Commissioning an R1155 for use with a T1154

 A brief word of explanation if you'd like to read on.. This example of an R1155 had been factory modified to cover the Trawler Band; something which I'd overlooked before discovering and attempting to fix certain tuning discrepancies.

 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 !

Having struggled with the circuit diagram in a copy of AP1186 I decided to PhotoShop it and produced a version suitable for anyone attempting to carry out basic refurbishment of an R1155. This divides the overall circuit diagram into four parts together with resistor and condenser parts lists. The pages are A4 printable.

Printable R1155 schematic plus parts lists

 

 

 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 screws 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 designated "R1"

I moved the HT input from my home brew PSU to one made by Solartron. This let me raise the HT from zero and control 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.

 
 Above... Once I'd got the refurbishment underway I decided to build a simple power supply using some of the parts previously removed from the chassis. One reason is the way the R1155 receives its HT supply. HT negative is connected to a network of components rather than the chassis. This is done to develop various negative bias voltages and makes it awkward to use a lab bench supply. As you can see the new PSU is very basic. Connections are made to the 8-way Jones plug via a choc bloc and mains is fed in via an old computer power supply socket. The front panel is part of an old computer case. I might add a meter and a switch or two to the front panel later.

 Further rummaging around the R1155 chassis 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.

 

Tuning

Tuning

Aerial
   

 Aerial

 RF Amp
 

 RF Amp

 Osc
 

 Osc

 Waveband

 Low

 High

 Coil

 Value
 Code

 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
 10D/161

C59

 L9

 163uH

C64

 L15

 70.6uH

C70

 4

 200Kc/s

 500Kc/s

L5

 1462uH
 10D/162

C58

 L10

 1374uH

C63

 L16

 248uH

C69

 5

 75Kc/s

200Kc/s

L6

 11.426mH
 10D/163

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)

The local oscillator (right), RF amplifier 2 (centre) and RF amplifier 1 (left)

 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.

 

 

 

 

 

 

 

 

 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 L4? 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 (L5 and L6 below)...

 

 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 noticed 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 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
 

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. 

 

 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 light 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 lettering 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 covers probably all the 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 screws. 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? Perhaps the old range 3 coil was too tricky to remove so was just disconnected and left in place?

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.

Note that these voltages and currents result from my home brew power supply so will be representative only. Not only that, but later you'll read that I found a leaky condenser responsible for some of the HT current.

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 so 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 (10C/979) 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. Its 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 (picture below). 

 

 

 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 same 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.

 
 The R1155 has several triple 0.1uF 350 vw condensers (like the one below) which are in tubular aluminium cans bolted to the chassis. These will all warrant investigation as they eventually develop an electrical leaks which reduce whatever voltages they're decoupling as well as not properly performing their decoupling function. I've described a method for restuffing these cans here. The cans are not always easy to remove from the chassis because of accessibilty, but it's a worthwhile project to replace them with new parts. The method I've described has a bonus. To refit a can you can pull out the new capacitor assembly which is held inside a section of drinking straw, screw the can back in place, then push the new capacitor assembly into the can. This considerably simplifies can replacement. The leads can then be trimmed to length and soldered in place. The capacitors are 0.1uF, size 1210 (3.2mm x 2.5mm) and are type X7R rated at 500 volts. The wires are high voltage/high temperature. Pricewise, these or similar ones vary considerably from 3p to 10p if you shop around.. but most suppliers offer lowest prices in quantities of a couple of thousand. I was lucky and bought a couple of hundred for 3p each.

 

 

 Before I'd decided to tackle these triple condensers the refurbishment had been going well, but suddenly there had been a sizzling noise and smoke when one section of one of the cans had failed. It seemed sensible to replace all six of these cans before proceeding. This had the advantage of being able to remove a large number of new, bright orange, decoupling capacitors I'd been fitting as work proceeded. In addition to the tubular cans there's a triple condenser in a cube-shaped grey block adjacent to the tuning condenser and a couple of metal-cased condensers screwed to the chassis that I should replace.

 

 

 These old condensers are sometimes still in perfect condition but as the larger version in the R1155 had become red hot I thought this example might be on the way out.

