Wireless Set Canadian No 52 Receiver

 As you can see from the picture below this receiver was made in Canada during WW2.

 

 

 I've never had one of these sets before. The upper panel is fitted with Zeus fasteners allowing the panel to be detached for access to the valves, which appear to be plentiful in number.

There's no case so maybe this example originally came from a complete set-up including power supply and transmitter which would have shared a large case?

 

 Below is the block diagram plus schematic

 

 

Click the schematic above to see the receiver circuit full size

But before looking at the circuit note the pin numbering of the valves below with black as standard British numbering and red as used in the Canadian documentation

 

 

 

 

 The thirteen valve line-up (with equivalent codes) is as follows :-

V1A RF Amplifier, ARP3

V1C Mixer, ARP3

V1B Conversion oscillator, ARP3

V1D 1st IF amplifier, ARP3

V1E 2nd IF amplifier, ARP3

V2A Detector and AVC, ARDD1

V2B Noise limiter, ARDD1

V1F Heterodyne oscillator, ARP3

V1G 1st AF amplifier, ARP3

V1H 2nd AF amplifier, ARP3

V3A Crystal calibrator oscillator, 12SC7

V3B Crystal calibrator multivibrator, 12SC7

V3C Crystal calibrator harmonic exaggerator, 12SC7

 Valve details:-

Note that I'm quoting British valve base numbers as per Wireless World Valve Data books, not those given in the circuit diagram.

ARDD1=10D1=12Y4G=2D13C=CV1300
Heater 13.0 volts at 200mA
Max input 50 volts RMS and max rectified current 1mA
B5: 1=a', 2=a'', 3=h, 4=h, 5=k

 

ARP3=9D2=12VPA=CV1321=CV1106=VR106
Heater 13.0 volts at 200mA
Anode 250 volts and 10.5mA, ra=0.6Mohm
Screen 125 volts and 2.6mA
Grid -3 volts and gm=1.65 mA/V
Variable mu
B7: 1=Metalising, 2=a, 3=g3, 4=h, 5=h, 6=k, 7=g2, TC=g1

 

12SC7=CV540
Heater 12.6 volts at 150mA
Anode 250 volts and 2mA, ra=53Kohm
Grid -2 volts and gm=1.3mA/V
IO: 1=Metalising, 2=a'', 3=g'', 4=g', 5=a', 6=k, 7=h, 8=h

The valves are generally 13 volt/0.2A heater types designed for use with a 12-volt battery (= circa 13.2 volts).

The 12SC7 is a double triode metal valve with an International Octal base. This has a 12.6 volt heater taking 150mA

The intermediate frequency (IF) is 420KHz.

I should mention component identification.. tricky because wiring harnesses are generally used between valve pins and resistors and condensers.

 

A couple more views before I power up the receiver maybe for the first time in over 70 years?

Above the rear view showing the power connector (top right) for frame-mounting with matching transmitter etc. and below with front uppermost with loudspeaker central. No nasty unreliable wax condensers. Where non-standard resistor values were specified by the designers you'll see instances of paralleling standard values, for example 600Kohm = 2 x 1.2Mohm (below centre).

 

 

 

 These low voltage power supplies are very useful as they allow you to crank up the current limit to avoid any nasty explosions and smoke. With valve heaters their resistance when cold is very low so the voltage stays low and gradually increases as the heaters warm up. In this case 10 heaters at 200mA and 3 heaters at 150mA plus a couple of dial lamps should be about 2.65 Amps but due to slight voltage drop in the wiring of half a volt and the fact that the correct heater voltage should be 13 volts for the 10 B7/B5 valves the measured current is only 2.3Amps.

Both the main receiver and the crystal calibrator are operating to draw this current. In order to reduce battery drain in the field the calibrator can be switched off, which is the setting I'll be using for most of the testing.

Below, the chassis with the top section of the front panel detached.

I'm using my Solartron HT power supply for testing. The front panel meter on the receiver reads low at 200 volts with 250 volts running 80mA from a variable HT supply.

The tuning dial is set to 80 metres and I can hear an SSB QSO coming in nice and clearly, although I found the Het Tone control only works when fully anti-clockwise.

