Restoring a Marconi CSR-5 A Canadian WWII Classic · The Marconi CSR-5 and CSR-5A1 The Canadian Marconi Company (Marconi) designed the CSR-5 general coverage communications receiver

Restoring a Marconi CSR-5 – A Canadian WWII Classic – Gerry O’Hara

Background

I joined the Society for the Preservation of Antique Radio in Canada (SPARC) radio museum as a

volunteer some 16 years ago while living in Coquitlam, BC – almost ‘on the doorstep’ of this treasure-

trove of vintage radio goodness. I soon realized that the Museum had far too much ‘stuff’, and the

storeroom was filled to the brim with everything from tape recorders and TV test equipment, to

domestic receiver chassis, ham transceivers and various communications receivers. One type of

communications receiver that seemed omni-present was one I had not seen before, although it looked

strangely familiar to me. This was the Canadian Marconi Company (Marconi) Model CSR-5/CSR-5A, built

for and supplied to (primarily) the Canadian Navy in WWII. Rarely seen outside of Canada, its distinctive

half-moon dial reminded me of similar dials on other sets of this era from my ‘previous life’ in the UK,

eg. the British Marconi R1155 and Pye P.C.R. 2, both

advertised widely in the surplus market in the UK in the

1960’s – ahhhh, those were the days!

One of the first guys I became friends with at the SPARC museum was another ‘Gerry’ – a really friendly

guy with a passion for radios born out of his early years in the Canadian Navy as a wireless operator. In

that role Gerry had used RACAL RA17’s (one of the best tube receivers ever in my humble opinion) and

the more venerable Marconi CSR-5/CSR-5A – in Gerry’s own words:

“…This [the CSR-5] is the receiver that I used

personally in the navy, along with the

transmitter CM11. The older 2nd world war

ship's were fitted with the CSR-5 radio's. The

newer ships used the Racal 17's. The land

station at Albro Lake that I served at, we used

the Racal's. I did a hitch at both the Receiving

Station at Albro Lake, and also the Transmitter

Station at Newport Corner's Nova Scotia. At

Newport Corner's we had up to 25 or more

transmitter's on air at one time. Ship to Shore

communications. Broadcast for Atlantic, and fixed service with Whitehall England. At the

transmitter site, two people were on watch at a time. A senior Technician and a Junior. I was

the Junior. Any transmitter that was

master oscillator controlled had to

have the frequency checked every

hour, any transmitter that was on

Crystal control, you only had to

monitor the frequency every 4 hours.

The largest Transmitter was on the LF

band at 73.6 KC's. Had an output

capable of 250 KW, normally run

around 180 to 200. It was called the

‘TE147K’ (photo, right), built by RCA

https://sparcradio.ca/

Restoring a Marconi CSR-5 Gerry O’Hara

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special projects. I was told that 3 of them were around the world. The control panel took up

about a 40 foot wall, with Bus-like Steering Wheels as Knobs for tuning. Loaded up antenna

strung between a triangle of three five hundred and fifty foot towers. You could walk around the

ground underneath it, with a florescent 4 foot bulb in your hand, and it would light up.”

Over the years, SPARC had acquired several examples of each of these receivers, and as part of the

museums de-acquisition program for duplicate sets, Gerry had purchased a RACAL RA117 (the RA17’s

‘cousin’) and a Marconi CSR-5. Gerry’s RA117 was restored by another SPARC member around a decade

ago, and Gerry now felt it was time to have the CSR-5 restored. A few email exchanges later (and a

month or two for me to ‘clear the decks’ of other radio projects) and the CSR-5 arrived in Victoria for me

to start work on its restoration, including constructing a suitable power supply from scratch.

The Marconi CSR-5 and CSR-5A1

The Canadian Marconi Company (Marconi) designed the

CSR-5 general coverage communications receiver in 1942. It

was designed to be capable of receiving AM and CW signals

in the ‘low’ and ‘high’ frequency bands with a claimed

accuracy of 0.5% of the dial setting on any frequency.

Coverage was split into six overlapping bands: 79 – 207KHz,

195 – 518KHz, 1.5 – 3.5MHz, 3.55 – 7.65MHz, 6.8 – 16.1MHz

and 14.9 – 30.3MHz.

A Canadian government document titled “Signals Production Branch, Department of Munitions &

Supply”, dated October 15, 1943 refers to the initial order for the Marconi CSR-5 receiver thus:

“…One of the first jobs undertaken by the Inter-Services Committee on Design was the approval

of a Receiver for general communications work, which would be standard for all Services.

Late in the summer of 1942 the Committee prepared a specification covering the desired

equipment and this specification was sent to all radio manufacturers in Canada with an

invitation to submit a design.

The invitation was accepted by only two firms, R.C.A. Victor Company proposed their Receiver

Type AR88 which had just been designed by their United States affiliate, R.C.A. Victor, Camden,

N.J. Canadian Marconi Company submitted their receiver Type CSR-5.

In November 1942, the committee sat to compare the two receivers with the specifications. They

finally decided on the type AR88 with slight modifications.

Orders began to come in for the AR88 receiver before the end of 1942. By the end of August,

1943, R.C.A. Victor Company had orders totalling approximately 5,400 sets from Canadian Army,

R.C.A.F., B.A.T.R., British Army, and New Zealand.

1 The CSR-5A was a development of the original CSR-5, incorporating a number of generally minor circuit changes/improvements, along with some cosmetic and mechanical changes. This is discussed briefly in this article and a more comprehensive reference (link) is provided for additional information


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The original delivery forecast for this receiver was July, 1943. Design modifications instituted by

R.C.A. Victor (US) delayed the final ordering of materials to the extent that no sets had been

delivered by the end of August. Deliveries did commence in September.

Meanwhile, the Canadian Navy had placed orders for type CSR-5 Receiver instead of the AR88.

Between March and August, 1943, this Service ordered a total of 740 sets. New Zealand also

placed an order for 100 of the sets.

At the end of August, 1943, no CSR-5 receivers had been delivered, although original forecasts

were for July. The latest forecast for a start of deliveries is December, 1943.”

So it seems the CSR-5 was off to a bit of a shaky start…

nevertheless, Marconi must have delivered eventually

and thereafter these sets seem to have survived the

test of time - they were in use in the Canadian Navy

through to the 1960’s and became a stalwart of the

‘old school’ post-WWII Canadian ham shack since they

first appeared on the government surplus market.

