Commissioning an R1155 for use with a T1154

 I've been getting a T1154 transmitter up and running for use on the amateur bands and I decided to pair it with one of my R1155 receivers. I have two, of which one has been too far modified in terms of the front panel, but the second, although much modified inside, still retains most of the original front panel. It's a version "E" and has the early tuning knobs and is the same as a receiver I used to use back in the mid-1950s. The first task is to examine the chassis and see exactly what's been done to it and what work is needed to get it running again. The plan is to get the receiver working with the minimum of work. Some people would strip the whole thing down and rewire it, but the result is no longer a 70 plus year old receiver. Below are some pictures showing the condition at Day One. As this is the first R1155 I've worked on, the job will be mainly a learning exercise.

This example has been modified to produce a working receiver, I'd guess in the 1960s and thankfully the modifications were done sympathetically to preserve the look of the receiver. See another conversion that took no account of this !

 

 Pretty well original, just missing the 4-pin Jones Plug for the DF function and connector securing posts. I cleaned up the dial some time ago so it looks quite acceptable. The headphone jack socket was fitted to a blanking panel which I removed when I cleaned the dial.

 
 Here you can see evidence of fairly extensive modifications: The DF parts have been removed and a mains transformer fitted together with a rectifier socket and smoothing condenser, but no choke. I suspect this was there but had been removed as there was evidence of cut wires at the smoothing condenser tags and no continuity from the rectifier to the receiver's HT line.

 

 Underneath, the RF compartment is missing its cover. Apparently added is the black transformer.. see later.
 

 The added mains transformer
 

 Missing V6, also the metal cans for V8 & V9. V6 should be a VR100, equivalent to a KTW62, which is what's known by some as a high gain 6K7. I didn't immediately have one so I fitted a KTW63 which has a slightly lower gain.

 

 
 Left the added rectifier socket located in the original location of V2, a valve used in the DF section.

 

 Above you can see the receiver which is a version type "E" carries the label showing No.1 Signals Depot. This was located at West Drayton during WW2.

 It seems there's not too much to do. I'll remove the mains power supply, fit any missing or non-functioning valves, tidy up the Jones Plug area and check the audio output circuitry so it reflects the original design. Then power it up and sort out any problems then maybe make a new screen for the RF compartment.

 Removing the mains transformer was a bit tricky because two securing scews were inside the RF compartment and I needed to detach the row of trimmer condensers C57-C61 to get at them. Looking further I spotted that V9 looked odd and removing it showed it was marked 6K6GT and the penny dropped. The mods included loudspeaker output. The jack socket wasn't for headphones, it was for a loudspeaker. I decided to leave this modification in place and maybe fit the jack socket to the left of the two 8-way Jones Plugs.

 Right.. the old transformer which I may use later for an external PSU. This view is the underside of the transformer which was fitted using long 4BA screws each with a pair of brass spacers to keep the tags clear of the chassis

 

Below: Empty space after removing the power supply.

 
 

 Right.. the 6K6GT where V9 should be..

Below.. parts from the old power supply

 

 I also found that switch S1 at the top right corner had been rewired as a mains switch. The other two DF switches were in place but had been disconnected. See an article written in 1946 which shows a typical R1155 conversion for amateur radio use. Wireless World 1946

The article is useful as it shows a nicely simplified circuit diagram of the receiver and only the circuitry of interest. I reckon there's a mistake in the power supply and output circuit. The circuit diagram shows a KT63 without an output transformer and, as most people with a knowledge of valves will realise, the screen of the valve will draw excessive current and ruin the valve if the anode is left open circuit. This article may well have been the one used by the chap that modified my example.

 

 This looks rather odd doesn't it....

To make room for the mains transformer this can has been detached from the chassis and lifted upwards and sideways so it's now situated above the tuning condenser. A result of lateral thinking.

It carries filter components to notch out any commercial stations operating close to the IF of 560Kc/s. I'm not too sure about the unscreened lead which may introduce broadcast signals.

To check heater continuity I connected a 6-volt battery to pins 3 & 4 of Jones Plug P1. The valve heaters came on. I'll also check the HT connection (the easiest way is a smoke test). As always, when tackling a receiver with an unknown history the first step is to confirm the viability of proceeding. Any complicated mechanical parts need to be serviceable and the yaxley switches need to work properly. If all is well I'll proceed to swap any bad components, then align the IF strip and front end. So far everything looks OK, although I'm a bit unhappy about the rubber covered wire which is used in the set. Some of this is brittle and liable to shed insulation and short out. This in itself may not be a show-stopper because lots of receivers in the 20s and 30s were wired up using bare wire.

Next, I made up a cable using an 8-way Jones socket and plugged it into P1, put the receiver on its right hand end, and connected the cable to my home brew power supply. The connections reflect those in the T1154 into which the cable from P1 usually terminates.

