Radio Boulevard
Western Historic Radio Museum


the
hallicrafters inc.

 
SX-28

"a pre-war masterpiece"

 

(includes SX-28, SX-28A, AN/GRR-2 & R-45/ARR-7)

PART 1 - History, Various Models, Dating your SX-28 by Serial Number,
 Estimated Production Figures, Serial Number Log 

PART 2 - Engineering & Production Changes, Restoration Hints & Suggestions,
Performance Expectations, Competition Comparisons

by: Henry Rogers - WA7YBS/WHRM


  

YES, I know it's a SX-32. BUT,... it's just a great photo of

 KH6GQ, USN Lt. Wm. Griffin

 

the hallicrafters inc.
SX-28
(includes SX-28, SX-28A, AN/GRR-2 & R-45/ARR-7)
 

"a pre-war masterpiece"

PART 1

The SX-28 is one of those receivers that just about every ham has a passionate opinion about. No other communications receiver, even those that are better performers, has such a dedicated following. Certainly, the SX-28's top performance that combines great audio with an impressive appearance is responsible for the enthusiasm of its fans . This article provides a detailed history of the SX-28 production and how it evolved during WWII to become the SX-28A. Serial number analysis and a serial number log along with a chronological listing of Engineering Upgrades provides tools for accurately dating your receiver. Today, hundreds and hundreds of SX-28 receivers have been restored and are in use in Vintage Ham Shacks around the country still providing great performance with incredible, bass-rich audio. The SX-28 remains one of the most popular of the "pre-war masterpieces."   H. Rogers - Nov. 2011
 

The SX-28 Receiver

The SX-28 Introduction


Hallicrafters announced the SX-28 "Super Skyrider" in July of 1940. The receiver's ultimate design was the result of the analysis of more than 600 requested reports, including input from government engineers. Twelve Hallicrafters' engineers were assigned the project of creating a receiver that not only satisfied government and commercial users but also gave the hams a receiver that performed better than any previous Hallicrafters. Additionally, the SX-28's modern, 1940 styling was to compliment the receiver's great performance.

The circuit utilized 15 tubes in a double preselection front-end on the top four bands and single preselection on the lower two bands. The frequency coverage was .55 to 43MC in six bands. Amplified AVC, Lamb Noise Silencer, Calibrated bandspread, Push-Pull Audio were some of the features incorporated into the design. The SX-28 would become an all-time ham favorite, famous for incredible audio coupled with amazing sensitivity, stability and selectivity - all at a reasonable selling price. Shown to the left and below are pages two, three and four of the multi-page advertisement in July 1940 QST that announced the SX-28. Page one of the ad states that the SX-28 was ",...mechanically and electrically designed by twelve engineers in our own laboratories." It further states that an exhaustive analysis of more than 600 requested reports, including input from government engineers were used for developing the performance specifications. Typical of a new product advertisement, conceptual artwork is used rather than actual photographs. Oddly, the ad states that the Super Skyrider is a 14 tube receiver but this is more than likely just an error from the advertising department.

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Also shown on page two is the Jensen-Hallicrafters R-12 bass reflex speaker, an option that was available for $29.50. The text also mentions that a receiver with all of the features of the SX-28 could sell for as much as $250.00 but Hallicrafters' price of $159.50 was ",...figured on a slide-rule."
 

Pre-WWII Versions

1940 SX-28 SN: H-119051

The first few production runs of the SX-28 receivers have a several differences from the later production units. SX-28 SN H-119051 left the Hallicrafters' plant on October 29, 1940 - about two months after the SX-28 introduction and most likely from the second production run. It has most of the characteristics of the first SX-28 receivers, e.g., the front panel is painted blue-gray, no upper-center panel screws flanking the main dial bezel are used, it has the early style ANL circuit. By the time this receiver was built though, Hallicrafters had already changed the first RF amp tube from a 6SK7 to a 6AB7.

In 1950, the receiver's first owner, Paul Mauch, sold this SX-28 to W6EYC, Ray Umbraco of Richmond, California. 55 years later, I purchased this SX-28 from W6EYC's son. I totally rebuilt this SX-28 and the performance is incredible. It is an excellent  example of  the very early SX-28 production.

The Hallicrafters-Jensen R-12 Bass Reflex Speaker

1941 SX-29 SN: H-130170 with matching R-12 floor speaker

When the SX-28 was introduced in the July 1940 issue of QST, it was shown with a large bass-reflex speaker. This was the Hallicrafters-Jensen R-12. There were actually three speakers available from Hallicrafters that were compatible with the SX-28. The PM-23 - a 10" table speaker - was standard. Also available was the Jensen-Hallicrafters R-8, an eight inch speaker in a small bass-reflex cabinet. The largest speaker-cabinet available was the R-12. The R-12 speaker-cabinet utilizes a wide-range 12" Jensen PM speaker with a 5000 ohm Z matching transformer to match the audio output of the SX-28. The R-12 cabinet is made up of five panels that clamp together using internally mounted clips. The back of the speaker screws in place and seals the cabinet except for the bass reflex port. The wood used is a soft lumber core that has a soft wood veneer. R-12s were painted a dark silver-gray, Hallicrafters called it "gunmetal," and the decorative incised arch was filled with red paint. Originally, the wire screen grilles were flocked with a champagne colored mohair but this seldom survives today. R-12s were only available from late-1940 up to the beginning of WWII, which accounts for their rarity today.