They really are ‘built like a battleship’ – no flimsy parts

in these radios. However, even though they are

solidly-built, the receiver chassis is not overly-heavy, weighing in at a ‘mere’ 58lbs without the case

(68lbs with case and shock mountings) – a lightweight when compared to the ‘competition’ (the AR88)

at over 100lbs. However, much of this ‘skinniness’ is due to the power supply being a separate unit to

provide additional flexibility for a variety of installations. Indeed the supplied power supply units were

large and very heavy.

CSR-5/CSR-5A receivers saw three forms of service:

• Receivers for rackmount operation. These would be supplied with the WE-11 (AC only) rack

mount power supply and a protective cover;

• Receivers for standalone operation. These would be

fitted in an vented enclosure and come with the

standalone VP-3 AC/DC power supply; and

• Receivers destined for use with CM11's transmitters.

These would not come with any enclosure or either of the

above power supplies.

Circuit Description

The CSR-5/CSR-5A is an 11 tube single-conversion

superhet of conventional design using a (nominal) IF

frequency of 575KHz. The tube line-up is 6SK7 (1st RF),

6SG7 (2nd RF), 6K8 (Mixer/Converter), 90022 (Local

Oscillator), 6SG7 (1st IF), 6SK7 (2nd IF), 6B8 (Detector/1st

Audio), 6H6 (AGC/Noise Limiter), 6F6 (Output), 6SK7

2 A 6C4 tube is fitted in the unit under restoration – this seems a common substitute and works well


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(BFO) and VR150/30 (Voltage stabilizer – for the Local Oscillator/Crystal Oscillator and BFO). Schematics

for the CSR-5 and CSR-5A are included at the end of this article for reference.

The antenna stage includes a protective ‘discharge gap’ that triggers at 100v applied to the antenna3,

and a 1Kohm resistor as a ‘radiation suppressor’ (to mitigate radiation of the local oscillator signal).

Provision is made for both single wire and dipole antennas. Single-tuned coils are used in the

antenna/1st RF, 2nd RF and Mixer stages, with IF traps installed in the 1st RF stage cathode and plate

circuits. The mixer tube serves double duty as either a conventional mixer or as a crystal

oscillator/converter when fixed-frequency (crystal) operation is desired.

Four IF bandwidths can be selected, with a single crystal filter switched-in on the two narrowest

settings. Unusually, no crystal phasing control is provided on the front panel, rather this is pre-set using

a trimmer during IF alignment. Two double-tuned and one triple-tuned IF transformers are used,

together with a single-tuned circuit on the grid of the 1st IF amplifier. AGC is applied to the two RF

stages and the 1st IF stage, with the gain of the second IF stage adjusted by a switched cathode resistor

in the widest bandwidth setting. The noise limiter is a conventional series-diode type. The BFO is a

conventional capacitor-tuned circuit, with the BFO signal being very loosely-coupled directly to the

detector diode. The two audio stages are conventional, with the output transformer providing a variety

of outputs to match low and high impedance speaker/phones requirements. A three position tone

control is provided, switching capacitors between the output tube grid and ground. A nominal 150vDC

is supplied by the stabiliser tube to the local oscillator and BFO plate circuits. The heater circuit is

somewhat unconventional, designed to operate on 12v AC or DC, thus the (6v) tube filaments are

arranged in a series/parallel arrangement to accommodate this voltage.

Power is supplied to the unit from an external source – the receiver requires 12v AC/DC at 2.3A and

250vDC at 115mA, with a power consumption of around 75W at 117vAC line voltage. A ‘Supply’ switch

on the front panel is used to remotely switch the line voltage to the external power supply.

Note: the CSR-5A manual contains several errors, eg. in the RF alignment and voltage tables.

CSR-5 v CSR-5A

One commonly asked question is the difference between the CSR-5 and CSR-5A. This is addressed in an

article on Jerry Proc’s website here4. In that article, Tom Brent (a SPARC Museum member) comments

on this issue thus:

“I have seen so many modifications and ‘hatchet-jobs’ to these radios which only offer confusing

clues but there are few items on the comparison list that unmistakably identify a CSR-5 from a

CSR-5A. As originally manufactured, it is impossible to put a CSR-5 in a 5A cabinet and vice versa

but I have seen numerous -5A cabinets with locator pins cut out to enable a -5 to be installed, as

well as -5 cabinets with the power connector opening enlarged to allow installation of the -5A

receiver. I have seen crystal filter covers (which bear the part number) that have obviously been

3 A wire antenna produces a static charge as wind blows across it. This effect is more pronounced when a radio is installed aboard ship. The ‘discharge gap’ was installed to protect the CSR-5’s front end from this effect 4 There is also an article on Jerry Proc’s site here that covers the (matching) Marconi CM11 transmitter, as mentioned in my friend Gerry’s quote above

http://www.jproc.ca/marconi/csr5a.html

http://www.jproc.ca/marconi/cm11.html


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switched, audio transformers changed and many dial escutcheons with labeling that doesn't jive

with what is behind the panel.

The escutcheon is a leading source of confusion as to whether a receiver is a -5 or a -5A. In the

1950's and 1960's the escutcheon was repainted and silkscreened, part of a refurbishing

program that many CSR-5's went through5. Some escutcheons were simply painted black and

some were painted black and silkscreened or stencilled with the CSR-5A designation. The is no

evidence so far of any repainted dial escutcheon with "CSR-5" (non "A") script on it. So, to set

the scene here - at an RCN overhaul depot, perhaps dozens of radios being refurbished, the

mistake of putting an "A" dial escutcheon on a non-A radio could easily have happened.

The 6SK7 vs 6SG7 tube issue still remains, at least in my mind, somewhat confused. There is the

clear notation in the CSR-5 manual that states (contrary to what is shown elsewhere in the

manual) 6SG7's have been substituted for V2 and V4 during the production run. Further, most of

the CSR-5's I have encountered have had the original "6SK7" labels removed or scratched out

and, in almost all cases, neatly relabeled "6SG7" with a rubber stamp. This could possibly

indicate it was done at the factory although I suppose the repair depots could also have been

issued with a rubber stamp. Curiously however, we still find this haphazard relabeling on the

CSR-5A. I would have thought that if they could change the silk screen used to print the dial

escutcheon and panel labeling, surely they would also change the one used to label the chassis.

But who knows, maybe in the flurry of wartime activity at Canadian Marconi someone forgot to

institute the change and the chassis was still being produced with the "6SK7" label at V2 and V4.