The pin numbers are marked on the Jones socket body and are labelled: 1: HF Aerial; 2: Trailing Aerial; 3: LT+; 4: LT-; 5: 220V Rx HT+; 6: Headphones; 7: 220V HT+; 8: 220V HT-. As I understand the position, there's no reason why the R1155 can't use 6.3V AC for it's valve heaters, but this voltage has to be DC in the T1154. Receivers using an internal home-brew PSU invariably used AC for the heaters so are not entirely compatible with the T1154. The 220V HT supply at Pin 5 is switched to the R1155 from the T1154 as is the DC heater voltage which is routed via the Mode Switch on the T1154. The HT connection at Pin 7, is unswitched by the T1154 and is provided for using the DF function which is independent of the transmitter. Another point of note is connection of HT negative, As with the 1200V HT negative supply to the T1154, the 220V HT negative of the R1155 provides bias supplies and is therefore not directly connected to the chassis. This means that the two supply voltages cannot share the same transformer secondary winding if full wave rectification with centre-tap return is used.

If I continue to make changes to my home brew PSU I'll add a 220V independent output.

Initially the heaters didn't come on but that turned out to be oxide on the plug pins. Setting the HT to 230 volts, I connected the HT wire. The loudspeaker burst into life with lots of white noise so something's working. Turning the wavechange switch didn't produce any crackling and after 30 seconds smoke began to rise from the top of the chassis from somewhere around the wavechange switch gear wheels. HT current was showing as around 100mA, which is a bit high so maybe a leaky condenser and a burning resistor? Thinking back... does this fault explain the missing HT choke? It may have gone open circuit when faced with lots of HT current. Did the owner get as far as diagnosing the open choke, then removed it and didn't get any further?

 
 The origin of smoke in any unrestored R1155 will be this HT negative feed resistor

I moved the HT input from my home brew PSU to one made by Solartron. This lets me raise the HT from zero and controls the current resulting in the smoke. I found the resistor responsible was R1 which is fitted above chassis on top of the block condenser C1/C92/C94. The manual is a bit vague about R1, its value being given as either 2,000 or 4,700 ohms. But, why would R1 get very hot? Its purpose is to help provide bias voltages, however it will carry most of the HT current so if the current is excessive the resistor's rating might be exceeded.It looks like 2000 ohms so if 100mA flows through it the thing will dissipate about 20 watts and it looks like maybe a 2 watt resistor, hence the smoke. If it was a 2 watt resistor then an HT current of 40-mA will result in 3.2 watts. So, it seems something is drawing too much HT current. First guess is perished rubber covering (of which there's a lot), second is a badly leaking condenser and a prime candidate is whatever has been used to drive the 6K6 grid (making it draw loads of current), but most likely is all three. Simple enough to check, just unplug the valves. I also need to check the modified circuitry because the audio amplifier V8 is still present, so that whoever did the mod must have retained this and connected its anode to the grid of V9 via new condenser.

 Further rummaging around revealed several poor condensers and swapping these resulted in some reception. All the bands were alive but very patchy indicating alignment and overall gain were way out. I settled on Radio 4 on 198KHz. While I prodded with my multi-meter the HT current suddenly shot up and more smoke appeared. It seemed to be coming from a small red resistor at one end of the RF box, at least this looked charred when I'd switched off power and it measured open circuit. The 2.2Kohm resistor, R42 which is the anode feed resistor for the RF amplifier section of the frequency changer valve was open circuit. Checking its decoupling resistor proved this was to blame, having no capacity and a DC resistance of less than 1Kohm. I replaced the two parts and turned on the set. This time it came on with lots more audio and much more lively.

 
 Above, testing a typical old condenser (this one is supposed to be 0.1uF and was made in 1943)

Alignment was next, but soon came to a dead stop because the slugs in the IF transformers except the last one, L21, were damaged and immovable. I turned to aligning the five wavebands. I'll set down the details here because it may be useful for anyone thinking about this task. First the wavebands (restricting myself to the R1155E) together with their relevant coils and trimmer condensers.

Aerial
 

 Aerial

 RF Amp
 

 RF Amp

 Osc
 

 Osc

 Waveband

 Low

 High

 Coil

 Value

 Trimmer

  Coil

 Value

 Trimmer

  Coil

 Value

 Trimmer

 1

 7.5Mc/s

 18.5Mc/s

 L2

 0.74uH

 C61

L7

 0.77uH

 C66

 L13

 0.70uH

 C72

 2

 3.0Mc/s

 7.5Mc/s

 L3

 5.64uH

 C60

 L8

 6.21uH

C65

 L14

 5.83uH

C71

 3

 600Kc/s

 1,500Kc/s

 L4

 158uH

C59

 L9

 163uH

C64

 L15

 70.6uH

C70

 4

 200Kc/s

 500Kc/s

L5

 1462uH

C58

 L10

 1374uH

C63

 L16

 248uH

C69

 5

 75Kc/s

200Kc/s

L6

 11.426mH

C57

 L11

 10.5mH

C62

 L17

 699.2uH

C68

Now, because the R1155 is not that different from other communications receivers, the location of the coils and trimmers is not logical, being dependent on mechanical layout, and therefore cannot be guessed. If you're fortunate to have the RF compartment metal cover, the various range markings will be present. In my example the cores of the coils have been removed and cuts made in their ends so they can be adjusted from the space between the front panel and the RF compartment. The designers intended the coils be adjusted from the rear of the receiver through a tangle of wires.