SX-28 SN H-130170 with the Jensen/Hallicrafters R-12 Bass-Reflex Speaker shown in the photo left was originally sold in 1941 as a combination to W6ANX, Theron "Woody" Woods, whose QTH at the time was Los Angeles, California. This SX-28/R-12 combination was donated to the Western Historic Radio Museum in 2004 by Fred Jensen K6DGW on the condition that both units be restored. Fred had acquired the combination from Woody Woods' son after it had been discovered, stored in Woods' basement, in Auburn, California. I totally rebuilt the SX-28. Fortunately, it was "dead-stock" with no modifications and the receiver had only one serious problem. This was an unusual problem of very low gain caused by a broken powdered-iron slug in T-3 (last IF transformer.) I replaced T-3 with a good condition unit from a "parts set" SX-28. The R-12 was in pretty "rough" condition with peeling veneer and warped panels. All of the panels needed to be wetted and then clamped to straighten them. After the panels were straight and dry, I had to reglue the veneer and add some patches where the veneer was missing. I matched the paint by removing the "h" grille and using the "unfaded" paint that was protected by its mounting as the color sample. Performance of the SX-28 with the R-12 is fabulous. Vintage AM ham stations sound incredible and AMBC and SWBC are a pleasure to listen to with lots of bass available. Although several other pre-war communications receivers have audio output stages that can rival the SX-28, there is a certain appeal to listening to a receiver with such dramatic presence as the SX-28, especially when used with the R-12 speaker.

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

SX-28 Chassis H-130170

The photo right is H-130170, a mid-1941 production SX-28, showing the typical chassis layout. Of note is the power transformer which has the standard Hallicrafters' "h" embossed on the cover. The glass tubes in front of the power transformer are the rectifier 5Z3 and the two 6V6 push-pull audio output tubes. The BFO section is to the right of the 6V6s. S-meter amplifier, first audio, detector and the last IF transformer for the sections across the front part of the chassis. On the left side is the second and first IF amplifiers, the Amplifier AVC sections and the Lamb Noise Silencer.

Under the condenser box cover are the front end tubes, RF1, RF2, Mixer and LO. This is the standard condenser box cover found on all SX-28 receivers up to late-1943.

The "spotty" chassis is typical of cadmium-plated steel when exposed to light moisture.

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Hallicrafters  PM-23 Table Speaker

The Hallicrafters PM-23 was the standard speaker for the SX-28 and SX-28A. It was first introduced in 1939 for use with the SX-23 and was still available through 1946. The 10" Jensen speaker has a 5000 ohm to 8 ohm transformer to match the speaker to the typical Hallicrafters' audio output impedance. The chrome "h" was installed on all PM-23 speaker grilles until about 1943 when it was discontinued for the duration of WWII. At about the same time, the magnet cover was eliminated from the speaker frame. Most speakers are dated in some manner - ink-stamped on the frame or cone is most common. This PM-23 is dated "5-40" and was originally sold with SX-28 SN H-119051.

photo left: PM-23 speaker

photo right: Leo Meyerson W9GFQ with an early SX-28 & PM-23  -  QST April 1941

WWII Versions

1942 SX-28 SN: H-151197

SX-28  SN H-151197 left the Hallicrafters plant on February 21, 1942 and was purchased by W3ON, John Ridgway, who kept the receiver in superb original condition for his 55 years of ownership. I purchased the receiver from John, who was 85 at the time (1997) and living in Galena, Nevada. John stated that the SX-28 was ",....so damn heavy I can't even turn it on its side anymore!"  Note that the front panel on this receiver is very dark gray-blue-black and there are panel screws flanking the main dial bezel. Internally, the receiver has the redesigned Lamb ANL circuit and the bandspread dial is driven by a dial string. The W3ON SX-28 is certainly an excellent reference as to how the later SX-28 receivers looked when new.

Although H-151197 left the Hallicrafters' plant in February 1942, it was actually civilian purchase. It was April 1942 before almost all of the US manufacturing completely changed to "War Production." John purchased this receiver just before the civilian market ended.

Having seen hundreds of SX-28s over the years, I am fairly sure that H-151197 is probably one of the best condition, original receivers to have survived. It is all original parts with the exception of the S-meter load resistor. It has its original warranty card, the original inspection tag, the original bottom cardboard cover and the original manual. John kept his receiver in a "dark" room (usually the curtains were drawn during the day and only a small desk lamp provided light.) This lack of bright light and John's meticulous care has preserved H-151197 in an exceptional original state.

H-151197

AN/GRR-2  -  WWII Army-Navy SX-28A


During the later part of the SX-28 wartime production, some versions were built with heavy-duty parts and other changes that were certainly at the request of the Navy and the Signal Corps. These heavy-duty SX-28 receivers have a General Transformer Company power transformer that is potted, Korite dipped filter choke and audio output transformer and also feature the return to the gear-driven bandspread tuning. The Navy versions sometimes have different front panels that are wrinkle finish with a military tag in place of the "the hallicrafters inc." identification. These heavy-duty SX-28 receivers are typically rack mount configuration. Serial number H-169129, owned by W7KXB, is an SX-28 receiver with many of these heavy-duty characteristics. When the SX-28A was introduced in early 1944 (probably April, 1944) some of the first production SX-28A receivers were produced in the heavy-duty configuration. These "special" receivers were designated as AN/GRR-2 and were specifically built for military use. Though most of the SX-28A receivers built from 1944-45 were in the standard configuration with table top cabinet, it appears that only one production run was made for the AN/GRR-2 receivers since all known examples were built within April-May, 1944. The AN/GRR-2 receivers were quite different than the standard SX-28A (and the earlier heavy-duty SX-28 models) and featured rugged construction with fungus proofing, rotary switches that were wax impregnated and the IF transformers that were vacuum and wax impregnated. Like the earlier "heavy-duty" SX-28s, the AN/GRR-2 power transformer was the same potted unit made by General Transformer Company and the filter choke and audio output transformer were dipped in Korite (a black tar-like moisture proofing.) Also included was the heavy-duty gear-driven bandspread dial (that had been used in the early pre-war SX-28s.) The chassis wiring uses military type stranded wire with white cloth insulation. All AN/GRR-2 receivers are MFP treated and are exclusively in the rack mount configuration but its dust cover design allows the receiver to be used as a table top unit also. The AN/GRR-2 had its own US Army Signal Corps manual, the TM-11-874 which is much more detailed than the standard Hallicrafters' SX-28A manual. However, the AN/GRR-2 receivers have a front panel is copper plated under the paint for corrosion protection, the ball-end toggle switches have sealed bakelite cases and the S-meter has a bakelite case with scale mounted needle stops and a yoke type mounting system.

