders started "Doerle Receiver" clubs. The receivers generally were a regenerative detector in combination with a single stage of audio amplification. The antenna was capacitively coupled to the plug-in coil so no primary winding was used on the single RF coil but a tickler coil winding was used. Usually, type-30 tubes were specified but 201A tubes or 99 tubes were also sometimes used by builders (although they didn't have the gain that type-30 tubes did.) To keep costs down, the Doerle receivers were almost always battery-operated. Audio reproduction was for a Hi-Z headset. Doerle did come up with many improvements to the design by adding a RF amplifier and AC power supply as part of the plans.

Like any homebrew or kit, Doerle receivers are unpredictable as performers. Most homebrew builders weren't radio engineers or technicians. They weren't experienced assemblers like those that worked in radio factories so many homebrewers lacked the basics in good soldering ability. Most homebrew builders during the Depression didn't have any test equipment. Careful winding of the coils required experience and well-made coils helped to provide the best performance from the simple Doerle circuit. Doerle himself states that the coil wire, the coil forms and careful winding were necessary for top performance from the receiver. Since many homebrewers lacked basic electronic skills, very few adhered to layouts or even read the instructions or understood the information provided. So, most of the Doerle receivers will have a variety of problems from wiring lead dress and component placement to fundamental wiring errors. Plus, since the receivers were usually built during the Depression, used parts and sometimes wrong component values were used since the builder probably couldn't afford anything else.

As expected, the Doerle Globe Circler shown above doesn't work all that well. I don't think the builder even read any of Doerle's instructions since he violated almost all of the Doerle construction and material caveats. The receiver is mechanically well-built using several pieces of Atwater-Kent radio parts salvaged from mid-twenties sets. The builder did have a lot of confidence in his ability since much of the construction was assembled with glue and nails preventing any disassembly to check wiring and quality of workmanship. The use of an iron vane meter to monitor filament voltage was a very nice touch. At one time there may have been a second or third coil for other frequency ranges but the one coil that is present allows tuning from approximately 3.0mc up to about 6.0mc. Since the regenerative detector has very little isolation from antenna load, this Doerle Globe Circler prefers a fairly short antenna - fifty feet seems best. Longer antennae add so much inductance to the regenerative circuit there isn't enough plate tuning of the tickler to effect regeneration. The problems with the Globe Circler may be due to the coil construction which is very poor, using components with high dielectric losses, poor layout and probably poor soldering (which really can't be examined since the builder "sealed" the chassis.) The antenna load effect maybe due to over-coupling of the antenna and Doerle does mention several times about antenna over-coupling problems and need of a very small value antenna coupling condenser. But, as stated, I don't think the builder even read Doerle's instructions. However, the Doerle Globe Circler does receive 5.0mc WWV and a few SWBC stations. A few SSB 75M hams have also been received.

This Doerle Globe Circler would certainly benefit with a complete mechanical redesign and an electronic rebuild that adhered to Doerle's detailed instructions, that is, "detailed" for the thirties. Doerle mentions that his instructions cover the important facets of his receiver design but that the builder had some freedom of expressing their own ideas in construction. The "Globe Circler" isn't one of the names Doerle assigned to his receiver but it does illustrate the builder's "high hopes." The receiver performance could certainly be improved but, then it wouldn't be original and wouldn't serve as an example of the typical 1930s homebrew regen-set. 

Doerle's Book from 1935

Many radio enthusiasts still build Doerle regenerative receivers. Some builders prefer to use mostly vintage parts while others, trying to get "the most" out of the circuit, use modern equivalents. There's ample info on the circuits and performance reviews on the Internet. Typical of 1930s radio write-ups, don't expect a lot of theory or details on circuit function from the Doerle book (yes, I've read it.) It's written in the vernacular of the radioman of the time and is humorous in its style. It's a little short on theory but there's enough building data for a homebrewer to complete a receiver that would function as described. Doerle probably didn't know much more than the average well-experienced ham of the day when it came to the theory of receiver design but he did know "receiver construction" and how to get the most out of a simple, two-tube receiver.

NOTE: Where the heck did I find this Doerle Globe Circler? Of all places, right here in Dayton, Nevada. Around 2015, there was a massive "garage sale" here in Dayton. But, it was so massive it was being held in a vacant field a mile or so away from my QTH. There was an incredible amount of "stuff" just laying around in the field. From barbeques to horse saddles, old barely-running cars to house electrical and plumbing items. But, there were a lot, and I mean a LOT, of vintage electronics and ham gear also laying around in the field. I talked to the guy running the "sale" and he said all of the electronics had come out of a house and garage in Silver City, Nevada (halfway between Dayton and Virginia City.) There were several pretty nice ham-related items including a few boatanchor receivers and a lot of test gear. A real surprise was this Doerle receiver in amongst the junk parts. Price? $5.00.