However, there are a few items that are almost impossible to change and provide a good

method of establishing the actual model type:

1. The locations of the power switch and selectivity control are centered 1 1/2 inches below the

top of the panel on a CSR-5 and 2 inches below the top of the panel on a CSR-5A.

2. A CSR-5A has 3/8" holes in the top corners of the back wall of the chassis (to accept locator

pins in the cabinet); CSR-5's have no such holes.

3. A CSR-5 has a 2-screw terminal strip adjacent to the audio transformer; the CSR-5A version

has a 3 terminal strip.

4. A CSR-5A has adjustable slugs for band E and F RF coils that are mounted on an add-on plate

affixed to the top of the RF chassis (back-left corner); CSR-5's have no adjustment for these

coils"….

The article includes a very useful comparison table between the CSR-5 and CSR-5A and much more

discussion on the topic, and is well-worth reading6. Tom Brent’s comments on CSR-5 and CSR-5A

production numbers are also quoted thus:

5 Tom Brent (pers comm. March 2020) has clarified this statement, provided in the Addendum 6 At first I though Gerry’s set was a CSR-5A as the dial escutcheon and a label on the front panel clearly identify it as a CSR-5A, but the case has both a CSR-5 (top) and CSR-5A label (front). However, when I worked through Tom’s comparison list, I am certain this receiver has a CSR-5 chassis and that the front panel labels are incorrect


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"… I have CSR-5 serial numbers as high as 671 and CSR-5A numbers as low as 399. This indicates

two possibilities, the first being that CSR-5 serial numbers started at 1 and went up to 6717 (the

highest number I have found so far) and possibly beyond. The second part of this scenario has

CSR-5A numbers also starting at 1 and going up to 9738 (the highest CSR-5A that I have found so

far). Let’s round the highest numbers off a little and say that they produced 700 CSR-5’s and

1000 CSR-5A’s.” 9

Restoration Work

Initial Inspection

The CSR-5 arrived safe and sound in

Victoria courtesy of Purolator

(photos, right and on page 7) – the

only damage I could see was a bent

power connector on the rear of the

set, but it could have been like that

before shipping. I downloaded the

manual and schematic, which included a simple power supply circuit. Most components look original on

my preliminary inspection, except the electrolytics, three 10W power resistors and a 1W resistor. Note:

judging by its fibrous and rather friable nature, I suspect the wire insulation in this set may include

asbestos in the weave, so I used caution when disturbing or stripping any of the insulation.

Restoration Considerations

I advised Gerry that if this was my set and I wanted to do a ‘sympathetic’ restoration, I would likely only

re-stuff the visible tubular paper caps and the one original tubular electrolytic cap, and make repro

period parts for the remainder. Gerry agreed with this general approach to the work.

Some points of note, as discussed with Gerry:

- The tubular paper caps in this set are not typical construction – they are metal-bodied caps with

cardboard sleeves. I advised Gerry that I could re-stuff these using my standard ‘slit, gut, stuff and seal’

technique, which is fairly quick to do, however, I would normally just fill the ends in with brown hot-melt

glue and this would not look completely ‘original’. To make these more ‘original’ looking, I would have

to drill out the innards of the metal sleeves, drill a hole in the metal end for one of the capacitor wires,

re-stuff the metal tube with a new capacitor and then seal one end with the hot-melt glue (this would

be much more of a time-consuming process, and Gerry opted for the simpler/quicker method);

- Some paper caps may not be tubular – they may be ‘domino’ style (masquerading as mica

dielectric caps). These are much more difficult to reproduce and, if of narrow cross-section, cannot be

re-stuffed, and must be reproduced, eg. by moulding;

7 The serial number on the label on the case of this receiver is 282, thus it is possibly a fairly early example (if it was supplied with the same chassis as it accommodates now…) 8 Jerry Proc notes that the highest CSR-5A serial number he has found (up to 2014) was 1062 9 Tom Brent (pers comm. March 2020) has since revised his assessment of the CSR-5 serial numbers. His most recent thoughts on this are provided in the Addendum


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- Three of the

electrolytics were

replacements, and so these

would not warrant re-

stuffing, instead I proposed

to Gerry that I fabricate

something ‘sympathetic’, ie.

print out repro labels from

some caps of the same era,

form tubes out of card, stick

the labels on and stuff these

repro cap bodies;

- On checking some

resistor values I noted that

around 80% were within a

20% tolerance of their

nominal value – better than

many sets of this era, but

some would certainly

warrant changing out.

Given the type of many of

the resistors (small carbon

composition types), these

would be difficult to

reproduce properly to the

same size, though instead

the replacements could be

‘disguised’ somewhat using

paint or amber shellac. In

my experience, more

resistors could drift out of

tolerance during soak-

testing of the receiver and

therefore a more thorough

check would be made once the set was operational.

Once Gerry was in agreement with the approach to restoring the set, the first steps were to:

- Clean above and below the chassis, gearbox and dial/controls;

- Re-stuff 12 of the exposed tubular paper caps (photos on page 8), however, accessing one was

problematic: the problem one is in the antenna coil compartment (C14), an AGC bypass cap to the 1st RF

stage. Removing it would likely have caused collateral damage (I tried and stopped), so instead, I left it

in place and disconnected the end connecting to the RF coils and ‘faked’ that connection with some

insulating sleeve, so it looks like its connected (but isn’t), and replaced the cap in the circuit with one of


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the same value hidden underneath an adjacent tag board (you

really have to look hard to see what has been done!);

- Re-stuff one small tubular electrolytic (C89);

- Replace 5 tubular paper caps (not re-stuffed) hidden under

one tag board, and one cap on another tag board hidden in the

corner of the chassis (that cap was really hard to spot and had been

replaced previously with a plastic-body paper cap);

- Lift the second horizontal tag board and replace 4 tubular

paper caps underneath (not re-stuffed);

- Remove the two (replacement) can electrolytics. One had

two dry joints on it – on the output tube bypass cap and the

smoothing cap to the stabilizer tube.

The wirewound resistor (10W) on the output tube cathode was a

little ‘baked’ in appearance, but measured exactly what it should

(400 Ohms), so I just cleaned it up and left it in place. Two other

power resistors had been replaced previously with (three) ceramic

types – all of incorrect values, so these needed to be replaced.