 
 A view of the RF compartment with its array of trimmers and coils (minus its metal cover)
 Below are the locations of trimmers and coils corresponding to the 5 wavebands (ignore coils in square brackets at this point). Access is tricky for some of the coils. and if they've been messed about too much some cores may need drilling out and replacing.

 

It's usual to start alignment with the local oscillator and from left to right: C61, C60,  C57, C59, C58 (Ranges 1-2-5-3-4)

 

 Corresponding local oscillator coils from right to left, top L15, L14, L13, [L9] then the bottom row right to left L16, L17, [L18=osc choke, L10] (Ranges 3-2-1-4-5)

 

 RF amp 2 from left to right: C66, C62,  C65, C64, C63 (Ranges 1-5-2-3-4)

 

 Corresponding RF amp 2 coils from right to left, top [L13], L9, L8, L7 then the bottom row right to left [L18], L10, L11, [L12=IF trap] (Ranges 3-2-1-4-5)

 

 RF amp 1 from left to right: C57, C58,  C61, C60, C59 (Ranges 5-4-1-2-3)

 

 Corresponding RF amp 1 coils from right to left L3, L2, [L1] (Ranges 2 & 1) (L1 = dummy loop)

 Pictured below are two further coils located at the rear of the RF compartment which are not easily identified in the official drawings. I guess they're for lower frequency ranges. Also, I've noted some coils above which are not concerned in basic alignment. These are L1, which is described as "Dummy Loop", L12 "IF Filter" and L18 "Choke, Ranges 1 & 2". L12 is wired into Range 3 and is used to provide a notch at the IF, 560Kc/s. I'm still looking for L4, L5 and L6 which are the Aerial coils for the three lower frequency bands and there's also a discontinuity between the aerial connections on the Jones plug and the front end RF amplifier, V3. L18 is wired across L13 and L14 (the two short-wave local oscillator coils) and is tapped to provide coils L18a & L18b which will provide rejection of any strong local signals close to the IF.

 

 Centre of box... what's this coil; is it part of the suppression of interfering MF station circuitry?

 

 End of box... what's this coil, wired to Range 3 trimmer but with connection to a coupling winding cut? What's that 2.2Kohm resistor?

 Anyone contemplating working on an R1155 will need to understand the wavechange switch. The various published circuit diagrams show the wavechange switch to be chiefly responsible for selecting one set of coils from the five sets corresponding to Ranges 1 through 5. The switching is not altogether straightforward however because of the two major functions of the receiver viz. normal reception and direction finding and the two different aerials found on aircraft (What if one aerial is not available? Well, there's an aerial switch in the installation which can provide suitable connections so that if one aerial is not available, another can be used). You'll see in the circuit diagrams that the wafers making up the switch are identified by a series of letters. The four wafers are "z", "y", "x" and "w", starting from the geared end. Each wafer has a front and rear; "f" is at the geared side and "r", logically, towards the back of the switch. Each side of a wafer can carry two single pole 5 way switches each comprising a "wiper" plus 5 "outlets" making 12 possible connections or a total of 24 possible connections per wafer. These possible 24 are not all fitted to all wafers. The circuit diagram shows 7 sets of switches: FS.zf, FS.zr, FS.yf, FS.yr, FS.xf, FS.xr and FS.wf. The set FS.wr is not included in the circuit diagrams. There are two basic types of switch, a simple one of five "select" plus a type used to short-circuit coils that are not part of the set used for the selected waveband. The tags on each side of a wafer are numbered 1 to 12, including two "select" tags "6" and "12".

To aid legibility the circuit diagrams duplicate wafers FS.zf and FS.yr . Also somewhat confusingly, you may note that connections between front and rear wafer tags, where applicable for the "shorting" wafer switches, is not shown in the circuit diagram. This feature is supposed to be indicated by a circle, instead of a letter, shown in the centre of the wafer drawing as shown in FS.yf, however FS.zr omits this information.

Ordinarily, anyone contemplating restoration of an R1155 will not need to know any of this detailed information unless there's a problem with the switch or, as in my example, there have been extensive modifications that have gone wrong. This might happen if the DF circuitry has been removed without taking account of its effect. Below is a summary of the wavechange switch functions. Published circuits show the wavechange switch in the Range 1 (the highest frequency) position. Note: I need to check the following table for errors.

