The R1116 Receiver

The first picture shows the receiver as it was delivered here. Compare with end result...

 

 

  This interesting old receiver belonged to the late George Williams, whose friend Howard James kindly passed on to me George's collection of radio bits and pieces together with the R1116. It has a 4-core cable soldered to the pins of the power supply connector plus a flying lead which I assume was for its loudspeaker.

This example is quite old, being the version without the "A" suffix. There are a few very indistinct markings on the metalwork, possibly ?.R.W. Could this be Pye Radio Works? Condensers look earler than those used in typical WW2 radios and the resistors also look earlier and I spotted one dating from the early 1930s.
 

 This ex-RAF superhet receiver is pretty rare nowadays and I knew very little about it when I first saw it. Various sources said it was used in the Fairey Swordfish and the Short Sunderland and from the valve line-up I think it must have been designed around 1933/34 and was probably in production up to WWII. There was a matching transmitter, the T1115, and both were superseded by the R1155/T1154.

From the type number, and general construction, it's the same vintage as the old RAF wavemeter, the W1117

The valve line-up uses old 2-volt British-based battery-types and these, as can be seen below, are mostly contained in metal cans.

 AM CODE

 CV, Post 1942

 COMMERCIAL

 TYPE

 FUNCTION

 V1

VU33

 CV1033

-

 Diode

 Transmit Side Tone

 V2

VR82

 CV1082

220TH 

 Triode heptode

 1st Mixer

 V3

VR83

 CV1083

 220VTP, VP21

 Pentode

 1st IF Amplifier

V4

VR82

 CV1082

 220TH

 Triode heptode

 2nd Mixer

V5

VR83

 CV1083

 220VTP, VP21

 Pentode

 2nd IF Amplifier

V6

VR44

 CV1044

 210DDT, HD24

 Double diode triode

 Detector/AVC/Audio amplifier

V7

VR21

 CV1021

 210LF, L21

 Triode

 Push Pull Audio Output

 Waveband range switching is slightly odd. There are two tuners each provided with a waveband switch and tuning dial so that either can be left set to a given transmission. The user can listen to either of two transmissions by selecting either LF or HF. The various controls are coloured yellow and green for easy identification although some of the knobs in my example are missing their coloured inserts..

The wavebands, calibrated in Kc/s and Mc/s are as follows:-

 Range

 Lower

 Upper

 1

 142Kc/s

 315Kc/s

 LF

 Yellow

 2

 315Kc/s

 700Kc/s

 LF

 Yellow

 3

 700Kc/s

 1600Kc/s

 LF

 Yellow

 4

 2Mc/s

 4.4Mc/s
 HF

 Green

 5

 4.4Mc/s

 7.3Mc/s

 HF

 Green

 6

 7.3Mc/s

 12.0Mc/s
 HF

 Green

 7

 12.0Mc/s

 20.0Mc/s

 HF

 Green

 The outer case is made from aluminium because the receiver was designed primarily for airborne use. Further clues to this are the provision of remote volume control and a DF loop facility.Ranges 1, 2 and 3 are available for DF working

 

 Underneath, the receiver chassis is made from steel and is nicely compartmentalised for rigidity and performance.

Two separate aerial tuners are provided and, together with the two sets of waveband switches, my guess is that this was done to give rapid switching between traffic reception and direction finding. Without this feature the operator would have had some difficulty maintaining contact with base. As can be seen, if one studies the front panel layout, there are still a number of controls to set before the two features can be selected.

You can see from the simplified circuit diagram that the receiver is a double superhet with the first IF 1.7Mc/s and the second 100Kc/s.

A quaint touch is the provision of a grid bias battery near the rear of the chassis. The reason for this feature is the use of directly heated 2-volt valves. Circuits for this type of valve cannot readily cater for automatic bias and consequently, to reduce HT consumption and provide peak performance, provision has to be made to apply a negative voltage to several of the stages.

The two groups of reception bands use colour-coding, particularly reminiscent of the dials used in the later T1154 transmitter. This was probably designed to help the operator, who may have been in semi-darkness, although the layout of the controls is pretty logical.

Scale illumination is provided by small lamps fitted under the hoods over the tuning dials.

 

 

 Compare this picture with that at the top of the page. I tried various cleaners but couldn't get the front panel looking respectable until I rubbed a light machine oil on it and it was transformed.

 Here's a simplified circuit diagram

And here's a detailed version from Alf G3WSD

 

 I puzzled over what was connected to the two tuning dials until I peered inside. A separate front-end is supplied for HF and LF reception so the operator could leave these tuned and switch between the two, but frequency selection is accomplished by permeability tuning which is relatively unusual. Above, you can see some of the gear wheels. I couldn't see what those semi-circular shiny metal pieces are for unless a couple of screens were fitted to keep dust out of the gears. Another possibility is some sort of dial lock could be fitted, however, reading the AP all is almost revealed. A pair of 4-1 slow motion drives can be added to the receiver. The clue is perhaps in the outer edges of the tuning disks which are machined rather than smoothly finished. What these look like is anyone's guess.