The AN/GRR-2 shown above is SN: HA-2703 and fortunately it has the fungus proofing stamped date still legible, May 27, 1944. Even though it was a special-build receiver, the AN/GRR-2 still has the standard Hallicrafters' ID plate with serial number riveted to the rear of the chassis. HA-2703 has its original heavy-duty dust cover installed.

AN/GRR-2 Chassis - The AN/GRR-2 chassis is very similar to the standard SX-28A in appearance. The exception being the AN/GRR-2 power transformer, as seen in the photo to the left. Standard for the SX-28A and the AN/GRR-2 is the "clip-on" condenser box cover with louvers. All tube types and locations along with the other above chassis components are similar in appearance to the SX-28.

AN/GRR-2 MFP Date Stamps and Production Numbers - I have received a couple of reports regarding AN/GRR-2 receivers and their MFP date stamps. A report was received from IØGEM - owner of AN/GRR-2 sn HA-2766. Maurizio reports that the MFP date stamp is May 27, 1944. This AN/GRR-2 is 63 serial numbers after my AN/GRR-2 sn HA-2703, which is also MFP date stamped May 27, 1944. It's unlikely that all 63 serial numbers were assigned to AN/GRR-2 receivers, so this date stamp doesn't really reveal any information regarding AN-GRR-2 production quantity. Another interesting report came from Chuck K3XU, who sent me his AN/GRR-2 serial number, HA-2506, which is 260 serial numbers before HA-2766 and it is MFP dated May 9, 1944, sixteen days before both HA-2703 and HA-2766 were MFP date stamped. HA-2686, a standard SX-28A, was produced during this time which shows that AN/GRR-2 receivers were not the only type manufactured during this period. It is also interesting that only 260 serial numbers were issued in a 16 day period indicating that production that used the "HA" prefix was fairly low at this time. Since the serial numbers of these three AN/GRR-2 receivers seem to track the MFP date stamps, it is reasonable to assume that it is likely that the MFP treatment was applied at Hallicrafters. Carl WA1KPD has reported his AN/GRR-2 SN: HA-2278 with MFP date-stamp of April 26, 1944. This is the earliest AN/GRR-2 reported, so far (also the earliest SX-28A.) The span of serial numbers from HA-2278 to HA-2766 is 488 numbers. As mentioned, there are standard SX-28A serial numbers within that 488 numbers so the estimate of about 300 AN/GRR-2 receivers built is certainly possible.

R-45/ARR-7

WWII Airborne SX-28A Search and Surveillance Receiver

 The R-45/ARR-7 was an airborne search and surveillance MF and HF (.55 to 43mc) receiver that was primarily used for visual analysis of enemy radar and other types of signals. Much of the R-45 circuitry and design was borrowed heavily from the SX-28A. However, since the receiver was primarily for search and surveillance, a motor drive tuning was provided for automatic scanning of operator set frequencies with reverse direction switching provided at each end limit of the tuning scan. The receiver also provided Panadaptor and Video Outputs that were designed to feed into specific airborne versions of typical panoramic adapters and oscilloscopes. The oscilloscopes sometimes had built-in oscillators to create lissajous patterns for audio analysis of incoming signals (Video output is from the 6V6 audio stage of the receiver.) The lissajous patterns (based on the oscillator input) allowed the operator to measure radar pulse rates and thus identify the particular type and origin of the signal. The panoramic adapters monitored the output of the Mixer stage of the receiver and provided a visual representation of the spectrum surrounding the receiver's IF passband. This allowed the operator to "see" signals that were outside the receiver's passband and couldn't be heard. But they could be seen on the panadapter thereby alerting the operator to tune to the signal for further investigation. The R-45's circuit is very similar to the SX-28A, although it is "stripped down" to the essentials and considerably lightened for aircraft use. The R-45 uses 12 tubes (not counting the rectifier located in the PP-32 power pack) and has six tuning ranges. Some of the similarities to the SX-28A include using the same Micro-set coils in the front end and providing six selectivity steps, three of which utilized the crystal filter. The main circuit differences from the SX-28A include the use of a VT-150 voltage regulator tube (the SX-28A didn't use any VT voltage regulation,) using a 6SK7 1st RF amplifier tube (the SX-28A used a 6AB7,) using a 6AB7 "re-radiation" tube (to prevent LO leakage to the antenna,) the Noise Limiter which is just a clipper circuit (instead of the fabulous Lamb Noise Silencer,) no bandspread provided and the "militarily" basic audio output system which is just a capacitive coupling from the 6V6 plate to drive the headphones. The audio output of the R-45 is really only for headphones but a 600 ohm speaker system will provide ample volume even though the audio quality is considerably inferior to the SX-28A. When airborne, the R-45 was powered by the PP-32 power pack that provided the heater voltage (6.3vac) and the B+ (+275vdc) but the scanning motor drive was powered by the aircraft battery system (+24vdc at 350mA when operating.) Additionally, the PP-32 operated off of 115vac 400 cycle provided by the aircraft's ac system.    >>>

>>>  The PP-32 actually was able to power three receivers and the R-45 was usually paired with the VHF R-44/ARR-5 which was the airborne version of the S-36. Like most WWII equipment, not all R-45 receivers were built by Hallicrafters. Other contractors included Belmont Radio Corporation. The R-45 shown in the photo is from 1944 and was built by Hallicrafters. It is mounted on the original aircraft shock mount. The R-45 receivers do not use the standard Hallicrafters serial number metal tag and do not use the HA serial numbers.