 Wafer  Function
 FS.zf V4 osc grid circuit C35 connects via tag 12 to oscillator reaction winding tuned circuits L13 to L17 on tags 1-5
   L13-L17 tuned circuits on tags 7-11 connect to tuning condenser on tag 6 (see also FS.zr)
 FS.zr  V4 osc anode on tag 6 connects to tuned circuit L13 to L17 taps on tags 1 to 5
   Tags 7-11 are wired to FS.zf tags 7-11. Osc coils L13 to L17 common (R35) on tag 12 shorts unused coil reaction windings on tags 1 to 5, plus R35 connects to unselected higher frequency tuned circuit taps.
 FS.yf  Tuned cct common on tag 6 shorts out unselected coupling coils on L7 to L11 on tags 1 to 5
   
 FS.yr  V3 anode on tag 12 connects to RF output coupling coils on tags 1 to 5,
   V4 grid circuit on tag 6 connects to RF amp tuned circuits on tags 7 to 11
 FS.xf  Mode switch on tag 7 connects to aerial coupling on HF coils L2 & L3
   V3 AGC line on tag 1 shorts out unused aerial coupling coil inputs
 FS.xr  Top cap, grid of V3 at tag 1 connects to tags 7-11 aerial coil tuned circuits L2 to L6
   Mode switch on tag 7 connects to aerial MF tuned cct taps
 FS.wf  Mode switch on tag 6 connects to MF aerial coupling A on L4 to L6 on tags 8 to 11;
   Mode switch on tag 12 connects to MF aerial coupling B on L4 to L6 on tags 2 to 5

 
 Looking for the nth time at AP2548A to clear up loose ends I spotted L4, L5 and L6, which are hard to miss being contained in large cans originally located in the space occupied by the mains transformer. Are they important? Well, they're used for the medium and long wavebands so in terms of amateur radio operation are not vital. Studying the mystery coil fitted on a bracket at the end of the RF box, it might be a medium wave aerial coil added to replace L6? Adjusting trimmers C59, C58 and C57 should reveal whether or not any coils are present. I suppose I could always find suitable replacements and fit these because I find the LF bands fairly interesting. If anyone has an R1155 less the DF coils here's what you need...

 Aerial Coil

 L2

 L3

L4

L5

L6

 Inductance

0.74uH

5.64uH

158uH

1462uH

11.426mH

 While I'm on the subject of tuning I'll briefly set out the local oscillator settings. If the receiver hasn't been messed with you won't have any trouble but if a core has been twiddled or been replaced then you need to be very careful. A table below shows the possible configurations for the R1155. The lowest frequency band is interesting because the local oscillator sweep is very small. Also, look at the negative frequencies for the two lowest bands. Take Range 5, with the tuning condenser set at near minimum capacity and the dial reading 200Kc/s. The IF of 560Kc/s can be arrived at by subtracting 360Kc/s from 560Kc/s or by subtracting 560Kc/s from 760Kc/s. However, as the tuning condenser is meshed the 360Kc/s local oscillator frequency will drop to say 300Kc/s and the resulting response would be 260Kc/s. In other words the dial is reading one way, lower in frequency, and the receiver's response is reading higher. This means that you've tuned the local oscillator to the wrong setting. Quite easy to do if the receiver has been messed with or a tuning slug has been replaced. One way to check is to tune a second receiver (or a spectrum analyser) so it can hear the R1155 local oscillator. If you don't do this check you may spend hours of fruitless twiddling. This also applies to the higher frequency bands if you try and align the receiver listening to the image response by mistake. You can see the effect if you input from a signal generator a strong signal, say 10mV at 10Mc/s with the R1155 set to Range 1. Turning the tuning knob will result in lots of responses but the two strongest will be 10Mc/s and either 11.12Mc/s or 8.88Mc/s. These are twice the IF or 1.12Mc/s apart from the dial reading. As the R1155 local oscillator should always be tuning higher than the indicated dial frequency (for all wavebands) the image should be 11.12Mc/s. If you hear strong responses at 10Mc/s and 8.88Mc/s you've set the local oscillator to 9.44Mc/s by mistake. This is quite easy to do and will result in reduced overall sensitivity.

 It reminds me of a time many years ago when I was calculating the local oscillator and image responses in the design process for receivers in the Skynet satellite anchor station at RAF Oakhanger. I wasn't responsible for the calculations for the X-band receivers in the satellite itself, but I recall there was a major problem once the thing was in orbit and too late for twiddling. I mean, who has a plastic screwdriver 22,200 miles long?