Originally the two duplicated sets of receiver controls were coloured yellow and green, but only a few remain preserved. Top right has a 25pF variable condenser wired into the DF loop circuit under a metal shield, but other pictures, and AP1186 show a second aerial socket (and there are drillings for an aerial socket under the new control so either this was an official modification or, much more likely, an amateur modification perhaps published in a magazine), and lower down a different knob has been fitted.

Below, the parts list stuck inside the receiver outer case (not entirely helpful unless you know AM codes off by heart). Does "G.P." stand for General Purpose? Many components seem to be mounted in completely inaccessible postions.

 

Everything appears to be in place. Some of the valves are a bit wobbly and a couple have loose top caps but on the assumption it used to work, and it seems complete I decided to see if it actually works. The first task is to replace the power lead which is perished rubber covered cable. I have umpteen mains leads with 2-pin mains plugs (every time I bought a computer monitor it came with two power leads so I built up a collection of a few dozen). Cutting off both ends revealed a standard brown/blue/green-yellow cable which is a change as years ago it was a US style lead with confusing colours.. eg black is live. As HT- and LT- share the chassis as a common connection I chose brown as 120 volts, blue LT + and green/yellow as HT- and LT-. I have a home-made mains power supply and I used that. It gives me a range of HT, LT and grid-bias voltages. I also removed the audio cable and cleaned it up before refitting it across the small panel labels T+ and T-. Two other connections are available but these are used for the T1115 transmitter microphone because the designers cleverly? used the R1116 audio valves as a microphone amplifier (involving yet more tricky circuitry).

Below are the resistor and condenser values.

 

 At first I tried a loudspeaker, but reverted to headphones because nothing much could be heard. It seems there are lots of problems (hopefully minor), coupled with complete ignorance of its operation, but I've listed things as I noticed them... with comments which were covered in the restoration work.

  The volume is working at maximum in non-AVC mode (fixed)

 The volume control rotates end to end but does precisely nothing non-AVC mode (fixed).

 The control marked AE RES doesn't do anything (it works in D/F mode).

 All the rotary switches are intermittent (switch cleaner worked OK).

 On the LF ranges the D/F position gives better audio than Traffic (fixed) .

 The LF aerial tuner seems to have a bent plate and shorts at two-thirds clockwise setting (fixed).

 A loudish hum was present. This improved a lot when I added extra smoothing (OK on good PSU).

 In CW the result was a hummy rumble superimposed on stations (fixed).
 In R/T-AVC stations were clear but without AVC stations were uncontrollably overloading the receiver (fixed).

 Other findings...

 The aerial tuning controls are very critical and in some HF ranges can tune the image (design failing).

 Apart from the uncontrollable volume control everything appears to work.. after a fashion (fixed).

 All the valves are serviceable with filaments at 2.0 volts (glass and tops super-glued).

 The added upper right trimmer seems to be an antenna trimmer (later modification).

 Everything works at 90 volts. I tried 120 volts but the output was deafening (fixed).

 Dial readings seem quite accurate eg Irish Radio One tuned at 250Kc/s and Radio 4, 200Kc/s.

I read the description and checked the circuit diagram. My guess is the volume is uncontrollable because there's a faulty automatic switch for disconnecting the internal volume control when the external volume control plug is in place. That switch is almost certainly in poor condition as are all the other switches in the receiver. Yaxley switches and most other types are self-cleaning when they're used, but of course without plugging in the external control the volume cntrol switch has just gone high resistance. Fortunately, I bought a new can of switch cleaner recently so that should sort out most of the faults. Now that the switches are getting less unreliable I can see some other problems more clearly. For example... if I switch to R/T (AVC) the volume control works, albeit a trifle crackly, but after a few score wiggles it should quieten down. There's no chance of using switch cleaner everywhere because the wavechange switch is in a sealed compartment from which the lid is unremovable due to complete inaccessibility of an invisible screw.

Switching to CW mode produces a loud hum that reminds me of something shorting out and this may be the case as when turning back to R/T it takes about 10 to 20 seconds for audio to recover. Previously turning to CW behaved differently but since then I reduced the HT voltage from 120 down to 90 to stop overloading due to the inoperative volume control. Looking at the circuit diagram one candidate is C47 which is connected across the BFO valve filament and if this was killing the LT it may take a little time for that to recover? V8 might also be duff? (Later I found the cause was that the BFO was miles off frequency).

Another puzzle is that I get better results from Radio 4 with the bandswitch on D/F rather than traffic.