The repro electrolytics were fabricated and ‘aged’ to match the

appearance of other parts in the set, along with another electrolytic

(100uF, 50vw) that had been replaced previously with an orange-

coloured 100uF 150vw ‘Sprague Atom’. This was re-stuffed using a

100uF 50v part and the case ‘aged’ with a coat of amber shellac

(photo, below). I used ‘Sprague’ labels for the repro caps so they

matched this one’s manufacturer. The two dual repro electrolytic

caps were then installed using the original clips to secure them in

place, and the power resistors were replaced with new ones of the

correct values. I spaced the power

resistors away from the phenolic

mounting board so they would dissipate

heat better and so they would not

overheat the phenolic or the

electrolytics on the opposite side of the

board.

Checking capacitor types against the

component list confirmed that some of

the 0.01uF capacitors were still in circuit

and were not tubular paper types,

except two tubular paper ones that I was

finding elusive... (C19 and C37). The


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others were possibly ‘domino’ style paper ones (though could be mica) – I decided that I would need to

investigate these on the chassis, ie. C91, C92, C110, C116, C118, C129. Also C84 (0.004uF) and C85

(0.001uF) may be ‘domino’ paper caps. Of these, only C110, C118 and C129 are ‘critical’ as they are on

higher voltage circuit nodes. These ‘domino’ caps are of Aerovox or Solar manufacture (not the dreaded

‘Micamold’ thank goodness). The removed tubular paper caps mostly tested good for leakage

(>100MOhms) and capacitance values (well within 20%), except one 0.01uF cap of a different type that

tested very leaky – however, I only tested the caps at 30vDC, so they could be have shown some leakage

at higher voltages.

On further checking, I confirmed that the caps listed above are indeed all domino style, though I could

not be sure if they were paper or mica without destroying one of each type. However, only C110

(0.01uF) and C129 (0.01uF) have any appreciable voltage across them in service (152vDC for C110, and

250vDC on C129). C110 is buried deep in the RF section so access is difficult – I therefore decided to

leave it and do some more ‘sleuthing’/cross-checking as to the capacitor dielectric types using the

manufacturer and part numbers identified in the components list. I did check C110 in-situ and it tested

perfect, with absolutely no measurable leakage at 30vDC. I also tested C118, which was leaky (around

2Mohms at 30vDC). This started me thinking that maybe some of the 0.01uF domino caps were mica

and others paper. The parts list shows three types of ‘domino’ style 0.01uF caps:

- Solar manufacture Type ‘MWW .5-11-20’ (C91, C110, C129). This cap type number is also used

for some smaller value caps (so are most likely mica dielectric);

- Solar manufacture Type ‘MWDW .5-11-2’ or ‘MWCW .5-11-2’ (C17, specified as a 2% part, and

its in an IF trap tuned circuit, so will definitely be mica);

- Aerovox manufacture Type ‘1467S’ (C92, C116, C118).

As C129 was easily accessed (its under the power supply connector

cover on the rear apron of the receiver), I decided to check that

cap, as it’s the same type (Solar MWW .5-11-20) as C110. It also

tested perfect. So I did a forensic deconstruction of C129 as it was

easily replaced and hidden in service, and confirmed that it was

indeed a mica dielectric type. Therefore C110 is also mica (as will

be C91), being of the same part number, and therefore did not

need replacement. Of course I replaced C129 as I destroyed it in

the investigation!

So, only the Aerovox manufacture Type 1467S are possibly paper: I

replaced C118

(V9 screen

bypass) – even though it should only have 27vDC

across it, as it was easily accessed. I decided to mill

out the body of the original cap (photo, above) and

install the new cap in the milled-out section (photo,

left). That left C92 (6.3vAC V9 heater supply across

it) and C116 (4.8vDC V9 cathode bias across it) – in


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both cases, even quite large leakage would not be an issue (I confirmed voltages once the set was

operational – both were ok).

Next steps included:

- Installing the re-stuffed ‘domino’ cap:

no-one would ever know… (then I realized its

hidden by the BFO cover anyway – doh!) – the

re-stuffed domino cap is indicated by the

yellow arrow in the photo, right;

- Re-installed the front panel and side

panel, cleaned the knobs and installed them on

the control shafts;

- Checked a few more resistors – some

were a bit out of tolerance, however, I decided they would be ok for initial test purposes, and that I

would re-check all resistors after the set had been running for several hours;

- Checked the RF gain control (multi-pole switch) and confirmed it was working ok;

- Cleaned the bandswitch wafers with Deoxit on Q-Tips. Some are inaccessible, but I resisted

spraying Deoxit into them (this is a ‘last resort’ in my book, used only when the switch is causing

problems), and also lubricated the switch detent mechanism;

- While cleaning the bandswitch, I finally found the two ‘missing’

tubular paper 0.01uF capacitors(!) – I had been checking them off

on the schematic and the parts list and was puzzled why I could

not find them. These are C19 and C37, which short the primary

windings of all the RF transformers not in use (this function is

termed ‘Primary Shorting’ in the components list). They are

buried right at the bottom of the deep RF unit and are well

obscured by wires, other parts, the switch wafers and shaft (I had

peered into this compartment many times and had not spotted

them!) – yellow arrow in photo, left. These are the metal-

encapsulated paper dielectric type (Aerovox Type M489, 0.01uF

400vw) that were present elsewhere in the set – none having this

Type number were leaky when I tested them. I managed to test

both of these ones in-situ and they both tested perfect (at least

no detectable leakage at 30vDC). Given this, I decided to leave

them in circuit. I could have changed them out, though with

some considerable difficulty: access to their connections to the band change switch wafer is relatively

straightforward, if a little constrained, but their ground connections are completely obscured, so I would

have had to find another local grounding point for each replacement - not easy(!), risking collateral

damage to several other components, and having to temporarily remove several other parts to provide

access. Gerry agreed that leaving these caps in place was the correct approach in this case.


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Also while cleaning the Band Change switch, I noticed that it can be rotated through a full 360 degrees,

so each Band can be switched in twice during a full revolution – I am not sure it should do this as when

on Band ‘C’ in one half of the rotation, the ‘Primary Shorting’ caps do not function correctly – perhaps a

missing contact on the shorting wafers(?). This is not really a problem, but I advised Gerry that it was

probably best to just use the ‘correct’ half of the Bandchange rotation, as indicated by a white spot on

the band change knob. Perhaps a mechanical stop could be fitted?;

I tested all the tubes except the VR150/30 stabilizer tube. I noticed that the first RF tube is a ‘6006’

(high grade 6SG6), but it should be a 6SK7. These tubes are somewhat interchangeable, but I changed it

for a good 6SK7 anyway. One of the 6SG7 tubes (IF section) was weak, so I changed that for a good

6SG7. Also, the 6F6G output tube tested as ‘marginal’, but I find tubes in this condition usually work ok,

so I left it in. All the other tubes tested ok.

