Navy Department - Bureau of Engineering
15KC to 600KC
Date: July 13, 1933
by: Henry Rogers WA7YBS
TRF with Tracking BFO Receiver - History
|Before WWI, the Navy published in their wireless books
that vacuum tubes were unreliable. Their detector of choice was a silicon mineral. After all, what
could go wrong with it?,...it was a "rock!" But, the Navy wanted better
performance and, when the SE-1420 was developed in 1918, that radio
receiver's ability to extract weak signals out of the ether and amplify
those signals to thunderous volume levels impressed the Navy Department.
Hundreds of SE-1420s and their variants were produced just after WWI
ended and well into the 1920s.
The superheterodyne offered the possibility of that consistent performance since many of its adjustments were somewhat "fixed" thus requiring the radioman to essentially just tune the dial and adjust the volume. Certainly the improved selectivity afforded by converting the incoming RF signal to an intermediate frequency for better control of the overall amplification was also attractive to the Navy. The first longwave superheterodyne produced for the Navy was the gigantic RAA-1 receiver. This 1931 receiver, weighed over 400 pounds and had four different, two-stage IF amplifiers and four different frequency BFOs selected by the band switches on both the tuner and the IF amplifier sections. It was a mammoth receiver that was as complex as it was expensive.
The Navy needed a receiver that was easier to maintain, easier to produce and was less expensive than the extravagant RAA. Some experimentation had been in the works to further develop the TRF receiver, that is, a receiver with several cascade RF amplifier stages ahead of a detector and several audio stages (no frequency conversion) into a communication receiver. >>>
>>> TRFs had been popular in the mid-1920s as AM BC radios and while most were rather anemic performers, the Neutrodyne TRF circuit provided outstanding reception.
National Company was likely the first to produce a TRF communication receiver that also featured a "tracking BFO" to allow CW reception. Their RIO and RIP medium wave receivers were part of that company's AGS family of receivers that had developed from a Department of Commerce contract for airport receivers. The RIO and RIP provided the necessary low frequency coverage required for the radio navigation systems that were being developed at the time. The RIO and RIP were produced in early 1933.
Whether the Navy was aware of National Company's medium wave receiver or whether the Navy had their own designs going on at approximately the same time, the Navy's TRF with Tracking BFO longwave receiver was the RAG. It tuned 15kc to 600kc and the matching RAH tuning 300kc to 23mc for medium and high frequency coverage. The contract to build these receivers was issued July 13, 1933 and the contractor was the unexpected Hygrade Sylvania Corporation. Prior to the RAG-RAH, nearly all Navy gear had been contracted to RCA.
Apparently the RAG and RAH were not exactly what the Navy wanted. Only one small contract was issued. The RAG receivers operated on batteries while the RAG-1 operated on a separate AC power supply. The RAH was similar in setup. Within a short time, RCA offered the Navy, the RAK and the RAL receivers. These two receivers are very similar in physical appearance to the RAG-RAH but they were a TRF with a regenerative detector circuit. Perhaps because of the Navy's well-known preference for RCA-gear, the RAG-RAH weren't ever ordered again BUT the RAK-RAL were produced for years and went through eight versions while being produced up through WWII. The RAK-RAL were excellent performers but the capabilities of the RAG-RAH are, for the present, unknown.
Not that the RAG was the end of the TRF and Tracking BFO concept. The Navy had RCA design the ultimate version of this type of circuit to be installed in a well-designed, robust package. That receiver was the RBA. Designed around 1940, the RBA takes the TRF-Tracking BFO concept to a point where there was almost no LF receiver produced that could equal its performance until at least a decade later. RBA receivers were still being used by the Navy two decades after WWII ended, proving that the TRF-Tracking BFO concept, when well-executed, was a top performing circuit when used on medium wave, low frequency and very low frequency.
|photo left: National Company had several
contracts with the Department of Commerce to provide receivers for
airport communications, starting with the RHM receiver in May of 1932.
The RIO shown to the left was the Medium Wave receiver that National supplied for Air-Ground
Navigation-Communication in early 1933. It was one of the first receivers to use the TRF with Tracking BFO circuit for LF reception.