As I delved into the faults I realised I was looking mainly at the effects of dirty switch contacts. There are so many involved in each receiver function, it needs only one high resistance contact set to prevent an important feature from being activated. This became apparent when suddenly the volume control started working on Range 3 CW Traffic. However this was not the case if AVC was off..When the receiver is not employing AVC it uses the -10.5 volt bias supply to provide a cut-off source for the RF/IF valves (=a manual voltage level for AVC) as shown below. Switches S8-A and lower S7 select the wiper of R16 pot which is fed by the 10.5 volt (-ve BIAS) via S8-C and upper S7. R16 provides the cut-off voltage with respect to ground via R21 (R21 sets the minimum bias level or maximum volume). In AVC mode the volume control R16 wiper is grounded and the live end of R16 connected to the audio output (junction of R22/R31). R22 appears to provide a rough and ready balance of audio, by shunting a proportion of audio to ground, to minimise the change in volume as S8 is moved from AVC to manual RF gain control. Because R22 is 50Kohm it's likely to have drifted high in value so switching to non-AVC mode will result in an increase in volume, however this method of equalising audio is a bit hit and miss anyway. R22 measured as around 70Kohm which doesn't help in keeping the operators hearing in good shape.

 

During testing I was using grid bias supplies from my home-brew power supply but I decided to make a grid bias battery to avoid unnecessary hum. These batteries were used in many early receivers with the express purpose of significantly reducing HT battery drain at essentially only the cost of a grid bias battery (around a shilling or 5p in modern money). Current drain from these batteries was insignificant and they usually lasted the life of a radio, or until the contents just fell apart from corrosion. As I have dozens of used AA cells with around 1.4 volts terminal voltage I used a set of seven because the R1116 needs, a not very critical, minus 10.5 volts for volume control, minus 6 volts for the audio amplifier and minus 1.5 volts for the output stage. To accept the R1116 plugs I drilled holes in the top of a set of M5 screws and used these with solder tags for battery connections. The new battery fits the holder which I measured as taking a battery 5.75" x 2.75" x 0.875" or if you prefer 146mm x 70mm x 22mm. To complete this I need to print some paper labels.
 

 

 

 

 Here's a similar 15 volt grid bias battery and, from its general details, I made labels. The length of the 15-volt battery is proportionally longer because it uses 10 cells compared with 7 for the R1116 battery. The size of the photo can be adjusted in printer settings to exactly fit the new battery (shown below), allowing for overlapping of the ends and the bottom edge. The extra brightness of the image is necessary to get a decent print and I made two matching sides with numbering reversed. The paper labels can be stuck to the thin card used to cover the battery.

Click for the PDF versions.

 

 

 
 
 

 Picture of battery with labels to be added later.

One reason for making the ersatz grid bias battery was to remove one of the possible causes for lack of volume control (and absence of audio) in R/T and CW reception. After switch cleaner had been squirted around I did get volume control in R/T (AVC) and a little in CW mode but switching to the centre, R/T position, resulted in no audio or a deafening blast in the headphones when ether the grid bias + or -10.5V plug was removed. Comparing information in the AP (Air Publication AP1186) reveals several errors and, with component accessibility generally next to impossible, this makes fault finding difficult. Looking at the circuit kindly drawn by Pete, G4GJL shows the 10.5 volt supply from the grid bias battery is connected across the volume control, R16. Turning this control anti-clockwise in non-AVC modes should place an increasing cut-off voltage onto the control grids of V2, V3, V4 and V5 in much the same manner as AVC is applied to these valves via S8A Position 1. This latter wiring is in place and works correctly. Oddly the third position of S8A also works but S8A Position 2 fails to work. Looking at S8 and the adjacent tagstrip it looks like some resoldering has been carried out so the question must be whether at sometime in the history of the receiver a wiring error was made, otherwise a faulty switch might be to blame. In the worst case a new switch can be fitted, but studying the circuit diagram reveals that S8D is only utilised in Position 3, so swapping the wiring for this with any section faulty of S8 is a simpler option. The logic behind the switch wiring is simple but may be confusing so the next step is to confirm that the wiring is correct. One simple test is to measure grid bias current into the -10.5 volt terminal when the ON/OFF switch is turned to ON. I measured 8uA in both R/T and CW positions so at least the volume control is drawing current through R21. Below a wiring diagram showing S8.

 

 Now comes a perfect example of Sod's Law. I'll detach the itinerant 4-pole 3-way switch so I can either swap it for a good one, or get better access to rewire the contact sets to avoid the bad contact. The knob has been replaced in the past and by turning it to one specific point I can almost insert a screwdiver to slacken it, but first I needed to remove the AE RES knob which came off easily.. so far so good except the screwdriver, now aligned properly didn't seem to bite the grubscrew.. that's because it was broken.. no slot and the knob was firmly in place. I can now either lever off the knob (which I then cannot re-use) and detach the switch, or try and rewire it in-situ, or even work out why A2 is open circuit...

