Radio Boulevard
Western Historic Radio Museum

 

WWII Communication Equipment - Part 3

WWII Ally Radio Communications Equipment


includes:
 

Marconi/RAF ~ R1155 ~ The "Lancaster Bomber" Royal Air Force Receiver

Kingsley Radio Co. ~ AR7 ~ Australian Army "HRO Knock-off" Receiver

Marconi's Wireless Telegraph Co. ~ C.R. 300/1 ~ Royal Navy Receiver

Canadian Marconi Co. ~ CSR-5 ~ Royal Canadian Navy Receiver


featuring comprehensive write-ups with lots of photos



photo right: British radio enthusiast operating the RAF T1154 Transmitter and R1155 Receiver

 

WWII Ally Radio Communications Equipment


photo above
: R1155A sn:34471, appears to be a very original "A" version showing the three Jones connectors in the lower right corner of the panel (I do have the plugs for all three connectors.) All inputs and all outputs to and from the receiver go though these connectors. The "Speed" switch is not original and the left-side Jones plugs retaining post is missing on this receiver. Some of the nomenclature plates have the paint worn off from use. However, even very original looking receivers always seem to have some changes incorporated. At least this receiver had only minimal and reversible mods.

Marconi's Wireless Telegraph Company, Ltd. (British Marconi)

R1155  RAF Aircraft Receiver



During WWII, most large and medium British bombers were equipped with the combination receiver-transmitter known as the R1155/T1154. The combination is shown in the header photo above from the UK Radio Communications 2006 Equipment Guide. The R1155 receiver not only provided signal reception from 75kc up to 18mc, it also provided the radio operator or the navigator with received signal "direction finding" capabilities. An external "Right-Left crossed-needles" meters provided a Visual Indicator and allowed the operator to determine a signal's location relative to the aircraft's fuselage or direction of travel. Additionally, navigation by a "homing beacon" was also a feature of the receiver. Though originally a Marconi design, during WWII several different British companies built the R1155 receivers (EKCO, Plessey, Phillips, Gramophone Co-EMI, to name a few.) Many times the R1155 is now dubbed "the Lancaster Bomber receiver" from its service onboard AVRO Lancaster bombers during WWII but the R1155/T1154 was also used on Halifax bombers and Mosquito medium bombers and in many other types of British aircraft. Sometimes two R1155 receivers were present onboard certain types of aircraft. It depended on whether the navigator station had its own R1155 for DF/nav purposes or whether just the radioman had a receiver and relayed info to the navigator or to the pilot. The receiver was also used to a certain extent after WWII with some examples having service tags dating well-into the 1960s.

Circuit - The R1155 receiver incorporates ten tubes in its circuit however two tubes are exclusively for the "Right-Left" DF indicator circuit, one dual triode tube is for the R-L meter drive and one tube is a tuning-eye tube leaving six tubes to function as the receiver. All tubes are standard British WWII military types (VR99, VR100, VR101 and VR102 types) with optional civilian equivalents listed (and most can be substituted with USA tube equivalents since the tube sockets are standard US octal type though performance may vary somewhat when compared to using the specified tubes.)


 

Single preselection is used with a converter tube circuit and two 560kc IF amplifiers. Audio output is transformer coupled and is intended for a Hi-Z headset (5K output impedance.) All voltages to operate the R1155 are supplied through the T1154 transmitter. An interconnecting cable runs from the transmitter to the right-most Jones plug, P1, on the lower front panel of the receiver. The left-most of the Jones plugs is P3 which is for the loop antenna connection (there's a vari-C trimmer and optional fixed C inside this plug) and the center plug is P2 for the Visual Indicator connection (R-L meter.) All inputs and outputs to and from the R1155 are routed through these three Jones connectors. Voltages required are +6vdc tube heaters (parallel connection) and to compensate for 12vdc systems an external Type 47 Resistance Unit was installed or for 24vdc systems a Type 52 or 52A Resistance Unit was installed. The +230vdc B+ and a negative bias of around -30vdc were provided through the T1154 by one dynamotor-type system power unit (called a "rotary transformer" in the manual.) The "VOLUME" control operates as a sensitivity control when the AVC is off (furthest CCW position on Master Switch MS) and as an AF Gain control when AVC is selected. The BFO is turned on when HET is switched on. The small panel hole above the dial next to the METER AMPLITUDE control allows adjusting the HET oscillator frequency. The small panel hole to the right of the MS allows adjusting the loop antenna trimmer. All of the controls along the upper section of the front panel are for the direction finding operation. Receiver only controls are Band Change, MS, HET on/off, Volume and Tuning. The R1155 worked in conjunction with several auxiliary pieces of equipment that included the Visual Indicator Type 1, the Loop Antenna compass, the Antenna Switching panel Type J, Type 192 Mic/Tel panel. Sometimes the setup included two Visual Indicators at each station (radioman and navigator.) Up to three antennas could be connected to the R1155, the loop antenna, the sense antenna and the trailing wire antenna, depending on the service the receiver was going to perform (communication or navigation) and on what frequency the receiver was operating.

The "A" in R1155A indicates that MW filters are installed to eliminate broadcasting interference at the IF (560kc.) "B" indicated the receiver had additional filters for operating near radar systems. There were several designated internal options available running up to a "N" version. Most variations indicate SW (radar filters) and/or MW (AM-BC filters) internal filtering, construction material (aluminum or steel) and in some cases end use. Some versions were for mobile-land use, some were used in ground schools and there were two types for marine use (air-sea search-rescue aircraft.) There were several types of 230vac 50cps power supplies available for land use. Some R1155 receivers were built on steel chassis with steel front panels and steel shielding. These were probably for ground use or installations other than airborne - the steel receivers are noticeably much heavier than the aluminum receivers.


 

photo above: A very original example of a R1155B receiver with lots of "use patina." It appears to be virtually complete and all original although judging by the "mod plate" (modifications record - the metal tag to the right of the band switch) this receiver has had several "upgrades" installed over the years. "B" versions had internal filters for operation near radar in addition to the MW filters. Note the six-digit serial number indicating that production quantities of R1155 receivers was quite high. Also, note the dates on the various tags in this receiver,...1967,...this R1155 was in use for quite a long time after WWII. This example is fitted with the improved two-speed tuning knob. This receiver is also fitted with the "blocking plug" that has the "COMMUNICATION RECEIVER" tag on the front indicating this R1155B was used in a "dual receiver" set-up where the navigator had the DF R1155 and the radioman had this receiver and the DF abilities couldn't be used. This receiver also has the Jones plugs retaining strap installed.       

photo from: eBay UK

DF Controls - The R1155 used an external "cross-needle" Visual Indicator meter (actually two meters within the unit) to show visually if the airplane was on-course. First a beacon station was tuned in. Then the receiver was switched to "BALANCE" which connected an antenna coil into the circuit and METER BALANCE was adjusted for the two meter needles to be equally in the "crossed" position. The receiver was then switched to VISUAL and the loop antenna placed perpendicular with the fuselage and the airplane steered toward the beacon which showed the crossed-needles on the meter when on-course. The pilot would deviate his course slightly and if the crossed-needles moved off center-downward the beacon was behind the airplane. The pilot would turn around, the course aligned and then any deviation moved the needles off center-upwards, indicating the beacon was ahead. As the airplane approached the beacon the signal would get stronger and METER AMPLITUDE was adjusted to keep the crossed-needles near the center of the field. METER DEFLECTION HIGH-LOW changes the sensitivity of the meter depending on the signal strength of the beacon. Alternately, if a specific direction of an unknown signal was desired, then the receiver was switched to the "bi-directional" horizontal figure-8 position (loop antenna and sense antenna) which then allows the direction of the signal, as referenced to the loop's position relative to the airplane's fuselage and its direction of flight travel, to be determined. With the signal tuned, the loop antenna is rotated watching the TUNING INDICATOR (eye tube) looking for the minimum signal or a null. The loop is then rotated -90 degrees and the AURAL SENSE pushed to the right, if the signal is reduced in strength then the signal originates from the right side of the airplane. If the signal increases, then the loop is rotated +180 degrees, the AURAL SENSE pushed to the right and the signal should decrease again indicating the signal origin is to the right of the airplane. The reverse can also be determined by alternately pushing AURAL SENSE both L and R, which ever produces the lowest level signal is the correct direction of the signal origin. The SWITCH SPEED changes the multi-vibrator phase switching rate of the two loop antenna amplifiers, in essence, electronically (not physically) rotating the loop antenna 180 degrees at the speed of the multi-vibrator circuit selected. The speed settings are LOW 30hz for a voice beacon (like using an AM-BC station as a homing beacon) or up (high 80hz) for a CW or tone beacon.
RAF Modifications - It's common to find complete and original R1155 receivers that are missing V1,V2 and V9. When the radioman's receiver was paired in the airplane with a navigator's R1155, then these three tubes were removed from the radioman's receiver. These were the three main DF tubes and if the receiver was just to be used as a "receiver," V1,V2 and V9 were pulled to drop the tube heater current requirements (900ma drop, almost an amp.) The tube heaters are wired in parallel so pulling tubes that weren't needed wasn't a problem. Also, a dummy plug (called a "blocking plug") was inserted for the loop antenna cable and the Visual Indicator cable when the R1155 was just to be operated by the radioman.

Nowadays, if the missing tubes are going to be replaced, V1 and V2 are X66 tubes that are inexpensive and easy to find. V9 is a dual triode, VR102/BL63, of which the USA equivalent is the 6F8G. Audiophiles have driven the price of both the 6F8G and the VR102/BL63 into the stratosphere. Why? Because the 6F8G is the pre-WWII predecessor to the ubiquitous 6SN7 dual triode which seems to fascinate audiophiles. In the USA, it's probably easier (less expensive anyway) to find a 6F8G at about $20 to $50 (for used/tested good) rather than to try and compete with the audiophiles for a VR102/BL63 at over $100 a piece.

