Western Historic

RADIO  MUSEUM

Pre-WWII Ham Gear

1930 - 1941

photo: W7GPI, Reno Diedrich, Toppenish, WA -1939 - Breting "12" Rcvr & Homebrew Xmtr

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

The National Co. started in business manufacturing toys and parts in 1914 (as the National Toy Co.) In the mid-twenties, National supplied 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. It was a five tube, regenerative detector with RF stage, audio driver and P-P audio output. The receiver used plug-in coils and was powered by a separate power supply. 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.

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. The little 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 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) and parts and coils were available from National up well into the fifties.

Hammarlund Mfg. Co., Inc.  -  Comet Pro

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. When Hammarlund-Roberts went out of business in 1931, Hammarlund Mfg. Co., Inc. entered into the shortwave receiver market with the introduction of the Comet Pro. Arguably, the first successful commercially built superhet offered to the ham market, the Comet Pro circuit used eight tubes along with plug-in coils, bandspread and a built-in power supply. Some early models had wooden cabinets and separate audio amplifiers. The audio output evolved from a 27 to a 47 and finally a 2A5. In 1933, a crystal filter was added. Later versions added AVC requiring an additional tube. There were several upgrades in coils, tube line-up and other additions made during production which lasted up until 1936. The Comet Pro was used by many professionals, both military and commercial. It was also taken on several expeditions to the Arctic and Antarctic.  The Comet Pro was popular with amateurs and could be found in many ham shacks in the thirties.

1932 National Co.- RHM Airport Receiver

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

The very rare (but equally famous) National AGS receiver had its origins with National's RHM receiver (shown in photo left.) The RHM was designed to fulfill a Department of Commerce contract to supply modern receivers for airports in 1932. It seems likely that Herbert Hoover Jr. and his West Coast design team were involved in some of the design work of the RHM. The RHM was National's first superhet but only a handful were built. To take advantage of the prestige the Government contract had given them (and to profit through additional sales to the general public,) National adapted the RHM for ham use and dubbed it AGS. It was an expensive receiver selling for $265 in 1933. Both the RHM and the AGS used first class materials and components throughout resulting in performance and reliability that was incredible for the time. There were several variations throughout its short production life, mostly involving tube types and calibration procedures. The most significant variation was the Single Signal AGS-X which was designed specifically for the ham market. Also at this time, National started to offer ham bandspread coils for the AGS. Frequency coverage changed as the AGS evolved. The RHM version only tunes up to 15mc while the later AGS tunes up to 20mc. By 1934, even 10 meter coils were being offered for the AGS. However, the list price of nearly $300 was beyond most ham budgets of the time. Actually, if the ham waited until the introduction of the HRO in early 1935, he could then pick up a new AGS for about $123.00 (from Leeds.) Uses nine tubes (10 with PS rectifier), a separate power supply and plug-in coils. I have owned the RHM shown for about 16 years and it is all original and has its complete original coil set in the rack mounted coil holder. The power supply is homebrew and provides two things that the originals did not - a pilot lamp and a B+ switch. The original RHM/AGS did not provide a way to switch off the B+ for coil changes - the operator either had to turn off the receiver entirely or change the coils "hot", that is with the B+ on. This RHM functions quite well with 75 year old components - every part was the best that was available at the time. Today, the RHM performance seems antiquated and crude but in 1932 it was "state-of -the-art" and the fact that it is still operating and is still accurate in its dial readout is testament to National's build quality and Herbert Hoover Jr. and James Millen's design capabilities. This same design team again worked together in 1934, producing the famous HRO receiver.

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

In 1933, National introduced the FB-7, a seven tube scaled-down version of the AGS, offered so hams could buy a superheterodyne at a realistic price, (about $65 with accessories.) The FBX came out after James Lamb's article in QST about Single Signal receivers and crystal filters. The FBX incorporated Lamb's crystal filter. Amateur bandspread and general coverage coils were available. At least three different models of AC power supply were offered but the 5897 was recommended to provide sufficient voltage for the type 59 audio output tube. An "A" suffix denotes the use of air-spaced trimmers in the IF transformers, rather than compression trimmers. The receiver shown is the FBX-A from 1934. The FB-7 was very popular and found in many ham shacks in the mid-thirties.