I removed the ‘discharge gap’ in the antenna circuit (photo,

right) – it was discoloured inside and there was something

rattling about inside it – its not really needed unless the receiver

is to be operated onboard ship (see footnote #3 on page 4).

Also, the antenna input circuit had been re-wired slightly – R61,

the ‘anti-radiation’ resistor, had been disconnected (‘hanging

loose in the breeze’), and C1 re-connected in its place. This is

probably a good modification (and easily reversed), though R61

should probably have been removed, so I did that.

Preliminary Testing

At this stage I felt all of the essential issues had been addressed and it was time to check if the receiver

was able to function. I jury-rigged a power supply, using a 12vAC 4 Amp transformer for the heater

supply, and a Heathkit stabilized power supply for the 250vDC HT+ supply, connected through the

existing power connector on the receiver rear apron using a spade connector and a two pin Cinch line

socket.

The set powered-up and worked

reasonably well – drawing around

100mA HT+ at 250vDC. All

controls seemed to function ok –

though some more switch and

control cleaning was obviously

required. A short video of the

initial function test can be viewed

here. Only one dial lamp was

working, but not a problem – I

thought I may be able to convert

them to 6v operation if I could not

find suitable 12v bulbs. I left the

receiver running for an hour or so

and it seemed happy enough

(photo, left).

https://www.youtube.com/watch?v=Nas7wFKBNFs&feature=youtu.be


12

I also checked a few voltages and the AGC which was working well. The two remaining tubular paper

caps buried deep in the RF compartment, as I suspected from the schematic, had almost the full HT+

voltage across them, ie. around 240vDC. They tested fine on my 30vDC ohmmeter (zero detectable

leakage, ie. over 100Mohms), so will likely be just fine for many years. If they develop a dead short

(unlikely), they could possibly burn out the primary windings in the affected RF stage on the bands not in

use, but most likely the current would flow through the lower-resistance windings on the shortwave

band coils and burn out R10 or R21 ‘plate filter’ resistors instead. Given this, I agreed with Gerry to

leave the two original caps in place and fit a quick-blow fuse in the HT+ supply that would protect these

resistors. The two ‘Primary Shorting’ capacitors would not affect the actual performance of the receiver

if they eventually became a bit leaky, and even if their capacitance degraded over time or become open-

circuit, the only effect may be some harmonic resonances on some of the bands.

I next carried out some more ‘deep’ cleaning, including:

- Using Q-Tips and Deoxit to carefully clean the selectivity, crystal and tone switches;

- Remove the covers from

the main tuning gang and

cleaned/lubricated the

tuning gang assembly –

photo, right (lots of grime

build-up in there!!);

- Cleaned all the

tubes/sockets, including

Deoxit cleaning of the tube

pins;

- Cleaned (Deoxit), and

lubricated all controls

including shafts and shaft

bushings (drop of light

machine oil).

I could not find any suitable

insulated bulbholders needed to convert the dial bulbs to the more common 6v (I needed two non-

grounded types), however, I found some 12v bayonet bulbs and they did the job – the dials looked much

better illuminated. Next, I:

- Re-installed the covers on the Crystal filter and BFO unit;

- Re-installed two (good) resistors that were replacements that had been installed sloppily on a

couple of the tag boards;

- Tested/re-tested resistors on all the tag boards and in the point-to-point wiring – the majority

were well-within 20% of their nominal value, these being mostly 10% or 20% marked parts (I usually

leave resistors in circuit if they are within 20% of their marked value). A few were significantly outside

this tolerance and needed to be changed out, eg. R22, a 70Kohm screen dropper resistor, connected to


13

a leaky bypass 0.01uF cap, now measured 192Kohms – see more on this later. I had some resistors of

similar style to those in the set, but they were also (NOS) carbon composition types and would likely

drift high in use. I therefore recommended to Gerry against fitting those. Instead, I proposed to

disguise modern parts (high stability metal film resistors) either by visually ‘toning down’ their

appearance with paint or shellac, or, in the case of the larger ones, moulding some epoxy putty around

the new part and then painting/shellac coating. At this stage I counted a total of 6 resistors that should

be changed out, though noted to Gerry that I may find a few more later as the work progressed.

Once agreed on the approach with Gerry, all necessary resistors were replaced with repro or ‘disguised’

(visibly aged) ones: I ended up replacing 11 in total - some of these were marginally within 20%, but I

changed them out anyway. All remaining original resistors (or previous replacements) tested within this

tolerance, including those buried deep in the RF compartment (phew!) – those ones are only grid leaks

for the mixer and oscillator tubes, so non-critical in value anyway. I also changed-out one of the

previous replacements on a tag board even though it tested within

tolerance (a ceramic-body Erie part that did not look like it belonged).

Only one resistor was repro’d – a 1W resistor (R57): this should be a

60Kohm part that measured over 75Kohms, so I used a 27Kohm and a

33Kohm resistor in series (both 1W, so its now a ~2W resistor, though de-

rated from this due to the epoxy putty sleeve around it providing a degree

of thermal insulation) – photos, right.

The receiver then went back on soak test – some voltages had changed, but

the performance seemed much the same as before (not surprising – tube

radios generally are very tolerant of out of spec resistors unless in a critical

part of the circuit). However, I noticed the audio was distorted on music

played through my SStran3000 local transmitter, which sounds fine on

other sets. Changing the 6F6 output tube for a NOS tube did not help (I

thought the original weak-testing 6F6 might be developing secondary

emission). I then found that the distortion was only present on the widest

selectivity position, and changing the RF gain, AGC in/out and audio level

did not change it. This was an odd fault that I could not recall before

changing the out of spec resistors, however, it could have been present.