I identified the connections which are labelled "C" for common, two marked "2.5" and one marked "1" and checked them with my ESR60.

Readings were:-

2.62uF @ 0.10 ohms

2.86uF @ 0.4 ohms

1.23uF @ 0.16 ohms

Next, I'll check them by applying HT.

Across a series resistor of 100kohm connected to 300 volts DC I measured 29 volts for the 1uF, and 17.5 volts and 4 volts for the 2.5uF. These voltages represent less than a mA of leakage, but are symptomatic of a problem that can only get worse.

 

 The leakages were not too bad but in the interests of longevity I decided to fit new innards in place of the waxed paper/aluminium. I guess the condenser is rated at no more than 350 volts so found some plastic capacitors rated at 275 volts AC (about 389 volts DC). The old condenser has a pretty small volume for a 1940s component and fitting the new parts wasn't easy.

The top of the condenser is fitted with a soldered lid, with a lip of a couple of mm, carrying four terminals. Each terminal comprises a threaded brass rod with a hole through the centre, a solder tag and a special dished 4 BA nut. Condenser wires pass through the holes and are soldered into the nuts. I had to remove as much solder as possible then drill out the holes so wires would pass through then soldered to the nut.

 

I found in my junkbox a number of 1uF 275VAC capacitors and managed to squeeze in eight of them. I needed eight because all were lower than their marked values (a cost saving ploy by the manufacturers??). I fitted two groups of three and a pair, giving me two 2.7uF and one 1.5uF.

Bearing in mind the larger 4uF block condenser had failed suddenly this one, unmodified might have done so in the future.

Fitting is easy as it's attached to the chassis with threaded holes by 4BA screws.

 After refitting the new old condenser the R1155 worked perfectly, but I'd forgotten to add R1, the 2.2Kohm resistor. It didn't seem to bother it. I measured 65 volts between the chassis and C1 and 45 volts after I'd fitted R1. Presumably there's enough resistance in the bias chain with AVC on or off to let the set work OK and it's only essential in other modes? I suppose I should make resistance checks to confirm this. I've now finished stuffing two more triple condensers. It took only minutes. I used a piece of copper wire an inch long, soldered three chip capacitors to it then added three red wires to their ends and a black wire to the coper wire. Squashed 3 inches of plastic drinking straw and pushed the assembly into it and capped it with the end of a cotton bud. With the can drilled out using a drill fitting the hole I can push the capacitor assembly into place once the can is refitted to the R1155 chassis.

 Up to this point in proceedings I've been connecting my aerial to a capacitor sticking out of the coil pack. Whoever modified the receiver back in the 1950s probably added this to bypass the switching arrangements. If I intend to use the R1155 in conjunction with a T1154 this modification is not ideal so I need to plan exactly what I'd like to do in respect of connecting an aerial. The first thing to consider is the switching arrangements in the T1154 as that is where the send/receive switch is located and this switch handles antenna switching. Operating on shortwave bands is relatively straightforward but an option is open to use new amateur bands on 136KHz and 472-479KHz (600m) so this might be taken into account in any tidying up of the switching within the receiver.

After studying the circuit diagram I found that the main aerial inputs to the receiver, ignoring all the DF arrangements (all that circuitry has been removed anyway), are tappings on the RF amplifier coils for the two long wave bands and the medium wave band and a coupling coil for each of the two short wave bands. These five inputs need to connect to Pins 1 and 2 of the 8-way Jones plug. Pin 1 is designated "Fixed Aerial" and Pin 2 "Trailing Aerial" and it might be useful to include an extra switch on the front of the receiver to combine these so a long wire can be used for general reception. It's likely that the capacitor connection I'm currently using merely connects to the grid of the RF amplifier as it appears to work on all five wavebands. In the original circuit two condensers C100 and C102 are used to isolate any DC present at the R1155 longwave and short/mediumwave aerial circuits (respectively) from the T1154.

Missing from my receiver are coils L5 and L6 so I'll need to find some and fit these for optimum results. From the table (above) these were 1462uH and 11.426mH respectively. To make things simple I may use a coupling coil for the aerial rather than tap these.