 Range

 Coverage

 Local Osc-LOW (WRONG)

 Local Osc-HIGH (CORRECT)

 Image Response

 1

 7.5Mc/s to 18.5Mc/s

 6.94Mc/s to 17.94Mc/s

 8.06Mc/s to 19.06Mc/s

 8.62Mc/s to 19.62Mc/s

 2

 3Mc/s to 7.5Mc/s

 2.44Mc/s to 6.94Mc/s

 3.56Mc/s to 8.06Mc/s

 4.12Mc/s to 8.62Mc/s

 3

 600Kc/s to 1,500Kc/s

 40Kc/s to 940Kc/s

1160Kc/s to 2060Kc/s

 1720Kc/s to 2620Kc/s

 4

 200Kc/s to 500Kc/s

 -360Kc/s to -60Kc/s

760Kc/s to 1060Kc/s

 1320Kc/s to 1620Kc/s

 5

 75Kc/s to 200Kc/s

 -445Kc/s to -360Kc/s

 635Kc/s to 760Kc/s

 1195Kc/s to 1320Kc/s

 Before I proceeded to deal with shortcomings in the front end, I'd notice horrible double-humping of the tuning of strong test signals so clearly not all was well with the IF amplifier. There are three IF transformer cans and each has two coils tuned to 560Kc/s. All are chewed up, some more than others. The usual method of swapping a damaged iron dust core is to break it up and remove the pieces then fit a new one. Sometimes, if the thing can be removed without further damage it can be turned round and the slot at the other end used instead. In my set the cores were locked almost solid and I decided to drill one of them out. I did this with the screening can in place and I inadvertently damaged the winding so I had to remove the screening can to replace it. As it was the can in the corner of the chassis it came off easily after removing a pair of 4BA nuts. I measured the undamaged coil and found it was 200uH without its core. After winding a new coil on a suitable former I fitted it and checked its inductance then removed turns until it was something like 200uH. The R1155 AP gives the primary coil as 250.5uH and the secondary as 251.5uH, presumably with the cores in place.

Fitting it was tricky as the new coil former needed to be positioned so that its core could be accessed through the hole in the screening can. After everything had been reassembled I turned on the power supply and the signal generator and commenced to align the IF amplifier. It started well, but after a few minutes smoke billowed out from the vicinity of the next screening can. To cut a long story short, I cut the three live leads to the can containing condenser C29 which is adjacent to the IF transformer and fitted new condensers C29, C30 & C31. The hard part was fitting a new anode feed resistor R30 (2.2Kohm) because this was fitted inside the IF can and detaching this was not easy because one nut is hidden away.

 I removed the triple condenser (3 x 0.1uF) which was bolted to the chassis and tested it. First I measured its capacitance. The three sections weren't too bad measuring 0.16uF, 0.16uF and 0.2uF, and their DC resistance seemed fine with the multimeter registering over 30Mohms. However as one of the condensers had seen off the anode feed resistor I checked the three using an HT supply. Setting the voltage to 300V I fed this across each condenser in turn with a series resistor of 1Kohm so I could test for leakage. The first condenser was OK showing only about 2mV across the resistor, but the other two leaked badly and the longer I left them the higher the leakage, disconnecting them at 50V across the resistor. I then re-tested the supposedly good condenser and this too, after heating up from the others, was just as bad.

Having got the IF strip adjusted to what I thought was 560Kc/s (previously there were at least two clear tuning points ie. a double hump) I attempted to align the front end. Here I had difficulty as can be seen when I measured the local oscillator frequencies. To do this I used a small search coil connected to my spectrum analyser and turned the tuning knob on the R1155 to each end stop and waveband in turn. Although every waveband had previously produced broadcast signals I'd had trouble aligning most of them.