I measured between the 10.5V grid bias plug (unplugged from the GB battery) and gound and saw 29Kohm in CW mode. This must mean that the total resistance of R21 (10Kohm), if it's present, and the pot must be 29Kohm, although I've already mentioned that components are inaccessible, and there are differences between the drawings in the AP. One such difference are connections to R21 so all is not exactly clear. This resistor is used to limit the maximum gain by limiting the proximity to ground of the RF and IF AVC line and is shown as wired direct to R16 in the main circuit diagram and to S8 in both the simplified circuit and in the component wiring diagram. But where is R21 as it does not appear to be in the location shown in the wiring diagram ? Not only this, but the grounding point on the back of the cover over S4 is missing. It was in place at some time because a QA check mark is visible at the screw hole, but was either removed when an official modification was made or by a previous owner. As the duplicate aerial socket is also missing, being replaced by a trimmer, this also is in the "mod-by somebody" category. Could R21 have been removed in order to increase overall gain?

 

 

 

 

 

 

 The 50Kohm volume control potentiometer

 I did manage to fix the uncontrollable volume in non-AVC modes, but the fault was very strange although it did fit perfectly with the clues. The resistance measurement of 29Kohm was correct but wrong. A 50K pot plus 10K should measure 60K not 29K, but a 17K pot and a 12K resistor does equal 29Kohm.

I decided to look at the 50K volume control pot shown above. This is hidden below the AE RES pot so I detached the two knobs, removed the top pot, then unsoldered the near end of the 50K pot. It measured 17Kohm so I unsoldered the wiper and noticed a resistor hidden inside a brown sleeve. That's R21 and it measured 12Kohm instead of 10Kohm.. hence 17K + 12K = 29K. As luck would have it, the resistance of the volume control is very critical. Because the bias feed is -10.5 volts, the volume control potentiometer (acting as RF/IF gain) will be feeding a bias of -4.4 to -10.5 volts to the RF and IF amplifiers. Because of this range, almost certainly one or more valves will be cut off hence virtually zero signal will get to the rectifier hence no audio.

Once it was completely disconnected and removed the pot still checked out at 17K, but I noticed the metal cover, marked R16 in ink and 50,000 ohms on the side, must have been swapped from the original and refitted to the wrong value replacement... Maybe, I thought, the repairer hadn't realised the importance of fitting the correct value pot as ordinarily this doesn't matter too much? However, I detached the cover to investigate further and found the pot had a solid carbon track rather than being wirewound, but it was glazed over which somehow didn't look right. The glaze was over about 80% of the area but looked slightly patchy, so with nothing to lose, I attacked it with switch cleaner and a cloth. After several tries the track started to increase in resistance and, after several attempts, the glaze had gone and a clean matt finish remained.. and.... it measured 49,700 ohms. I refitted the cover and put back the two pots but not before changing the old 10K (=12K) to a modern 10K, fitting this inside the original brown sleeve. The 2K-less ohms will allow more RF/IF gain at the maxim volume control setting.

Switching on the set proved all was now well with all three modes working correctly.

 Now that the receiver is functionally working correctly I moved it to the test bench for alignment. I found the audio output fails to provide enough power to drive a standard low impedance speaker but certainly good enough to use headphones even with the volume control almost fully anti-clockwise. The first step was to get the BFO working. All that was necessary was to tweak the trimmer in the BFO can located under the chassis. This was miles out but the BFO worked perfectly once the trimmer had been adjusted.

I noticed that because of the separate aerial tuning circuit, using a long wire resulted in all sorts of spurious signals... for example amateur SSB was clearly audible with the receiver dial set to around 350KHz. At this point I decided to call it a day and move onto something new, but first some pictures of the R1116 as it is today.

  

 

 

 A few comments before closing... the grid bias battery needs finishing off to make it look more authentic and, when re-assembling the case, I discovered there is no way to fix the top cover in place. I hadn't noticed until now that the fixing points were either broken or missing. It's possible that these were corroded and had sheared off at some point in the history of the set? Also the under-chassis shielding cover is missing (there are no less than nine screw holes for it). You'll probably notice that I haven't tackled the missing green and yellow coloured inserts on the various knobs and two knobs appear to be the wrong type but, as the replacements are no newer than the receiver and I have nothing better, these will have to remain (and anyway I already mentioned that the grub screw in the mode switch was sheared off).

At this point everything works correctly and, much to my surprise, only one component needed changing and that, the volume control limiting resistor R21 wasn't that bad. Incidentally, those shiny semi-circular fittings under the tuning dials were for additional slow-motion tuning mechanisms but I have no idea what these looked like. Maybe someone will solve this puzzle some day?

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