Although simple in design, the RIO performance is first-rate. A separate
power supply was required.
photo right: The ultimate in TRF with Tracking BFO receivers, the Navy RBA receiver, in this case, the RBA-6. These "over-the-top" receivers supposedly cost the Navy $3000 each during WWII production. The Navy made up for the initial high cost though,...the RBA was such a great design with excellent performance, the Navy was still using them two decades after WWII ended. The RBA used a separate power supply and an armored interconnecting cable.
|Hygrade Sylvania Corporation
- In 1901, Frank Poor and an unknown partner started a small business
that rebuilt light bulbs. The bulbs were cut apart, the filament
replaced, the bulb evacuated and resealed and then the bulb was sold at
a price that was less than a newly-built bulb. The business was
initially located in Middletown, Massachusetts. It wasn't too long
before Frank Poor
bought out his partner, moved the business to Danvers, Massachusetts and
named the company "Bay State Lamp Company."
Soon, Frank's brothers joined him in his new business.
In 1909, the Poor brothers started the Hygrade Incandescent Lamp Company to replace their old lamp rebuilding company with one that built new bulbs. Their increased production of new lamps required a new and larger plant in 1916 along with a move to Salem, Massachusetts.
In Pennsylvania, the Novelty Incandescent Lamp Company was producing small lamps for various purposes and had been in business since 1906. In 1922, Bernard Erskine purchased the company and renamed it "Nilco Lamp Works." In 1924, Nilco formed Sylvania to build and sell radio tubes.
In 1931 Hygrade, Nilco and Sylvania merged together to form "Hygrade Sylvania Corporation" with Hygrade building and selling light bulbs and Sylvania building and selling radio tubes. Other electric products were added to production as the company continued and, in 1942, the company name was changed to "Sylvania Electric Products Inc."
In 1959, Sylvania was purchased by General Telephone and became Sylvania-GTE. In 1993, OSRAM purchased the company and, by 2017, a Chinese consortium called LEDVANCE owned Sylvania.
Model RAG-1 - Type CHS-46042 - Serial Number: 1
Circuit Description - The RAG-1 Type CHS-46042 is an eight tube, TRF receiver that also employs a tracking BFO the is adjusted to always be 1kc higher than the receiver's tuned frequency. Additionally, the RAG-1 uses a bias-controlled AVC that acts like a limiter to keep the receiver output from over-driving the operator's ear with unexpected strong signals or static bursts. An audio filter is selectable for wide-band (OFF position) or 450hz to 750hz or from 750hz to 1300hz. The tuning ranges are 15kc to 30kc for Range 1, 30kc to 85kc for Range 2, 85kc to 140kc for Range 3 and 140kc to 600kc for Range 4. The tuning dials are a 0-100 lower dial and a 0-10 upper dial with ten revolutions of the 0-100 lower dial showing from 0 to 10 on the upper dial. Sensitivity controls the cathode bias of the RF amplifiers and therefore the gain of the amplification ahead of the detector.
Tubes used are (3) 6D6 - RF Amplifers, (1) 76 - Detector, (1) 6D6 - BFO, (1) 76 - 1st Audio Amplifier, (1) 41 - Audio Output Amplifier, (1) 84 - AVC Limiter, (1) 80 - PS Rectifier. Voltage required is 6.3vac for the tube heaters and +180vdc for B+ (5.0 vac was required for the PS rectifier and was supplied by the PS power transformer.) The audio output impedance at the TEL jack is 600Z ohms. The audio output power is only 250mW implying that earphones were the intended reproducers to be used. Sensitivity is rated at an impressive 1uv to 4uv. Power Supply was identified as CHS-20032.