The valves top right (below) are the RF amplifier, mixer and local oscillator. Access for fault-finding is pretty good except the power connector will need removing to get at the wiring to two of the three RF valves. The set of nine RF trimmers and dust cores are nicely labelled and arranged as are the IF trimmers. Top left are the all-metal crystal calibrator valves.
 

 The receiver came to life with 250 volts HT (instead of no more than 150 volts) and running 80mA which is actually very stable but seems too high for comfort. It's quite likely there are leaky condensers or bad resistors to blame. The meter also reads low and suggests that resistors have drifted high. Checking the valves at the meter gives the following.. Note these valve readings are measured at the valve cathodes except for V1b whose grid current is monitored. Figures in brackets are from the handbook. True HT was 250 volts and LT 12.5 volts.

HT 200(150), LT 9.2(12.5), V1a=2(2.3), V1b=15(7.0), V1c=2(3.0), V1d=15+(11), V1e=15+(11), V1f=7.5(3.2), V1g=0(2.3), V1h=13(9.6)

No doubt these readings will provide some clues to explain the reason for the elevated HT? First I'll need to check the meter sensitivity, then compare the various cathode resistor etc values against those given in the circuit. At first sight V1b, V1d, V1e and probably V1h are drawing too much current with V1a, V1c and V1g too little, and the resistor from the HT line looks to be more than 20% high in value.

After a few minutes checking resistor values, intially under the lower chassis, I found an open circuit resistor marked 1Mohm (audio amplifier, V1g screen grid resistor=R59b). I fitted a replacement and switched on the receiver, gradually turning up the HT. At 172 volts it became quite lively and 80m SSB QSOs resolved vey well. A check of the metered points was now as follows (with the HT now reduced from 250 to 172 volts.. but still slightly higher than the nominal 150 volts):

HT 145(150), LT 9.2(12.5), V1a=1.5(2.3), V1b=9.5(7.0), V1c=0(3.0), V1d=14(11), V1e=14.5+(11), V1f=5.5(3.2), V1g=2.2(2.3), V1h=9(9.6)

Now V1c (the mixer) which previously read 2.0 is now reading low at zero volts. Looking at the circuit diagram the bad resistor appears to be the anode/screen grid resistor R48h as one end of the new resistor is sitting at 167 volts and the other at 14.5 volts. A new 100Kohm resistor on Tagboard AR restored the current through the mixer.

At this point I decided to check the metering circuit. The meter used in the receiver has an FSD of 0.5mA so the various resistors to produce correct readings can be worked out and compared with the marked values and more importantly their measured values. From some of the readings above it's likely that several resistors may need changing. As that point I haven't found a key to the resistors and condensers so I halted proceedings in order to identify these and mark them up on pictures, mainly tagstrips.

 Click to see Parts Listings Resistors Condensers Miscellaneous

Below.. parts identified.. an ongoing process

Note that, as was common in much WW2 equipment, component numbering was in three parts: Type of component (V, R, C, L, etc.), a number representing the physical item (eg. 2, which might represent a resistor value in ohms, tolerance and wattage) plus its circuit identifier (a, b, etc). Another point to mention is that it was common in British-designed receivers to use a minimum number of valve types. This meant you could reduce the number of spare valves, and also manufacturers could concentrate on producing many valve types in bulk.

As I identify the parts I'll add the circuit identifiers. Most small components in this receiver are fitted to tagboards and sometimes these are remote from other associated circuit parts. The drawing below shows the location of the various tagboards which are shown further down this page.

Note that several resistors are hidden under decoupling condensers, for example R31a and R20g on Tagboard BR.