One voltage that had changed significantly with the new resistors was the

screen grid voltage on the Mixer tube – the screen grid resistor (R22) was

much higher in value than it should be: it looked like it was marked as

20Kohm, and measured 192Kohm. The parts list specifies 25Kohm, so I

replaced it with a 27Kohm part. However, the screen voltage then

measured much higher than the voltage table lists – its listed as 38v (and

measured 22v with the original resistor), and was now 62v, even using a

1,000 Ohms/volt meter as specified in the voltage table. The mixer screen

grid resistor is indicated as 25Kohms on the parts list, though a hand

annotation on a tag board diagram in the manual says ‘25Kohms or

75Kohms’. The colour bands on the resistor appeared to me under my LED

bench lights at night as a 20Kohms (red-black-orange) resistor, but when


14

viewed in daylight the next day I could see that it was actually

originally a 70Kohms part10 (violet-black-orange), ie. the red

‘turned’ to violet in different lighting conditions (photo, right) –

though this could have something to do with my red-green colour

blindness problem... Anyway, I subbed a 75Kohms part as R22 and

the screen grid voltage now measured 38vDC as per the voltage

table, and the receiver was a bit more sensitive;

The distortion on the broadest selectivity setting was still present - I could not see how the Mixer screen

voltage would cause that anyway. I figured it sounded like signal overload on the RF or IF stages, or

even the detector stage, eg. the AGC action was not working correctly on the broadest selectivity

setting, giving too much IF gain. Examination of the schematic showed that on all but the broadest

selectivity setting (minimum selectivity), one of

the two (series) cathode bias resistors (R59) on

V5, the 2nd IF amp, circled yellow on photo, left,

is shorted to ground by the selectivity switch

(S11). AGC is not applied to V5 (only the two RF

stages and the 1st IF stage) - the 2nd IF stage is

thus ‘fixed bias’. However, shorting out one of

the cathode resistors affects the bias condition

and hence the gain of that stage. These resistors

are both indicated as 400 Ohms on the parts list

(R34 and R59), though a 500 Ohm resistor was

fitted in place of R34 (which measured

1.17Kohms) and I had replaced it with a 470 Ohm

part. Experimenting with the value of R59 showed that the distortion could be eliminated by dropping

the value to below 400 Ohms: 330 Ohms gave the exact cathode bias voltage shown on the voltage table

(5.6v using a 1,000 Ohms/volt meter), though a small amount of distortion was still present. Reducing

this resistor value to 270 Ohms or below eliminated the distortion on the minimum selectivity setting

and the cathode voltage was only slightly off the value in the table. I thought that this condition may

partly be due to some misalignment of the IF stages, so decided to wait until I had checked/adjusted the

IF and RF alignment before I made a final determination on this resistor value.

Soak Testing and Alignment

I generally followed the alignment procedures

described in the manual. However, for the IF

stages, instead of the optional (and strange)

use of an FM-modulated signal and BFO to

confirm the bandwidth settings, I used a

home-brew ‘wobbulator’ (photo, right) to

visually check the response curves on a ‘scope.

10 Tom Brent’s comparison table also notes that in the CSR-5 this resistor can be either a 20Kohm or 70Kohm part. It also notes that C123 (2nF output tube plate bypass cap) should be checked and connected to the correct transformer terminals (4 and 5) – this was checked and was ok

http://eddystoneusergroup.org.uk/Restoration%20projects/Alignment%20using%20a%20Wobbulator.pdf


15

The photo, right,

shows this setup on

the bench: the

wobbulator is sitting

on the receiver side

panel. The ‘scope to

the lower right is

showing the

sawtooth raster

output from the

scope on the left

(the raster signal is

used by the

wobbulator to scan

the input signal

across the receivers’

IF passband), and

the ‘scope on the

left is displaying the

passband at the receiver detector stage. The actual IF

frequency, ie. that of the crystal, was determined as

574.525KHz (the nominal IF frequency of the set is 575KHz).

The IF alignment was actually not far out and I did not need

to tweak the crystal trimmer. I did manage to get a few more

dBs out of the IF amplifiers by careful and repeated

adjustment. The photos, left, show the response curves for

each of the selectivity settings: 1 (minimum) is shown on the

top photo, through 4 (maximum) on the bottom photo.

Settings 3 and 4 have the crystal switched into circuit giving a

sharp peak on an asymmetrical response curve needed for

CW reception in poor conditions, eg. adjacent channel

interference. Unusually, this design does not have a front

panel ‘phasing’ control as most single crystal filters do;

I found the RF stages alignment on some bands to be

significantly ‘off’, especially Band ‘A’, where the set had been

misaligned to the image frequency. I always double-check

the local oscillator is set correctly on the shortwave bands

when I align sets, as this is a common problem on single-

conversion superhets that have likely been aligned many

times by folks that had poor test equipment and/or

knowledge of what they were doing - I use a modern digital

frequency-synthesised receiver tuned to the signal frequency

plus/minus the IF frequency (as appropriate) for this purpose.

Also, on the CSR-5/CSR-5A, the local oscillator on Band ‘A’ tracks below the signal frequency, and above


16

the signal frequency on the other bands, which can be easily forgotten during the alignment. An 11/32”

socket and insulated blade alignment tool are needed for the alignment work (photo, below).

After re-alignment, the

receiver’s performance

on all bands was certainly

‘up to snuff’, with only a

little degradation of

sensitivity towards the

low end of Band ‘F’, ie,

below around 100KHz,

which is consistent with

the typical sensitivities

listed in the manual.

Following the re-

alignment process, I

determined that the

optimum value for the

2nd IF stage switched

cathode resistor (R59)

was 180 Ohms. This value keeps the gain of the receiver approximately the same on all selectivity

settings and gave no distortion on the widest setting, so I installed that value in the set.

At this stage the set had been running for approximately 50 hours on and off, and seemed very stable.

Given this, I considered the work on the chassis to be almost completed, though much more soak testing

was to take place to prove reliability. The next job was to wean the set off its temporary sources of

power so it could be used independently, ie. I needed to build a suitable power supply.

Power Supply

Having recently downsized and sold-off a fair amount of my accumulated ‘radio junk’, I was scratching

about to locate the necessary parts – especially the transformer, choke and a suitable case. While I was

searching through boxes and packing crates, I did find a suitable pair of Cinch connectors – a 6 pin non-

reversable chassis plug and a matching cable socket. I only had to file out two existing screw holes in

the power supply connection box on the rear of the receiver chassis slightly to make this socket fit.