The OUTPUT meter measures the audio output level and has a scaling
switch that allows changing the meter full scale or turning the meter
off. The FILAMENT meter acts as an ON/OFF indicator and also measures
the tube heater voltage.
photo above: The RAG-1 in the shop. A temporary "close looking" bandswitch knob installed to test the band change actuation.
|RAG-1 SN: 1 - Condition at
Present - No doubt, SN:1 was not treated very well at one
time during its later life. Various descriptions of "dropped from the
deck onto the dry dock,..." or "down for the count and kicked in the
face,..." are some of the colorful descriptions of SN:1's present
condition by former owners. Obvious is the missing cabinet and the
missing bottom cover (it's possible that this receiver was mounted in a
marine console and that accounts for the missing cabinet.) Also apparent is the bend to the upper right
corner of the front panel. Additionally, the right side-rear-bottom of
the chassis has a severe impact "crunch" that has also resulted in some
damage to the components and mountings located under the chassis. On top
of the chassis there are damaged shield covers and other bent metal
problems. The input coaxial cable has been cut and it's input location
damaged. The power cable has also been cut. The OSC. TEST push button
has been removed and a cup washer-screw used to cover the hole. The
ON/OFF toggle switch is missing. The band switch knob is missing. The
front panel grab handles are missing.
It looks like most of SN:1's circuitry is still present. There are a few missing things but overall, it's mostly all there. That helps because one doesn't have to figure-out what goes where and how did this or that connect up. RAG-1 SN:1 was acquired on January 31st, 2020.
|Lack of Documentation Problem
- The RAG-1 is a rare receiver. Only a handful were built and very few,
if any others, survive. When the search began for a manual, a schematic
or even a vintage B&W photograph of the RAG-1, it became apparent that
these receivers were only used for a very short time. It probably wasn't
necessary to ever go beyond printing the initial number of manuals.
Since the receiver was not in service long, few photos exist (any?) and
probably nobody ever needed any repair information, thus very little, if
any, documentation has survived.
If you, the reader, knows of any RAG-1
information or documentation that's available
than what's in the "Catalog of Naval Equipment") let me know via this
photo left: Shows the top of the RAG-1 chassis. The gear that drives the tuning condenser is fibre. Note the "chopped" brown cloth-covered power cable. This is a shielded cable with six wires inside. This would be two wires for the AC power switch connection to the external power supply, two large gauge wires for the tube heaters, one wire for the +180vdc B+ and one wire for B-/chassis. Most likely, the tube filaments are floating and chassis connection was by way of a center-tap on the filament winding of the power transformer. The coaxial cable also is cut. There probably was an antenna input box mounted behind the tuning condenser that is missing. It may have had passive filters inside and a mechanical mounting for the coaxial cable.
Tubes right to left, 6D6, 76, 6D6, 6D6, 6D6 (has no shield cap.) Tubes rear vertical bottom to top 76, 41, empty socket - 84 tube is missing.
photo right: Shows some of the "crunch" damage done to the right side-rear-bottom of the chassis. Also, some of the damage to the various shielded covers. Note that the side panel is missing from this side of the receiver.
|photo left: Shows underneath the RAG-1 chassis.
Apparent is the damage to the components where the major chassis
"crunch" occurred. The
large circular components are coils that are wound like a solenoid.
There are some other components in that corner of the chassis that have
either broken or the mountings have broken.
photo right: Shows the bend to the front panel. Although this is probably going to be easy to straighten, it will require dismounting the front panel to do the job properly and without damage to the original paint.
|UPDATES: I plan on starting the RAG project as soon as it warms up around here. Mainly, this is because all of the work has to be performed in the shop and winter temperatures in the shop are usually in the thirties. At the latest, by March things have warmed up to the point where working out in the shop isn't quite so frigid. As significant progress is made on this rebuilding project, more additions to this article will be uploaded. This RAG-1 write-up will be like the RAA-3 write-up in that both are continuing logs that document the restoration or rebuilding process. Unlike the RAA-3, which has significant mechanical (cabinet) and electronic problems (tuner and IF/AF unit) still remaining, the RAG-1 rebuild will be almost all mechanical.|
|Feb 17, 2020 - Started a Detailed
Inspection - I pulled all
of the tubes. The Type-84 tube (AVC limiter) was missing but all others were present. All
of the tubes but one were USN types and a few had vintage repair or test
stickers. Of the tubes with stickers, all of the top-most stickers were
marked "Pearl Harbor Radio Laboratory" with places for test results.
Unfortunately, none of these stickers were dated. Two
tubes had enough of the next lower sticker showing to read "U.S.S.
