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 sensitivity. 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, or Tuned Radio Frequency receivers, had been popular in the mid-1920s as AM BC radios and while most were rather anemic performers, the Neutrodyne TRF circuit provided outstanding sensitivity and excellent reception.
National Company was likely the first to produce a commercial-military 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 its matching receiver, the RAH, tuned 300kc to 23mc for medium and high frequency coverage. The RAH actually had a couple of significant differences when compared to the RAG. The RAH had an extra RF amplifier stage bringing the total to four RF amplifiers using 6D6 tubes. The RAH's seven tuning ranges utilized plug-in coil assemblies that came in a storage case identified as CHS-47090. 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 (though both receivers can be battery operated.) 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 at least 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
commercial 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. The RIO shown is SN: 3.
photo right: The ultimate evolution of the TRF with Tracking BFO receiver design, 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 that is adjusted to always be 1kc higher than the receiver's tuned frequency. The tuning condenser gang that's closest to the front panel tunes the BFO, which is always operational as the RAG-1 is "primarily a CW receiver." The RAG-1 Sensitivity is controlled by varying the "grid bias" according to the USN Catalog description. Typically, the RF cathodes have a variable positive voltage that is derived from running the B+ through a divider network to reduce the bias voltage to a much lower level. The end of the divider is usually a "Sensitivity" potentiometer to chassis for adjustment of the bias voltage. After the triode detector stage extensive audio filtering stages are in the circuit which limit the response to about 1300hz. Another adjustable audio filter, called "AUDIO TUNING" has a feature the allows "peaking" the desired CW tone. There are two ranges selectable for 450hz to 750hz or from 750hz to 1300hz and a "wide band" position selected with the "OFF" position that removes the tunable audio filter from the circuit. The audio line has a bias-controlled AVC that acts like an output limiter to keep the receiver's audio output from over-driving the operator's ear with unexpected strong signals or static bursts. The AVC limiter tube is a full-wave rectifier that is on the audio line to chassis, acting something like a clipper limiter. The AVC LEVEL control sets the output level maximum by adjusting where the AVC rectifier tube begins to conduct the audio to chassis. Signal levels can't increase above setting of the AVC LEVEL control. 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.
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.
photo above: The RAG-1 "as and when" received. It's been in this condition for decades with a bent front panel and more serious damage to the chassis. A temporary "close looking" bandswitch knob was installed to test the band change actuation. It's amazing that the Filament meter has survived the front panel bend with no damage, yet the lower dial escutcheon glass is broken.
|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
have survived. The search for a manual began with the former
owners starting in 2007. Their postings on various Internet sights proved
fruitless even though several attempts were tried over many years. I'm
not sure if the CHS-46042 identification was ever used in these
searches. I've found that according to old Navy lists for documentation,
the receiver is listed as CHS-46042. However, I think the same lack of
information will result no matter what identification is used. The RAG-1
was used though WWII, so why is any information so elusive? It's apparent that
the contract was for a small quantity of these receivers. After all, it
was 1933. What were the demands on the Navy at that time? Most equipment
contracts were for small quantities and certainly the RAG was in that
category. It probably wasn't
ever necessary to go beyond printing the initial number of manuals.
However, the RAGs that were put into service apparently were used up
through WWII so there must be vintage photographs of radio rooms on
smaller, older ships where the RAG and RAH were installed. As to a
manual,...I'm sure one is out there somewhere,...it's just a matter
getting the requests out and having patience.
If you, the reader, knows of any RAG-1
information that's available other than what's in the "Catalog of Naval
Equipment", that would be schematics, manual, other documentation, or
even vintage B&W photos, let me know. Use this e-mail link:
RAG-1 CHS-46042 SN: 1 - Rebuild
|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. An unusually warm February has allowed work to start on the RAG-1.|
photo left: Shows the top of the RAG-1 chassis. Note the "chopped" brown cloth-covered power cable. This is a shielded cable with six wires inside. 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. 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 a selectable condenser or inductor (like the RAK receiver input) inside or it might have just been a mechanical mounting for the coaxial cable. According to the USN Catalog description the antenna input is tuned but that is probably the larger first gang of the five-section dual tuning condenser.
Tubes right to left, 6D6-BFO, 76-DET, 6D6-RF3, 6D6-RF2, 6D6-RF1 (has no shield cap.) Tubes rear vertical top to bottom 76-1stAF should be installed in empty socket, then the type 41-AF OUT. The lowest socket is for the type 84-AVC LIMITER but a type 76 was installed.
