INTRODUCTION

The WS No.11 is an HF radio transceiver (a combined transmitter and receiver) with a common frequency selecting dial. This is a general purpose set for communications over short distances, 20 miles. The frequency range is 4.2 to 7.5 MHz on both transmit and receive. There is a variable frequency dial, but there is no provision for crystal control. The transmitter on high power, provides 4.5 watts CW, and 1.5 watts R/T output. When switched to low power, the transmitter provides 1.5 watts CW, and 0.6 watts R/T output. The radio can use a vertical whip or a long wire aerial

Picture 1: WS No.11 Front View

The receiver uses 6 valves and is a super heterodyne type with and IF frequency of 475 kHz, and includes a BFO for receiving morse code. The transmitter uses 2 valves to send AM and CW signals. However, the transmit signal is generated from the receiver. The receiver local oscillator is mixed with the BFO, buffered by the receiver RF amplifier, before being applied to the transmitter PA valve. So the transmitter actually uses 3 of the receiver valves, thus actually employing 5 valves in the transmitter. By using the receiver oscillator, the transmitter is automatically on the receive frequency. This method removes the need for NETTING. The oscillator used for CW is called the BFO (Beat Frequency Oscillator), but the manual refers to it as the Beat oscillator, or Heterodyne oscillator, or IF oscillator.

The radio weighs 43 pounds and is 19.5 inches wide, 8.5 inches high, and 12.25 inches deep. The power supplies add additional weight and size, 14 and 11 pounds, 4.5 inches wide, 8.5 inches high and 11 inches deep.

There are four different power sources. For portable use, the radio can be operated from batteries (6 volt and 240 volt). For vehicle use, the radio can be operated from a dynamotor power supply, either 6 volt or 12 volt. For high power use, an additional high power dynamotor can be added, thus there being 2 dynamotor power supplies, for HP operation.

The radio is intended to replace the Wireless Set Number 1. The Manual is dated 1939 and the radio was issued to Cavalry, Armored Corps, Artillery, Signals, Motorcycles, and the School of Signals. The radios were a standard issue for trucks, tanks, and as a portable station. The Long Range Desert Group used them in the Egypt desert. Many of the WS No.11 radios were abandoned when the BEF evacuated from Dunkirk. The Germans used the radios and provided their own operating instructions, in the German language.

Britain was unable to produce the number of radios required for use, so samples were given to Canada and Australia, and they were asked to produce the radio, using locally available materials. The Canadian version was made by Canadian Marconi and the Australian version was made by AWA. They had to be the same size as the original British radio, and have the same connectors, so that they could be swapped into a vehicle, and be completely electrically the same.

Picture 2: WS No.11 Inside View

CONTROLS

All the controls are on the front panel.

Along the top, at the left hand side, is the switch that selects MAN, AVC, or CW control of the receiver gain, marked as REC. Next is the aerial terminal, marked as AE. Next is the ammeter for measuring the aerial current on transmit. It plugs in and the 350 mA meter, used for low power, can be changed for a 1 A meter, for high power. Next to the right, is the REC AE TRIMMER, used to peak the receiver tuning. This will change as the dial is moved across the frequency band, and depending upon which aerial is used. Then there is a watcholder. At the right are 3 transmit controls. The first is the HP/LP switch. The HP position needs the extra external HP power supply. The next control is the modulation level, marked as MOD. This determines the amount of speech modulation applied. The last control at the top right, is the emission control marked as the SEND switch and selects SPEECH or CW.

In the middle, at the left hand side, is a small chart (TUNING TABLET) that contains the tuning switch settings. The operator can write the values for his current setup. There are suggested settings on the chart. The gain control is below this, marked as REC VOL. This is an audio gain control for AVC, or an RF gain control for MAN and CW. The large metal casting, protruding from the front panel, is the tuning dial. It has a frequency window, reduction gearing, and a tuning knob. The tuning knob, labeled FINE ADJUST, is used to change the frequency. The knob in the center is not used, until the T shaped clamp in the center is slackened. This is then the main tuning, and allows a quick traverse to a new frequency. The window at the top, shows the dial frequency. This has a large snail cam inside, and the pointer moves down as the dial is rotated. There is a dial light behind the pointer and the frequency scale.