Post-WWII Versions

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1945 SX-28A, SN HA-25583

This early example of the civilian SX-28A (probable build date November 1945) doesn't have the "SX-28A" designation on the front panel even though earlier serial numbers have been reported with the "A" panels. Civilian production started in September 1945 and continued until around July 1946 when the new 1947 models were introduced. The front panel identification was changed to "SX-28A" in November 1945, so HA-25583 must have been one of the receivers built with an "old stock" panel from intermixed stock.

 

 (I  purchased this receiver at a CHRS swap meet in the 1980s. I restored the receiver and repainted the cabinet with Illinois Bronze "French Gray" Wrinkle Finish paint - too bad it's no longer available. I used this SX-28A  for several years but reluctantly sold it in 2004)

 

Production History and Serial Number Analysis - SX-28 to SX-28A

Dating an SX-28 Receiver by Serial Number

Why is it so difficult to find production information on the Hallicrafters' receivers? After all, they were one of the "big three" (Hallicrafters, National and Hammarlund) from the late thirties up into the 1960s. Unlike National, a company that just recently went out of business (1991) or Collins, a company still in business (though owned by Rockwell,) Hallicrafters was unfortunate enough to have been purchased by Wilcox Instruments, a division of Northrop, in the early 1970s. Wilcox was also known as Wilcox Electric and was located in Kansas City. One of the first orders of business at Wilcox was to DESTROY ALL of the Hallicrafters records and archives. I wrote a letter to Hallicrafters in 1975 that was forwarded to Wilcox Instruments. They did reply to my letter but made it very clear that no records or archives existed anymore. I have also had visitors in our museum that worked at Wilcox Instruments in the 1970s and were present when the orders were issued to destroy the Hallicrafters' archives. There were protests from the employees ordered to carry out the destruction but it was to no avail. Some records were "smuggled" out of the plant but it was only a fraction of what was destroyed. Most of these surviving records are probably in private collections. Since there are no company records available for reference to production dates or quantities, we have to use other methods to reconstruct what most likely took place during the SX-28 production period.

HALLICRAFTERS' SERIAL NUMBERING METHODS UP TO WWII: Hallicrafters' serial numbers on early equipment consists of a number sequence in addition to a manufacturer code number. This was because prior to late 1936, Hallicrafters' receivers were built by contractors, such as Howard Radio Company or other contractor companies. When Hallicrafters was able to build their own equipment (late 1936) they began assigning a serial number consisting of an "H" prefix followed by five numbers. The serial numbers were assigned sequentially to all products as they left production and not exclusively to any model line. There are exceptions to the "H" followed by a five digit number format. Accessories and smaller items that were serialized sometimes have an "H" followed by a four digit number.

Estimating a dynamic, like production, is difficult and we are going by assigned serial numbers compared to inspection tag dates and date codes on components. Inspection tags tie a serial number directly to a known manufacturing date. Date codes can be used as a double check to assure a production estimate "makes sense." Additionally, many radio manufacturing companies reduced or stopped their production during the early summer months, at least prior to WWII, so we are not counting May or June as "full" production months until 1942. Most companies used this time for design and tooling changes along with new product introduction.

By mid-1938, Hallicrafters' serial numbers were up to H-80,000. A dated inspection tag shows SN H-83879 was assigned on November 11, 1938. Another dated inspection tag shows that serial number H-85531 was assigned on December 19, 1938. These two tags are separated by approximately one month and show that 1652 serial numbers were assigned during that time period.  >>>

>>>  By late-1939, the numbers were in the H-100,000 range. By estimating that Hallicrafters assigned between 1600 and 2000 serial numbers per month at this time, the SX-28 production should start (approximately) with serial number H-115,000. VE3CSQ owns SX-28 H-116368 which happens to still have its original inspection tag that is dated September 27, 1940. This is the earliest SX-28 inspection tag that has turned up (so far.) SX-28 SN H-119051 was assigned on October 29, 1940, about one month later and shows that 2683 serial numbers were assigned (mostly in the month of October.) This shows that Hallicrafters was increasing their output, perhaps preparing for the 1940 Christmas sales season and also probably due to increased demand as the company grew. It appears that from August 1940 up to about May 1941, production was approximately 2000 to 2500 average assigned serial numbers per month. Variations in output occurred since there was always a rush in the late fall towards Christmas and then a subsequent slowdown in the winter to spring season. Another original inspection tag has turned up on a pre-war SX-28 owned by Robert MacIntyre - H-127986 with a tag dated March 19, 1941. During the fall of 1941, Hallicrafters must have again increased their manufacturing capacity because, starting in October 1941, production seems to be at a rate of about 2,500 to 3,000 assigned serial numbers per month. By February 1942, the serial numbers were up to H-150,000. SX-28 SN H-151197 was assigned on February 21, 1942. Comparing SX-28 H-127986 3/19/41 to SX-28 H-151197 2/21/42 gives a total of 23,211 serial numbers assigned in that 11 month period. Remember, these numbers are for all Hallicrafters' products and while they can determine a probable date of manufacture for a particular receiver, it requires other data to determine what percentage of production the SX-28, or any other product, represented.