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 triangular shaped side panel is missing from this side of the receiver.
|photo left: Shows underneath the RAG-1 chassis.
Apparent is the damage to the component mountings where the major chassis
"crunch" occurred. The
large circular components are coils that are wound like solenoids and are
part of the audio filter circuitry. The mount is a fiber type material
that has "pulled out" of the chassis mounting screws. There are two of
these "breaks." The entire mount actually has four coils attached.
Luckily, only a couple of wires broke and these will be easy to repair. All of the components in this corner of the
will have to be dismounted to allow access for tools to straighten this
severe bend. Eventually a complete bottom cover will have to be
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. Further down this page are photos showing the "straightened" panel.
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 chassis with a long braided connection. The coaxial center conductor connected to the small feed-thru terminal and then to the neon lamp and the antenna input circuit. Since the coaxial cable shield is connected to the chassis the center conductor must be the only connection to the bracket or the box. The USN Catalog is specific about the input C being about 200pf (a typical 200ft shipboard end-fed wire) and that the antenna input is tuned. That might imply that the coax center conductor just connects to the feed-thru terminal on the back of the tuning condenser.
Feb 18, 2020 - Knob Removal
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 wasn't a spline anymore and was actually "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.
|Hamster Modification Found!
- Note the non-original Sensitivity pot (far left in photo with
two large gauge cables connected.) The value of this pot is 500K which
is far to high of a resistance for a variable-R positive cathode voltage gain control which should be more in the
1000 to 5000 ohm range to adjust a divider network that varies the level
of positive voltage on the RF amplifier cathodes. Each RF amp cathode
has original 3000 ohm fixed resistors on the cathodes as part of the
network to reduce the +180vdc B+ down to the low level needed for
positive cathode levels that in essence induce negative grid bias to
control the gain of each RF amplifier tube. When these large gauge wires (actually shielded cables)
were traced back it was found that they
connected to the first audio tube grid (type 76.) Also, adjacent to the
Sensitivity pot, note the wire wound
resistor and its connection of three wires on one end with the other
grounded. It appears that someone in the past has modified the RAG-1
Sensitivity control and changed it to be a Volume control and tied the
three RF amplifier cathodes to ground through the fixed
3000 ohm WW resistor in order to have a non-adjustable (fixed bias) Sensitivity
Note the red wire that exits the band switch area (routed over the tub capacitor.) This is the cathode connection to the BFO tube. This means the BFO has been deliberately disabled. Probably also why the TEST OSC switch was also removed.
It looks like someone in the past has tried to modify the RAG-1 to have a fixed level of sensitivity, to not have a functional BFO and to have a Volume control on the audio stages. Sounds like modifications to receive AM signals. But, for AM BC, only around 540kc to 600kc would be received. Any other AM function, such as MCW or ICW signals doesn't seem very likely as the motive for the modification. Also, reception of LW BC would seem unlikely. Like most old non-documented hamster modifications, the reasons are lost in the past and nowadays, in our effort to "restore to original," these modifications don't make any sense.
Finding a correct vintage 1000 to 5000 ohm potentiometer and returning the Sensitivity control to original and returning the BFO to functionality should hopefully be fairly routine. The RAK and the RBA receivers use a similar RF gain control design.
The photo to the left shows the band switch area after the two shields were removed. Note the antenna trimmer condenser at the right side of the photo. The shaft and coupler have been removed so the shields could be removed.
photo below left: Shows the cup washer and screw that replaced the OSC. TEST switch which originally was more than likely a push-button switch. Also, the ON/OFF switch is missing.
photo below right: This is a close-up of the hamster modification area showing the cut BFO tube cathode wire dangling, the three RF amplifier cathode wires connected to a wire wound resistor to chassis (for fixed sensitivity.) Note how the ground is achieved with the cup washer in front and a large flat washer and solder lug inside the chassis. The screw holes noticeable on the side wall of the chassis are for mounting the triangular side panel that supports the front panel (and is missing.) Note the front coil can and how it is slightly bent due to the chassis being bent. Note the links that allow selecting either AC or BAT operation. There are two wires from under the AC-BAT links that have been cut very short (wonder where they went.)