In the center of the front panel, is a large white lever switch. This changes the radio from receive (REC) in the upper position to transmit (SEND) in the lower position. To the left is a 13 position switch to select the aerial tap (AE TAP). To the right is a 13 position switch to select the anode tap (AN TAP) on the power amplifier. To the right again is the transmit tuning capacitor, marked as SEND AE TUNE. This does not interact with the REC AE TRIMMER. Finally at the right, is the 10 point input connector from the power supply. There is an earth terminal located just above this, for connection to the adjacent power supply.

Picture 3: WS No.11 Control Layout

Along the bottom row, at the left, is an EARTH terminal, so that a counterpoise can be connected. Then there is a small Bakelite panel, that has the audio connections. There are 2 headphones sockets (PHONES) and a LINE connection. In the next position, at the left, is a connection for an external morse key, used for the remote control. Then there is the CRASH level control, that allows the clipping of large audio peaks. In the centre, is the VALVE TEST PANEL. This allows testing of the valve anode voltages within the radio, and also the connection of an operators lamp if needed. Next to this are 2 buttons. The top one can be pulled out, to enable remote control, marked PULL FOR R.C. The bottom one can be pushed in, (PRESS TO TUNE) which allows the radio to zero beat to a received station, using the main tuning dial. The BFO is turned on at 475 KHz and the variable BFO control is in-operative. To right of this is the BFO control, marked as CW HDYNE. Next is another small bakelite panel, that has the microphone and morse key jacks. At the extreme right is the high power input socket, only used when running high transmit power.

MECHANICAL DESIGN

The radio is a conventional mechanical design. There is a large chassis attached to the front panel. These are all made of aluminium, and the radio slides out forwards from the aluminium case. The receiver is located at the left hand side (looking at the front), then continues along the back, then along the right hand side. The transmitter is in the centre. The tuning capacitor, valves, and the IF transformers all have shields. In addition to the metalized valve shield on each valve, there is a detachable shield can. There are shields beneath the chassis as well, and most components are mounted on tag strips. There are 4 angle brackets, which hold 44 bolted on can mounted capacitors. The central transmit receive switch operates 2 multi contact switches, by means of a series of levers.

Picture 4: WS No.11 Back View

There is a lid which attaches to the front to protect the controls. When the lid is removed, it has 2 feet that fold out, and this makes a small table 8 inches high, that the radio can rest upon. This is useful for portable operation.

When mounted in a vehicle, a set carrier frame is used. This holds the radio in place and allows the Low Power supply to be attached to the right hand end. If high power operation is required, the set carrier can be extended to the right, and the High Power supply added to the right hand end. If there is no space for the extension, the High Power supply can sit in a cradle on the top of the carrier frame and is secured by a leather strap.

The aerial used for vehicle operation is a whip. When the radio is used for ground operation, a larger whip, or a top loaded whip, or a long wire aerial may be used. If required, this can be placed at some distance from the radio, using an Aerial Coupling Unit Type C. Alternatively, if the operator is required to be some distance from the radio, a Remote Control type A is required.

Picture 5: WS No.11 Bottom Shield

ELCTRICAL DESIGN

This radio was the first designed radio to be a transceiver, not just a transmitter and a separate receiver in the same case. What this means, is that when you have tuned to a station, you do not need to adjust the transmit frequency, as they are the same. There is no need to NET to the station, as the transmit frequency is derived from the receiver frequency.

The WS No.11 uses 8 valves. The receiver uses 6 of these valves, and is a super heterodyne type. The transmitter uses 2 valves. In addition, it uses 3 valves of the receiver, 5 in total. All the valves are directly heated valves, with an earthed metalized coating on the glass.

When receiving, the aerial is connected to the RF amplifier valve (a pentode type ARP4) and there is a tuned circuit, which uses the main tuning dial. This is a three gang variable capacitor. In addition to this there is a knob which can be adjusted to allow for different aerial matching, when receiving. This is the REC AE TRIMMER control. There is AVC on this stage.

The plate of the RF amplifier is tuned with the main tuning dial, and capacitor coupled to the next stage.

Picture 6: WS No.11 Circuit

The mixer is a pentode and triode in the same envelope (type ARTP1). The plate passes through a double IF transformer (which has 4 tuning slugs), with a pass band of 9KHz. This is coupled to the next stage. The IF frequency is 475 KHz.