Amateur Modifications - Like the BC-348 here in the USA, there are a lot of surviving R1155 receivers in the UK today. But, also like the '348 in the US, a complete and all original R1155 is a rarity and difficult to find. The R1155 was available on the British surplus market for very low prices starting in the mid-to-late-1950s. And, like the hams in the USA with the BC-348, the British hams bought the R1155 as an inexpensive way to obtain a decent receiver and then "modified" the R1155 to suit their needs. Most often the direction finding circuits were entirely extracted from the receiver since they weren't going to be needed but the space they had occupied on the chassis was going to be needed for their ham mods. With the right side of the chassis nearly vacant, an AC power supply was generally built into the receiver. There were other mods that were published in the British ham magazines of the time that advocated even further destruction of the receiver's originality. The result is that today, like the BC-348 in the USA, very few "complete and original" R1155 receivers exist.

A Minimally Modified Example - Mods to SN:34471

SN:34471 appeared to be very good looking example that was complete and original, that is, until it was examined in detail. Here's a list of the types of mods that might be found in almost any R1155 receiver that seems to be "all original" and that assessment is based on using photographs or a cursory visual examination for the inspection process. Not that I'm complaining! This receiver was very easy to return to original.

1. V1 & V2 Grid Leads Mod - V1, V2 and V9 were missing which wasn't too surprising. A close look when installing a couple of X66 tubes for V1 and V2 revealed that the grid cap wires for these tubes were gone. Wire was "cut" from junction of C56 and R57.   New grid leads made with rubber insulated wire to correct.

2. The grid lead for V9 was still present but had been wrapped with friction tape to insulate.   Removed tape and installed grid lead on the 6F8G that was installed for the V9 function.

3. Trailing Ant Mod - R62 (static drain R) was disconnected from pin 2 of the P1 Jones-type receptacle. This resistor was in place to drain static build-up from the trailing wire antenna.   Resoldered R62 for originality.

4. HET OSC Mod - It was noted that a couple of non-original looking wires (bright orange and blue plastic insulation) exited the RF box on top of the chassis. Tracing the two wires revealed that it was a mod that parallel-connected an air variable with the HET ADJ condenser with a non-original air variable C mounted in the METER BALANCE position. This mod was to provide a front panel BFO control. This mod resulted in a missing R51 (a 20K linear taper pot) that was for the METER BALANCE circuit. Luckily, the three wires that were connected to R51were still present.   Desoldered orange and blue wires and removed. Removed non-original air variable C. Installed vintage 25K pot and connected original wires.

5. A non-vintage 18.2K WW resistor added to the switched B+ in series from HET switch to the BFO tube circuit. This may have been to reduce the BFO level (for weak CW stations) or it may have been to compensate for the addition of Mod #4. Removed WW resistor and reconnected original wire to HET switch.   >>>

>>>  6. V9 Mods - There appeared to be some modifications that were never completed involving V9. A small audio output transformer was mounted under the side rail. Only one end of the primary winding was connected to pin 3 of V9. There were no other connections to this transformer with the opposite end primary wire not being connected to anything. The secondary was shorted together with a jumper. Perhaps it was going to be used as a choke. The original wire from pin 3 to L26 had been cut and removed. R65, a 10K resistor, was disconnected from pin 5, one of the grid inputs on V9. The jumper wire between V9 cathodes, pin 4 to pin 8, had been cut.     Installed new wire with rubber insulation to replace missing pin 3 to L26 wire. Reconnected R65 and resoldered cathode jumper wire.

7. Multivibrator Speed Switch - wasn't an original component. Made in USA toggle switch.    Removed non-original switch and replaced with an original R1155 toggle switch.

8. Nomenclature Plates - I wondered about the gold color on the Band Change, MS, Logging Scale plates and the SN plate. I closely examined each and they are original. I believe the paint was worn off because these are the most used controls and the radioman was probably wearing heavy insulated gloves that tended to "scrub off" the paint and "polish" the base metal. I think the serial number plate is another matter. It appears original and was probably "over cleaned" during an earlier restoration.
 

Luckily, these mods to SN:34471 didn't remove very much of the original circuitry or too many original components. Return to the original circuit and configuration was easy to accomplish.

Original Example with Aluminum Construction

Top of the chassis on SN:34471. The construction is all aluminum. The cylinder that is mounted over the MW RF coils is the MW filter which is a wave trap network for 560kc. The two tubes on the far left are the loop amp/multivibrator tubes. Behind the tuning condenser are the RF amplifier and Converter tubes. In the shielded compartment is the BFO/AVC tube. The upper most tube to the right of the shielded compartment is the Detector, Meter Limiter and Audio Output tube. The next tube down is the R-L meter amplifier and to the right of it is the 2nd IF amplifier. The tube with the shield cap is the 1st IF amplifier tube. The horizontal, panel-mounted tube is the tuning eye tube.

Bottom of the chassis on the same receiver. Full shielding for the HF RF section and band switch which are within the aluminum shielded box. Note the right-angle gear drive for the band switch (actually easier to see in the lower photo.)

 

Modified Example with Steel Construction

This is the top of the chassis of SN:68154 showing how the steel construction appears. Note the corrosion on the cover of the BFO tube housing and the rusted area on the left rail. Where the chassis can be seen it has some spotting. This receiver has been severely modified. Note the Hammond power transformer upper left and below it the 5Y3GT and the filter choke. Also, compare this chassis to the one in the photo above (SN:34471) to note how many of the original components are missing. The large glass tube to the right of the BFO housing is the added 6F6 audio output tube.

Apparent is a strange yellowish corrosion on the steel shield over the band switch compartment. Compare this chassis photo to the one above to note how much of the original circuitry is gone. The transformer mounted upper center is the Lo-Z audio output transformer that provides an 8 ohm output from the 6F6 output stage.

 

A Ham "Extremely Modified" Example SN:68154

Here's a R1155 receiver that has had just about everything involving the DF circuits removed from it and even more done to the remaining circuits. Even the serial number identification plate doesn't match the receiver. What makes it unusual is that this receiver is the "steel construction" version so it wasn't used on aircraft but was a ground receiver.


photo above
: R1155A sn:68154 is typical of the majority of surviving receivers. Severely stripped of its DF circuitry and "input-output" Jones connectors to install an AC power supply. The actual identity of this receiver is questionable since its chassis and panel are steel making it either a D or E version. It's unknown why the "A" version tag is installed. The good thing about this receiver is that it was bargain-priced ($38+shipping.) Though its originality has suffered, this receiver has been somewhat resurrected and is operational as a receiver only.
To the left is R1155A, tagged as SN:68154. Like many R1155 "hamster'd" receivers, all of the DF circuits and components are gone, including the controls themselves. Additionally, the receiver's ID/SN plate shows the receiver is a R1155A but it's built on a steel chassis with a steel front panel and steel shielding. This receiver is actually either a R1155D or E, both of those versions used the steel construction. Since the DF section was "stripped out" it can't be determined if the MW filter was present or not (which, if present, would have indicated it was an E version.)

The Mod Rundown,...

1. Removal of all DF circuitry, wiring and components - All DF controls removed. MW filter removed (if this was an E version.) Much of the hardware was also removed and discarded. Most original knobs gone. 

2. Antenna input - This is a brown bakelite binding post terminal-type that was "hacked" into the upper right side of the panel.

3. MS (Master Switch) Relocation - Of note is the vacant MS area. The switch was moved to allow the installation of the power transformer which is located directly behind the panel where the switch had been. The MS was moved to the METER BALANCE (pot control removed) location (upper left side of the panel) and only two positions were wired - AVC and Manual Gain with BFO on.

4. Power Input Changes and Electrodynamic Speaker Intentions - The Jones connectors were entirely removed and an aluminum plate installed. The four pin tube socket had been intended for an electrodynamic speaker with the field coil doubling as the power supply filter choke. The AC power ON switch is the only original type R1155 toggle switch. SN:68154 was modified in Canada so the power transformer used for the AC power supply was a 115vac primary type built by Hammond. AC power cord exits out the front of the panel.

5. Lo-Z Audio Output with a Boost - With the VR102 dual triode R-L meter driver removed, a 6F6 audio output stage had been added at that location. A Lo-Z audio output transformer was added after the original Hi-Z audio transformer had been removed.

6. Logging Scale - The Fine Tuning logging scale was removed sometime in the past.

7. Cabinet Destruction - Two one inch diameter holes were punched in the top of the cabinet. Nine one inch diameter holes were punched in the right side of the cabinet. I suppose that those onboard AC power supplies and high power audio sections do get hot. 

Mod Makeover - I had to perform a few minor repairs to get the receiver operational but these were just small problems that had developed over the years of moving and storing and then shipping the receiver (from Arizona to Nevada.) The majority of the serious rework was correcting the mod-design flaws and basically making the mod changes a bit more professional-looking.

I replaced the amateur-looking raw aluminum subpanel in the lower right section of the main panel with a new black wrinkle subpanel. I also removed the old brown bakelite dual post antenna terminal and filled the non-original holes with epoxy and painted over to hide the fill. I added military-style Antenna-Gnd push terminals on the new sub-panel (although for a Brit receiver they should have had "A-E" and "E" engraving.) I added the red jewel pilot lamp because the R1155 has no visual indication that the power is on (the dial is not illuminated.) I replaced the 1920s-era phone jack with a single circuit phone jack with a toilet seat cover that's marked "Speaker 2nd Audio" - both jack and seat were out of the BC-342 junk box.

I eliminated the four pin tube socket and discarded the idea of using an electrodynamic speaker. I rebuilt the AC power supply to use a filter choke instead and to have the audio drive a PM speaker. The mod had used a 5Y4G rectifier tube and it was found to be defective. I rewired the socket to use a 5Y3GT which is much easier to find and physically smaller. The defective can-type multi-section electrolytic (not original) was removed to have room to install the filter choke. I then used two new axial-type electrolytics mounted under the chassis. I left the AC power cable exiting out the front because any other exit route would further destroy the already seriously damaged cabinet.   >>>

>>>  I had to leave the MS in the Meter Balance location since the power transformer prevented moving it back to its original location. I did move the HET wires from the MS and repurposed a vintage toggle switch to now separately operate the HET (BFO) from the correct location.

The "re-do" did require some rerouting of the "mod routed" wires. Many of the wires had rubber insulation which has a tendency of drying out and then falling off whenever the wire is flexed. I had to replace several wires that were in this condition. The dial cover was removed and thoroughly cleaned which improved the transparency of the original convex plastic. The dial scale was also cleaned which greatly improved the dial appearance. A new gasket was made for the mounting interface. Most of the vacant holes were fitted with control knobs even though all are "dummy knobs," that is, just for appearance. Since the receiver was far from original I painted-over the yellow hand-painted lettering.