NOTE on Serial Numbers and Production Runs: It is interesting that the very early SX-28s seem to be in two production runs as referenced to the serial numbers reported so far (May 2009.) We have many serial numbers reported in the H-115xxx to the high H-116xxx range but we have only three serial numbers from the H-118xxx and 119xxx range (with one other H-119xxx unit known to have sold on eBay.) No serial numbers have been reported assigned to SX-28s from the H-117xxx range. Also, the H-115xxx and H116xxx receivers have the 6SK7 RF amp while the H-119xxx receivers have the 6AB7 RF amp - a specific change to the production receiver. This could imply that SX-28s (at least the early pre-war ones) were built in production runs of some fixed quantity rather than just a constant built rate. The production run method is certainly how most companies did handle their build schedules, especially when their production was not to specific orders and the company produced more than one type of product. As more serial numbers are collected the picture of how Hallicrafters handled their production schedules might become clearer. Keep reporting your SX-28 and SX-28A serial numbers and thanks to all who have reported their numbers so far, it has provided valuable information. An e-mail link for reporting your SX-28/28A serial number is provided below in the "Assigned Serial Numbers - Serial Number Log" section.

WWII SX-28 Production Serial Numbers, Military Versions and the Introduction of the SX-28A - 1942 to 1944

During WWII, Hallicrafters' output again increased significantly, however the nature of the production changed from amateur receivers and transmitters to equipment required by the military. After about April 1942, it was impossible for civilian amateurs to buy receivers like the SX-28, as everything produced at Hallicrafters was destined for military or government use. Consequently, SX-28 and other "amateur" receivers accounted for less and less of the total production output. Use of the "H" prefix serial numbers slows down during WWII. Towards the end of 1943, the serial numbers were up to H-180,000. Hallicrafters decided to end the "H" prefix and start a new "HA" prefix with numbers beginning at 1000. It appears that the change over to the "HA" prefix happened around December 1943 or possibly January 1944. As a result, SX-28 serial numbers beginning with the "H" prefix end around H-183,000 but some very late production SX-28s will have serial numbers with the "HA" prefix. In fact, three SX-28s have turned up that have the "HA" prefix serial number (HA-2126 is one of them.) HA-2126 does have the old style SX-28 coils installed in the old style RF box, indicating that it is indeed an SX-28 and not an SX-28A (the other two "HA" receiver photographs did not show the underside of the chassis and the RF coils so they could not be positively identified as SX-28s though all of the other SX-28 indicators were present.) This receiver shows that SX-28 production continued into the early part of 1944 with the introduction of the SX-28A probably occurring around April of 1944. The earliest SX-28A reported is actually an AN/GRR-2 version with a serial number of HA-2506 (there is one reported SX-28A with the serial number HA-2385 however this number was not reported directly to me by the owner, so consider it hearsay.) This AN/GRR-2 serial number is most likely from late April or early May 1944. Certainly, Hallicrafters was in the process of designing the "SX-28A" upgrades at the time of the change over to "HA" serial numbers but the indications are that the "HA" prefix was certainly not specifically for the SX-28A model. It is possible that Hallicrafters intended for the SX-28A production to coincide with the beginning of the "HA" serial numbering sequence but the new coils and harnesses required new assembly procedures/models and new test/alignment methods which may have delayed the SX-28A introduction for a short time. Use of the "HA" prefix serial numbers for 1944 and 1945 progressed very slowly as the demand for other types of military equipment was by far of greater quantity than for surveillance receivers, like the SX-28A, SX-36A and the few other users of the "HA" prefix serial numbers.

SX-28 SN: H-180455 - This receiver is very late in the SX-28 production, dating from around September 1943. It is obvious that this receiver has the heavy-textured front panel and the main tuning and bandspread knobs are the later "webbed" type. This receiver also had the louvered cover over the tuning condenser that is screwed to the top of the condenser-RF box. This receiver illustrates that the late production SX-28 receivers were fitted with parts that formerly were thought to be exclusive to SX-28A production. H-180455 is owned by Oliver Gerondeanos who also supplied the photograph.

SX-28A Post-War Production and Serial Number Dates for SX-28A on Front Panel

When WWII ended in August, 1945, Hallicrafters almost immediately started civilian production of several pieces of equipment that had formerly been for the military. The civilian SX-28A production started in September 1945 and most dealers at that time were offering to take "advance orders" for when they actually got the SX-28As in stock. Though the use of serial numbers for the SX-28A had been rather conservative during the war, the production use of the HA serial numbers for civilian amateur equipment market from September 1945-on was fairly rapid. It is likely that all SX-28As with serial numbers higher than about HA-16000 are probably post-war production - remember, other receivers were also using the HA prefix serial numbers, so even though probably only about 1000 to 2000 SX-28As were produced during 2/44 thru 8/45, other equipment accounted for the remainder of the serial numbers assigned.

The appearance of  "SX-28A" on the front panel occurred rather quickly after civilian production began in September,1945. Paul Rosen CET owns the earliest seen SX-28A with "A" on the front panel, with a serial number HA-25171. This puts the addition of "A" in the front panel nomenclature to around September, 1945. However, I owned a later serial number, HA-25583, which didn't have "A" on the front panel. Also, KF4TP owns two SX-28A receivers, one is HA-27742 without the "A" on the front panel. His second receiver is HA-27748 which does have the "A" on the front panel. Only six serial numbers separate these two receivers and date the assignment to around September, 1945. The separation of HA-25171 with the "A" and HA-27742 without the "A" is 2571 serial numbers. HA-31195, an "A" front panel receiver, has its original inspection tag dated October 8, 1945. This is about 5000 serial numbers after the earliest "A" reported and indicates that "A" front panels were available either at the end of WWII or just after.

Since these serial number assignments all occurred during the "Christmas Season rush," production would have been at its highest volume for the year, probably at least 1000 units per week (especially of the lower cost receivers that made good Christmas presents.) This would make the actual time interval between the assignments of HA-25171 and HA-27742 about two weeks. It is very likely that intermixed stock accounted for this interesting anomaly and in a "production environment" this would be considered a common occurrence.