The triode oscillator in this valve is tuned by the same tuning capacitor from the dial. It oscillates above the received frequency. It is coupled to the screen grid, as injection for the mixer.

Picture 7: WS No.11 Top View

The grid of the first IF amplifier (a pentode type ARP4), comes from the first IF transformer. The plate passes through another double IF transformer, and is coupled to the next stage. There is AVC on this stage.

The grid of the second IF amplifier is connected in the same way (type ARTP4), and comes from the second IF transformer. The plate is coupled using a third double IF transformer, to the last IF stage. The BFO is injected into this amplifier, by using an unconnected pin on the valve socket. This stage has no AVC control.

The grid of the third IF amplifier, is also the same (type ARP4), and comes from the third IF transformer. The plate is coupled using a single winding IF transformer, to the detector.

The detector diode is a WESTECTOR, a metal rectifier in a small tube, an older style of solid state diode. The audio is filtered and applied to an audio amplifier pentode (type ARTP1), and the to the output transformer. This has 2 diodes (small selenium stacks), back to back, and a level control (CRASH LEVEL) so that any loud noises (atmospherics) can be clipped. The headphones jack is on the front panel.

The triode in the second ARTP1 is wired as the BFO, and used to receive CW signals. This has a variable control, to change the BFO frequency by 10 KHz. A press button on the front panel (PRESS TO TUNE) operates the BFO, so that accurate tuning to an incoming signal can be achieved. The BFO uses a fixed frequency for this function.

Picture 8: WS No.11 Underneath View

At the same point where the audio detector is located, is the AVC rectifier. This diode is also a WESTECTOR. The AVC voltage generated here, can be switched IN to provide AVC for the RF amplifier and IF amplifier, when the REC switch is in the AVC position. The REC VOL control is an audio gain control. When in the MAN position, the AVC is disconnected, and the REC VOL control becomes a manual gain control. This is the same for the CW position, but the BFO is turned on as well. There is a voltage divider from the HT to the -1 volt back bias point, to allow an offset (or delay), before the AVC operates, and this prevents the AVC from affecting low level received signals.

There is a valve test panel on the front of the radio. This enables the voltage drop across the anode resistance of each valve to be measured. The positive lead of the measuring meter is placed on the RED symbol. When the negative lead is placed on the terminal for any valve, the voltage can be measured, and the current drawn by that valve can be determined. Alternatively, the negative lead can be connected to earth, and the anode voltage of each valve can be checked, by placing the positive lead on that valve test pin. This can all be done, without removing the radio from the case. There are also 2 pins, that provide 6 volts, so an operators lamp can be connected. In addition, the 6 volt filament supply can be measured.

All the filaments are connected in a series and parallel arrangement, so that the radio can use 6 volts for the filaments. The valves are a 2 volt filament type, so 3 valves in series, are powered by 6 volts. Other valves have an RFC between them to isolate the filament to prevent any signal coupling. The RFC has a 1 volt drop across it, so these add up to 6 volts as well. The power amplifier valve has a 6 volt filament. The 6 volts input is applied to 4 individual pins on the 10 point input connector.

Picture 9: WS No.11 Filament Arrangement

There is a 0.1uF capacitor from each filament pin to earth, to prevent any coupling between valve stages, and to protect against any introduced external noise (possibly vehicle noises). There are 3 other 6 volt input pins on the connector. One goes to the dial lamp. Another goes to the operators lamp connections on the test panel. A further connection is used for powering the microphone and the keying relay. The external carbon microphone requires power. The keying relay is used for CW transmission, and also when the remote control box is used.

The bias arrangement for the radio is dependent on the filament voltage drops of each valve, the back bias from the HT negative resistors, and the AVC voltage. The bias is complicated. The back bias uses 4 resistors in series, and has a total drop of 28 volts negative, with respect to earth, thus providing -28 volts, -11 volts, -2.5 volts, and -1 volt. This may vary, depending on the current drawn by the radio. The gain control is across this voltage divider, from the top (-28 volts) to the third resistor (-1 volt). The gain control selects this bias voltage when in the MAN switch position. When in the AVC position, the bias voltage from the rectified received signal is used.

