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
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
Restoring a Marconi CSR-5 Gerry O’Hara
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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
Restoring a Marconi CSR-5 Gerry O’Hara
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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
Restoring a Marconi CSR-5 Gerry O’Hara
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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
Restoring a Marconi CSR-5 Gerry O’Hara
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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
Restoring a Marconi CSR-5 Gerry O’Hara
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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
Restoring a Marconi CSR-5 Gerry O’Hara
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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
Restoring a Marconi CSR-5 Gerry O’Hara
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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
Restoring a Marconi CSR-5 Gerry O’Hara
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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.
Restoring a Marconi CSR-5 Gerry O’Hara
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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).
Restoring a Marconi CSR-5 Gerry O’Hara
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
Restoring a Marconi CSR-5 Gerry O’Hara
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
Restoring a Marconi CSR-5 Gerry O’Hara
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
Restoring a Marconi CSR-5 Gerry O’Hara
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
Restoring a Marconi CSR-5 Gerry O’Hara
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;
Restoring a Marconi CSR-5 Gerry O’Hara
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:
Restoring a Marconi CSR-5 Gerry O’Hara
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+
Restoring a Marconi CSR-5 Gerry O’Hara
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.
Restoring a Marconi CSR-5 Gerry O’Hara
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
Restoring a Marconi CSR-5 Gerry O’Hara
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
Restoring a Marconi CSR-5 Gerry O’Hara
22
Ab
ove
: si
mp
licit
y o
f o
per
atio
n is
key
, in
clu
din
g fa
irly
-we
ll th
ou
ght-
ou
t fr
on
t p
anel
erg
on
om
ics
(at
leas
t fo
r ri
ght-
han
ded
peo
ple
), w
ith
th
e tu
nin
g, v
olu
me
an
d B
FO p
itch
co
ntr
ols
on
th
e ri
ght
Restoring a Marconi CSR-5 Gerry O’Hara
23
Restoring a Marconi CSR-5 Gerry O’Hara
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)
Restoring a Marconi CSR-5 Gerry O’Hara
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.
Restoring a Marconi CSR-5 Gerry O’Hara
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
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