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

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

1935 HRO SN: H-103

National Company, Inc.  -  HRO, HRO Senior 

National announced the HRO receiver in October 1934 but it was about March 1935 before the first receivers were delivered. James Millen headed the mechanical design team and Herbert Hoover Jr. 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 uses 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. It was an expensive receiver selling for about $200 with power supply and four coils in 1936. The HRO used 10 tubes (nine in the receiver and one in the PS) and featured double pre-selection on all of the plug-in coil sets. Plug-in coils for several frequency ranges were available and either general coverage or amateur bandspread were selectable on the amateur coil sets by relocating  four "jumper screws" on top of the coil assembly. The micrometer dial was based on a Sperry Gyroscope design which resulted in very smooth operation and the scaled range of 0-500 gave the user the equivalent of a linear dial twelve feet long. The precision nature of the micrometer readout allowed for extremely accurate reset capabilities. For hams, the dial readout vs. frequency graph allowed the operator to figure out where he was tuning 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.

There were several minor changes incorporated into the HRO from its 1935 introduction up to WWII. Generally, the earliest examples have coil assemblies with white background graphs with black nomenclature, no pilot lamp, a nickel plated micrometer dial, black chassis, round IF cans, a "NC" on the dial pointer and a non-illuminated S-meter with a push-button switch. The HRO shown in the photo above is serial number H-103, built in September 1935, showing that by that time the S-meter switch had changed, the graphs were now black and the pilot lamp was incorporated. 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. A rack mount version was also offered - it featured a crackle-finish, aluminum front panel. In 1936, the HRO Junior was introduced as a reduced price version that eliminated the S-meter, the Crystal Filter and the bandspread coil feature (also, only one coil was included in the discount purchase price of $99.) With the introduction of the HRO Junior, the standard HRO became known as the "Senior." Also in 1936, the nickel plated tuning dial was changed to a black lacquered version, chassis paint went from black to gray and the IF transformer shields were changed from round cans to square cans. In 1937, the S-meter became an illuminated unit and the following year the identification tag was added to the upper right corner of the panel.

1940 HRO Senior SN: 463-K

There were many other subtle changes that were incorporated into the HRO during its long production, however the receiver was so well designed from the start, no major engineering circuit changes were necessary until after WWII. During WWII, many HRO receivers were rack mounted HRO Junior versions that had designations such as RAS, etc., (the RAS used a 175kc IF making its coil sets unique.) The standard WWII table version was designated as the HRO-M. The WWII coil sets did not have the bandspread option on any of the coil sets. Use of the HRO Senior as an intercept receiver in England during WWII was very successful. The HRO circuit was upgraded to JAN parts and metal octal tubes by the end of the war and the designation was changed to HRO-5. After WWII, the HRO-5TA and then the HRO-5TA-1 were National's 1946 models. In late 1946, an HRO-6 was offered for a short time. It was identical in appearance to the HRO-5TA1 but had a different Noise Limiter circuit. The 1947 HRO-7 was the first major departure in appearance with a modern styled, light gray cabinet and the change to a couple of more modern tubes, one of which was a voltage regulator tube. The major design changes occurred with the HRO-50 receiver (built-in power supply, P-P audio, three IF amplifiers, direct readout dial) and HRO-60 receiver (added double conversion above 7mc.) A tube-type HRO-type receiver remained in National's line-up, albeit modernized, up to the mid-sixties. The HRO shown in the second photo 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. The HRO is an incredible performer with fabulous sensitivity and undoubtedly the best bandspread of its time. Why these great receivers are not found in more vintage ham stations today is a mystery but is probably due to the HRO's rather basic appearance with non-illuminated dial that required correlation with graphs and the requirement of several accessories. More details on the HRO-5TA-1 and the HRO-60R on the "WWII Receivers and Post-War Ham Gear" webpage.

For more detailed information on the Pre-WWII National HRO Series of receivers, including Production Estimates, Serial Number Assignments, Performance and Restoration, click on
"National Co. - HRO Receiver - 'The Cream of the Crop'"  in the index at the bottom of this webpage.