 

 

 Cct Ref

 Value

 Cct Ref

 Value

 Cct Ref

 Value

 Cct Ref

 Value

 C1

 20pF

 C11

100pF 

 C31

 2pF

 C48

 0.002uF

 C2

 4-30pF var

 C20

 0.01uF

 C34

 80pF

 C49

 25pF var

 C3

 0.1uF

 C26

 0.002uF

 C43

 250pF

 C50

 150pF

 C4

 441pF var

 C27

 500pF

 C44

 1004pF

 C51

 1pF

 C7

 100pF var

 C29

 350uF

 C45

 1060pF

 C8

 50pF

 C30

 150pF

 C46

 1349pF

 C10

12uF 

 C31

 0.01uF

 C47

 7pF

 

 Cct Ref

 Value Ohms

 Cct Ref

 Value Ohms

 Cct Ref

 Value Ohms

 Cct Ref

 Value Ohms

 R4

 8

 R25

 3K

R43 

 25K

 R52

 200K

 R13

 300

 R27

 5K

 R44

 30K

 R54

 250K

 R14

 300 var

 R28

 5K

 R45

 30K

 R55

 300K

 R17

 500

 R29

 5K var

 R47

 50K

 R56

 500K

 R19

 600

 R31

 10K

 R48

 100K

 R58

 600K

 R20

 1K

 R32

 10K

 R50

 100K var

 R59

 1M

 R23

 2K var

 R33

 10K var

 R51

 150K

 R60

 4M

 

 

 

 

 

 

 

 

 

 

 

 
 
 

 Valves are not too fussy about resistor values. Often the original values are specified as widely as +/-20% but components (in this receiver dating back to 1944) can drift way beyond this (very rarely downwards) and eventually reach the point where circuits don't work very well.

The first fault was the excessive level of HT needed to hear anything because the 1Mohm resistor feeding an AF amplifier screen grid was open circuit. Then the mixer suddenly ceased to draw much current and then I discovered the BFO would only work when the meter switch selected the BFO valve. The 1Kohm cathode resistor measured 4.6Kohm (this resistor was shunted by the 0.5mA meter circuit when V1f was selected).

When the meter switch was set to LT it read 9.2 volts instead of 12 volts because the monitor resistor comprising a parallel pair of 60Kohm resistors measured 69 and 70Kohms. Similarly the HT read 40% less because the parallel pair of 1.2KMohm resistors measured 1.5 and 1.7Mohms. When this types of resistor fails it can also vary in resistance depending on the voltage across it so removing it and measuring its resistance with an ohmeter may not fully account for the low meter reading.

 Once the worst resistors (a sample shown above) had been swapped the receiver worked surprisingly well and was very stable reading 80m SSB. I noticed that the selector switch that was supposed to allow AVC to operate had no effect in either AM or CW settings so a further fault is waiting to be discovered. V2a is used for AVC by rectifying the IF signal. The other double diode at V2b as a noise limiter is working properly.

AVC is developed by one of V2a diodes fed by C8a (50pF), However the AVC is what's termed "delayed AVC" and this only operates once the detector diode is turned on. The cathode of V2a is fed by the positive voltage across the cathode resistor of V1h (R19a) so, if R19a is high in value AVC may not operate. That voltage is smoothed by a 12uF condenser (C10a) and these types of condenser rarely survive but it seems the Canadian version made in 1943 is fine... a bit high in value but a very low ESR... a little over half an ohm.

Now that more bad resistors have been swapped here are the monitored readings.. Note: V1f must be read in the CW setting, otherwise it will be zero, and LT is slightly low due to cable losses. During fault-finding and repairs, the HT voltage had been reduced progessively from 250, to 172 and finally 150 volts as the receiver performance had improved.

HT 150(150), LT 12(12.5), V1a=1.0(2.3), V1b=1.0(7.0), V1c=3.5(3.0), V1d=12(11), V1e=12(11), V1f=2.5(3.2), V1g=1.5(2.3), V1h=7.5(9.6)

Still some anomalies.. including V1a and V1b?

Note that on Tagboard KR you'll see pairs of resistors in parallel. My guess is that these had been selected to provide a better tolerance than standard resistors because they are used for metering important voltages. For example to provide the correct deflection on the 0.5mA meter (M1a) from the 150 volt HT line you need 600Kohm. To get close to this value a pair of 1.2Mohm resistors were used in parallel. Although R58a is specified as 600 Kohm it's actually 2 x 1.2Mohm.