Approximately 4000 SX-28A receivers were produced with the "A" designation on the front panel. If this estimate is based on earliest serial number encountered with "SX-28A" on panel (HA-25171) to latest SX-28A serial number encountered (HA-53445) this results in 28,274 serial numbers issued with 15% assigned to SX-28A receivers equals 4241 receivers with "SX-28A" on front panel. However, since the earliest "A" appearance happens before the Christmas Rush and there are several examples of "non-A" panels that post date HA-25171, we are going to assume that intermixed stock accounted for a lower percentage of "A" panels used in production for a short time (two weeks or so.) Since this is an approximation and is taking into account intermixed stock, the number of 4241 receivers is rounded off to about 4000 units. Also, since this estimate is just for the post-WWII production, 15% is used for SX-28A percentage of assigned serial numbers since there were several other models also using the "HA" serial numbers. By July 1946, the new 1947 models were introduced with the SX-42 taking the "flagship" position that the SX-28 had occupied for the past six years. The SX-28  had provided pre-war hams with a great receiver at a bargain price, while during WWII the SX-28 filled many different occupations from intercept to entertainment.  The SX-28A eased front end manufacture and alignment while conserving necessary materials and, after the war, hams still had an opportunity to purchase a brand new version of a receiver they may have become familiar with while serving in the military. Revered, admired and respected,...the SX-28 and the later SX-28A were and still are among the great pre-WWII receiver creations.

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1945 Military-Commercial SX-28A Rack Mount Receiver, SN HA-11774

The military and some government users purchased the SX-28A in the rack mount configuration, with characteristic rack mount top dust cover and (though it can't be seen) bottom cover. Some are fungicide treated which sometimes leaves a red colored coating on solder joints and around tube sockets. The circuit is identical to the standard cabinet SX-28A though some of the rack mounted SX-28As had plexiglass windows in the dial covers. These receivers are different than the US Army Signal Corps AN/GRR-2 receiver in that they will have the standard audio output transformer and choke along with the Hallicrafters' power transformer. Additionally, these receivers have the dial string drive on the bandspread dial. Also, long handle toggle switches are used along with the metal cased S-meter. 

This receiver is owned by: KØDWC, Charles Cusick, Dayton, Nevada

  Identifying SX-28As that have "SX-28" on the Front Panel

From its introduction in early 1944 until the front panel designation change in September 1945, all SX-28A receivers are identified as "SX-28" - at least according to the front panel. As far as Hallicrafters was concerned, the designation "SX-28A" applied only to receivers that had the Hi-Q, Micro Set coils in the front-end. Nowadays, all Hallicrafters enthusiasts agree with this definition. However, there are several characteristics that can be used to identify an SX-28A without turning the receiver on it side to look at the coils thru the slots in the bottom cover. These are known as the SX-28A "indicator parts." They are not entirely reliable for ID but, generally, it's a quick way to tell from a distance what the receiver is. ALL SX-28A receivers will have webbed tuning and bandspread knobs, a heavily textured front panel, a clip-on louvered condenser box cover and a serial number prefix "HA." While all SX-28As have these parts, unfortunately we can't say that none of the SX-28s would have had these parts installed. It is known that some of the very late SX-28s were fitted with webbed knobs. Certainly, some of the late SX-28s have a louvered condenser box cover though it was mounted with screws (not clip-on.) It is known that the heavy-textured front panel also made its appearance prior to the introduction of the SX-28A. >>>

>>>  The changeover to these later parts seems to be on SX-28 serial numbers higher than H-180,000, or in late 1943. The change to "HA" prefixes began around January 1944 (possibly as early as December 1943) and seems to only predate the introduction of the SX-28A by a couple of months. This series of events would account for some late SN SX-28s that have webbed knobs (H-181958, HA-2126), louvered condenser cover (H-173611, H-174842, HA-2126) and heavy textured front panel (H-178848, H-181715, HA-2126.) Since these parts were incorporated into late SX-28 production, we can't be 100% sure just by looking at these parts if a receiver is an "A" or non "A."  Even the appearance of the "HA" prefix in the serial number is not a sure indicator. Three SX-28s have turned up with the "HA" prefix serial numbers (HA-2126 is one, the other two have not been confirmed.) These receivers have all of the SX-28A indicator parts (louvered condenser cover is screw mounted though) but the coils are the old SX-28 style and the RF box is the old SX-28 style. Though it is likely to change as more SX-28s are photographed, it does appear that for now the SX-28A exclusively uses the clip-on condenser box cover and does not have the auxiliary relay socket and will, of course, have the Hi-Q Micro Set coils. ONLY the Hi-Q Micro Set coils are the 100% sure indicator since they were the reason for the designation change. Fortunately, if it's really important to know in advance of purchase whether the receiver in question is an "A" or non-"A",  you can turn the receiver on its side and, if you've seen what the Hi-Q Micro Set coils look like, they are visible thru the openings of the bottom cover

Component Date Codes for Build Date Confirmation

There are three date-coded parts used in the pre-war SX-28 that provide specific information as to when the part was made. From that, one can certainly assume that the receiver was built later than that date. The audio output transformer is usually stamped (on top) with a numeral month and year, e.g., "2 Stc 41", or February, 1941 (the "STC" separating the month and year is the logo for Stancor.) The filter choke is also sometimes stamped in the same format, however use of a date code on this part seems to have been sporadic. These parts are only a source for early SX-28 models as, by early 1942, Stancor had eliminated the date code information. The bass choke is another part stamped with a date code. SX-28 SN H-119051, built 10-29-40, has a date-coded bass choke "10 Stc 40" showing that it is possible for newly arrived parts to be immediately used by production. The date coded bass choke disappeared about the same time as the dated coded filter choke. Photo right of the top of the bass choke showing the date code information. The logo is for Standard Transformer Corporation (Stancor.) 55-010 is the part number. 10 is the month and 40 is the year of manufacture. This bass choke is from SX-28 SN H-119051 (10-29-40.)