Breting Radio Mfg.  -  Breting 12

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

Patterson Radio Co.  -  PR-16C

Patterson introduced their 16 tube receiver in 1935. After engineer Ray Gudie left Patterson over a wage dispute, Emmitt Patterson tried engineering the new PR-12 but soon discovered he was completely out of his element. Patterson hired Karl Pierson to complete the PR-12 but Pierson took one look at it and scraped the whole project. Karl Pierson designed the PR-16 in just a few weeks as the "new" Patterson receiver. The PR-16 featured parallel RF amplifier tubes (2-6D6s) which, in theory, increased the gain and reduced thermal noise. It also allowed the receiver to be advertised as having two RF amplifiers, even though there was only one set of RF coils per band and the receiver is essentially a single preselection front-end. The incredible audio section has three stages of Push-Pull audio using a 6A6 dual triode, two 76 triodes and two 42 output tubes supplying 18 watts of low distortion audio power. Chrome chassis, band-in-use dial masking, illuminated R-meter, crystal filter, two-speed tuning - all for the low price of $101.70, (1936 price.) Even though the parallel RF amplifiers are unconventional and no other manufacturers ever tried to market the configuration - the PR-16C is a good performer with good sensitivity, nice mechanical bandspread and powerhouse audio. Built at the Gilfillan plant.* This PR-16C belonged to W6BBK, who bought it new in 1936, using part of his WWI veterans bonus to fund the purchase.

 The Hallicrafters, Inc.  -  SX-9 

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

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

Radio Manufacturing Engineers, Inc. started in business in the early thirties, founded in Peoria, Illinois by two hams - E. Shalkhauser, W9CI and Russ Planck, W9RGH. Their first receiver, the RME-9 and RME-9D (built from 1932 to 1935,) incorporated all of the basic ham requirements into a nine-tube, bandswitching superhet with built-in power supply. For its time, the RME-9D was a first-class receiver that suffered with an archaic tuning and bandspread dial. The RME-69 was announced in November 1935. Using nine tubes, a stout chassis and a tight, compact layout, the RME-69 provided the user a receiver with lots of sensitivity along with great performance features and a tuning and bandspread dial system that was "velvet smooth" - even though the dial nomenclature was miniscule. The "Compensator" control (located between the two main tuning knobs) allows the operator to keep the RF and Mixer stages "peaked" for any frequency tuned. "Stand-by" is actuated by pulling the Audio Gain control knob. A terminal on the rear chassis allows the station transmitter's AM signal to be monitored through the receiver. The Carrier Level meter is calibrated in both "R" units and in db (with 48db equal to R-9.) The standard RME-69 covered .55 to 32MC and sold initially for $135 - the price was raised to $151 in 1937. Throughout production various improvements were incorporated into the design. The RME-69A was an AC or Battery operated version and the RME-69B was battery operation only. Late in production changes were made to the mounting of the BFO switch and headphone jack, the mounting of the two dial lamps and the Crystal Filter design. Another late offering was the Lamb Noise Silencer, designated as the LS-1 option (there was also an LS-2 variation for battery operation.) The LS-1 added two extra tubes to the circuit. A popular RME accessory was the DB-20 Pre-selector, introduced in October 1936. It provided the user with two tuned RF stages ahead of the RME-69 with an advertised gain of 20 to 25 db along with reduction of images. When the RME-69 was used with a DB-20, three tuned RF amplifiers were in operation - sensitivity was incredible and images were no longer an issue. A VHF Converter was also available. RME also offered the DB-20 and the RME-69 installed into one very long cabinet. The matching speaker is mounted in an unusual trapezoid shaped cabinet. In 1939, the RME-70 was introduced and the RME-69 was slowly phased out of production. About 6500 RME-69s were built from 1935 up to about 1940. Shown in the photo above is our 1937 RME-69 SN 1931 with its matching speaker and matching DB-20 Pre-selector. If you are aligning an RME-69 be aware that it has a decidedly different front-end with no trimmers to compensate for variations in the coil windings of the RF or Mixer sections. This was because the coils were all pre-tuned before assembly and all coils should be identical from receiver to receiver. Whether they have aged the same over the past 70 years is an unknown but most seem to have weathered time quite well. Since the alignment requires some special information, it is lucky that the quirky alignment procedure is in Rider's VOL. X. The RME-69 by itself is an average performer since it only has a single RF amplifier, however when rebuilt and aligned, the RME-69 used with the DB-20 preselector is an almost unbeatable vintage receiver.

Radio Manufacturing Engineers, Inc. always advertised themselves as a small, engineering oriented company that would incorporate any custom features into their models per customer request. Special order finishes and extended tuning ranges were common requests. Shown in the photo above is a custom ordered RME-69 SN R841 with a light blue wrinkle finish applied to the cabinet. Also custom ordered for this receiver was extended tuning (.55 to 42MC) and a special bandspread condenser that reduced the vernier action of the bandspread - certainly not something a ham would have wanted!