The RF amplifier has the variable bias voltage, connected to its grid, so has either MAN or AVC controlled gain. The mixer has a resistor connected to an RFC and then connected to the 3 volt filament pin. This provides a fixed grid bias of -2 volts. The mixer suppressor grid has a fixed bias of -2.5 volts from the back bias voltage divider. When oscillating the mixer triode, develops its own bias across its grid resistor. The first IF amplifier has the variable bias voltage, connected to its grid, so has either MAN or AVC controlled gain. On the second IF amplifier, the fixed grid bias comes from the 2 volt side of the filament. There is a resistance voltage divider, which provides -1 volts for the grid. On the third IF amplifier, the fixed grid bias comes from the 3 volt side of the filament. There is an RFC here, and the voltage drop across this, provides -1 volt for the grid. The audio amplifier has a small part of the variable bias voltage, connected to its grid, so has either MAN or AVC controlled gain. When oscillating, the BFO triode develops its own bias across its grid resistor.

In the transmit mode, the RF amplifier has a fixed grid bias of -1 volt. The transmitter mixer has a fixed grid bias of -2 volts, and a screen grid bias of -2.5 volts. The power amplifier has a fixed grid bias of -2.5 volts from the back bias voltage divider. The screen grid is grounded for CW, or has -11 volts when sending speech.

When the radio is switched to transmit, the receiver triode oscillator is still operating. This is used as the transmit frequency oscillator, even though it is 475 KHz higher than the transmit frequency. The oscillator output is connected to the screen grid of the transmit mixer (type ARP4). The plate circuit has a compensating capacitor to allow for the differences between receive and transmit operation. The BFO is turned on, and is coupled to the transmit mixer grid. The normal BFO variable control is switched out, and a fixed coil is connected, to set the BFO at exactly 475 KHz.

The output of the transmit mixer is connected to the RF amplifier, which is now used as a buffer amplifier and filter. There are several frequencies present, the BFO frequency, the oscillator frequency, and the transmit frequency. The aerial tuned circuit and the plate tuned circuit, only allow the transmit frequency to pass through. The grid and plate circuits each have a set of compensating capacitors to allow for the differences between receive and transmit operation.

The transmit frequency is now connected to the power amplifier grid. The plate output is connected to the tank coil by the AN TAP switch (anode tap). This switch has 13 positions and must be adjusted for the maximum aerial current. The switch position will vary, depending on the frequency. The SEND AE TUNING knob is used for fine adjusting of the aerial current.

The aerial connection also has a switch (AE TAP) which has 13 positions and is adjusted for the maximum aerial current. The current is read on the meter, which is connected to the aerial terminal.

The transmit signal is always applied to the power amplifier grid, while the SEND lever switch is down. When sending CW, the screen HT supply is earthed through the keying relay. When the morse key is pressed (local or remotely) the keying relay applies HT to the screen. The screen voltage is higher when the power switch is set from LP to HP. The screen grid is earthed. When sending RT, the lower HT is always connected to the screen. When the power switch is set from LP to HP, the power amplifier plate supply is connected to the 3 pin front panel connector, to be supplied with a higher voltage from the HP power supply. The screen grid is connected to the microphone transformer secondary. The bias is changed from -11 volts for LP to -28 volts for HP.

The microphone is connected to the 6 volt supply, through the transformer primary. It has a gain control to set the modulation level. The external LINE input is also connected to this transformer. RF is picked up by a rod near the power amplifier. This is rectified by a third WESTECTOR and filtered to be applied to the audio amplifier. This is the side tone for the transmitter.

ACCESSORIES

This is a general purpose radio set, and it has several accessories so that it can be used in different applications.

When fitted to vehicles with a whip aerial, there is a capacitor (type X5 5KV) which is in series with the whip connection to the radio. This is located on top of the mounting frame. It is intended to protect the radio and the operator, from high voltages, perhaps from whip contact to overhead power lines.

Picture 10: WS No.11 Capacitor X5 5KV

A remote Aerial Coupling Unit Type C, allows the aerial to be located at a distance of up to 30 feet from the radio. This allows a remote rod aerial to be tuned. There is a variometer to match the aerial, and a meter to show the aerial current. The mater can be used for HP working, or by pressing switch, for LP working. There is a special 15 foot cable for coupling to this remote unit.