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On some SX-28A and GRR-2 models a date was ink-stamped on the back of the condenser box when (and if) the receiver was fungicide treated. A stenciled form was applied to the condenser box with all of the treatment information including the year. The actual date was rubber stamped in a space provided. Usually, the format is a small "month-day" - MAR 7, for example that was rubber stamped and then a larger, two numeral year, e.g. "45" for 1945, which was part of the stencil. The date coded MFP stencil provides an indication of when the receiver was built since it seems likely that Hallicrafters applied the MFP and stamped the receivers at that time. Normal production processes would have the MFP applied just before the receiver was completed on the production line. The next step would be going to final test. The MFP date should be within a day or so of the final date on the inspection tag that would have been included with the receiver when it shipped. Photo right is of the fungicide treatment stencil which is usually located on the back of the condenser box. The date of "45" is part of the stencil. The smeared rubber stamped date is "MAR 7." This stencil is on Military Rack Mount SX-28A SN HA-11774.

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Assigned Serial Numbers - August 1940 to June 1946

The following chart is based on observed serial numbers compared to dated inspection cards and date coded parts or date coded stamps on SX-28, SX-28A and AN/GRR-2 receivers. It is an approximation that takes into account the slow increase in production in last part of 1940, the dramatic increase in production through 1941 and into the first third of 1942, the drop in production during WWII (especially 1/44 thru 8/45) with the subsequent increase of civilian SX-28A production starting in September 1945 and running through the first part of 1946. Dated inspection card confirms H-116368 was assigned September 27, 1940 and another dated inspection card confirms HA-53513 (on S-40 receiver) was assigned on June 18, 1946.

Earliest SX-28 serial number encountered:  H-115251 (owned by K7MCG)

Latest SX-28 "H" prefix serial number encountered: H-181958 (seen on eBay)

Latest SX-28 serial number encountered: HA-2126 (seen on eBay)

Earliest SX-28A serial number encountered: HA-2278 [AN/GRR-2] - (WA1KPD )

Earliest SX-28A serial number with "SX-28A" on front panel: HA-25171 (owned by P. Rosen)

Latest SX-28A serial number without "A" on front panel: HA-27888 (owned by M. Kaplan)

Latest SX-28A serial number encountered: HA-53445 (owned by WØFB)

 

     MONTH/YR.                               SERIAL NO. RANGE

Aug 1940  to  Dec 1940 . . . . . . . . . . H-115,000    to    H-124,000

Jan 1941  to  Dec 1941  . . . . . . . . . .   H-124,000   to   H-145,500

Jan 1942  to  Dec 1942 . . . . . . . . . . . H-145,500    to   H-166,500

Jan 1943  to  Dec 1943 . . . . . H-166,500  to  H-183,000/HA-1000

Jan 1944  to  Dec 1944 . . . . . . . . . . . . HA-1000    to    HA-8,500

Jan 1945  to  Dec 1945 . . . . . . . . . . .  HA-8,500   to   HA 35,500

Jan 1946  to  June 1946 . . . . . . . . . . . HA-35,500   to   HA-55,500

 

 Serial Number Log

SX-28, SX-28A and AN/GRR-2 Receivers

 

In keeping with the tradition started with our DD-1 article of providing a log of known serial numbers for receivers, we are now providing the same resource for SX-28, SX-28A and AN/GRR-2 receivers. The serial numbers are sorted by date of manufacture (more-or-less chronologically) and by model type. Having an online source to reference your serial number will provide you with data as to approximate date of manufacture and general identification. If you have sent me your SX-28 serial number in the past and it is not in the log, please send it to me again and I'll make sure it is listed. When sending your serial numbers be sure to let me know the specific type of SX-28 or 28A receiver you have. Send your serial numbers to:

 WHRM - SX28 SERIAL NO. LOG

SX-28 Pre-war - 8/40 to 1/42:  H-115230(?), H-115251, H-115254, H-115270, H-115275, H-115290, H-115357, H-115410(FCC), H-115420, H-115850(FCC), H-116208, H-116223, H-116239, H116268, H-116293, H-116332, H-116362, H-116368*, H-116391, H-116418, H-116425, H-116877, H-118962, H-119039,  H-119051*, H-120672, H-120692, H-120728, H-120814(FCC), H-120864, H-124230, H-124389, H-124417, H-125569, H-127986*, H-128056, H-128095, H-128195,  H-130170, H-132850, H-136487, H-136508, H-139526, H-142268, H-142317, H-142467, H-142501 Other Military SX-28 or SX-28A Rack Mounts (not AN/GRR-2) - 4/42 to 9/45:  H-163132(HD), H-169129(HD),        H-169146(?HD ver in std cab), H-181853(RBY-1), H-181856(RBY-1), H-181862 (RBY-1), H-181943(RBY-1), HA-2215, HA-9667(28A), HA-9705(28A), HA-11774(R),
SX-28 WWII - 2/42 to 1/44:  H-151071(2/42civ), H-151071, H-151194 (2/42civ), H-151197*(2/42civ), H-151307*(2/42civ), H-151492, H-154424**, H-156776, H-158937, H-158997, H-159006, H-161034, H-162685, H-164727, H-164758, H-164784, H-164953, H-164996, H-165900, H-165949, H-166062, H-167025, H-167187**,  H-167827,  H-167872,  H-167990,  H-170655,  H-170912, H-171964 (RCF?), H-172184, H-172381, H-173611, H-173684, H-173791, H-173798, H-173858, H-173999, H-174190, H-174254, H-174256, H-174842, H-176307, H-176470, H-177313, H-177442, H-178848, H-180447, H-180455, H-180586, H-180715, H-181157, H-181159, H-181692, H-181715, H-181915, H-181958, H-181970, HA-2105, HA-2126, SX-28A civilian without "A" on panel - 8/45 to 9/45:  HA-22033, HA-22184, HA-22267, HA-22658, HA-22950, HA-23114, HA-23121, HA-23349, HA-23367, HA-23374, HA-25272,
HA-25562, HA-25583, HA-27742, HA-27755, HA-27808, HA-27852, HA-27888,