The same applies to the 10Kohm metering resistors R32b and R32c which are each made from 2 x 20Kohm.
 

 The receiver is now working well enough to check calibration etc. Using a portable receiver I found the BFO was tuning from 406 to 411KHz, fully anti-clockwise to fully clockwise which is odd as I can resolve LSB. I then checked the IF. No luck injecting a signal at the aerial terminals (see later for the reason) but I connected the signal generator to the top cap of the mixer and found the IF was on the correct frequency of 420KHz although I'm not sure if the Sharp setting is exactly lined up to this. I checked each waveband and the worst discrepancy was an error of 300KHz where a dial setting of 8MHz responded to 8.3MHz on Range 2.

The next day I aligned the IF amplifiers and the BFO to 420KHz. This entailed connecting an audio wattmeter across the loudspeaker and setting my signal generator to 420KHz with 80% amplitude modulation, then connecting the signal to V1b, the mixer top cap. With the volume turned up and the minimum RF signal I adjusted the sharp and wide IFT trimmers, reducing the RF input as the audio level increased to minimise any effects of AVC. The receiver sensitivity, which was already good, improved dramatically and, after resetting the BFO to centre on 420KHz, SSB was easier to resolve. The next step is to adjust the IF response so that it's symmetrical with a good skirts. This used to be done using a wobbulator (or even manually by plotting the curves) but using a spectrum analyser it is very easy. After that I can then align the RF front end so that frequency coverage matches the dial readings and has reasonably flat response across each of the three bands.

Below a view of the BFO signal measured at V2a, Pin 3 (signal rectifier anode). Because the BFO setting potentiometer does not give a linear tuning range it's not ideal to set the Het.Tone knob to its centre position at 420KHz. To get a balanced setting I first measured the tuning limits, then calculated the average frequency and with the control at its centre position adjusted the BFO trimmer to this frequency. As you can see the BFO range is 4.5KHz (equating to +/- 2.25KHz) so the pot was centred at a reading of about 419.08KHz. The end result gave a range of 421.332-416.832=4.5KHz. With the Het.Tone knob in its centre position the BFO frequency was a little over 419KHz.

 

 

 

 BFO with setting at maximum frequency

 BFO with setting at 420KHz

 BFO with setting at minimum frequency
 
 Up to this point, the IF had been adjusted using an audio wattmeter for maximum output. I've found through experience that this method rarely gives the correct results. Usually the centre of a tuned signal ends up either higher or lower than the correct IF by as much as a couple of KHz. To get a better idea of the IF response a very high impedance probe feeding a spectrum analyser was connected to V2a Pin 3 (signal rectifier anode) and the analyser tracking generator connected via small condenser to V1b (mixer) grid. The trimmers seen on the "IF Tuning" picture above are grouped under Sharp and Flat. These are very interactive and have extremely sensitive settings but, by trial and error, the response curves for the two bandwidth settings were centred on the 420KHz centre frequency. The fundamental shape of these two curves will be governed by the components originally fitted in manufacture and it's not sensible to check these as it would almost certainly involve replacing both condensers and coils as all will have drifted over the years from their original characteristics. What we're looking at below is the best performance of the 1944 receiver some 70 odd years after manufacture.

 

 

 

Sharp Setting 

As you can see, the overall scan was 400 to 440KHz making each division 4KHz. The skirts are 60dB down with the 3dB points about +/- 500Hz around 420KHz.

 

 

 

Flat Setting 

In the broader setting the signal was 4dB stronger. The skirts are better than 65dB down with the 3dB points about +/- 2KHz around 420KHz.

As a comparison my R1155 has skirts 50dB down so the 52 receiver would seem to have a superior performance, perhaps because of its more spacious interior layout?

Another reason is of course degradation of parts, for example the dust cores used in the R1155 IF transformer coils.