Picture 11: WS No.11 Aerial Coupling Unit Type C

There is a special adapter for connection to the remote aerial cable. There is a large insulator for the external whip.

Picture 12: WS No.11 Insulator for Ground Mounted Whip and Aerial Coupling Cable.

The Remote Control Cable connects the radio to the unit. It plugs into the headphones, key, and microphone sockets on the radio. The counterpoise is connected to the EARTH terminal.

Picture 13: WS No.11 Remote Control Cable and Counterpoise

The Remote Control Unit Type A allows the radio to be operated from a distance. It is the same one as used by the WS No.1. It requires 2 remote controls, and 2 operators, one at the radio, and one at a remote distance. The operator present at the radio, changes from RECEIVE to SEND, and tunes the radio. The operator at a distance can call by buzzer or by the phone line, or use the morse key. There is a buzzer at each end to attract the operators attention.

Picture 14: WS No.11 Remote Control Unit Type A

Picture 15: WS No.11 Headphones CLR Mk III

Picture 16A: WS No.11 Microphone No.3

There are 2 meters required, a 350 milliamp thermo couple for low power, and a 1 amp meter for high power. The meter plugs into the front panel.

Picture 16B: Ammeters for Low and High Power

POWER SUPPLY (LP)

The LP (Low Power) supply unit is used for receive and when the transmitter switch is set to low power. It is a separate unit, in an aluminium case, and is normally placed at the right hand end of the radio, on the mounting frame. There is a 2 point cable required for connection to the main 12 volt battery, or a 6 volt battery if the 6 volt unit is used. It provides 240 volts DC. There is a 10 point cable for connection to the radio. In addition, if a HP supply is used, two 3 point cables are required as well. This supply was made by McMICHAEL RADIO Ltd. in 1940.

Picture 17: WS No.11 Power Supply Unit LP

The LP supply unit has 2 levels with a horizontal chassis. The lower level has the dynamotor, and this is mounted on a steel plate with rubber insulation between it and the bottom of the case. The upper level has an aluminium panel supporting the filtering and dropping resistors. The plate is often bent, as it has no strengthening ribs, and it supports 2 filter chokes. When the power supply is dropped, or it is returned roughly to the case after a service, the weight on the chassis can bend it. This also applies to the dynamotor, and this can bend its mounting plate as well, which may occur when the PSU is dropped on its rear end.

The supply has 3 separate functions; generate high voltage for the radio, provide dropping resistors for the valve filaments in the radio, and provide connections for the HP power supply. The 12 volts DC input comes in through the 2 point connector and goes to the large ON/OFF switch.

The 12 volts DC then goes through a filter to the dynamotor input brushes. The filter has 2 windings and 2 capacitors. There are another 2 capacitors actually on the dynamotor, actually on the input brushes. The output of the dynamotor goes though a single filter choke and 2 capacitors. At the output brushes, are another 2 capacitors actually on the dynamotor. There is a resistor across the HT supply. The output voltage then goes to the 10 point connector for connection to the radio.

The 12 volts DC then goes to 8 high wattage resistors, which are voltage droppers for the 8 low voltage circuits. R22A goes to the 10 point connector on pin 1, then goes to the radio and then to the valve filaments in V2A and V2B. R25B goes to the 10 point connector on pin 2, then goes to the radio and then to the front panel, so that a small lamp can be connected to the TEST panel. R23A goes to the 10 point connector on pin 3, then goes to the radio and then to the valve filaments in V1B and V1D. R25A goes to the 10 point connector on pin 4, then goes to the radio and then to the dial lamp in the radio. R23B goes to the 10 point connector on pin 5, then goes to the radio and then to the valve filaments V1A and V1C and V1D. R24A goes to the 10 point connector on pin 6, then goes to the radio and then to the power output valve filament V3A. R25C goes to the 10 point connector on pin 7, then goes to the radio and then to supply the carbon the microphone circuit, and the keying relay. R25D is for the ON dial light in this LP supply.

Picture 18: WS No.11 Power Supply Unit LP Circuit

Picture 19: WS No.11 Power Supply Unit LHS

Picture20: WS No.11 Power Supply Unit TOP

Picture 21: WS No.11 Power Supply Unit RHS

This unit requires one 2 point connector for the voltage input. It requires a 10 point cable for connection to the radio. If the HP unit is connected, it requires two 3 point cables.