Mechanically, the two-speed dial knob assembly needed a complete overhaul in order for it to function as intended. The smaller front knob is 1:1 "fast tuning" and the larger back knob is 1000:1 "extremely fine tuning." The conical drive wheels had been greased and the cork friction gasket was also greased. Needless to say, the drive wheels didn't move the reduction plate until all of the grease was removed and all surfaces thoroughly cleaned. This two-speed tuning knob was a constant source of problems when the receiver was in use during WWII probably because the reduction drive relied on friction only. By mid-WWII an improved replacement tuning knob was available. However, not many R1155s had the improved two-speed knob installed so this example does have the commonly encountered, older, problem-prone, original two-speed knob installed.

General Performance - Overall, the R1155 performance results will depend on the operator's expectations and experience with vintage gear, the operator's QTH and the antenna used. The R1155 is a capable receiver as far as sensitivity is concerned and a resonant or tuned antenna will allow excellent reception of most HF signals. Audio is for phones but SN:68154 had a 6F6 audio output stage added so it easily drives an 8Z loudspeaker. BFO provides enough carrier for either CW or SSB copy and the "extremely fine tuning" function allows easy tuning of those CW or SSB signals. The tuning eye tube only functions on AM signals. The IF bandwidth is fairly broad and not really adjustable. For its use on an aircraft during WWII, sometimes with the plane being shot at, narrow bandwidth would have been a disadvantage. If the radio op needed to change frequency under those conditions and was searching for a homing beacon signal, a broad IF would make finding such a signal easier. Also, at altitude the interior of the airplane was cold and the radio op wore flight gear that included insulated gloves which made any "fine tuning" nearly impossible (sometimes it was a "gloves off" operation performed as quickly as possible.) The lack of a crystal filter or other means to narrow the IF bandwidth isn't surprising. For what is essentially a "one RF amp, converter and two IF amps" receiver, the R1155 does a surprisingly good job. Though, if up against the BC-348 with its "2 RF amps, Mixer, LO, three IF amps and a Crystal Filter," the R1155 would probably come in second as a radio receiver in such a comparison.

The R1155's desirability nowadays probably isn't its performance as just a receiver. The original R1155, with its ability to DF with its associated rotatable loop antenna and sense antenna, its ability to drive an external R-L indicator meter and also perform adequately as a radio receiver make the "complete and original survivors" the most interesting and desirable versions. However, the majority of R1155s didn't make it past the hackers that, in their enthusiasm to perform yet another "surplus to ham radio conversion," have relegated most of these historic receivers to a "relic" status.


The photo above shows R1155 SN:68154 after reworking was completed. I think it looks a lot better than it did,...and now it functions quite well, but just as a radio receiver. In car collector parlance, one can think of SN:68154 as the "daily driver" - kinda beat and you don't care if it gets a scratch or two. Then SN:34471 is the "all original, only trailered to shows" example that looks good but might not run all that well.

 

Kingsley Radio Company, Melbourne, Australia - AR7

During WWII, both the Allies and the Axis copied the famous National HRO Receiver. The Axis copies were shown in a 50th Anniversary brochure that National published in 1964. Probably the "knock-off" that got the most use was the Kingsley AR7, built during WWII by Kingsley Radio Company of Melbourne, Australia. Kingsley submitted the design (probably around 1940) as the K/CR/11 but after the design was accepted, the receiver became the AR7. Though the AR7 uses a micrometer dial and plug-in coil sets, that's about as far as copying the National HRO went. The AR7 did use two RF amplifiers but uses a Converter stage instead of a separate LO and Mixer. Eight "American-type" tubes are used in the receiver and two in the power supply. Frequency coverage is 138kc up to 25mc using five plug-in coil sets. Two IF amplifiers are also used operating at 455kc. An S-meter amplifier circuit provides the user with a front panel Calibration control. The audio output is a single 6V6 to a dual impedance output transformer that provides 600 Z and 1750 Z impedances. A Crystal Filter is provided. All AR7s are rack mounted and came with a rack mounted power supply that operated on either 240vac or 12vdc. A rack mounted speaker was also included. Some receiver housings had four coil storage cubbies, two on each side of the receiver. Normally, the receiver was lowest in the table rack with the speaker in the middle and the power supply on top. The Australian Army referred to the AR7 as "Reception Set No.1" and sometimes had the panels painted green. Normally, the AR7 panel, since it was a stainless steel overlay, was left unpainted with the nomenclature slightly polished to improve readability.

After WWII, many AR7s were installed at various airports around Australia where they served as tower and air to ground receivers. Many were modified to have crystal controlled frequency reception with the LO coils removed from the coil set and a crystal controlled fixed frequency oscillator installed to allow specific frequency reception with no tuning. Some receivers also had the AVC modified while others had different scales installed on the S-meter. Most AR7s don't have the original audio output transformer as it seems this component was easily damaged. Banks of AR-7s could be found at various airport communications facilities and some tower installations would feature a fairly stock AR7 that could still be tuned. The photo to the left shows a typical Australian airport receiving station with a dozen AR7s setup in racks.

Today, many AR7 receivers are in dismal condition due to heavy use followed by indifferent storage. Most receivers are incomplete and don't have the original power supply or speaker panel. Many suffer from corrosion and most are non-functional unless they've been restored.

Performance of a functional AR7 is impressive. They are similar to HROs but do have their quirks. For instance, the micrometer dial tunes "backwards" when compared to the PW-D of the HRO. That is 500 on the AR-7 is the lowest frequency of the coil set installed while it's the highest frequency with an HRO. Also, the S-meter works "backwards" with FS being "0" and mechanical zero being "S-9." The ability to calibrate the S-meter for the particular coil set being used is a nice feature and not one that is found on the HRO. Coil sets are steel construction and very heavy while the HRO sets are all aluminum. With all of the use that the AR7 provided, both in WWII (and especially post-WWII) it obviously was a great performer and very stable. The AR7 shown above is functional and doesn't have too many modifications to it. Great audio, although it doesn't have the original audio output transformer but rather has the commonly installed replacement transformer made by Rola. Unfortunately, the Rola transformer only has a single 600 Z ohm winding for the audio output.

 

Marconi's Wireless Telegraph Company, Ltd.
The Marconi International Marine Communications Company, Ltd.
for the Royal Navy

Type C.R. 300/1  - VLF-LF-MW-SW Receiver - 15kc to 25mc

The C.R. 300 was one of the "square box" Marconi/Royal Navy receivers that grew out of the original C.R. 100 versions. The C.R. 300 receivers were built mostly towards the end of WWII in 1944. Many were installed on Flower-Class Corvettes that the Royal Navy used as escorts and protection for convoy shipping. Many of the Corvettes were built in Canada and served in the Royal Canadian Navy during WWII. Additionally, some Corvettes were sold to the USA under lend-lease and operated by the US Coast Guard during WWII.

The C.R. 300 had the widest continuous frequency coverage of any of the C.R.-Series receivers spanning 15kc up to 25mc. However, the price for the wide frequency coverage was the change from the double preselection used in the C.R. 100 Series to single preselection (only a single RF amplifier) and then the circuit complications caused by the need of a dual frequency IF section. There were two versions with the C.R. 300/1 having a 500kc crystal calibrator and the C.R. 300/2 having a 690kc crystal calibrator. The latter provided harmonics that fell within maritime frequency bands and there were calibration index markers on the tuning dial that indicated where those harmonics should be heard when the calibrator was on. Some versions of the C.R. 300 were built into early-1946.

The circuit is an eight tube, single preselection superheterodyne that tunes continuous from 15kc up to 25mc in eight bands. The slide rule tuning dial has an illuminated "rotating drum" that shows the selected band-in-use scaling when the band switch is actuated. The two non-illuminated scales within the circular bezel are logging scales for accurate frequency reset-ability. Two different IFs are employed with 98kc used on Band 1 and Band 4. The remaining bands use a 570kc IF (see Performance section for issues related to this IF.) Each IF shielded-can contains slug-tuned transformers (permeability tuned only with fixed C) for both 98kc on the bottom and 570kc on the top. Two IF amplifiers are used in the circuit with the frequency switching occurring via the band switch. Audio output drives an internal 5" Rola speaker (3.5Z ohm VC) that's located on the right side of the panel. Two phone jacks provide 60 ohm outputs for headsets although the manual clarifies that the 60 ohms is DCR and the impedance is actually 600Z ohms. These phone jacks also provide circuit switching that turns off the panel loudspeaker when a headset is plugged in. The large left side chassis connector (PS2) provides power input along with remote loudspeaker (3.5Z separate winding) and external 600Z headset output and the "desensitizing" remote switching access pin (remote switch used to connect pin to chassis to "desensitize" the receiver.) 

A separate power supply is used to operate the C.R. 300. The Type 889 Supply Unit can operate on 230vac @ 50hz, +220vdc, +110vdc and +24vdc. It looks like dual vibrators on the chassis but only one vibrator is used in the circuit for the DC operation with the other vibrator being a spare unit. An efficient 0Z4 gas-filled cold-cathode rectifier is used for +250vdc B+ supply (no rectifier filament required.) The receiver's tube heaters are in series-parallel and operate on 24 volts. If 24vac is used then one side of the heater supply is tied to chassis but not in the power supply, only at the receiver power input connector (PS2.) The receiver's power requirements are 24 volts @ 0.95A and +250vdc @ 60mA.


photo above
: Marconi C.R. 300/1 receiver SN:2388 from late-WWII. These receivers were mostly used onboard RN Flower-Class Corvettes. The C.R. 300 had the widest frequency coverage of the C.R.-Series Marconi receivers at 15kc up to 25mc in eight tuning ranges. The dual tuning knobs have the rear knob with more direct "fast tuning" ratio and the front knob is the "vernier" or "slow motion" frequency adjustment. The dial lock clamps the metal skirt of the rear tuning knob. The "OFF" position between PHONE and CW will turn off the B+ but leave the tube heaters on. It was provided for "warm-up" time or for front panel actuated standby. Two phone jacks are provided. These jacks also provide switching that turns off the panel loudspeaker when a headset is plugged in. The front panel loudspeaker is a five-inch diameter Rola PM type with a very large magnet. The VC Z is 3.5 ohms and the audio output to the loudspeaker is capable of producing up to 2 watts of power. By comparison, the Phones are 600Z ohms and are driven by about 500mw of audio. NOTE: Photo taken before clean-up.