I could not find a transformer with both high voltage and 12vAC secondaries. However, I found a NOS

Hammond HX272FX transformer that proved suitable for the power supply. This transformer has 300-0-

300vAC @ 150mA, 6.3vAC @ 5A and 5vAC @ 3A secondaries. Connecting the 6.3vAC and 5vAC windings

in series gave well over 12vAC on no load, so ok for the heater circuit (it specifies 12vAC). I also found a

brand new-in-box 11H, 125mA choke. With these parts as a basis, I:

- Used 2 x 1N4007 (1000PIV 1A) diodes in a full wave rectifier circuit on the high voltage

secondary of the HX272FX transformer;

- Due to the high transformer HT winding voltage, I designed a choke-input filter comprising the

11H choke-32uF reservoir cap-300 Ohm (nominal) resistor-32uF smoothing cap;


17

- Assembled this on the

bench, jury-rigged with temporary

soldered joints and flying leads

fitted with croc clips - photo, right,

to check it worked ok before

building the power supply (rats

nest or what!);

- Connected this temporary

arrangement to the Cinch

connector and checked voltages:

on a 117vAC supply, the heater

voltage when powering the sets’

heaters measured 11.85vAC –

slightly low, but the set seemed to

be working fine. The HT+ voltage

was also slightly low at 240vDC with a 300 Ohm dropper resistor: changing this to 200 Ohm gave exactly

250vDC output at 100mA HT current draw;

I was a bit concerned that the HT+ voltage would peak too high before the tubes heated up, but this was

actually ok, peaking at only 275vDC before being brought down to the nominal 250vDC with the set

drawing typical HT+ current (HT+ current draw from the set varies between 90mA with full AGC action

and 110mA under no signal conditions).

The 2 x 32uF 500vw cap used was a new chassis mount twin can type, so should be very reliable - I have

fitted these in several RACAL and other comms receivers power supplies.

While searching my garage for a suitable chassis/case for the power supply I came across a couple of old

ATX computer power supplies (I had kept these for parts, such as the IEC socket). I wondered if all the

parts would fit into one of these computer power supply boxes – to my amazement they did! (photos,

below right and on page 18).

Before transforming the ATX supply into a CSR-5/CSR-5A supply, I left the receiver on soak test with the

power supply components connected on

the bench in the temporary arrangement

to see how warm the transformer,

dropper resistor and choke became after a

few hours. I decided to leave the old

computer fan in place, running off the

heater supply via a single rectifier diode

and 100uF capacitor filter, providing

around 9.5vDC: it’s a 12vDC fan, but would

still provide some air flow through the

power supply box at this reduced voltage

(and is very quiet at that voltage). Once I

was satisfied that the power supply was

functioning correctly, I:


18

- Drilled the additional holes needed in the

old ATX computer power supply case;

- Installed all the new components into the

case and wired them up per the schematic

attached to the end of this article;

- Added four plastic feet to the base of the

case;

- Included a fuse between the power

transformer HT winding centre-tap and ground

(250mA), protecting the transformer, choke and

rectifiers. The other fuses are in the transformer primary (1.5A) to provide overall protection from

overload/shorts etc, and in the HT+ line immediately before it goes to the receiver (150mA) to provide

additional protection for circuits in the receiver, as well as for the power supply. This fuse is fitted

internally in the power supply and uses an in-line

socket. The other fuses holders are panel-

mounted and can be changed without opening

the case. I installed a small LED on the front

panel of the power supply, located below the IEC

socket, and is wired such that it indicates if HT+ is

going to the receiver when lit. If it goes out and

the orange neon pilot light stays on, one of the

HT+ fuses has blown, most likely the internal

(150mA one). This saves opening the power

supply case to check the fuse;

- Found a suitable umbilical cable: an 8 conductor plus screen cable connected as follows to the

line socket (photo, below, right):

• Pin 1: No connection (could be used for a speaker in the future)

• Pin 2: Two black and a green wire, sheathed yellow, 12vAC heater (ie. three wires for

additional current-carrying capacity)

• Pin 3: Blue wire, sheathed blue,

Receiver Front Panel ‘Supply’

switch

• Pin 4: Screen plus two black

wires, sheathed black, Ground

(ie. three wires for additional

current-carrying capacity)

• Pin 5: White wire, sheathed

white, Receiver Front Panel

‘Supply’ switch

• Pin 6: Red wire, sheathed red,

250vDC HT+


19

- Fitted a sprung

retaining clip to the power

supply connector box on

the rear of the receiver to

prevent the Cinch

connector becoming

loosened easily, and

blanked-off the hole where

the old connector was. I

also stuck some insulation

on the chassis inside the

box as a precaution against

shorts.

After running the power

supply powering the CSR-5

for a few hours (photo,

left), I added a few

suppression components: a

0.01uF 275vAC X2-Class safety cap across the power transformer primary, a 0.01uF 1600vw ceramic cap

across each 1N4007 rectifier, a 0.0047uF 1600vw film cap between the choke input and ground, and a

0.01uF 1000vw ceramic cap across the heater supply, adjacent to the 1N4007 rectifier feeding the fan. I

also fitted a 150Kohm 2W ‘bleed’ resistor across the HT+ line so if the umbilical to the receiver was

accidentally disconnected, which automatically switches the power supply off, the filter caps would

discharge safely in a few seconds.

The old ATX power supply label was covered over with a new label providing details of the new power

supply specification and the umbilical connections to avoid confusion for future owners.


20

Cosmetics

Apart from thoroughly cleaning the chassis/front panel as described above and vacuuming/wiping-over

the case with a cloth moistened in rubbing alcohol, no cosmetic work was undertaken on this receiver,

as, overall, it is in reasonably good cosmetic condition (photo, bottom of page 19).

Closure

The set was ‘boxed-up’ and has been used for many days since the work described in this article was

completed and continues to provide stalwart performance… The CSR-5 is not a ‘stellar’ performer, but

can ‘hold its own’ against most communication receiver designs of WWII that I have used over the years.

A brief video of the finished set working can be viewed here.

It could have been improved for CW operation by including a front panel crystal phasing control,

stronger BFO injection and a dual-speed tuning mechanism. That said, I think two of its main design

features were its physical robustness and ease of use – probably both highly-desirable on a ship in rough

seas! – and it certainly achieves those. Also, it’s a pity it does not have the Broadcast Band included: this

seems to be the case in many Canadian forces radios – the more cynical of my radio friends say this was

to prevent ‘slackers’ from tuning into their favourite music when they should have been working -

diligently listening on the LF or SW bands. Hmmmm, well... maybe?