Chassis Inspection before Panel
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.
photo 1: There are two tuning condensers stacked one over the other. Note how the lower fibre gear is driven by the split-gear which is driven by the tuning shaft of the lower 1-100 dial. The lower fibre gear then drives the upper fiber gear and since these two gears are the same size and mesh, both the upper and lower tuning condensers are synchronized and tune simultaneously. The lower condenser is much larger than the upper condenser but the upper condenser also has trimmers for each section. The upper condenser sections appear to be connected in parallel with the lower condenser sections.
photo 2: Smaller tuning condenser. Note the bent brackets on the rear mounting plate. Note the first gang (rear most) of the tuning condenser and how this is much larger than the other gangs. This is the antenna tuning section for matching an approximate 200pf antenna load (175pf to 600pf range.)
Notice in all of the photos that show underneath the chassis that each solder joint has a dab of red paint. This is from Sylvania and was confirmation that the solder joint was visually inspected at the time of manufacture.
Feb 27, 2020 - Front
Panel Dismount -
This was actually easily accomplished. The panel is only mounted to the
chassis with twelve 10-32 hex head
screws. All screws threaded into large pem-nuts. The two meters were
dismounted in placed into plastic bags. The meter dismount was also easily
accomplished because the meter mounting screws threaded into the aluminum panel
with no nuts on the backside of the panel. There were split-ring lock washers under the screw
heads. All hardware was placed into plastic
bags. All bagged parts were then placed in a "banker's box" cardboard
box to keep all parts in the same location which eases the reassembly.
Cleaned the dust and dirt off of the top of the chassis for a closer
inspection. There doesn't seem to be any indication of rodents or other
contaminates. Aluminum shows no signs of corrosion. There are some
indications of light corrosion on the tuning condenser but it's a white
color powder-type of corrosion that seems to brush off easily. Three
brackets were bent on the tuning condenser divider plates. This was
probably caused by the fairly severe dent to the shield that covers the
condenser. The brackets were straightened by bending them back into the
correct position. Removed the two dial escutcheons. The lower escutcheon
had a broken glass that will have to be replaced. Cleaned the front panel to see the condition. It has
some scratches and a rectangular "tape" residue deposit but overall,
other than the bend, the panel is in reasonably good condition and
wouldn't benefit from any restoration other than straightening the bend.
Feb 29, 2020 - Panel Straightening - I used a 2 pound body hammer and lots of wooden spacers. I used heavy poster paper as padding to prevent marring the paint (any more than it already was.) There were two bends to the upper right of the panel. One bend was between the two most upper right panel screw mounting holes. The larger bend was more-or-less diagonally across the meter hole. These types of bends have to use wooden spacers to force the new bend (which corrects the unwanted bend) to occur at the proper place. Once the spacers are in place then the panel is tapped aggressively with the hammer (and padding is necessary) until the bend is about right. The small bend was straightened first and the large bend after that. Once the two major bends were straight, then the smaller, subtle bends along the edges and around the screw holes can be straighten. This requires using wooden blocks to direct the force of the hammer blow exactly where needed. I worked my way all around the panel edge to straighten minor bending that has happened because the receiver hasn't been in a cabinet to protect the panel edges. The main thing is to always use a heavy poster paper pad between the hammer and the front of the panel to protect the paint. When finished, the panel was cleaned with Glass Plus. It looks nice and straight but still has a lot of "patina of age" since the front panel paint is far from perfect (and the straightening process didn't add any "new patina.") Photo to the left shows the straightened panel setting in front of the RAG-1 chassis with the formerly bent area closest to the camera.
Chassis Next - The next step is to straighten the chassis. This is going to require substantial disassembly of the right-rear corner area of the chassis. Since there aren't any schematics or a manual available, I'll have to make a wiring diagram of the area as it's disassembled. As the components are dismounted it will become obvious as to what damage occurred to the mounts and other component damage because of the impact that caused the "crunch" chassis bending. Once the area is stripped of parts and there's access to the chassis corner, I'm going to see how much I can straighten the aluminum by using a 0.5" steel backing plates held in place and clamped together using large C clamps. This can impart tremendous pressure and should bend the aluminum back into its original position.
Mar 2, 2020 - Audio Bandpass Filter Solenoid Coil Mount and
Chassis Straightening - I dismounted the broken part of the
solenoid coil assembly from the chassis. The entire mount consists of three
pieces of 1" wide by .25" thick fiber material that forms an upside-down,
Screws are used to secure the pieces of the mount. To this assembly four
solenoid coils are mounted using long 10-32 screws and nuts.