Front panel controls are ON-OFF toggle switches for POWER, AGC and NL. The mode switch has PHONE-OFF-CW-CALIBRATE where the OFF position turns off the receiver B+ but keeps the tube heaters on. BANDCHANGE has eight positions. PASSBAND is W-wide, M-medium, N-narrow and F. F is a filter position that is extremely narrow primarily for use in the LF and VLF ranges. H.F. GAIN is the RF Gain control and L.F. GAIN is the AF Gain control. Behind the round cover (upper right of panel) is the "desensitizing adjustment" (a slotted-shaft pot) which is a remotely switched-in adjustment of the RF Gain that allows reducing the receiver sensitivity during transmitting. The desensitizing action works against chassis-ground and is accessed at the left side power input connector.

For emergency, when all power to the vacuum tubes is no longer available, a chassis-mounted, carborundum-type crystal detector can be connected into the RF/Ant coils and the RF amplifier tube grid bypassed. The output of the crystal detector is routed to the plate of the 6V6 audio output tube which essentially connects the crystal detector to the audio output transformer. The desired signals can then be tuned on the main dial (though only using the RF/Ant coils for frequency selection.) This detector was only for emergencies and it's sensitivity was very limited. Phones were usually necessary and mode of reception was either MCW or AM Voice.

There was an input shown as R.I.S. that stands for "Radar Interference Suppression" which was an external device that connected to the R.I.S. coaxial input (on the left side of the receiver chassis) and ultimately connected to the suppressor-grid of the RF amplifier tube. The R.I.S. device would block the radar pulse-rate interference if the particular ship happened to be equipped with radar.

The C.R. 300/1 SN:2388 shown appears to have a Noise Limiter that is actuated with a toggle switch labeled NL ON/NL OFF. However, the switch has no connections to it and there is no circuitry in the receiver for a Noise Limiter function. The nomenclature is "stenciled" and appears to possibly be from a RN Depot upgrade that wasn't completed. The data plate apparently was removed for the NL toggle switch hole. The C.R. 300 manual doesn't mention a NL upgrade but that's not really surprising. On the "Ben Nock G4BXD - British Military Wireless Museum" website, the Marconi C.R. 300 photographed and shown there appears to have the NL upgrade installed. That particular receiver doesn't have the stenciling but has the small "on-off" tag normally found with toggle switches. That receiver also has its original data plate installed. There are other photos on the Internet showing C.R. 300 receivers with the NL circuit installed.

photo left: Top of the chassis showing the tuner section on the right and the dual IF, det/agc and audio stages on the left. The shield-can and tube on the far lower left is for adjusting the 500kc calibration oscillator. The upper shield-can in the vertical row of four (has the red & blue dots) adjusts the BFO. In front of the BFO is the bandpass filter "F" assembly (has two compression trimmers.) The other five shield-cans are the dual IF transformers including the Mixer to 1st IF transformer on the Tuner chassis. The seven small chassis mounted cylinders are triple bypass capacitors. The Crystal Detector is next to the rear-most tuning condenser (Ant-RF tuning.)

Notes on Tubes Used - The original required tubes were,...RF Amp - ARTH2* (C.R. 300/1 version) or KTW61 (C.R. 300/2 version,) Converter - X66 or 6K8G, IF Amp (2) - KTW61, Det/AVC - DH63 or 6Q7G, BFO - KTW61, AF Output - 6V6G, Cal Osc - KTW61.

* There's some confusion (on my part) that the manual's tube list clearly shows multiple times that V1 is an ARTH2 in the C.R. 300/1 version. However, the ARTH2 is a mixer tube, a hexode-triode tube (like the X66 or 6K8,) while the manual's schematic clearly shows V1 as a pentode (like the KTW61.) My C.R. 300/1 has a KTW61 installed for V1 and it seems to work fine except the sensitivity begins to drop above 6mc (even after alignment.) The ARTH2 should work in the V1 position since the triode plate isn't connected to anything and the triode grid is tied to the hexode suppressor grid so the triode is effectively out of the circuit. I don't have an ARTH2 to try right now but when I do I'll perform a test and add the results here. ARTH2 tube ordered Oct 5, 2020

ARTH2 Update - Oct 9, 2020 - With the ARTH2 tube installed as V1 (RF Amplifier) in the C.R. 300/1 it was quickly observed that the receiver had noticeably increased reception gain, that is, louder signals. This increase in sensitivity was noticeable below about 6mc but became very obvious as the tuned frequency was increased. The usual drop in sensitivity starting around 6mc when using the KTW61 RF Amp tube didn't happen and sensitivity remained good up to 16mc (top of Band 7.) Signals were received on Band 8 but the sensitivity begins to drop off by about 18mc which is sort of expected with WWII vintage gear. With the ARTH2 RF amplifier, 40M signals are strong and 20M DX signals can be easily copied (and some 20M DX stations are even strong.) So, the ARTH2 is the correct tube as indicated in the manual and empirical testing shows that using the specified ARTH2 tube is very important for C.R. 300/1 sensitivity.

Substitution Tube Notes - In most applications a 6K7G tube can be substituted for the KTW61 although there might noticeable reduction in gain. 

The 6K8G in place of the X66 and the 6Q7G in place of the DH63 are recommended substitutes shown in the C.R. 300 manual. The 6V6G is original equipment.

A 6R7G tube can also be substituted for the DH63 if the 6Q7G isn't available. Specs aren't quite the same but it will function until either a DH63 or 6Q7G is found.

Due to the tube socket shroud for mounting the tube shield, the 6K8 and the 6Q7/6R7 or, if used, the 6K7, must all be "G" versions (older style "G" not the "GT" versions.) Metal and GT versions of these tubes use larger bases that won't fit through the opening of the shroud. The 6V6G was standard equipment so that socket doesn't have a shroud or tube shield and a 6V6GT can be used. 

photo right: Under the chassis showing the RF section above with the eight coils per band in the Ant/RF stage rear, Mixer stage middle and Oscillator forward. The small cylinders are trimmer capacitors for each coil and each coil L is adjusted with a slotted powdered-iron slug. Below are the IF, Det/AVC and audio output stages. The BFO and detector/AVC/1st AF amplifier stage are within the shielded compartment. The hole in the shield provides access to adjust the 98kc BFO. The date written in pencil on the cross divider is 3-10-46. This might be an assembly date or it might be an inspection date. It could also be a repair date. Most components are date coded in 1944.

 



photo above: The Marconi C.R. 300 lid badge. Note the serial number 2388. There are later badges that show both "C.R. 300/1" and "C.R. 300/2" so SN:2388, having a 500kc crystal calibrator, should be considered a "1" version however that's not what's on the badge. Maybe an early version of the "1."

Emergency Crystal Detector
 

To the right is a close-up of the Carborundum Crystal Detector that was for emergency use if ship's power was lost. The yellow sleeved lead is the grid cable that needed to be removed from the V1 RF amplifier tube grid cap and attached to the slotted screw standoff on the left side of the fiberboard which is the input to the crystal detector. The "cat's whisker" (which is more of a metal strap) was then moved over to contact the carborundum mineral that's at the tip of the crystal mount. Since carborundum detectors must be under some slight pressure to function, the springiness of the strap and the right side adjustments allow varying the pressure applied to the crystal. Pressure was adjusted for best sensitivity. The crystal output was internally connected to the 6V6 plate which shouldn't have B+ since there's no ship power. This tube plate connection was also the input to the AF output transformer allowing Phones to be used for reproducers. The receiver was then tuned (only the Ant/RF coils are in the circuit) for the desired frequency. The sensitivity of the crystal detector limited the reception to only strong signals that were MCW (modulated CW) or AM Voice. CW couldn't be demodulated with a crystal detector.

Refurbishment - Started Sept 12, 2020 - C.R. 300 SN:2388 was in very complete and very nice condition for a shipboard receiver. It was obviously completely neglected as far as any operation or maintenance for the past several decades. There were six or seven components that were replacements that appeared to be for minor repairs. These minor repairs probably took place in Canada since USA parts were used (some of the Corvettes were built and used by the Royal Canadian Navy.) Otherwise the receiver was original. The tube socket shroud had been removed from the detector/AVC tube to be able to install a metal 6Q7. Luckily, the shroud is mounted with screws and nuts. The NL ON-OFF switch was probably never mounted. There wasn't any circuitry for a NL although the panel was stenciled for the addition. The location of the NL switch hole required removal of the small data plate. I added a matching style toggle switch just to fill the hole.

The Type 889 Power Unit was a disaster. Many parts were missing. Many parts were broken. There was severe paint damage. The 0Z4 was replaced with a 5Y3GT (that substitution can't function correctly.) The power connection terminal block was hanging by a few wires and the mounting flanges were broken. No doubt, someone had spent considerable time trying to rebuild, modify, repair or do something to this Type 889 unit. Since it appears it was never really functional after the "hamstering" it never was able to power up the receiver. That was lucky since that has preserved the receiver from an amateur hack-job and that is probably why the receiver is more-or-less functional on almost all original parts. The Type 889 is covered in its own section further down this write-up.

I powered up the C.R. 300/1 using a Lambda 25 adjustable B+ supply set for the +250vdc and I used a 25.6vac 1A filament transformer for the tube heaters. I powered the filament transformer with a variac so I could have some adjustability for that voltage also. I used alligator clip test leads to connect power to the receiver by way of the large left side connector, PS2. 