 Range

Measured Kc/s

Osc Low & High

Resulting Kc/s 

Tuning

  Correct Kc/s

Dial Reading

Correct Kc/s

Osc Low & High

 Inductor

& Trimmer

  Problem

5

 652

 92

< 75

 635

 L17

 Osc frequency too high

 792

 232

 >200

 760

 C68

 Osc frequency too high

4

 784

 224

 <200

 760

 L16

Osc frequency too high

 1090

 530

 >500

 1060

 C69

 Osc frequency too high

 3

 1749

 1189

 <600

 1160

 L15

 Osc frequency too high

 3600

 3040

 >1500

 2060

 C70

 Osc frequency too high

 2

 3370

 2810

 <3000

3560

 L14

 Osc frequency too low

 6840

 6280

 >7500

 8060

 C71

 Osc frequency too low

 1

 7750

 7190

 <7500

 8060

 L13

 Osc frequency too low

 18170

 17610

 >18500

 19060

 C72

 Osc frequency too low
 Looking at the above table you can see that whilst ranges 1,2, 4 & 5 are alignable range 3 looks badly wrong. Because the local oscillator was so far out I tried unscrewing and screwing the core fully out and then fully in to check its tuning range. In the table below you can see that it's impossible to tune the medium waveband to line up with the dial markings (as per the readings 1530 and 840 which represent the minimum local oscillator frequencies achievable) . In fact it almost looks as if someone in the dim distant past has modified the set to tune top band instead of the medium waveband. In most superhet receivers the designers use what are called "padder" condensers to get the local oscillator and tuning condenser to set the desired waveband edges. The padder condenser for range 3 may therefore be faulty. The R1155 local oscillator is different to many receivers because it's the anode of the oscillator that carries the tuning rather than the grid. Range 3 coil is L15 and the padder is C75 and this must be too low in value. If not, as all the other wavebands are within spec, either coil L15 is faulty or the dust core is not increasing the inductance of L15 sufficiently. C75 should be 537pF. Very odd, I disconnected one end of C75 and it measured 1,002pF so I removed it and discovered it had 1000pF 5% marked on it.

Tuning Core

 Measured Kc/s

Osc Low & High

 Resulting Kc/s 

Tuning

 Correct Kc/s

Dial Reading

Fully out

 2090

 1530

<600 

Fully out

  4410

 3850

>1500 

Fully in

  1400

 840

 <600

Fully in

 2950

 2390

>1500 

 Clearly the inductance isn't high enough to allow alignment of range 3, but as the padding condenser will effectively negate the effect of inductance, I decided to shunt it. Adding more and more capacity almost achieved the minimum frequency but shorting out the padder did the trick. I was able to align range 3. As I tuned the various stations on the medium waveband however it was plain that they were not on their normal dial settings. Classic Gold in Bournemouth on 828Kc/s was nearer 780Kc/s so I investigated the IF strip. Sure enough it was peaked on 589Kc/s rather than 560Kc/s. I tracked down the reason to a coil sitting away from the main set of coils. This is a notch filter which is supposed to stop strong signals near to 560Kc/s from getting into the receiver. Previous attempts at IF alignment had been skewed because of the notch filter. Once I'd temporarily added an extra iron dust core to the coil the receiver responded to 560Kc/s at the aerial and IF alignment was possible. I used a spectrum analyser with a tracking generator and set up the IF response. When I checked Classic Gold again it was sitting at the right place on the dial.

Below is the response curve for the R1155 IF with maybe a little distortion to the shape due to a little loading by the probe at the rectifier diode? The vertical divisions are 20Kc/s apart and the centre line is 560Kc/s. By my reckoning the skirts are about 40Kc/s wide at -50dB or 20Kc/s at -20dB. My aim at this time was to correct the centre frequency rather than to get the narrowest curve.

Below are the inductance values for the IF coils and the BFO coil just in case you need to replace one as I did.

 COIL

 PRIMARY

 SECONDARY

 L19-IF1

 244.5uH

 251uH

 L20-IF2

 250.5uH

 251.5uH

 L21-IF3

 132uH

 254.5uH

 L22-BFO

 272uH

 

 

 After finally managing to get Range 3 roughly aligned I decided to find out why the padder was 1000pF. Checking the circuit, I found that by disconnecting the padder and the trimmer I could measure the capacitance of the tuning condenser. It turned out to be 85-560pF including the trimmer and strays and 55-530pF including strays rather than the 660pF (plus strays) version used in later models. This explains the larger Range 3 padder as the smaller one wouldn't give a wide enough tuning range. I also investigated the 0.1uF condenser which decouples the oscillator anode feed of 22Kohm. As this was almost completely inaccessible I broke off the wire leading to it and connected this to a new 0.22uF. As far as I could tell the old condenser was serviceable. I still have to strap out the 1000pF padder to get correct alignment so I'm left with the probability that the Range 3 coil hasn't enough inductance. I wonder if the tuning core is the problem because the coil looks original? Another slim possibility is the coil primary and secondary windings are connected back to front ie. tuning the lower inductance primary instead of the larger secondary.

As the oscillator works normally and I don't have any iron cores that increase the inductance of L15 more than the one fitted it will be relatively straightforward to just add a second coil in series with L15. To work out the details:

Target frequency for tuning 600Kc/s = 600+560=1160Kc/s; Capacitance 550pF in series with the padder of 1000pF= 354pF.

Correct inductance of L15 is 70.6uH but calculated inductance is 53uH given 1160Kc/s and 354pF.

Shortfall 70.6-53= 17.6uH. This is achievable with 60 turns on 0.5" former wound over 1" using 27 or 28SWG enamelled wire, however when I tried this the receiver became unstable so I removed the trimmer panel, then removed the coil, L15. This is done by removing the two 6BA nuts, easy because the former has 6BA screws held in place with locknuts. I measured the coil and found it was 53uH as calculated. Rather than modify the old coil I found a suitable former in my junk box and wound it with a 70uH coil. To do this I used 37SWG wire and prepared the former by wrapping it with double-sided tape. This prevented the wire unravelling. After around 70 turns of the 115 required I made a loop in the wire for the coil tapping point then finished winding the turns. It measured 70uH as predicted. I then taped over the coil with more double-sided tape and wound about 20 turns for the feedback coil using 32SWG wire. This measured about 7uH and much to my surprise the new coil worked perfectly. Pictures below...