Above: view of the receiver installed in its case with the lid open – this provides easy access to all tubes,

dial bulbs and most of the RF section trimmers and slugs, including the IF traps, however, some RF

trimmers are located under the chassis. The BFO coil tuning slug can also be accessed easily, however, all

the IF transformers and the crystal trimmers need the chassis to be removed from the case to be accessed

https://youtu.be/f8cEK3JqgHU


21

Above: under-chassis view of the restored CSR-5 with the RF compartment and main screening plates

removed. The RF screening plate has access holes for some of the RF stage trimmers and should be in

place during alignment. The rectangular shield (upper centre of photo) screens the BFO circuitry


22

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24

Above: completed power supply unit with information label attached. Below: Aaarghhh! – which

model of receiver is this? – very confusing labelling… (left - on the case, right - on the front panel)


25

Addendum

CSR-5 Serial Numbering and Refurbishment Program – Updated Assessment by Tom Brent

A copy of this restoration article was forwarded to Tom Brent for his information and comment. Tom

kindly responded as follows regarding the serial numbering system used by Marconi, and on the

refurbishment program that contributed to the confusion of set types:

CSR-5 Serial Numbers

“…Jerry Proc and I started corresponding (before email) about CSR-5 receivers way back in 1992.

It was also around that time that I was advised by a former Canadian Marconi employee that

none of the wartime records of the company were left in existence, they had all been destroyed.

A fair bit of the info on Jerry's webpage was conjecture based on tidbits of information that did

not tell the full story. Most of the conclusions we made have stood the test of time as new

information came in but… there are some items that need updating.

When we began, the Canadian Marconi (CMC) serial number system did not seem to make

sense. For example, we were aware of CSR-5A receivers that had lower serial numbers than CSR-

5's (non-A). Around 2002 I decided to list all the serial numbers I had collected on a spreadsheet

that also included the CMC type number as well as the specification number and other details

that appeared to be "differences" in various receivers I had collected info on. At that point

everything started to make sense and that is when I came to the conclusion that each variant of

the CSR-5 has a specific type number and it would appear there was a serial number series

started for each of those type numbers. I originally assumed that each of these series would

have started at "1" but because the lowest CSR-5 serial number we have ever come across is 119,

I am now thinking that perhaps CMC started their serial numbering at 100. I could be entirely

wrong on this but I think there must be a reason why we have collected many serial numbers in

each hundred range between 100 and 1100 but not a single one below 100.

There are 6 CSR-5 receiver type numbers that we are aware of:

105865 CSR-5Y

110480Z CSR-5 receiver used in CM-11 transmitter-receiver

110480AZ CSR-5A receiver used in CM-11A transmitter-receiver

110835W CSR-5 receiver 19 inch rack mount with dust cover (no cabinet) - all known examples

are painted wrinkle black

110930Z CSR-5 stand-alone receiver in desktop cabinet

110930AZ CSR-5A stand-alone receiver in desktop cabinet

Type numbers 110480Z and 110480AZ were serial numbered sequentially, the changeover from

CSR-5 to CSR-5A came somewhere between serial number 350 and 384. The highest serial

number I have for this type is 399. The same holds true for type 110930Z and 110930AZ where

the changeover came at or after serial number 816 and the highest serial number located thus

far is 1070.


26

To summarize, there are 6 type number series for CSR-5 receivers, and the current evidence

suggests there were 4 serial number series, each beginning with serial number 100 (or perhaps

101?)…

Only one example of the CSR-5Y (type # 105865) is known to exist. It was part of a triple diversity

setup, similar to the RCA DR-89 which of course used three AR-88 receivers. This was a space

diversity system (as opposed to frequency diversity) in which the receivers were held on

frequency by a separate oscillator feeding all three receivers… There is also a photo showing the

complete system on Jerry's webpage but unfortunately it is not very clear.

I am currently aware of 5 rack-mount receivers (type 110835W) and all are painted wrinkle

black. Three of these receivers are in Canada (I have two) and two are in Australia. I have seen a

number of photos showing these sets in use at the Canadian Department of Transport (DOT) air

radio stations in the 1950's and 1960's. My hunch would be that these were purchased from

surplus channels following the war rather than a direct purchase from Canadian Marconi but I

have no evidence that directly supports this. However, because DOT purchased other war assets

equipment such as AT-3 transmitters, VRL and TE-236 receivers, etc., it also seems likely to me

that the CSR-5's were obtained by DOT via the same route.”

Refurbishment Program

“…Dial escutcheons were

repainted and there was a

refurbishing program for

these receivers... I have still

not come across any

repainted escutcheons that

say "CSR-5" (non-“A”) on

them. I do not think a

‘mistake’ was made when a

repainted escutcheon reading

"CSR-5A" was applied to a

non-“A” receiver. Rather, if it

was all they had and the original escutcheon on the receiver was deemed to need replacing, the

fact that it read “CSR-5” or “CSR-5A” was of little or no consequence. The repainted escutcheons

are easy to recognize since the Marconi script is not stylized ( written on an angle) like the

factory originals were11…

My original conclusions on how to discern the CSR-5 from a -5A still hold true, nothing has

changed.

However, to add to the confusion surrounding these sets, my records show at least one

identification plate that reads "CSR-5" yet shows an “A” type number and specification number

and it was definitely a CSR-5A receiver.”

11 As is the case with the receiver being restored in this article, ie. the ‘Marconi’ script is not stylized. An example of an escutcheon with the original stylized script is shown on Page 3 of this article

1

3

5

2

4

6

Cinch 6 Pin Chassis

Plug (viewed from

rear of line socket)

Speaker (Optional)

Nominal 6.3vAC+5vAC in series (12vAC under load)

300-0-300vAC

200 Ohm (5W)

Hammond 272FX Transformer

Cinch Connector (line socket numbering, NOT chassis plug numbering (its different):

- Pin 1 = Speaker (optional connection)

- Pin 2 = 12vAC heater supply

- Pin 3 = Receiver panel Supply switch

- Pin 4 = Ground (common)

- Pin 5 = Receiver panel Supply switch

- Pin 6 = HT+ (250vDC under load, 280vDC when tubes ‘cold’)

2 x 32uF

500vw

1.5A

150mA fuse (in

line fuseholder*

Neon

Pilot

100uF

25vw

1N4007 12vDC

FAN

150Kohm (2W)

0.047uF

1600vw

0.01uF

1600vw

0.01uF

1600vw

0.01uF

275vACvw

(Class ‘X2’)

* Miniature red LED ‘fuse blown’ indicator on the HT+ line to receiver (Pin 6 of Cinch socket) not shown. This is fitted with a 330Kohm series resistor

0.01uF

1000vw

250mA fuse

Documents

Restoring a Marconi CSR-5 A Canadian WWII Classic · The Marconi CSR-5 and CSR-5A1 The Canadian Marconi Company (Marconi) designed the CSR-5 general coverage communications receiver