Tuning Dial Rebuild - The tuning shaft operates a gearbox to drive the tuning condenser. The tuning shaft is coaxial with the inner shaft being a reduction drive. A pulley is mounted to the main tuning shaft that uses dial cord to drive the slide rule dial pointer. To access all of the dial drive parts it was necessary to remove the cabinet and the front panel. With the cabinet and panel removed, then the logging dial index can be removed which then allows the logging dials to be removed. The logging dials were cleaned with Glass Plus. The dial pulley is the inner-most unit on the tuning shaft. I had to loosen the pulley to access the dial cord. I noted that the spring-load for the dial cord was totally relaxed due to the dial cord having stretched over the years. I had to add a knot as a spacer to take up the slack. Once the dial cord was the correct length again, it was then routed as needed and the pulley and dial pointer adjusted to track mechanically. Then the logging dials were remounted and aligned. The dial drum was extremely dirty but responded well to Glass Plus for cleaning. I had to add a spacer on the left side of the dial drum mount to keep it centered and in calibration (the slide rule dial resolution is vague, the logging dial scales are used for accurate frequency reset-ability.) I used light grease to lube the dial pointer track, the ball bearings in the gearbox and applied machine oil into the coaxial tuning shaft. The anti-backlash split-gears were also lubricated. The end result was the tuning was now very smooth and light with no backlash or binding. The panel was cleaned and the dial window and the logging dial window (both plexiglass) were cleaned before remounting the panel.

Audio Problems - Although SN:2388 did basically function using "test bench" power, the loudspeaker audio level seemed to be somewhat less than expected. I had no output on the PHONES line and the remote speaker line was also very low in audio. I disassembled the front panel loudspeaker bracket that also doubled as a mount for the audio output transformer in order to have easy access to test the audio transformer windings. All audio output transformer windings tested okay except that when I desoldered the audio line from the transformer to the phone jacks (and external phones,) the DCR of the transformer pin 4 to pin 6 (chassis) changed from 1.0 ohm to around 330 ohms DC. With the "phones line" disconnected, I powered up the receiver and now had lots of audio on the loudspeaker line. 

Further isolation of the External Phones shielded cable from the Phones jacks back to the External Phones terminal on the side power connector made it obvious that there was an internal short. The shorted cable was almost entirely sleeved in yellow fabric lacquered tubing along with other wires and cables in its run from the front of the receiver chassis to the opposite side-rear. This sleeving made it impossible to remove the shorted cable without damaging the fabric tubing. I had almost decided to just leave the cable isolated and just not have an External Phones output but as I moved the shorted cable  I noticed a rough hole right through the yellow sleeve and through the black rubber sleeve that was covering the cable. This ragged hole was right inline with where one of the bottom cover mounting screws would be located. Obviously at sometime in the past someone had installed a screw that was "too long" with "too sharp of an end point" when mounting the bottom cover and this screw had penetrated the cable sleeve, the cable and the center conductor causing internal damage to the cable resulting in the short. The cable damage caused the short to still be present even after the screw was removed.

photo left: Inside dual IF transformer number 4 showing the upper transformer for 570kc and the lower transformer for 98kc.


photo above: Shows the side connectors. The large power connector is PS2. The upper left is Antenna Input. The upper right is the R.I.S. input. Lower left is the ground stud.

To repair the cable I first had to dismount the two phone jacks to have access to the connections. With the jacks in a good accessible position, I cut just the shield part of the cable just above the hole and then pulled the shield down towards the end. This revealed the insulation damage to the center wire which I then covered with a wrap of friction tape. Then the shield was pushed back to cover the tape and to be in contact the other end of the cut shield. I wrapped the shield joint with 32 gauge copper wire and then soldered the shields together. I then pushed the black rubber sleeve back in place covering the soldering job on the shield. I resoldered the cable wire end to the two phone jacks and remounted them to the front panel. I then reconnected the External Phones end of the cable to the side connector. A resistance check now showed 330 ohms DC which is the DCR of the "phones" winding of the audio transformer with no shorts to chassis.

Other minor problems discovered while doing the audio repair were a broken wire at a junction terminal board that was from the audio section of the receiver. The AGC toggle switch had broken both rivet heads that held the switch together. The switch worked but it was beginning to slightly spread apart. I pushed the rivets back in place and soldered small wires into the rivet ends to provide a fairly strong "head" to hold the switch together.

A quick power up test showed that the C.R. 300/1 now had plenty of audio. AM-BC stations only required the LF Gain to be advanced about 25%. So, the low audio problem was caused by a chassis short on the Phones line. Even though there are separate windings for the loudspeaker, the external loudspeaker and phones, the shorted phones winding was enough of a load on the audio transformer that it reduced the entire audio level. 

IF Alignment - IF is adjusted for 570kc using just the top slugs for peaking. The IF for Band 1 and Band 4 is 98kc and that is adjusted using the lower slugs that are accessed under the chassis. Although the manual suggests using an audio output meter, this can get kind of annoying since you have to have a loud enough signal for the audio level to show on the meter. I used the AGC line instead since the audio gain can be kept very low. Since the RF gain and AGC plus the signal level determine the AGC voltage level, adjusting all alignments for peak works fine. All of the RF and IF slugs have a small slot that requires a long (but fairly small tip) fiber blade screwdriver. Using a steel screwdriver will add to the total L and the adjusted setting will change once it's withdrawn from the IF coil barrel. Although the top adjustments are easy to access, the under-the-chassis adjustments are through holes in the chassis and you really do need a "long" fiber screwdriver to access these. Additionally, the slugs are coated with a white powdery lubricant that looks terrible but works great. None of the slugs were stuck or even hard to turn.

BFO is adjusted in a similar manner in that the upper adjustment is for 571kc and the lower adjustment is for 99kc, in other words, adjust the BFO to be 1kc above the IF. However, this was the adjustment for the Royal Navy when the receiver was primarily used for CW. Nowadays, a lot of listening will be to SSB stations. It is more advantageous to set the BFO for zero beat with the IF. That way when tuning you can select USB or LSB by where you tune the signal to demodulate, that is, either above or below the signal center frequency. >>>

>>>  The Calibration Oscillator also has a slug trimmer accessed from the top. My C.R. 300 being a "1" version, has a 500kc crystal within the coil shield can. The easiest method of adjustment is to tune in WWV at 5mc or 10mc, switch on the Calibration Oscillator. Use N for bandwidth and tune for peak. Then adjust the Cal slug for zero beat.

RF Tracking Alignment - RF alignment per the manual uses the logging dial scales for frequency settings. This assumes that the receiver was going to have an accurate conversion table that provided the radio op with the settings for specific frequencies. The manual does caution that the slide rule dial isn't all that accurate. However, most modern users aren't going to create a logging dial to frequency conversion table except for just a few stations or net frequencies. Therefore, I just used the slide rule dial as a reference and adjusted for reasonable tracking accuracy. The top end of the band capacitive trimmers are cylinder-types and adjust very easily. The low end adjustment are the lubricated slugs. It's very easy to align the front end since each coil is clearly identified in the manual drawings. 

Reworking the Type 889 Power Supply Unit


photo above: The Type 889 Power Supply Unit in its "as received" condition. The terminal board on top is how the 889 was "programmed" to operate on either DC inputs or 230vac input.

The Type 889 was is in very "rough" condition. Besides its sorry cosmetics it had been completely altered from original. All of the wiring for DC operation was removed and several of the DC components were removed. Both of the plug-in vibrators were gone. The switch that selects the input voltage operation was totally disconnected. Additional holes were cut into the front panel. The terminal block for connecting power input had one of the mounting flanges broken. The fuse block was completely missing. The wiring and soldering were worse than "amateur" in quality. Workmanship was the worst of "hamster" jobs. The mods made were non-functional (and never would have been functional.)

Electrical Inspection - I noted that the 5Y3 (a modification) filament was connected to the same power transformer winding as the pilot lamp. That should have proved exciting if the lamp was ever changed with the power on. It was necessary to isolate most of the circuitry from the power transformer and to apply voltage to the primary of the transformer to test the which windings were going to be required. Most of the windings that were for DC operation from the vibrator had been cut, so only the AC operation windings were connected. I used a variac to apply a controlled input AC voltage level. My first connection was per the schematic and resulted in the correct secondary voltages if operation was going to be on 240vac input. I noted that the actual modified wired connections for AC input were connected to different taps on the primary than original (per the schematic.) I applied AC voltage at these connections and the resulting secondary voltages appeared to be somewhat correct with 120vac input. That's not too surprising since the receiver did come from Canada. Some pseudo-technician in the past had utilized other taps on the power transformer primary winding that were originally for DC inputs via the vibrator that now weren't being used (probably the 110vdc input.) These connections worked out for the primary to have almost the correct ratio to the secondary windings for proper voltage outputs, however, the actual voltages with 120vac input were about 30% higher than specified. Other components tested were the plug-in triple filter capacitor that tested good. The chokes tested good. The four 2uf oil-filled caps checked good. What wasn't correct was the 5Y3 filament operating on the pilot lamp winding. If operated in this manner, there's no isolation of the B+ on the 5Y3 filament winding and B+ would be floating on the pilot lamp to chassis. A better choice would be to go back to the original 0Z4 rectifier.

Reworking the AC Power Supply - The solder used didn't look like SnPb (real tin-lead solder.) Either the solder was defective (some amalgam that didn't flow correctly) or the soldering iron used was too cold. In any event, the soldering for the modifications was a very poor quality with several being "cold solder joints." The same wire type was used for all of the modifications. Since nearly all of the wiring was so poorly done, I stripped out the AC portion of the chassis and started over. I used mostly NOS vintage stranded wire for the rework. I had to repair the wires from the power transformer to the rectifier plates (HV) and also the wires to the rectifier pins 2 and 7 which aren't used but are tie-points for the pilot lamp wiring (as original.) Pins 2 and 7 aren't used because I wired the power supply back to using a 0Z4 cold-cathode rectifier. That way the winding only operates the pilot lamp (as original.)