 

The old Range 3 coil which looks original and whose main winding has an inductance of 53uH and a reaction winding of about 3uH.

On the right is the new coil with a main winding of 70uH and a reaction winding of about 7uH. The new coil has a tapped main winding and I made this about the same percentage as the old coil. The left pins are connected together and are wired to the main winding and the reaction winding like the original.

I first wrapped double-sided sticky tape along the former then wound 37SWG wire to achieve a single layer. The reaction winding was made with 32SWG wire in the same manner.

 

 Below, a view of the oscillator coils after removing the trimmer panel, and right after removing the Range 3 coil.
 

The new coil, not quite finished being tested in-situ to check its tuning. 

View after replacing the trimmer panel. 

 I was listening to our local radio station on 1359Kc/s when the sound went muffled and hissy, a puff of smoke arose from the front of the chassis and a resistor burnt out... yet another condenser has bitten the dust!

Further testing indicated that the three higher bands all suffered from a sharp dip in oscillator output at about two thirds mesh of the tuning condenser. This is a bit puzzling. Maybe one of the rotor plates has a blob of solder stuck to it? Further investigation required. I think it was due to too large a negative bias voltage or too low an HT voltage due to leakage in the HT line to ground.

 As there's no connection between the Jones plug aerial pins and the RF compartment, I'll need to sort this out. Originally the aerial (there were two.. the HF aerial and the MF aerial) passed via the mode switch and the DF circuitry so someone might have dispensed with this and just connected an aerial to the common circuitry associated with the grid of V3? As I plan to use the R1155 with my T1154 I'd like the aerial connections to be relatively original. I'd noticed the end wafer of the wavechange switch has had most if not all its wiring disconnected.

I decided to disconnect the receiver from the power supply and take it where there was plenty of lght so I could trace the aerial circuitry. It seemed to me that there were two different points for different wavebands where an aerial brought in stations. At the left of the dial is some white letteriung which I've deciphered as "RANGE 3 SCALE X2". I looked at the wavechange switch and noticed the lettering for Range 3 was much darker than the other lettering. Cleaning it revealed "3 - 1.2". I looked at the main label. It tells me its an R1155E but the Air Ministry code is 10D.NIV.400 (see below). So that explains the strange coverage for Range 3. This particular set has been modified to cover the Trawler Band and the coilset for the R1155L trawler band has presumably been fitted in place of that for the medium waveband of the R1155E.

My T1154 declares itself to be a Model "N" but it's not. It has four wavebands and just about covers Top Band, so I think it would be a good idea to swap back the receiver oscillator coil, then I can use the set-up on Top Band. That's if I can find the old coil....

 

 

 

 

 Above the unusual label. The US government issued a publication of almost 200 pages which has probably all UK abbreviations and includes the code "NIV" on page 161. Above, you'll notice that the label engraver baulked at drawing the crown between the letters "A M". Somewhere, in a locked filing cabinet in a dusty basement, there's a register which includes the definition of "400". Marked on the rear of the chassis is that same serial number, 73736, so at least that's correct.

 

 I suppose, to preserve the integrity of the old receiver, which may now turn out to be unique, I'll have to refit the old oscillator coil and, while I'm at it, swap those rusty 6BA screws!

I found the original coil after twenty minutes. Gravity had acted and it had fallen to the workshop floor where stuff is arranged in an archaeological fashion in strata. I spent ages working out the connections but finally turned on the power to find all was well. Tuning the dust core brought the band edge in line at 1.2Mc/s with the dial showing 600Kc/s and, after adjusting the trimmer brought 3Mc/s onto the 1.5Mc/s marking. The RF amplifier coil responded and aligned correctly but the aerial circuits have a problem which I discovered previously so the next step is to sort this out and check that the aerial feed is taken via the Jones plug to the T1154 output connector. A quick test using a long wire brought in several medium wave stations at the LF end of the band plus lots of signals that sounded like Russian jammers between 2 and 3Mc/s.

The next step was to replace lots of rusty screws with new brass 6BA scews. When I removed the screws securing the label shown above I found it was a label for something completely different that had been flipped over and re-used.

   This is the back of the R1155 label. This may be the only such label in existence as I've never heard of such an equipment. Pyrotenax was a copper clad cable.