WHITNEY" with test data. Some tubes had an even lower (older) sticker
and two of those had date stamps that could be read, 1937 and 1938. The "U.S.S.
WHITNEY" was a Destroyer Tender. These were repair ships that had many types of
ship repair shops onboard. Destroyer Tenders were usually
assigned to a flotilla of Destroyers and provided all types of emergency repairs and
refueling needs while at sea. These ships could also provide electrical power to
ships needing repair. Also, onboard desalination facilities could provide
showers and flushing needs for crews of the ship that was being repaired.
Also, berths were available for crews of ships being repaired, if
The radio shops of these types of ships generally could service and
repair most types of radio problems that would happen while at sea. They usually had a large stock of
The Pearl Harbor Radio Laboratory was a shore-based USN radio repair facility must have provided all levels of radio repairs. I haven't found any specific information about this facility but it probably was a pre-WWII operation.
The top cover was removed on the tuning condenser assembly for inspection. From observation of the neon lamp protection inside, it became apparent how the antenna coaxial cable was attached. A small feed-thru terminal provided the connection but it also looks like there was an additional small box (or maybe a bracket) mounted to the back of the condenser box. It looks like the coaxial cable was mounted there with the shield soldered to the outside and whatever was inside eventually connected the coaxial cable to the small feed-thru terminal and then to the neon lamp and the antenna input circuit. To have the cable shield soldered around the entire perimeter and to have that mount to an aluminum box there probably was a mechanical mounting of a brass feed-thru of some type.
Feb 18, 2020 - In preparation for front panel removal, I've started applying penetrating oil to the set screws on all of the knobs. This will be a continuing application everyday or so. When I actually start knob removal, I'll also use the application of heat from a soldering iron tip to have the heat directly onto the set screw. The expansion helps to loosen the set screw. The RAG-1 knob set screws used are the same type that were found in the RAA-3 knobs. These are a four-spline socket on an 8-32 screw. To remove these types of set screws required building a special tool since modern spline wrenches are six-spline for 8-32 size set screws. The tool worked on the RAA knobs so it should work here also.
Feb 26, 2020 - As usual, all set screws and knobs (dual set screws per knob) were removed easily except for one set screw in one knob. More penetrating oil and then heat applied didn't help on this knob (OUTPUT - ADD db.) The removal tool that was made for the RAA knobs worked perfectly so with close inspection it was obvious that the one set screw socket was "rounded." The only removal method that won't damage the knob will be drilling out the damaged set screw. Sometimes the drilled hole will allow the use of a screw extractor or a reverse flute drill. In this case, the reverse flute drill loosened the set screw enough that the knob could be removed. All of the other set screws were easily loosened and they weren't corroded or excessively tight. With the knobs removed now the front panel can be dismounted.
Chassis Inspection before Panel Dismounting - Stripped some of the cloth insulation off of the power cable and found it was a shielded cable with six wires inside. Two large gauge wires are for tube filaments, two orange wires are probably for the AC Power Switch, one red wire is probably B+ and the white/red wire is probably B-/Chassis. These wires will be traced out later to confirm the hook-up. Removed the two bottom shields from the RF box. Everything inside looks to be in very good condition with no corrosion. The multi-section band switch is in excellent condition. Slight bend on one shield can that's mounted on the inside of the chassis due to bending of the chassis. Not serious. One RF coil can shield on the top of the chassis has an odd rectangle hole that almost looks like it was deliberately "cut" out. There doesn't appear to be any damage to the components inside the can shield. Back under the chassis, I found one cut wire (very short) from the AC - DC terminal block that probably went to the AC power switch. No return wire could be found but it also may have been cut very short. One cut wire coming out of the RF box that looks like the B+ going in. Looks like this wire may have connected to the TEST OSC switch (which disabled the BFO by removing the oscillator feedback loop.) It appears that the SENSITIVITY control has been replaced sometime in the past. All wires that went to the TEST OSC switch (except the one from the RF box) are soldered to a 25w WW resistor that has its other end connected to chassis via a solder lug. This probably was done when the receiver was still operational as the mod looks somewhat professionally installed. Probably to eliminate the TEST OSC. function which seemed to be unnecessary anyway.
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