More Rework and Testing - Once the 889 was rewired it was given a "clip lead" test to see if everything functioned before the cosmetic work was started. As mentioned above, as wired and operated on 120vac, the output voltages were too high with the B+ running about +330vdc (should be +250vdc) and the heater voltage running about 33vac (should be 25vac.) Different taps on the transformer primary were measured for DCR and the next closest tap was tested but provided too low of voltages for output. However, when the power transformer was connected per the schematic for 230vac operation and that voltage level used as the input power, the output voltages were correct as specified in the manual at +250vdc for the B+ and 25vac for the tube heater supply. The only solution is to operate the C.R. 300 via the 889 on 230vac input, as designed. I have 230vac available out in the shop but not in the upstairs ham shack so I have to use a "step-up transformer" to have a 230vac power source available upstairs. Using the step-up transformer (which actually has an output of 244vac since our line is 122vac) produced +263vdc with a 65mA load for the B+. The tube heater supply was 25.9vac with no load and the pilot lamp was operating on 6.1vac. All voltages were pretty close to specs. Cosmetics - The front panel and the cabinet both required a total repaint. Additionally, the front panel had several non-original holes that had been hacked in over the years. I was a little hesitant to strip the front panel paint because of the silk screened nomenclature but about 80% of the silk screening was already missing so stripping the remaining paint didn't do that much damage. Fortunately, the Marconi tag was in good shape and removable. The non-original panel holes were filled with epoxy. Paint used was a Rustoleum product called "Granite Satin" which is pretty close to Marconi gray (just slightly darker.) I had to use a standard USN-style, WWII vintage fuse holder (didn't have anything like the original that was entirely missing.) I also had to use a different type of terminal block since the original one had a broken mounting flange (in fact, the terminal block used is gray rather than black.) The voltage input terminals on the block are now changed to just the 230vac input with Line-Line-Ground connections. The remaining three terminals provide monitoring access for the two lines for tube heaters and for the B+ line. When measuring the voltage outputs, for a correct reading, the receiver has to connected and operating to provide a load on the output voltages and to also provide the ground connection for the B minus line. Before painting the front panel, I metal-stamped "240 - 240 - 0 - 25 - 25 - 260" above the terminals to identify the voltage inputs with the left three being, L - L - G for 240vac input and the right three being Htr - Htr - B+ monitoring outputs. I also repositioned the Marconi data plate to be more visible above the power output connector. I also had to fabricate the bent metal piece that covers the terminal strip inputs.     Reassembly completed Oct. 4, 2020.
Power Cable Repair - The power cable only has four wires that actually connect to the 889. There are three other wires within the cable for remote phones, remote loudspeaker and remote receiver desensitizing. The cable appeared to be original with no indication that the receiver outputs were accessed by an accessory "pig-tail" cable the contained the remote outputs. Therefore, if the receiver outputs were needed, the end user had to make connections to the necessary terminals on the power connector inside the Type 889 and then route the needed wires out from there. The manual doesn't have any recommendation of how the remote phones, loudspeaker and desensitizing were accessed. Utilizing the power output connector of the 889 seems to be the easiest method (shielded cables should be used for these remote connections.)

There was some minor damage to the cable shield at one end where the shield had be cut which completely isolated that additional route for interconnecting chassis-ground between the receiver and the power supply. I had to repair the cracked insulation on two internal wires. Then wrap the wire bundle with a single layer of friction tape and then a single layer of electrician's tape. Next, a split section of RG-8U jacket was fitted over the wire bundle and then a short section of shield that was removed from some junk RG-8U was split and then fitted to make a shield "patch." The shield was soldered to each cut end of the original shield to form a continuous connection. Additionally, the connector has a tapered clamp the fits over the shield and provides a positive shield-to-connector contact. The patch was wrapped with electrician's tape to complete the repair.

Power ON Test - Before connecting the 889 to the receiver, the cable was tested for continuity and for shorts. The cable connectors are identical so it doesn't matter in which direction the cable is connected to either the 889 or the receiver. Since everything had been pre-tested individually in advance, the C.R. 300-1 powered up with no issues. The measured voltages while operating the receiver were +270vdc for the B+ and 23.9vac for the tube heaters, both within spec. The receiver operated the same as it had before when running on the Lambda and the AC transformer. I half expected some sort of noise from the 0Z4 tube but the receiver's audio was normal. I checked reception from 10mc down to 19kc (MSK station HOLT) with no problems encountered. Photo right shows the 889 after rebuild.   Oct 5, 2020

C.R. 300/1 Performance Details

This section contains a lot of information on the possibility of 570kc AM-BC stations interfering with the 570kc IF of the C.R. 300/1 receiver. This is a significant problem on Band 3 while listening at night. There's a lot of information presented on Wave Traps and resonant antennas as solutions. For amateur band operation, a resonant antenna will usually be all that's required. For NDB listening a wave trap is the easiest solution.   

The 570kc AM-BC to IF Leakage Problem on Band 3 - Actually using the C.R. 300 as a receiver in a vintage military amateur radio station today will depend on where in the spectrum you intend to operate, where your QTH is and when your operation is scheduled for. While the receiver is certainly sensitive and can respond to very weak signals there is a serious underlying issue with the 570kc IF on some bands. It's quite easy for AM-BC stations operating on 570kc to be strong enough that the receiver's IF will respond to the AM station along with the tuned incoming signal. The result is a heterodyne when tuning in signals and in some cases the AM station "beats" with the reception noise and produces a constant heterodyne (and sometimes even the offending station's audio modulation.) Band 1 and Band 4 use a 98kc IF and won't have this problem but the other six tuning ranges use 570kc and might have the problem. Listening or operating during the day is not too much of a problem unless there's a strong local 570kc AM station. Nighttime propagation however allows 570kc stations from fairly distant locations to possibly produce strong enough signals that the 570kc IF would respond to them. Band 3 (200kc to 500kc) is the most seriously affected band and the closer one tunes to 500kc, the stronger the heterodyne interference becomes. Fortunately, back in the day, for shipboard installations, 500kc emergency frequency monitoring would have been accomplished using the generous "overlap" provided by Band 4 which tunes from 350kc up to 1000kc employing the 98kc IF.    >>>    >>>  The selectivity of the Ant-RF stage will certainly help on the higher bands but it does depend on how strong the offending 570kc AM BC station's signal is. As a test, I loosely coupled a RF signal generator to the C.R. 300 and found that I could detect a 570kc heterodyne signal up to about 10mc BUT this only simulates the effect that a very strong local AM-BC station might have. Most types of receivers that used an IF that might have operated at a frequency that also had strong RF signals present employed wave traps within the receiver input circuitry. These wave traps were adjusted to the IF and effectively nulled that frequency at the Ant-RF stage but all other frequencies would have been passed unattenuated. However, the C.R. 300 doesn't have an internal IF wave trap so the designers might have intended for the receiver to use an external wave trap that was maybe part of the ship's antenna system. It's also possible that the ship's antenna system was resonant just for specific frequencies of operation or the antenna was "short" for 570kc and therefore non-resonant and also having a small capture area. At any rate, it's surprising that the C.R. 300 doesn't have an internal wave trap. 
Wave Traps - Since only Band 3 is significantly compromised by the AM-BC to IF leakage problem, a wave trap is probably the easiest effective solution. Additionally, the wave trap will be a benefit on Bands 5 and 6, if the offending 570kc AM-BC station is local. The wave trap is connected between the antenna feedline and the receiver antenna input. There are two ways to create the wave trap. A "parallel" LC network will present a very hi-Z at resonance and a lo-Z at all other frequencies. A "parallel" LC wave trap would be connected in series with the antenna input. A "series" LC network will present a lo-Z at resonance and a hi-Z at all other frequencies. A "series" LC wave trap is connected as a shunt from the antenna input to chassis ground. I've used a "series" LC network wave trap on the C.R. 300 with good results. The wave trap is tuned as follows,...with a signal generator connected to the receiver antenna input with the wave trap installed. The signal generator set to 570kc If Band 3 is switched to and tuned, it will be noted that as the receiver is tuned to the high end of the band, near 500kc, the SigGen to IF leakage is intensely strong. At this point, the wave trap is adjusted for minimum response (usually variable C and fixed L in the wave trap.) The hi-Q of wave trap will result in the "null" setting being very sharp and fairly deep.   >>> >>>  As a test, then the signal generator is disconnected from the antenna input of the receiver and the regular antenna connected to the receiver. Then the output level of the signal generator is increased to maximum and loosely coupled to the receiver, that is, no "direct connection" but with a short (~20") wire lead near the antenna input. On Band 3, at the high end of the receiver dial, the 570kc signal might be heard. If it is then carefully adjust the wave trap C for absolute minimum response. It should be possible to entirely null the SigGen to IF leakage.

On Bands 5, 6 and 7 for average strength interference (nighttime propagation interference,) using a resonant (or tuned) antenna for the specific frequency of interest will usually be all that's needed. A resonant dipole cut for 80M and fed with coax won't respond very well to 570kc but does respond very well to the 80M band. The same is true for a tuned antenna using open feed line. It's also possible to use the 570kc tuned wave trap in the antenna feedline along with the resonant antenna for maximum attenuation. If there's a local interfering 570kc AM station, the wave trap and resonant antenna might both be necessary, especially on 160M and possibly on 80M.

More on Band 3 Problems for NDB Listening - The random length, untuned end fed wire antenna is the most susceptible to AM-BC to IF leakage since this type of antenna will respond to almost everything in the EM spectrum. The larger the random length or untuned antenna is the more likely that the 570kc leakage into the IF will become a problem. However, as a rule, the further from the IF that the receiver's tuned frequency is, the more likely that the selectivity of the receiver's Ant-RF stage will reduce the AM-BC to IF leakage to a minimum.

Listening for NDBs will require using Band 3. Copy of NDB stations becomes more and more difficult as the tuning approaches 400kc. By 500kc the heterodyning is constant. MW DX reception only occurs at night which is also when the AM-BC propagation is best. Using just a wire antenna for Band 3 will produce rampant heterodynes during nighttime listening. I've found that the series LC network wave trap works quite well at reducing the AM-BC to IF leakage to an absolute minimum when used with an end fed wire type of antenna. Another possibility (which I haven't tried) would be a hi-Q remotely tuned loop antenna that would provide the selectivity needed and probably work quite well for receiving NDBs. Additionally, installing a wave trap in the feed line of the loop would provide maximum 570kc attenuation. A shielded-magnetic loop (like the Pixel Loop) is broadband and responds to the 570kc AM stations as well as to the other MW signals. I found that the Pixel Loop was just as bad as the wire antenna for allowing heterodyne interference. A wave trap is necessary with the Pixel Loop. In my set-up, I use a 135' "T" antenna that is basically just a wire feed line. Using just the antenna for nighttime Band 3 listening, heterodynes are easily detected and become a problem by 350kc. I use a Series LC wave trap connected as a shunt (antenna feed line to chassis ground) to effectively eliminate heterodyne interference for nighttime listening for NDBs using Band 3.