Next, I was determined to trace receiver deafness. I found the coil I'd previously found mounted on a brass plate was a new Range 3 aerial coil and its return connection from its tuned winding was disconnected. This explains the deafness on Range 3. But if that coil is for Range 3 what are the three coils mounted in the coilpack? Certainly two are aerial coils for the top two HF ranges but what is the third? At least I've fitted some new screws to replace rusty ones. I suppose I should blacken the heads sometime...

 I'd guess that lots of R1155 receivers are missing their coil-pack covers so I've added these pictures of my home-made aluminium cover. It's held in place by seven 6BA screws rather than eleven in an original because I simplified the bending. I didn't drill holes for the coil adjustment at the rear because these coils are mainly inaccessible on my set and cores are all adjustable from the front. A cover is not essential but tuning and tracking will be optimum if it's fitted and final tuning made with the cover in place. I use a 4BA nut spinner for setting the trimmers so the holes are drilled to suit its diameter. Apart from the trimmer holes, I drilled one for adjustment of the IF rejector and one for the Range 3 aerial coil which, on my set, is fitted on a bracket at the rear.
 
 

 Having got the original Range 3 coil refitted and working, I wonder if the original receiver conversion (probably back in the 1940s) was comprehensive? Was the complete set of Range 3 coils fitted at the time? It may depend on the reason for the modification. Did the set need to be really sensitive? If the answer is in the affirmative, then coils for the aerial and the RF amplifier would have been fitted so that perfect tracking could be achieved. A clue might be the additional coil mounted on a small brass plate near the aerial switching wafer of the wavechange switch. This coil looks very similar to the oscillator coil and is indeed connected to the correct tag on FS.xr. Oddly there is a small 2.2Kohm resistor also fitted close to the coil and that looks to be fitted amateurishly. Possibly the chap that removed the DF parts and fitted the internal power supply was confused? The coil connections are cut and roughly resoldered which might support this idea.

I already mentioned that I need to construct a power supply for the receiver as I want to free up my workshop power supply and also because of the bias wiring which places the chassis at an odd voltage in respect of HT negative. I made a rough and ready chassis from a piece of chipboard and piece of computer case and wired up a simple power supply (with 6.3V AC for the valve heaters) using the mains transformer removed from the modified R1155. I connected this up and the receiver worked OK but, after about 30 minutes, the set had warmed up and I noticed the chassis voltage was slowly drifting upwards. Clearly there's HT leakage probably due to one or more of the remaining old condensers. I imagine the only practical solution is to remove all the old tubular condensers and fit modern parts, but read on.... For interest I checked the HT current. With the set just warmed up the HT current measured 68.6mA and with the valve heater feed disconnected this dropped to 30.3mA. The HT voltage measured 251.9V and the chassis measured 36.8V to HT negative.

I had my breakfast and then returned to the set. There was a rather nice warmish smell, like the inside of a 1950s government surplus shop I gingerly put my finger on the side of each of those metal tubular condensers screwed to the chassis. All were cold so I checked the HT current and it had risen to 114.3mA from 68.6mA. I checked the HT voltage and found it measured 172.5V. The chassis was resting upside down and I turned it on its end with the Jones plug uppermost so I could check another one of those tubular condensers for warmth. I didn't have to though because I could feel a warm glow coming from the grey metal clad paper condenser screwed to the end of the chassis. The sides were bulging slightly and it was clearly on its last legs. I clipped the wire feeding its HT terminal and the HT current dropped back to 62mA, the HT voltage jumped to 252V and the chassis measured only 20.8V. Tuning to Radio 4 showed the set was a lot more sensitive. The condenser is C93 and is marked 4uF. It had accounted for an HT drop of around 20 volts when cold and a whopping 80 odd volts and 50mA when hot. Oddly the working voltage isn't marked, neither is the manufacturing date. The resistance measured with an ohmeter is around 8Mohms (which I guess is a bit too low and was rising as the condenser cooled which is ominous) but strangely the capacity and ESR are normal.

 

 As the condenser is a substantial part of the R1155 I decided to keep it. Many metal condensers like this one are oil filled and anyway, whatever is their construction they seem to last for ages but maybe 70 years is condenser "end of life" ? Cutting it open was tricky but I have a large old Solon soldering iron and I found by cutting the ends of the base where damage wouldn't be visible with a hacksaw enabled me to unsolder the terminal panel. Inside I discovered a lump of aluminium and paper exactly the same as that in the failed metal cased condenser in the T1154 (see link below). It's also very similar to the construction of the standard tubular condensers used in this and other receivers from the 1940s. Clearly, something in their construction is degrading after 70 years and resulting in rising temperature and a sort of avalanche type failure.

Below, the 4uF condenser, but re-stuffed with two 2uF and a 1uF rated at 275VAC which should be OK up to about 380VDC. I drilled out about half the contents which was sufficient to accommodate the new components. See other bad condensers (these in an R206 Receiver) and another in a T1154.

 

pending....

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