 It's worth looking at the EMER in respect of aligning the IF strip. The method used is to inject the test signal at various points in the circuit and to peak the readings on the audio output. The method I used initially was similar to this but when I checked the results I found that adjustments had resulted in two humps in the wide setting. This produces an undesirable effect when tuning across a signal and with SSB may result in one or other peak being a KHz or two off-centre with the BFO having to compensate. If the BFO isn't able to track the signal, interference from adjacent off-frequency transmissions may result. Using the tracking generator got rid of the double hump by enabling the merging of the peaks from the IF transformers into a single peak at the correct frequency. Without a tracking generator it's also possible to inadvertently tune the narrow and wide responses to two different frequencies which is annoying because switching to the narrow setting to improve readability means having to retune the receiver.
 

 Next, I tackled the RF alignment. Trimmers and coil adjustments are logically laid out so it was easy. If anyone decides to tackle one of these receivers take care with the 3-30pF trimmers as they can seize and you'll end up with a broken ceramic rotor. Try rocking the slot right and left very gently using a snug fitting flat screwdriver. Because these trimmers can be a bit jerky in operation it can be tricky getting the oscillator trimmer to peak up a signal, especially if AVC is active so my suggestion is to readjust the tuning knob once the oscillator trimmer has been set. This way you can adjust the RF stage trimmers to exactly the same frequency as the oscillator setting. All three bands aligned nicely to the tuning dial settings. I noticed the highest band was slightly deafer then the other two. Something like 4uV compared with 0.5uV to see a similar decent rise in the audio wattmeter reading. Either the receiver never was as sensitive on the highest band or something is wrong (possibly the RF amplifier V1a because its cathode current as measured through R13a is close to zero) ?

Before I got underway with alignment I'd checked around V1a. The meter showed a very low cathode voltage compared with say V1c and V1d so I measured the cathode resistor and the resistor feeding g2. R13a, marked 300 ohms read 756 ohms and screen grid resistor R54c marked 250Kohm measured 2Mohm so I fitted a new 300 ohm and a new 240K ohm expecting to see a change in performance. In fact there was no noticeable difference, with V1a reading around 0.8 volts with the RF gain at max. On the subject of RF gain control, the WS52 design is slightly odd in that, rather than inserting extra resistance in the cathode of V1a and V1d (the 1st IF amplifier), the RF gain pot is used to select a voltage from zero to about plus 40 volts. As the voltage is increased it makes the grids of the valves more negative than their cathodes, reverse biasing and cutting off V1a and V1d. Looking at V1a, with its cathode at ground via R13 and with g2 and anode positive, current will flow through R13a developing a voltage. As V1a and V1d both have a cathode resistor of 300 ohms you'd expect the voltage across their cathode resistors to be much the same, however V1d has 12 volts and V1a has less than 1 volt, even after renewing the bad resistors. Both V1a and V1d have the same AVC voltage applied to their grids so what's going on? Is V1a low on emission perhaps?

Before leaving alignment, I'll mention the aerial circuit. There are two connectors on the front panel, one of which is marked "AE" and the second I'd naturally assumed was ground. When I started IF alignment I'd connected the signal generator across these two connectors and discovered what I'd thought was an astounding degree of attenuation of 420KHz between the aerial and the IF amplifier, so instead connected the 420KHz signal to the top cap of the mixer stage. Later, when I started RF alignment I found I needed tens of millivolts to hear anything in the loudspeaker, but when I disconnected the ground connection the speaker blasted out a very loud tone. The penny dropped and I found the two terminals both connect to the same input point and no ground connection is provided next to the aerial terminal. This is similar to the power connector at the rear of the chassis where no ground connection is provided. Clearly the overall frame into which the equipments mount deals with the LT and HT negative returns, as well as any grounding for the aerial. Because my receiver does not have an outer case and isn't mounted in a frame and uses a bench power supply, I lifted off the -1200 connection from its pin and instead wired this pin to chassis enabling all the power connections to be made by a single plug. Checking the circuit diagrams (I have two) revealed the poorer quality circuit shows aerial connections but the better quality circuit had strangely omitted any aerial connection. Whoever drew this had forgotten to show the aerial input terminals so I've now added them.

 
 Next.. I must tackle the crystal calibrator because I can only just hear one or two very weak Mc/s blips. Not too easy as the chassis needs to be detached from the main receiver.
 
 

 pending.. watch this space
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