SX-28A WWII - 4/44 to 8/45:  HA-2385, HA-2686, HA-2963, HA-3088, HA-3107, HA-3124, HA-3160, HA-3168, HA-3447, HA-3595, HA-3660, HA-9049, HA-9266, HA-9276, HA-9374, HA-9446, HA-9459, HA-11084, HA- 11089, HA-11299, HA-11346, HA-11509, HA-11513, HA-11776 HA-12324, HA-18969

SX-28A with "A' on panel - 09/45 to 6/46:  HA-25171, HA-27748, HA-30916, HA-30940, HA-30941, HA-30942, HA-31028, HA-31195*, HA-31397, HA-31624, HA-31633, HA-31704, HA-31746, HA-31762, HA-31821, HA-31897, HA-35075, HA-36548, HA-36592 (Rogers-Majestic #5027,) HA-36796 (R-M #5037) HA-36886, HA-36968 (R-M #5011,) HA-53170, HA-53212, HA-53241, HA-53258, HA-53404, HA-53445,

AN/GRR-2 (Mil SX-28A) - 2/44: HA-2278, HA-2506, HA-2546, HA-2703, HA-2766

R-45/ARR-7 - 39, 732
* = Receiver has original dated inspection card        **=Incomplete Receiver         civ = sales to civilians up to 4/42            (FCC) = Built for FCC use

R = Rack mount receiver with proper dust cover         HD = Heavy-duty version of the military SX-28         

? = Questionable data or combination, unknown owner                            R-M = Rogers-Majestic Canada

 

Estimated Production Figures for the SX-28 & SX-28A

PRODUCTION BY SERIAL NUMBERS: By using the total quantity of serial numbers issued between August 1940 and March 1942, one has about 40,000 numbers. Assuming that SX-28s accounted for about 15% of the numbers assigned, one arrives at a quantity of 6,000 receivers. One has to consider that the SX-25, SX-24, S-20R, Sky Buddies and later the S-27, SX-32, etc., all went into the production serial number use. Small tube-count, inexpensive receivers were much better "sellers" than expensive sets like the SX-28 and accounted for a much larger percentage of production and serial number assignments. An interesting advertisement in August 1941 QST seems to confirm that the SX-28 did not account for a large percentage of orders. The advertisement is for "Bob Henry W9ARA" in Butler, MO, a major ham equipment dealer at that time, (later became Henry Radio.) It shows a telegram from Bill Halligan congratulating Bob Henry on the placing a very large order for Hallicrafters equipment on June 26, 1941. Of the 140 receivers ordered by "Bob Henry W9ARA" only 20 are SX-28s, or about 14%!

From April 1942 through January 1944, manufacture of SX-28 receivers was at a much lower rate than in the pre-war days. However, since many of the less expensive, pre-war Hallicrafters' receivers were now not part of production, the percentage of serial numbers issued to SX-28 receivers increased. It is probable that the ratio of assignment of serial numbers to SX-28s compared to other equipment increased. It is possible that between 30% and 40% of the assigned serial numbers went to SX-28s during this period. Serial numbers assigned during this period should run from H-155000 up to H-185000 and from HA-1000 up to HA-2000. If we assume that 35% of the serial numbers went for SX-28s with about 31,000 serial numbers issued during this period, this would account for about 10,850 SX-28s built between April 1942 and January 1944. This would bring the total SX-28 production to about 16,850 receivers, (6,000 pre-war SX-28s plus 10,850 built during the war for a total of 16,850 receivers.)   >>>

>>>   The use of HA serial numbers started slowly in 1944 and progressed through August 1945 at a slow, steady pace. It seems likely that SX-28A and AN/GRR-2 production was less than 2500 receivers since the "HA" prefix serial numbers were assigned to other receivers such as the S-36 and S-27 (and possibly others.) With the end of WWII in August 1945 and the return to amateur radio production in September, Hallicrafters assignment of "HA" serial numbers increased rapidly. Hallicrafters enthusiasts agree that SX-28A production was somewhat less than that of the SX-28 production. The SX-28A production started around February 1944 with serial numbers around HA-2500. Highest SX-28A serial numbers assigned in June of 1946 are nearing HA-54000. If the SX-28A accounted for an average of 20% of the assigned numbers that results in about 10,300 SX-28A receivers - a reasonable figure. Again, other Hallicrafters receivers were accounting for the remaining 80% of the serial number assignments, e.g., S-40, SX-25, S-38, S-36A, etc. Total SX-28 and SX-28A production should be around 27,150 receivers, (16,850 SX-28s plus 10,300 SX-28As.) However, in a post-war advertisement, Hallicrafters stated that over 50,000 SX-28 and SX-28A receivers had been produced. To achieve this quantity of receiver, nearly 40% of all serial numbers assigned between 1940 and 1946 would have been assigned to SX-28 and SX-28A receivers - not likely. A more reasonable production estimate, that seems to reflect how many SX-28s and SX-28As are encountered today, is around 16,850 SX-28s and 10,300 SX-28As for a total of 27,150 receivers produced.

 

CONTINUE TO PART 2

 

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