1936 Hammarlund "Super-Pro" SP-10 from WMI, Lorain, Ohio
 

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

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

The first Super-Pro, the Model SP-10, had all glass tubes with vented shields on the all but the audio tubes. The audio section including triode connected P-P 42s driven by another triode connected 42 with potted audio transformers with an 8 ohm Z output. Some SP-10 receivers had a 600 ohm Z audio output that added resistors to the audio line output to achieve a 600 ohm Z while utilizing the standard 8 ohm Z transformer. The first, second and third IF transformers were variable-coupled and cam/lever controlled from the front panel Selectivity control. Additionally, the Input and Output IF transformers for the Second Detector and the Output transformer for the amplified AVC were also variable-coupled but adjustable via knurled nuts on threaded shafts that protrude out the top of each transformer housing. Since a 6B7 duplex diode-pentode was used as a detector, the IF signal was first routed through the pentode section of the 6B7 and with the tuned Input-Output IF transformers in the Second Detector stage, this comprised another IF amplifier stage bringing the total to four IF amplifiers. The front panel was .187" thick aluminum finished black wrinkle then engraved so the nomenclature would appear bright silver (when it was clean.) The separate power supply was designed to utilize the field coil on the standard 8"speaker (a 12" deluxe speaker was available at $25 extra.) The speaker was just that - a speaker, no cabinet was supplied. The Tuning Meter was not illuminated and had an arbitrary 0 to 5 scale (but with 50 divisions!) Since it measured total IF amplifier plate current, stronger carriers would increase the AVC voltage, reducing the IF gain thus resulting in a lower reading on the meter scale. When tuning in AM stations, one would tune for the lowest reading on the meter. Signal reports were based on the difference between the "no signal" meter reading versus the "signal' meter reading to calculate "db over noise." Bandspread was only operational on the upper three frequency ranges and used a 0-100 logging scale. The 12 gang BS condenser actually consisted of three sections per the four major gangs. These were bandswitch selected and optimized to give about 90% BS coverage on the 80,40 and 20 meter ham bands. The crystal filter option installation required a square cut out in the upper left section of the front panel to allow mounting of the crystal filter panel which had the crystal mount, the "on-off" switch and the phasing condenser mounted to it. The crystal filter option was designated with an "X" suffix added to the model type. In mid-1936, an "S" version was offered that had coverage from 1.2 to 40MC with bandspread on all five tuning ranges (identified with an "S" suffix.) This model was advertised extensively in ham magazines of the day. The SP-10 designation is a later identification addition, when new, the receiver was just advertised as the "Super-Pro." The SP-10 was in production for only nine months.

1937 Hammarlund "Super-Pro" SP-100X

The SP-100 series Super-Pro was introduced in January 1937. Changes included going to metal octal tubes in the RF front end and in the audio section - eight tubes in all were changed (2-6K7, 6L7, 6J7, 6C5, 3-6F6,) the other eight tubes remained large glass tubes, (3-6D6, 6C6, 2-6B7, 5Z3 and 80 - the 80 was a change from the 1-V tube used in the earlier supplies.) The separate RF and IF Gain controls of the SP-10 were combined into a single Sensitivity control on the SP-100. The "knurled nuts" adjustable-coupling Second Detector Input and Output IF transformers and the adjustable-coupling Amplified AVC Output transformer of the SP-10 were changed to fixed-coupling units on the SP-100. These two changes were incorporated because the SP-10 had a tendency to overload the front-end when receiving strong AM signals when operated in AVC. The front panel was still .187" thick aluminum, wrinkle finished then engraved and now reference scales were added to the BFO, Bandwidth, AF Gain and Sensitivity. The "unique" Tuning Meter remained unchanged but the audio transformers were changed to vertical mount, frame-types with 8 ohms Z audio output. Added to the rear chassis apron was a two input pin jack socket that provided a remote relay access to control the receiver B+ by paralleling the Stand By switch. Around the same time the size of the standard speaker was increased to 10 inches. The standard power supply still had field coil connections on all versions but chassis space was provided for the substitution of a filter choke to replace the speaker field coil which then allowed the use of a PM speaker. Although not mentioned in advertising, an "L" version was available that included longwave coverage 100-200KC and 200-400KC in place of the .54 to1.25MC and 1.25-2.5MC bands. The "L" model also featured a front panel "Phone" jack and a dual secondary winding on the audio output transformer.