Picture 22: WS No.11 Cables

POWER SUPPLY (HP)

The HP (High Power) supply unit is used only when the transmitter switch is set to high power. It is a separate unit, in an aluminium case, and can be placed at the right hand end of the radio, on the mounting frame. If there is not enough space in the mounting position, then it can be placed on the top of the radio, lying down. The mounting frame will allow both possibilities. There are two 3 point cables required for connection. One cable connects this supply to the LP power supply. The other cable connects the LP power supply to the radio. This supply was made by the AERONAUTICAL & GENERAL INSTRUMENTS LTD. in 1940.

Picture 23: WS No.11 Power Supply Unit HP Front View

The HP (High Power) supply unit contains only 2 components. One is the dynamotor, and the other is a filter capacitor. The filter capacitor is on the output high voltage line, and the size is 0.6 uF and 2000 volts DC. The dynamotor is screwed to a metal plate, which is rubber mounted to the bottom of the box. The dynamotor takes in 12 volts, and produces 480 volts DC.

Picture 24: WS No.11 Power Supply Unit HP Inside View

RADIO RESTORATION

The radio was acquired in reasonable condition. It was inside its case, and had the bottom cover protecting the circuitry, so it was in a generally good condition. Only the front panel showed signs of age. The black wrinkle paint uses engraved legends, and the paint around the engraving was flaking off.

The valves were tested and two IF amplifier valves (ARP4) required replacing. The Modulation Control was sloppy, so it was examined and the wiper was re-soldered. A small 6 volt lead acid battery was used to supply the filament voltage during testing. Each series string was tested separately. The valve pins were checked for the correct voltages. These were correct. The HT was connected to a bench power supply. A pair of headphones was plugged in, and a signal applied from a signal generator to the aerial terminal. Nothing was heard. The signal generator was changed to the IF frequency. It was connected to R6A, the grid of the mixer. Nothing. The detector WESTECTOR was removed and a diode inserted. Now there was a signal heard in the phones. The IF transformers were aligned. The signal was reduced until (at 10 dB Signal to Noise) the sensitivity was checked, but it was only 30 millivolts. This is poor, it should be better than 100 microvolts.

The valve panel on the front panel was checked, and most of the measured voltage drops were similar to those in the manual. The last IF, however has no drop at all. So the valve was drawing no current. At the socket, the filament voltage was good, the bias was good, and the plate voltage was too high. The screen voltage was very low. The screen bypass capacitor was disconnected, and the valve was now drawing current. The plate bypass was removed also, and 2 new capacitors were tacked in place. It was realigned, and the sensitivity improved. The capacitor is a can mounted HUNTS brand of 0.1 uF at 350 volts. The decision was made to replace all of them. As each capacitor was removed, a temporary capacitor (0.1 uF 400 volt) was tacked in place. The set was then tested each time. Eighteen capacitors were replaced. The set was realigned. The IF sensitivity was now 22 microvolts. This is a vast improvement.

Picture 25: WS No.11 IF and slug lock nuts

The locknuts were carefully fitted back on to the slugs to lock them in place. The photo shows the top 2 slugs locked. The bottom slug has a screw driver holding the slug in position, and the lock nut is about to be screwed into place. In the photo, the middle lock nut has not been fitted yet.

The oscillator slug and trimmer were aligned until, the dial was reading true. Then the mixer and the RF stage were aligned. The RF valve was noisy, making sounds when it was bumped. It was replaced. The sensitivity for a 10dB signal to noise was:

FREQUENCY (MHz)	SENSITIVITY (uV)
4.5 MHz	5 uV
5.5 MHz	4 uV
6.5 MHz	3 uV
7.5 MHz	3uV

This is reasonable for a 6 valve super heterodyne receiver, running off batteries. An aerial was connected, and several amateur stations were heard. The BFO worked and did not require adjustment. The SSB signals were easily resolved, using the BFO. The only problem was that when the BFO was on, the AGC was OFF. When a strong SSB station was talking to a weak SSB station, the gain control had to be continually adjusted.