Summarising:-

Jones Plug Pin 1 is wired to C102 (0.001uF) which goes to FSxr via the Mode Switch MSBf and MSdf with R63 (2.2Mohm to ground).

Jones Plug Pin 2 is wired to C100 (200pF) which goes to FSxf via the Mode Switch MSBf and MSdf.with R62 (2.2Mohm to ground).

 I decided to make a compromise by removing the RF wiring from the mode switch and instead have five aerial tuning coils selected by the wavechange switch with each one having a small winding for aerial feed then connect two feeds from these through to the Jones plug via C100 and C102 as before. This meant that I had to wind a pair of coils.. one each for Ranges 4 and 5. These two will connect to the trailing aerial connection with the other three to the fixed aerial. I'll also arrange for a spare panel switch to connect the Range 4 and 5 coil aerial windings to he fixed aerial connection. This will let me tune the reiver to any range using a single long wire aerial. It will also let me use the R1155 with the T1154 using two separate aerials.

I couldn't find a suitable coil for Range 5 in my junk box. The handbook tells me this should measure 11.4mH. So that it can track between 200 and 75KHz I had to use a former suitable for a core so that the inductance can be set correctly for 75KHz. I found a suitable former and wound 1100 turns of fine wire on it. This measured 9.2mH and I reckoned a dust core would easily increase this to the desired 11.4mH. I tried this out on the bench but couldn't get it to tune across a broad enough range, although by reducing couplings to the test equipment it improved somewhat. I reckoned that in-situ in the reiver it would be OK, but after adding it I discovered it wouldn't track. It would almost tune at the high end but there seemed to be excess inductance for 75KHz. Wondering if the coil had too much self capacity I did some tests and found this was about 47pF. I imagine this is higher than the original coils because mine uses a "scramble winding" of single thin copper wire. Traditionally low frequency RF coils use litz wire in a low self-capacity winding. I don't think the error in tracking is important but I'd like to investigate further.

Interesting is L4. This is shown mounted on the chassis adjacent to L5 and L6, but has been replaced by a small aerial coil mounted on a brass plate at the rear of the aerial coil compartment. Bearing in mind that this receiver carries a modified Range 3 it's possible this coil was added as part of the modifications to cover the new range 1.2-3MHz.

 

 

 Above are the two new aerial coils, L5 (left) and L6 (right). Each has a coupling winding which is connected to the wavechange switch at wafer FS.wf together with that for the Range 3 aerial coupling coil. The return path for these coupling coils is the receiver chassis, but the return for the two tuning coils is connected to the bias voltage carried on an 0.1uF condenser mounted underneath L1-L3. Connecting the aerial coupling windings for two new coils to the wavechange switch was tricky because the wafer contacts were buried in wiring and not readily identifiable because original wiring had been removed by the last owner and he'd never completed the modifications. L4-L6 had all been removed and discarded so that the added power supply parts including the mains transformer would fit on the chassis.

L5 has an inductance of 1.4mH and L6 9.2mH and because both home-made coils carry a fairly high parasitic capacitance their tracking is not perfect, but satisfactory. I looked around the Internet and found a really interesting and easy way to discover coil information. Basically it uses the fact that a square wave is rich in sine waves and one of these will be close to the resonant frequency of any coil under test. You need a square wave having an amplitude of something over say 5 volts, a 10Mohm resistor connecting the square wave output to the coil and an oscilloscope with a 10:1 probe also connected to the coil. My scope has a square wave test output and I guess that might do in place of the separate square wave generator? When the coil is connected and the oscilloscope adjusted you'll see a set of sine waves decreasing in amplitude from the square wave edge. The frequency of these waves represents the coil resonating with its self capacity so if you know the coil inductance (measure this on an inductance meter) you can calculate the value of self capacity. Also, the Q of the coil can be determined by counting the number of cycles to the point where their amplitude is exactly half the maximum value. I checked my new L6 and found it was 9.2mH + 47pF and my new L5 measured 1400uH + 27pF. L6 had 1100 scramble wound turns.