 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. The SX-9 was a significant improvement over earlier TRF models and somewhat anemic contractor-built superhets that Hallicrafters had been selling. Its performance is quite good, even though 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 SX-10 and SX-11 are the first Hallicrafters receivers that weren't built by contractors.


1936 TOBE "Special" Model H

Tobe Deutschmann Corporation

TOBE Amateur Communication Receiver Model H,  TOBE "Special" Model H, Wright-DeCoster/TOBE Loudspeaker

Radio kits were one way an enthusiast could purchase a fairly advanced receiver and only pay a fraction of the cost of a commercially-built receiver. Kit-building was very popular during the twenties when radio broadcasting was starting and the cost of a factory-built radio averaged over $100 (and that didn't include the accessories like tubes, loudspeaker or batteries.) By the 1930s, kit-building had lost some of its appeal since many broadcast radios were inexpensive by then. Amateur radio had been the domain of the "homebrewer" - someone who built their own equipment. By the mid-1930s, amateurs had accepted that the superheterodyne receiver was a superior performer on shortwave and most had decided that these modern receivers were just too complex for the homebrewer to tackle. Factory-built receivers were used in just about all ham shacks while the transmitters used were almost all homebrew.

Glenn H. Browning had been thinking about easing the complexity of homebuilt receivers around 1934. Just how to construct a kit-type superheterodyne that eliminated some of the more difficult tasks, especially those tasks that required special test equipment, was Browning's goal. He designed a receiver "front end" that used a tuned RF amplifier and a Converter stage with all of the coils necessary for four bands tuning from the AM BC band up to 22mc. Tobe Deutschmann Corporation offered the Browning Tuner (by then called the Tobe Super Tuner) as the foundation of a kit called the "Browning 35" (since it was going to sell in 1935) All of the components including the pre-built and pre-aligned "Tobe Super Tuner" were in the kit, even a loud speaker, for the very reasonable price of $46.

The Browning 35 was a general coverage receiver for shortwave listeners, hams and enthusiasts. What the hams wanted was an inexpensive "ham bands only" receiver. Tobe Deutchmann Corporation offered the "Tobe Amateur Communication Receiver - Model H" that was essentially the Browning 35 but only tuning 160M, 80M, 40M and 20M amateur bands in a band spread type of coverage. The Model H used the "Tobe 35H Tuner" that was a version of the Tobe Super Tuner that had a special tuning condenser for band spread coverage of 160M, 80M, 40M and 20M. There was actually some frequency coverage slightly above and below each ham band to allow for reception of a few short wave broadcasters, foreign hams and other stations outside the US ham bands. Since the front-end was pre-aligned, the builder had only to assemble the receiver (Tobe Deutschmann's instructions say "a few enjoyable hours" were required for assembly) and then do a minor "touch up" alignment to the triple-tuned IF and to the front-end. Instructions consisted of five large drawings showing the proper placement of components, a large schematic, written instructions and a booklet. There are a couple of pages that warn assemblers not to use acid or paste flux for soldering or "problems will result." Like all radio kits of the thirties, TOBE assumed that the builder had some experience so "step-by-step" instructions are not provided. The instructions are general information and only convey special information where needed. The builder was supposed to adhere to the drawings and the schematic for proper assembly. The large drawings are numbered 1 thru 5 so the builder would start with drawing #1 performing those tasks and then moving on the drawing #2, so on, until drawing #5 was completed and that had the receiver ready to test. Any detailed mechanical assembly instructions were thought to be unnecessary and that information is only shown in the drawings.

The Tobe Model H was available from 1935 up through 1936. The 1935 versions use seven glass tubes. The power transformer had both 6.3vac and 2.5vac windings so the builder could choose either 2.5vac tubes - (2) 58, (1) 2A7, (1) 2A6, (1) 56, (1) 2A5, (1) 80. Or, using 6.3vac tubes the line-up was (2) 6D6, (1) 6A7, (1) 75, (1) 76, (1) 42, (1) 80. There isn't a bezel surrounding the dial on the 1935 models. Instead, a small oval metal plate with logging scale and band select numbers is used. Dials on early versions will have the "TOBE" logo and receiver model information printed below the band scales. The 1936 models will have a large silver metal bezel surrounding the dial, integrated to include the logging scale and band select nomenclature. The "TOBE" logo and receiver model are printed on the bezel. The dial just has the band scales. In 1936, either the seven glass tubes circuit could be purchased or the eight metal tubes circuit could be selected. Also in 1936, a spring-loaded ball latch was added to the cabinet lid.