Using the C.R. 300/1 as a Amateur Vintage Military Radio Station Receiver - My amateur military radio operations are on 75M and are scheduled for mornings or late-afternoons. Also, there aren't any local 570kc AM stations in my area. This results in no detectible AM-BC to IF leakage interference when using the C.R. 300 as the station receiver on HF on 75M. I use a 135' tuned Inv Vee antenna fed with ladder line. No wave trap is necessary. If 630M operation is planned, luckily 472kc can easily be tuned on Band 4 where the 98kc IF eliminates the problem. 

As to the C.R. 300's signal reproduction, the audio response is somewhat better than communications grade especially on strong AM signals. Cabinet installation greatly improves the lower end audio reproduction. Although the top band (8) responds well to the signal generator, decent reception on this range would require an antenna with some gain. Band 7 and 20M reception would also benefit by using a yagi or quad. Note: At this time I'm using a KTW61 RF amplifier tube instead of the original ARTH2 tube. That might have an effect on the higher frequencies (Band 7 & 8) which do seem a bit insensitive when compared to Band 6 and lower. An ARTH2 tube and a DH63 tube have been ordered and an update on any performance changes will be added here. Oct. 5, 2020. UPDATE: Oct. 9, 2020 - Installing an ARTH2 tube as the RF amplifier does significantly improve sensitivity and the increase is especially apparent above 6mc. 40M signals are now strong and 20M DX signals are easy copy (and some are even strong.) Using 135' Tuned Inv-Vee antenna.  

The C.R. 300/1 will operate fine as a station receiver on 630M (use Band 4,) 160M, 80M and 40M ham bands. If you're using a tuned or resonant dipole for the antenna, you shouldn't experience any AM-BC to IF leakage. It's an interesting receiver to operate and virtually nobody seems to have ever heard of one being used as a ham station receiver. It's sensitive enough and the selectivity is very good. The audio response provides pleasing sounding AM signals at the panel speaker or a larger external loudspeaker can be used. I use the front panel PHONE-OFF-CW-CAL switch in OFF to turn off the B+ for standby when transmitting. The ART-13 transmitter being used has a vacuum antenna switch for receiver isolation during transmit. First "on the air" net use of the Marconi C.R. 300/1 was on Sept. 27, 2020. I didn't have the Type 889 finished so I powered the receiver using the Lambda 25 for +250vdc B+ and the 25.6vac transformer for tube heaters. The one hour long, 75M net was copied solid 100% using the C.R. 300/1. Operation of the C.R. 300 and Type 889 together "on the air" was the hour and a half long 75M net on Oct. 11, 2020. Copy was solid 100%. The ARTH2 RF amp tube had also been installed by that time.


photo above: The C.R. 300/1 and the Type 889 in operation. The 120vac to 240vac step-up transformer is on the floor behind the Type 889.

 

Canadian Marconi Company  -  CSR-5, CSR-5A

History - The Canadian Marconi Company started out in 1903 as The Marconi Wireless Telegraph Company of Canada. At first, the company was part of British Marconi but soon, with Canadian government encouragement, MWT of Canada became an independent company. By 1919, after the WWI wireless ban was lifted, MWT of Canada created Scientific Experimenter Ltd, in order to sell wireless ham equipment. By 1922, they were selling broadcast radios. By 1925, MWT of Canada had changed their name to Canadian Marconi Company and entered into a cross-licensing agreement with Canadian General Electric Co. Ltd, Canadian Westinghouse Co. Ltd and Northern Electric Co., Ltd to "protect" their manufacturing patents to the exclusion of other Canadian radio companies. At the same time in the USA the so-called "Radio Group" operated a similar "cross-licensing" arrangement headed by General Electric with Westinghouse, AT&T, United Fruit Company and RCA as the members. Around this same time, CMC became involved in radio broadcasting. During WWII, CMC grew as a company and produced communication equipment for the war effort. In 1953, the English Electric Co.,Ltd. purchased a controlling interest in CMC (50.6%.) Since that time, CMC has had a multitude of different controlling companies, different owners and many name changes.

The CSR-5 Receiver - In 1943, Canadian Marconi was contracted by the Royal Canadian Navy (RCN) to build a high quality receiver for their use onboard RCN ships. The RCA AR-88 had been approved for the Canadian military as the general purpose receiver but it wasn't specifically designed for use at sea (although it could easily do so.) The RCN wanted a "designed for sea use" receiver and wanted to do business with Canadian Marconi (even though RCA-Montreal built all of the AR-88LF receivers at that time.) The CSR-5 receivers were supposed to be ready mid-1943 but delays pushed delivery to either the end of 1943 or early 1944. Around 700 receivers had been ordered (and New Zealand wanted another 100 sent to them) so these receivers comprised the first of the CSR-5 receivers. Sometime in 1944, the CSR-5A was introduced. This version had several small changes inside and also to the exterior but basically the "A" was very similar to the earlier CSR-5. The CSR-5A was built up to 1945 with most of production occurring in 1944.


photo above: Training Radio Operators at RCN Communication School at HMCS Cornwallis, Nova Scotia in May, 1952. There were 53 radio training stations at the school each with a CSR-5 receiver.
photo from: Jerry Proc's CSR-5A webpage -  www.jproc.ca/marconi/csr5a.html

The total production quantity of CSR-5 and CSR-5A receivers wasn't particularly a large number,...CSR-5 authority Jerry Proc estimates that possibly 700 CSR-5 receivers were built and perhaps 1000 CSR-5A receivers were built (but he cautions that this is just an estimate based on known serial numbers and that the exact method of CSR-5/A serial number assignment is not really known.) My CSR-5 shown in the photos is Type 110930Z (table cabinet type) with the serial number "394."

The CSR-5 was used for several purposes, even though its intended primary use was supposed to be aboard ship. Shipboard use required extensive shielding in the receiver to allow its operation along side other equipment without causing interference or radiating the LO from the antenna and for the receiver's reception to not be interfered with by the operation of other shipboard equipment. The CSR-5 apparently met the <400pW LO to antenna requirement. But, the RCN found other uses for the CSR-5 such as surveillance and enemy signal intercept monitoring during WWII. Most CSR-5 receivers weren't installed onboard ships until the early 1950s. The later version CSR-5A was mostly built after the initial contract of CSR-5 receivers although it's possible that the production overlapped somewhat (probably mid-1944.) It's also possible that some CSR-5A receivers were built up into 1945 but the majority of receivers were built in 1944.

Design and Circuit - The CSR-5 receiver's frequency coverage was in two sections, 75kc to 530kc and 1.5mc to 30mc, in six bands. Each scale on the large illuminated dial was color coded. There are two known variations that swap the colors assigned to Bands B and A (might coincide with the CSR-5A introduction.) Also, on most dials the Mauve color (light purple,) usually assigned to Band B, is actually gray. The CSR-5A replaced some of the 6SK7 tubes with 6SG7 tubes (in the RF and IF) as the major change, however there were many other minor changes in the cabinet vents style, power connector orientation, dial scale index style, etc. Many of the earlier CSR-5 receivers were retrofitted with the 6SG7 tubes which may cause confusion as to the receiver's original designation. Additionally, the manufacturing silk-screen was not changed for the chassis, so many CSR-5A receivers will have hand-modified 6SK7 to 6SG7 tube identification (rubber stamped ink usually but sometimes hand-written will be encountered.) When installed onboard ships, a dual shock mount system attached to each side of the cabinet. The two shock feet on each side were mounted to an angle bracket that was bolted to the lower part of each side of the cabinet.

The CSR-5 has eleven tubes in the receiver with two RF amplifiers, Mixer (also provides Xtal Osc function,) LO (9002 miniature tube,) two 575kc IF amplifiers (dual wave traps are in-circuit to prevent IF interference,) Crystal Filter (Selectivity positions 3 and 4) AVC/NL, Det/1AF, AF output and Voltage Regulator. The RF Gain control is a stepped attenuator type with an average of about 10db of change for each step. AF output is 2 watts into a 10K Z load for loudspeaker, 500 ohms Z line audio and both Hi-Z (5000Z+) and Lo-Z 'phones (up to 1000Z.) The "Crystal" socket and "Crystal-IN" allowed drift-free operation though a crystal-controlled local oscillator function but the receiver still had to be tuned to the intended receive frequency for the RF and Mixer stages to be "in tune." There was a Panoramic Adaptor connection provided on the chassis (screw terminal connection.) Since a panoramic adaptor could be used with the receiver, a carrier level meter wasn't required. The panoramic adaptor had to have an input frequency range that would accept 575kc but the manual never specified where to find a manufactured panoramic adaptor with that input frequency capability. Most panoramic adaptors had inputs that ranged from 400kc up to 500kc since most receivers used the standard 455kc IF. More specifically, the US Navy receivers RBB, RBC used a 400kc IF, the Signal Corps Hammarlund Super Pro used a 465kc IF and the US Navy National HRO (RBJ) used a 456kc IF. Although the CSR-5 has the capability to allow panoramic adaptor use, it's unlikely it was ever historically set-up that way.
 

photo right: Chassis top of CSR-5 sn:394


The CSR-5 requires a separate power supply. The VP-3 provided 12vac Filament (series/parallel connections for all 6.3vac tubes except the BFO and LO that use series resistive loads) and +250vdc B+ with an input requirement of either 12vdc (vibrator PS) or 115/230vac. An AC only power supply was also available and designated as the WE-11. Two 6X5 rectifiers are used in the VP-3 bringing the receiver's total tube count to 13 tubes.

Shown in the photo to the left is the VP-3 power supply. The two terminals with hex nuts installed are for the 12vdc input if the vibrator supply is desired. Internally, to change from AC operation to DC operation, first the AC plug has to be inserted into the dual slotted opening on the chassis next to the rectifier tube. This actuates a switch under the chassis, S-2. Then the six pin "option plug - PL-1" is removed from the "AC" socket and installed into the "DC" socket on the chassis. Then the toggle switch on top of the chassis is flipped to "DC." This toggle switch usually has a guard that has to be removed to actuate the toggle switch. Next, connect 12vdc to the + and - terminals and make sure a four-pin vibrator (12vdc) is in the socket. My VP-3 is set up for AC operation. The outputs to the receiver are two cables with Jones plug connectors. I've wrapped the two cables so as to handle like a single large cable. At the receiver-end, the cable has a single Jones plug (female) that mates with the Jones plug (male) on the rear apron of the receiver chassis. This is a modification (I think) from dual Jones connectors to a single larger Jones connector.