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

Shown in the top photo is one of the 1936 "Super-Pro" SP-10 receivers that was used at WMI, a ship-to-shore radio station located in Lorain, Ohio. The lower photo is our 1937 SP-100X receiver that has been totally rebuilt and aligned. Performance is phenomenal and the powerhouse audio a pleasure to listen to. The SP-100X (SN:3387) is used as the main receiver in our 1937 Vintage Ham Station paired along with a 1937 Utah UAT-1 transmitter.

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

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

 The Hallicrafters, Inc.  -  SX-11 

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

 1936  NC-100  (SN 334D)

National Company, Inc.  -  NC-100 Series 

The NC-100 was introduced in 1936 and was National's first successful receiver to not use plug-in coils. Though James Millen insisted that the best receiver performance was achieved using plug-in coils, National's mechanical engineers offered a solution with the NC-100 receiver. A movable cast metal coil box called a "catacomb" contained all of the coils mounted in individual shielded compartments with short contact pins mounted in molded insulators on top of the catacomb . The band selector knob turned a rack and pinion gear mechanism that moved the coil catacomb into place engaging the proper coil set pins into short, fixed contacts mounted under the tuning condenser. The mechanical action simulated plugging in a three coil set for each band with the ease of turning a knob while keeping all of the unused coils isolated and shielded. The NC-100 was a general coverage receiver using 12 tubes including a cathode-ray tuning indicator that was included for AM reception. A crystal filter version was also offered - the NC-100X. In a short time a ham band only version, the NC-101X was introduced. The Micrometer tuning dial used on the early NC-100 is gray-blue with a red inner readout - very deco! All NC-100X versions seem to have a black inner ring and gray outer dial. NC-101X receivers are all black wrinkle finish and use the same black dial as the HRO. The later NC-101X receivers use an S-meter rather than the tuning eye tube. In 1938, the NC-100 was given a new, direct reading dial with mechanically articulated dial pointer that indicated the band in use along with a standard S-meter. The new version was dubbed the NC-100A and soon all the NC-100 series receivers featured this dial. The military ordered versions of the NC-100A with designations of NC-100ASD for the Signal Corps and RAO for the Navy. See "WWII Receivers and Post-War Ham Gear" webpage for more information on these sets. James Millen left National in early 1939, forming his own company, James Millen Mfg. Co.

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

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

Breting Radio Mfg. - Breting 14 

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

 The Hallicrafters, Inc. - Skyrider Diversity DD-1

In 1936, James Lamb and James McLaughlin custom-built an elaborate dual-diversity receiver for XE1G, Dr. James Hard, a wealthy and enthusiastic ham in Morelos, Mexico. In 1937, McLaughlin and Karl Miles, Chief Engineer for Hallicrafters, designed a version of the XE1G receiver for production. Hallicrafters began advertising the Dual Diversity DD-1 in June 1938. The dual diversity design utilized a shared local oscillator to provide single dial tuning which drove the seven-gang tuning condenser. Main tuning is accomplished with the left-side dial and bandspread uses the right-side dial. The massive Yaxley-built push-button switch assembly controlled AC power and bandswitching. The four meters monitored signal levels in each receiver, the signal balance between the two receivers and the common AVC line in S-units. 26 tubes are used in the DD-1, including the four VHF 1851 RF amplifier tubes which allowed the receiver to tune up above 40MC. The table version was to sell for about $300 for the basic receiver without the Power Supply, Power Amplifier, Diversity Action Meters or speaker, (these accessories increased the basic price by $120.) The DD-1 Console version included the fabulous 15" Jensen Ortho-Dynamic High Fidelity Speaker in a Hagstrom-designed Deco-styled Bass Reflex cabinet along with a matching wooden top housing the diversity action meters. The DD-1 Power Supply and Power Amplifier chassis were stowed on shelves built into the rear of the speaker console. The DD-1 Console was priced at $500 - nearly the price of a new Chevy coupe in 1938. Not surprisingly, the DD-1 was only advertised for about six months (last QST ad was 1/39) and total production is thought to be less than 150 receivers. As a specialized receiver it confirmed that Hallicrafters' engineers were capable of sophisticated designs but this "over-the-top" creation certainly wasn't what the Hams of the late thirties would have purchased for their station receiver.