In the above picture (the new L5-left and L6-right) you'll see two 2Mohm resistors. These are R63 and R62 connecting to Jones plug pins 1 and 2, fixed and trailing aerial inputs routed from the T1154 transmitter where they connect to the transmit/receive relay. To make the R1155 independent of the transmitter I intend to add a coax connector and a switch for combining these for long wire use in general reception. I fitted the coax socket and a headphone jack socket in the space adjacent to the two Jones plugs (still remaining in my example).

I also took a look at the slow motion drive (the early type 13 variant) because it had some backlash. I noticed the cork washer was loose so this needs to be re-glued to the underside of the part still on the spindle, then grease applied to the various parts after cleaning.

 

 The receiver was working perfectly before I added a small plate carrying an aerial socket and a headphone jack socket, removed the original toggle switch above the mode switch and fitted a double pole double throw type. I connected the aerial input connections at the Jones plug to the new switch and added a short between the two on tags and a wire to the new aerial socket. This lets me use the R1155 independently from the T1154 with a long wire covering all five wavebands. The headphone jack socket was then connected to the secondary of the audio output transformer and the new panel fitted over the unused Jones plug and the space to its left where a small Jones plug should have been fitted.

I turned on the set but could only hear a faint tinny sound from the loudspeaker. Plugging in headphones initially let me hear Radio 4 on 198KHz but this gradually faded out to just a faint hiss. My first guess is that one of the few remaing old condensers had failed. There can't be many left now but I suspect a screen or anode voltage is now very low... maybe around the 6K8 mixer/oscillator? The voltage across the bias resistor R1 measures 47 volts and HT to chassis 170 volts, but it turned out that all the components were fine and the 6K8 had stopped working. I plugged in a 6A8 that I had on the bench from another job and it worked OK except it didn't oscillate at all on the 7.5-18MHz band so I'll have to dig around for a 6K8.

 new plate

 I tested the performance of the front-end (with the 6A8 plugged in). To do this I connected my spectrum analyser tracking generator to the aerial and my high voltage probe to the anode of the mixer. When you do this with a tunable receiver you'll see two or three well defined signals. See a scan of the RF25 unit. The local oscillator and either or both main mixer products ie. Fosc +/- Fif. If the scan is broad enough to include the IF of the receiver, this also will be visible. I prefer to scan just the band in question as that is what you need to see to the check ganging of circuits. What you see is the performance of the receiver at whatever frequency the dial is set. With a receiver having two tuned RF circuits you may see either a nicely defined peak to the left or right of the local oscillator (depending on whether the design has the oscillator higher or lower than incoming RF), or a fat signal or even a double hump indicating the two RF circuits are not ganged properly. As the higher short waves are tuned you'll also see the image at the opposite side of the local oscillator. Below, in Range 3 scans there were two humps 1.01MHz and 1.07MHz. With a single conversion receiver (like the R1155 which uses an IF of 560KHz) reception in the highest shortwave band will be pretty poor in terms of image response.

Because of the higher proportion of capacitance to inductance at the low end of each band the width of the response ie. the selectivity will be better there and as the LC ratio increases so does the selectivity worsen. This is unfortunately a physical fact: to achieve a wide tuning range the band will have poorer selectivity at the high end and of course the image response will suffer.

With the scan extending to more than double or triple the local oscillator frequency you'll also see its second and third harmonic. Because of these extra (false) signals and the use of a long wire, the highest shortwave band will be full of signals, many of which are transmitting on frequencies miles different to the dial setting. In practice, unless one of these falls inside an amateur band these false signals are unimportant. Alas though, interference from low energy lamps, network cameras, computers and a whole host of unregulated electronic apparatus results in a high background noise level not helped by receiver-generated extraneous mixer products shifting extra noisy parts of the spectrum to the IF amplifier.

Below... scan results of the five ranges where the measured amplitudes reflect the tracking generator amplitude (constant over all tests)

 Frequency band

 Range 1: 75KHz to 200KHz

 Range 2: 200KHz-600KHz

 Range 3: 600KHz-1.2MHz

Range 4: 3-7.5MHz

Range 5: 7.5-18MHz

 Low end

 -28dBm

 -39dBm

 -35dBm

 -29dBm

 No osc

 High end

 -22dBm

 -4.7dBm

 -23dBm

 -31dBm

 No osc

 Spot frequency

 150KHz= -25dBm

 300Khz= -24dBm
     
 

 I'll repeat these measurements once I've fitted a new 6K8.