When completed, the Tobe Model H had one RF amplifier, a Converter stage, a single IF amplifier, a single detector, BFO, a first AF stage, an AF output and a power supply rectifier. After alignment the sensitivity was rated a 1uv and with the very selective RF tuning, along with the tertiary link-coupled IF transformers, the bandwidth was fairly narrow. The later 1936 versions of the Model H were also available with air-tuned trimmers for the oscillator circuit for better stability and accuracy requiring the Type 2A LO assembly be added to the 35H tuner which added about $10 to the selling price of the kit for a total of $56 for the metal tube version with air trimmers (called the "TOBE Special.") Tobe Deutschmann mentioned that a Crystal Filter IF transformer that was going to be available but it was never shown in their advertising as an option. Audio output was rated at 3 watts (with either a 2A5, a 42 or a 6F6 output tube) driving an electrodynamic speaker with a field coil resistance of 1750 ohms.

Although a speaker was included, it didn't have an enclosure. Complete Wright-DeCoster speakers with enclosures could be purchased to go with the Tobe receivers (see the Wright-DeCoster speaker shown below.) A front panel "standby" switch was provided for the Model H. The tuning dial is removable thru a slot in the top of the receiver cabinet to allow the user to install a customized tuning dial that provided markers to indicate ham "schedules" by call and by day of the week. Besides the main dial logging scale there is another logging scale that surrounds the tuning knob. Twenty divisions on the tuning knob scale equals ten divisions on the main dial logging scale. The dial illumination is provided by a dial lamp that is mounted to the tuning condenser shaft. This provides a "tracking" illumination that follows the dial pointer - very cool.

The TOBE "Special" Model H shown in the top photo is a 1936 version "TOBE Special" using all metal octal tubes and utilizing the air-tuned trimmers. Tube line up is 1-6K7 RF Amp, 1-6A8 Converter, 1-6K7 IF Amp, 1-6H6 Det/AVC, 1-6C5 BFO, 1- 6F5 1st AF, 1-6F6 AF Output, 1-5Z4 Rectifier. Along with the receiver I was also able to obtain all of the original instructions including all five of the large drawings, schematic, written instructions and the Browning 35 booklet. Also, the alignment dial and the main tuning dial. The "Special" photo shows the standard tuning dial inserted.



photo left: Top of the TOBE "Special" Model H receiver. The can at the upper left with the knob on top is the BFO and BFO adjustment.


1935 TOBE Amateur Communication Receiver Model H - This is the early version of the Model H using seven glass tubes. Note that the dial doesn't have the large bezel that was used on the 1936 models. This particular Model H is heavily modified. Not totally unexpected from "kit built" equipment. After all, the builder felt that he was totally familiar with the circuit and therefore felt qualified to modify it's design. In some cases, minor modifications made sense and sometimes improved the usability of a piece of equipment. Other times the mods were to repair the receiver when the correct parts weren't available (or affordable) and the parts used came from the "junk box."  Is this Model H restorable to original? The biggest problem is that the two TOBE IF transformers with the special tertiary link have been replaced with standard Meissner IF transformers. This change reduces the selectivity that the original transformers provided. Another very late period mod will require the removal of a 0A2 regulator that will require a hole filler plug. Also, somewhere in the history of this receiver the original 42 audio output tube was replaced with an octal 6F6 requiring finding a fiber board six-pin tube socket with "42" stamped on it. Other "originality" problems are simply due to years and years of repairs and random component changing. If I can locate the correct "T-1" and "T-2" TOBE IF transformers, then the rest of the receiver will be fairly easy to restore to original. Capacitors will have to be built and since I have the correct TOBE labels from the "Special" to copy that should be an easy task. First step is to find the two proper TOBE IF transformers. The restoration procedure will be similar to what I had to do to the TOBE "Special" when performing its restoration (described somewhat in the next section.)