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

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

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

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

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

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

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

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

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

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

1940 Sky Buddy S-19R

The Hallicrafters, Inc.  -  Sky Buddy - Models 5-T, S-19 and S-19R

Hallicrafters began production of the Sky Buddy line of introductory receivers in 1936 with the Model 5-T. It was designed for the beginning shortwave listener or as a young ham's "first" receiver. The intent of the Sky Buddy could be inferred from the young boy pictured on the dial of the early 5-T receivers. The later versions eliminated the boy from the dial since many adults were purchasing and using the receivers. The 5-T circuit was a "basic superhet" and used five tubes with a built-in AC power supply and built-in speaker. By 1938, the S-19 Sky Buddy was introduced and keeping with the new Hallicrafters' styling, a silver colored dial was used with a separate logging dial. Again, five tubes were used in the circuit along with a built-in speaker. The following year the S-19R was introduced and the tube count went up to six. This was due to the use of separate tubes for the IF amp and BFO functions rather than using a single converter tube for the dual function as the former receivers had done. The S-19R also changed the logging dial to a tuned bandspread function. On all models the speaker grille screen was originally flocked with a dark mohair that has seldom survived. The S-19R was produced up to 1942 and sold for $29.50. Performance was fine considering the circuit limitations and the intended use. The Sky Buddy line of introductory receivers continued after WWII with the S-38 line. All of the pre-WWII Sky Buddy receivers are power transformer AC operated while the post-war S-38 sets are all "transformerless" AC-DC operated.  

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

The masterpiece of pre-WWII Hallicrafters receivers. Introduced in July 1940, the SX-28 circuit boasted 15 tubes, covered .55 to 43MC in six bands, had P-P audio, ham band calibrated bandspread, Lamb Noise Silencer, Amplified AVC, on and on. Hallicrafters advertised that the SX-28 had been designed by 12 of their engineers based on 600 requested reports including input from the Government. The styling was beautiful and the performance incredible. Early versions of the SX-28 have gray panels but starting in 1941 the panel color was changed to black. About the same time the Lamb Noise Silencer was redesigned. A few months later the bandspread gearbox was replaced with a dial string drive. There were many engineering design changes throughout production. During WWII, Hallicrafters continued to redesign portions of the SX-28 and, at the beginning of 1944, a major redesign to the receiver's front-end prompted a designation change to SX-28A. The old front-end coils were replaced by smaller, Hi-Q Micro Set types that were mounted on removable chassis. The new coil design eliminated the majority of brass parts that were used in the early style coils. After WWII, Hallicrafters had nothing new to sell the hams as they had devoted all design and manufacturing to the war effort, so they offered the SX-28A as a 1946 model. The last 3800 SX-28As built have "SX-28A" indicated on the front panel (this is all of the 1946 production.) Hallicrafters published that 50,000 SX-28s (and SX-28As) had been built by 1946, however the serial numbers seem to indicate a production figure of about half that amount, around 27,500 receivers. Nowadays, many SX-28s and SX-28As are still being used in vintage AM ham stations because of their fabulous audio quality and classic "good looks." Most ham AM operators find the sensitivity, selectivity and stability quite acceptable for communications on vintage AM nets today. The SX-28 (SN H-151197) shown belonged to W3ON, John Ridgway (SK), who purchased it new in February 1942. In 1997, at age 85, John sold his receiver to me saying, "...it's so damn heavy, I can't even turn it on its side anymore." The W3ON SX-28 is in superb original condition and is an excellent example of how the pre-WWII SX-28 looked when new.

For the ultimate source in detailed information on the SX-28 and SX-28A history, production and engineering changes, dating by serial number information, competition comparisons click on 

"Hallicrafters SX-28, a Pre-war Masterpiece" at the bottom of this page 

The Hallicrafters, Inc. SX-28 and R-12 Bass Reflex Speaker During early production of the SX-28, three different speaker options were offered. The PM-23 was a 10" speaker in a table top, metal case. The R-8 was a small bass reflex cabinet with 8" speaker and the largest speaker offered was the Hallicrafters-Jensen Bass Reflex floor speaker, the R-12. Selling price was $29.50 and, together with the $159.50 that the SX-28 cost, represented quite a substantial investment in 1941. The R-12 uses a Jensen 12" PM speaker with 5000 ohm to 8 ohm transformer. The cabinet is constructed with panels made from solid lumber core with soft wood veneer. Paint was a dark silver color except for the decorative incised arch over the speaker opening that was filled with red paint. The cabinet panels are held together entirely with small internally mounted clamps. Originally, the wire screen grilles were flocked with a champagne colored mohair but most surviving examples have lost their flocking with years of use. This particular SX-28 (SN H-130170) & R-12 combination was purchased together, new in mid-1941, by W6ANX, Theron "Woody" Woods.