I fitted an equivalent X65 and made various measurements on Range 3 which is unusual in this particular version covering 1.2 to 3MHz (although the dial still retains the original marking of 600KHz to 1.5MHz). I moved the dial from the low end then to the high end as you can see below.

 
 

 Dial set to 600KHz (x 2) showing the RF from the tracking generator peaking at about 1.2MHz but with double humping indicating poor tracking between the aerial and mixer circuits.

 

 Dial set to 600KHz (x 2) showing the local oscillator at 1.757MHz indicating the correct IF of 560KHz.

 

You'll note the spike on the right which is the secpnd harmonic of the local oscillator, 15dB down on the fundamental. Although the two peaks look to be in the same ballpark the scale is logarithmic making the second harmonic about 33 times weaker than the fundamental.

 

 Dial set to 1.5MHz (x 2) showing the RF from the tracking generator peaking at about 3.02MHz.

 

You'll note that the RF response at the high end of the band is broader (x2) than that at the low end because the capacitance-inductance ratio is smaller making the receiver less selective.

 

 Dial set to 1.5MHz (x 2) showing the local oscillator at 3.455MHz.

The RF should be tuning at 3MHz but the oscillator isn't tracking correctly.

To be correct the oscillator should be 3.560MHz. This can be corrected by unscrewing the local oscillator trimmer condenser so increasing the LO frequency.

Once this has been done a second check needs to confirm the low end settings are still correct. If not the Range 3 oscillator coil needs to be adjusted followed by a further check at the high end.

 During testing I noticed something odd and reminiscent of my R208 investigations. As I tuned across the highest frequency band I noticed the local oscillator amplitude dramatically dropped at something like a third of the way from minimum frequency and the exact frequency of the reduction was affected by the tuning of the mixer coil. The R208 local oscillator was killed off on its highest band but the R1155 local oscillator doesn't actually fail, it just drops to a low value before increasing again to its original level.

Checking further I found that when ther mixer coil is tuned near to the same frequency as the local oscillator the oscillator amplitude falls and then stops oscillating when the mixer is tuned to the same frequency.

All is now resolved. The issue was this... the mixer coil for Range 1 (7.5 to 18MHz) was jammed in its coil in a retracted position with the core end flush with the top of the former. This meant the tracking was severely affected. Although the trimmers could peak the coils at both ends of the band the mixer coil was tuned alternately to the main signal or the image and crossing over at some point in the band, typically 9MHz. At that point the mixer and local oscillator coils were tuned to precisely the same frequency causing the 6K8 to block oscillation.

I couldn't retract the core but by gently easing it back into the former it slackened enough to get better tracking. By trial and error I worked out that the local oscillator should be on the high side of the incoming signal. Once the mixer was tracked to the oscillator I was able to track the aerial coil which was also miles out of adjustment. Checking at the top end of the range, an 18MHz modulated signal at 40uV had the same audio output as the image signal at 19.12MHz at a level of 1mV which represents an image suppression of 28dB. Further tweaking should improve this. The local oscillator amplitude is now pretty well the same amplitude across Range 1.

 
 Above, the receiver just about completed with its power supply. The left meter reads 62mA and the right about 230 volts between HT+ and HT- rather than the chassis which sits at about 50 volts above HT-. All the wavebands are now working pretty well using a long wire aerial and a final alignment check plus repair of the slow motion drive are all that's required before the R1155 can be tried out with the T1154. The power supply above is really for using the receiver in stand alone mode or as a general purpose HT/LT PSU for other valved sets. It's now relocated above the T1154.
 
 When I tested the receiver on a long wire I found the sensitivity on the two long wavebands was much less than another example that I have. I put this down to the home-made coils L5 and L6. These have excessive parasitic capacity and are wound from single enamelled copper wire whereas the correct coils have litz wire and are wound to keep parasitic capacity low. I've now obtained a set of three original style coils L4/L5/L6, two of which (L5 & L6) will replace the scramble-wound versions I fitted. It remains to be seen if sensitivity is improved once these have been fitted....
 

pending....

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