 


photo left: VP-3 Power Supply for the CSR-5 Receiver

Two types of loudspeakers were available for the CSR-5. A table cabinet speaker and a dual rack mount speaker. The table speaker was an eight inch diameter speaker with a 10,000Z ohm to 8Z ohm matching transformer. The dual rack mount speaker is virtually unknown although it is pictured in the manual. It's not specified in the manual if the speakers had individual inputs (most probable) or if the speakers were connected in parallel with a single input (unlikely.) The photo to the right shows two CSR-5A receivers installed onboard the RCN ship Athabaskan in the early 1950s. Note the Marconi loudspeakers mounted on the bulkhead above the receivers. These are the standard table speakers that were available for the CSR-5/A receivers. Also, note in this installation how the shock mount feet are mounted directly to the underneath of the cabinet on the receivers. This certainly simplifies the shock mount installation and reduced the width of the receiver when compared to the width if the standard shock mount brackets were installed. The receiver in the center of the equipment is a version of the RAK made by RCA-Montreal, the TE236, that was used to monitor 500kc (although it tunes 15kc to 600kc.)

The CSR-5 and 5A are found in a variety of different paint colors with the most common original color found being a wrinkle finish, light cream color with a slight greenish tint. Smooth finish gloss medium gray is found when the receiver was part of the CM-11 transmitter-receiver rack system. Light brownish-gray (beige) wrinkle finish is common in the stand-alone receivers. Many different shades of gray are often encountered and occasionally black wrinkle finish might be seen. Dark bluish-gray was also used at times. Along with the different colors, shades and texture variations will be found both black or white nomenclature (depending on the panel color used.) Some paint combinations are original but most of the really unusual variations might be from post-WWII military repaint jobs but, more often are from recent amateur restoration attempts where authenticity wasn't a primary consideration. Contemporary restorations involving repainting have to deal with the silk-screened nomenclature which usually complicates any refinishing plans. My CSR-5 SN:394 doesn't have the "Marconi" cursive script along with "CANADA  CSR-5" in block letters silk-screened on the center area of the escutcheon. Originally, the CSR-5 did have the silk-screened lettering on the dial escutcheon but, when receivers were refinished by RCN depots in the 1950s and 60s, many escutcheons were painted and usually lettering was silk-screened. But, if the silk-screening was done at a depot, whether the receiver was a CSR-5 or a CSR-5A, the escutcheon was (always?) screened as "CSR-5A." All "block letters" were used without the "Marconi" cursive script. I didn't have any method to do an authentic lettering job and, since there seem to be some "non-lettered" RCN depot precedents, I left my escutcheon without lettering.


photo above: CSR-5A receivers aboard the RCN ship Athabaskan in 1952.  photo from www.jproc.ca

Re-Restoration - I obtained CSR-5 SN:394 around 2010 from fellow ham and collector NU6AM. The receiver had been cosmetically restored earlier by K6DGH, who had had the cabinet and panel powder-coated in a brownish-gray color that was substantially darker than the beige wrinkle that has been found on some CSR-5 receivers. NU6AM, Jim, had obtained the receiver in "unfinished" condition and needing some electronic work. Jim did a "re-cap" job that was not particularly sympathetic using "yellow jackets" and IC electrolytics. I believe that Jim wasn't too impressed with the finished CSR-5 performance and that's why he eventually sold it to me. At that time, I repainted the dial escutcheon black wrinkle finish because it had been flat black with white rub-on "block" letters that weren't original (and were obviously an amateur application.) I also made new cables for the power supply to receiver hook-up since the cables that had been used were made from very small gauge wires that didn't look sufficient to provide the power supply connections without a substantial voltage drop. I didn't do anything else to the receiver except use it for a short time and then put it on display in the Western Historic Radio Museum in Virginia City, Nevada.

Fast-forward to 2020,...I had closed WHRM in 2012 and moved to Dayton, Nevada. The CSR-5 had been stored from the past seven and a half years in my "cool room" in the shop in Dayton (a well-insulated storage room where the temp extremes are from 30F to maybe 75F.) I had just recently gone through a Marconi R1155 and its impressive multi-colored arc'd dial got me interested in that large multi-colored dial on the Canadian Marconi receiver. I had to extract it from the "cool room" and bring it to the upstairs radio repair location to take a better look at it and reacquaint myself with how it performed. The CSR-5 still worked as it had,...okay, but seeming like it could do much better. The tubes tested okay but the band switch was very erratic and needed cleaning with DeOxit and a small brush. All controls were given the DeOxit treatment. The split-gears in the tuning gear box were stuck together so a flush with WD-40 loosened them and that eliminated the backlash. The BFO and NL toggle switches seemed non-functional but a "spray down the barrel" with DeOxit cleared up the internal oxidation that was causing the problem. I was pretty sure that neither of the former owners had never performed an alignment. If a full IF/RF alignment hasn't been performed, doing one will certainly improve performance significantly. The IF adjustments and RF L adjustments all have lock-nuts so be sure to loosen when adjusting and snug-up when finished (while watching the output meter to verify that the adjustment doesn't change with lock-nut tightening.) With this CSR-5, all of the alignment adjustments were far enough out that quite a bit of improvement was gained by the procedure, especially the tracking which now easily meets the 0.5% accuracy tolerance specification.

I checked the "problem C123" location since this receiver was a CSR-5 with a serial number lower that 816. C123 was entirely missing. It's not a critical component but it should be present to take care of high frequency transients and protect the output transformer primary. Also noted were two of the connections to T4 (output xmfr) weren't soldered and several others were "tack soldered" connections. All connections to T4 were completely redone. The RF Gain control connection to chassis needed to be redone. I shunted the "re-radiation resistor" in the antenna connection (it had been changed from original 1K to a 10 ohm carbon composition resistor, but I shunted it anyway.) That pretty much took care of the electro-mechanical rework.

Cosmetically, K6DGH had mounted the CSR-5 data plate on the front panel. It should have been mounted to the top lid of the cabinet (as originally done.) The data plate was installed on the front panel with drive pins which required using a C-clamp and spacer to push the pins out of the panel. I remounted the data plate to the cabinet lid (original holes with screws and nuts hardware already present.) The non-original holes in the front panel were filled with epoxy and then touched-up with custom matched paint. It's worth noting that the data plate, while for a CSR-5 Type 110930Z, is SN:682, yet stamped on each side and on the rear chassis apron of the receiver is "394" which I assume is the actual serial number. Cabinet swapping during RCN depot repair might account for the discrepancy but a later collector "parts swapping" is more believable. That would be that the data plate isn't original to the receiver and cabinet. At any rate, I consider "394" as the actual serial number of this CSR-5.

All of the front panel screws were fairly new but non-original type, black phillips head screws. The original screws used were round head slotted machine screws. I replaced all of the screws with the correct types. I wanted to set up the CSR-5 with the shock mounts. I found a set of shock mount feet (Barry mounts) on eBay and purchased the 1"x 1" mild steel angle locally. The angle brackets were built and then painted wrinkle finish using VHT Gray Wrinkle Finish. The VHT Gray has a lot of brown in the mix and it was a close match,...well, maybe one shade more towards gray but close enough. I've set CSR-5 SN:394 up as the station receiver with an ART-13A transmitter. Maybe not an original combination but both pieces are WWII veterans and work together nicely.

photo right: Serial number "394" stamped into chassis's rear left-side

Canadian Marconi Company CSR-5  sn:394  from 1944
 

Performance - Overall, the CSR-5 is a good performer that is fully capable of operating as a station receiver in an amateur vintage military radio set up. The receiver is robustly-built and that provides excellent stability which is helped by the VR tube and filament loads on the LO and BFO tubes resulting in very little drift after a short warm-up. Sensitivity is competitive, especially if the receiver has been "gone through" and has had a complete IF/RF alignment and is used with a full-size, resonant (or tuned) antenna. Selectivity is very good if the crystal filter is operating correctly. It's a minor negative point that there's no front panel Phasing control for the crystal filter. The IF alignment instructions have C-64, the phasing trimmer, set to minimum bandwidth which is generally the desired function for a Crystal Filter.

On the down side, the dial resolution is pretty vague, especially on SW. This is due to the wide frequency coverage of each tuning range and is typical (and expected) of any WWII vintage receiver. The logging dial and logging scale on the dial will provide an accurate method of frequency resetability.

I'm using an eight inch Jensen speaker mounted in a Northern Electric loudspeaker housing that matches the CSR-5 quite well. To match the 10K output impedance, I'm using a 8K ohm to 8 ohm matching transformer spare that originally was for the Signal Corps LS-3 loudspeaker.

T-R function is accomplished using the Send-Rec "AC receptacle" on the back of the chassis apron (or using the SEND-REC toggle switch on the front panel) utilizing the remote standby contacts on the T-R relay inside the ART-13 transmitter. The ART-13 also has a vacuum receive antenna switch for receiver isolation during transmit. The CSR-5 is a "heavy-weight" and when installed in the cabinet with the shock mounts weight is up around 75 pounds. Then add the VP-3 power supply at about 25 pounds (my cables are long enough so the VP-3 sets on the floor.)

Update - Oct. 12, 2020 - I've been using the CSR-5 in combination with the ART-13A for a few of months now. It has proven to be one of my favorite WWII receivers to use. I've found it to be sensitive enough for 100% solid copy on all military radio net operations on 75M. Selectivity is good enough for dealing with adjacent frequency activity on all occasions. Audio quality is good and allows for excellent voice reproduction. I use the logging dial for accurate frequency reset. Minor points might be the AVC action which has a very slow "release time" which for CW is fine but for Voice could be a bit faster - very minor. Also, no antenna trimmer on the front panel but it's matched to the antenna used. Great receiver.

For More CSR-5 and CSR-5A Info - go the Jerry Proc's fabulous webpage located on his extensive website on Canadian Radio History and Royal Canadian Navy ships. URL is www.jproc.ca for the extensive website and www.jproc.ca/marconi/csr5a.html for the webpage specifically for the CSR-5 and CSR-5A.

Also, an excellent article on restoring the CSR-5 receiver was written by Gerry O'Hara "Restoring a Marconi CSR-5 - A Canadian WWII Classic." There's a link on Jerry Proc's website to the SPARC location of that article that in a pdf format.

 

 

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