photo above: The 1935 TOBE Amateur Communication Receiver Model H

Observations on Restoring Radio Kits:  Even though the TOBE "Special" Model H kit provided the builder with excellent, large drawings for all aspects of construction along with detailed (for the thirties) written instructions, there is the possibility that any ham radio kit is likely to be fraught with problems that have the root cause being the lack of experience and minimal technical expertise of the builder. Most kit builders were not professional electronic assemblers. Most kit builders didn't have soldering skills that were even close to the professional assemblers found in "radio factories." Expect to find poor soldering joints, minor wiring problems, lead dress problems,...on and on. Most kit builders were not professional electronics technicians or engineers. Many didn't own any type of test equipment. You may find that you have to thoroughly go over all of the circuit inspecting for bad grounds due to mechanical assembly problems, poor solder joints, lead dress problems and wiring or component errors. For example, the 1936 "Special" Model H shown in the top photo was basically complete and original having only been recapped in the past. It did function but exhibited several problems, from a fairly high hum level to an AC modulated CW note. LO tracking was poor and couldn't be aligned. The articulated dial lamp assembly was missing. A thorough inspection found so many lead dress, component location and soldering problems that the only solution was to completely "strip out" the wiring and components and start over - this time following the recommended layout using professional wiring and soldering techniques. All of the original components were rebuilt or reused, including original TOBE capacitor shells used for the "restuffed" capacitors. The "newly built" Model H appears just like it had been assembled following the instructions back in 1936 (see photo to the right.) When finished, the performance was significantly better and also pretty much as described in the booklet. Unfortunately, the Tobe alignment instructions provided are useless since they assume you don't have any test equipment. I aligned the Model H as if it were a standard ham band superhet receiver with a 456kc IF and ended up with a receiver that has very good sensitivity, fair selectivity, vague dial information, very nice audio in the AM mode and average stability for the period. Back in 1936, for the expenditure of around $60 and a few nights of assembly and testing, the talented, experienced and thrifty ham would have ended up with a pretty good receiver at about half the price of a comparable factory assembled receiver.

photo above: The TOBE "Special" Model H chassis after rebuilding. The wiring and lead dress follows the TOBE instructions exactly as does the component placement. Note that all of the capacitor shells are TOBE brand, even the three that aren't red are TOBE brand.

Wright-DeCoster Loudspeaker Model 1000-B

 for TOBE Model H Receivers

When the TOBE Model H Amateur Communication Receiver kit was purchased a loudspeaker without enclosure was included. For an extra five dollars, an optional loudspeaker was also available for use with the various Tobe Deutschmann receivers, the Browning 35, the TOBE "Special" Model H and the standard TOBE Model H. There were actually two models that were available. The Model 1000-B, was an eight inch Wright-DeCoster electrodynamic speaker housed in a metal cabinet that was painted black wrinkle finish and sold for five dollars. The Model 900-B, was a six inch speaker in a similar type cabinet that sold for $4.50. For either model, the field coil DC R was 1750 ohms and the proper audio output transformer was mounted on the speaker frame. A four conductor cable with four pin plug connected the loudspeaker to the receiver.

The photo to the left shows the Wright-DeCoster/TOBE loudspeaker Model 1000-B that features an eight inch W-D loudspeaker. The grille cloth was originally silver and black but this example of original grille cloth has faded and discolored to now appear brownish tweed in pattern and color. The "sunburst" grille featured a small diamond-shaped metal badge in the center that is missing from this example (the badge seems to be missing from all actual W-D examples that I've seen.) The Model 1000-B is shown in the advertisement (right) that is from page 22 of the "Browning 35 with the TOBE Super Tuner" booklet.

Line-Bucking Transformer - Most of the radio equipment made in the 1930s was designed for 110vac or perhaps 115vac. Nowadays, most house line voltage runs over 120vac with some areas even pushing up to 125vac. The earlier radio equipment, if operated directly on today's "high line" AC house voltage will experience the following,...higher tube heater voltage, brighter dial lamps (resulting in higher heat,) elevated B+ levels, possible audio distortion due to skewed bias voltages and higher heat levels during operation. Most of the time the operation of pre-WWII gear is limited to testing or displaying the set in operation. Usually limited time operation at slightly higher AC line voltages doesn't cause too many problems. However, if long periods of operation are planned then maybe the higher AC line voltage might be a consideration. Of course an autotransformer (Variac or Powerstat) could be used but those are nice items for the test bench and probably shouldn't be tied up adjusting the line voltage. A "Line-Bucking Transformer" (LBT) is an easy way to adjust the line voltage down by whatever voltage the secondary of the LBT is operating at. For example, if a 6.3vac filament transformer is used it could be set up to lower a 122vac line down to 115vac. A 12.6vac filament transformer could be used to lower the same 122vac line to 110vac. The connections are very easy and finding the desired filament transformer is usually an inexpensive purchase. Additionally, the current rating of the filament winding allows a relatively small filament transformer to be used in a "bucking configuration" to operate a single piece of equipment. A 3A winding on a 6.3vac transformer is close to 20 watts of dissipation (just for the 6.3 volt drop) and would easily operate a typical receiver that dissipates around 100 watts to operate. If a large filament transformer is available, the output could be routed to a switchable power strip allowing several items to operated at the lower AC line voltage. Be sure to include a switch on the house line input side of the LBT. Lots of info on the Internet about LBT hook-ups.

Pre-War Ham Gear Part 2                                               Return to Home Index




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