At the base of this mount is a removable chassis and all of the audio solenoid coil wiring is
routed into this chassis. The input to this sub-chassis appears to be from the
tunable Audio Filter circuit and the output is to the grid of the first AF
amplifier tube (Type-76.) Only
three wires needed to be desoldered to isolate the audio filter chassis and then
it could be dismounted from the chassis. This dismounting was necessary
because the solenoid coil mount is actually screwed to the sub-chassis with the
screws that are under the sub-chassis. Once the audio filter sub-chassis was
out, then repair of the solenoid coil mounting system could be easily
I used a 0.5" thick piece of steel plate that measured about 3"x 8" as stiff (unbendable) backing material and used a very large C-clamp to pull the chassis bend back to somewhat straight. This afforded much more accessibility to the damaged area for easier removal of the audio filter chassis. There's no doubt that I'll have to dismount several other components both on top and underneath the chassis. These will be the parts that have been bent or "crunched." First to check that these parts are electrically undamaged and then to straighten the housing or the shield box. I won't be able to hammer-out the bend in the chassis for fear of doing other component damage by the severe vibration imparted by that method of "body work." I'll use the same sort of "clamp and bend" method along with "light hammer taps" to further straighten the chassis as this shouldn't cause any collateral damage.
|Mar 3, 2020 - Audio
Bandpass Filter Rebuild - Only three wires connect the Audio
Filter to the receiver circuitry. This sub-chassis is entirely passive
components consisting of six inductors and seven tub capacitors mounted
underneath the sub-chassis. Each inductor is about 3" in diameter. The
sub-chassis mounts under the main chassis with four ny-lock nuts that
thread onto chassis-mounted studs. Easy to remove the sub-chassis once
the "crunch" bend was straightened. Once dismounted all components and
the upside-down "U" mount are easy to work on. The fiber board mount
holding four inductors was broken in two places. These were repaired
using epoxy. Once the mount was fixed, then the "pulled out" terminals
were repaired and the coils connected back into the Audio BP Filter
circuit. The "pulled out" terminals were reattached by using multiple
"wraps" of 30 ga. wire through the eyelet and secure with solder. Once
the connecting wire was also resoldered, this repair method provided a
solid mechanical mounting. All of the connecting wire ends had to be
re-stripped and tinned so the solder joint would make a solid electrical
connection. To keep the joints looking original, I dabbed red paint on
the joints to finish up. I touched-up the fiber board end caps on
the inductors using black acrylic paint. This sub-chassis is now ready to re-install. But, now I have full
access to the "crunch" area of the main chassis and access to remove two
other bent parts, so, re-installation of the Audio BP Filter is "on hold"
until the other repairs are finished.
photo right: This is the Audio BP Filter out of the RAG-1 chassis after the rebuild. The rebuild consisted of epoxy repair of the broken upside-down "U" mount that holds four inductors. The left side vertical piece of the mount was also broken with the threaded inserts pulled out of the fiber material. Repaired with epoxy. Terminals were secured to the inductor end pieces and resoldered. Inductor fiber end pieces were "touched up" with black acrylic. Solder joints have been repainted red to conform with Sylvania's practice. It's hard to believe that this very large component's only function is as an audio bandpass filter,...but it is 1933 technology.
Mar 9, 2020 - Fixture Required - In looking at working under the chassis of the RAG-1 I've noticed that you really can't place the receiver upside-down on the bench because all of the weight would be on the tuning condenser structure. I have to build a jig to hold the RAG-1 upside-down. The easiest support would be three uprights at least 9" tall with some sort of base to keep the uprights in place. Using 3/4" plywood for a simple structure seems the easiest method of construction. The jig can also be used for the improvised arbor press to allow fixing the "dish" bend to the center of the chassis.
Mar 13, 2020 - Fixture Material - I bought the 3/4" plywood to make the fixture. Typical March weather in Nevada,...while February was unusually warm and dry, March has been very cold and snowy. Fixture building out in the shop is on hold until the weather improves.
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1909 - 1969
- 60 years of Radio Technology -
This website created and maintained by: Henry Rogers - Radio Boulevard, Western Historic Radio Museum © 1997/2020