I started working on the transmitter, and there was no output at all. I looked at the voltages and noticed that the bias levels were strange. I checked the main voltage divider, but the voltages were wrong. I switched it back to receive, and they were still wrong. After looking at the large wiring board, I could see a wire link joining 2 resistors, but it was in the wrong place. It should be one connection along. And the connection on the back of the board was wrong as well. As it was wired, resistor R9D was connected to the HT negative, instead of R11A (which was just floating). These were original factory connections, it had not been modified. The radio did work, with the low bias condition. I removed the link, put the link in the correct place, moved the wire on the back of the board, and powered it up. The sensitivity was improved to:

FREQUENCY (MHz)	SENSITIVITY (uV)
4.5 MHz	3 uV
5.5 MHz	2.5 uV
6.5 MHz	2 uV
7.5 MHz	2 uV

The transmitter BFO was checked, and it was running at 477.3 KHz. It was adjusted with the slug to 475 KHz. The transmitter frequency changer was giving out a signal, but it consisted of several frequencies. The RF amplifier was working as a filter and removed all but 2 of them. The power amplifier could be tuned to the correct frequency, and peaked, by using the AN tap switch and the SEND AE TUNE tuning knob. The AE tap knob was used to peak the tuning.

The spectrum analyzer showed a peak 475 KHz next to the main peak, and the tuning tablet was useful in selecting the correct tap positions. There was no reading on the aerial ammeter or anything on the dummy load.

It was noticed that if the transmit/receive switch was pushed to the end, then an intermittent contact was produced. It was required to be set just short of the full travel. A microphone was plugged in and modulation was seen on the oscilloscope, with about 50% modulation for a normal voice level, but 100% could be obtained with a loud voice. A side tone could be heard in the headphones.

POWER SUPPLY RESTORATION (LP)

The dynamotor was clean and turned freely. It was dismantled and the bearings were repacked with grease. The brushes and springs appeared to be in good condition. It was re-assembled and 12 volts was applied. It span up and generated 240 volts DC.

The connectors on the front panel had pins that the spring tension sides had broken away. The junk box produced 4 good connectors, one was new and unused. The connectors were replaced. They were held on by screws, and the wires were attached to the pins by nuts. The resistors were checked and all were good. The power was applied and the dynamotor span up. It was run for a while but the capacitors did not get hot. The case was sanded and painted green. The front panel was masked and painted black wrinkle.

Picture 26: WS No.11 Connector with Broken Pins

Picture 27: WS No.11 All the old Connectors with Broken Pins

There is a 6 volt version of this power supply. It is the same as the 12 volt version, except for 2 changes. There is a 6 volt input dynamotor is fitted. The high wattage resistors are shorted out, and directly connected to the 6 volt input.

Picture 28A: WS No.11 PSU as Found (Right)

Picture 28B: WS No.11 PSU with New Connectors Fitted

POWER SUPPLY RESTORATION (HP)

The dynamotor was clean and turned freely. It was dismantled and the bearings were repacked with grease. The brushes and springs appeared to be in good condition. It was re-assembled and 12 volts was applied. It span up and generated 480 volts. The capacitor did not get hot. The case was sanded and painted green. The front panel was masked and painted black wrinkle.

Picture 29: WS No.11 Dynamotor Dismantled

Picture 30: WS No.11 Power Supply Unit HP As found

CONCULSION

The WS No.11 is a useful portable radio, for ground station or vehicle use. It works quite well, but suffers from frequency movement, especially with voltage variations. It can load into a whip aerial, or a long wire aerial. There is some microphonic noises due to the battery valves used. The internal components, capacitors, resistors switches and chokes, all are hand labeled with white ink, as per the circuit diagram. Most components are accessible, but those under the wiring board are hidden. This example is quite clean inside, but suffered from corrosion on the front panel. The faulty can capacitors were the main problem. The 18 on the Ht supplies were replaced. The others on the filaments, and the bias lines were not changed. There is excessive filtering on the filament lines, possibly to prevent interstage coupling, and possibly to remove any external electrical noise. The radio is easy to use, but has low power. The parts were difficult to locate, as it waited for about 10 years before, I had all the parts required. The radio is quite rare as many were lost at Dunkirk.

REFERENCES

Signal Training Volume III, Pamphlet No.19, Wireless Set No.11, 1939

Wireless for the Warrior, Louis Meulstee

Copyright
Ray Robinson vk2no

INDEX