Moreton Cheyney "Silver Knight or Silver Dragon" ?

 

 

 

 Below I found the following records for this receiver. In the first, I left in place a couple of other lines which support the fact that surplus receivers were eagerly awaited by radio amateurs and Moreton Cheyney were in business to supply receivers to fill the stopgap. It would be worth the five pence (a letter plus twopence halfpenny [=1p]) to discover what was on offer, but looking at the 1949 company address is quite revealing. 52a Gaol Road, Stafford is only a stones throw from Stafford Gaol and appears to be the room(s) above the words "SUPPLIES LTD". I traced the owner of 52 Gaol Road to a Mr E.A.Boult who was running an engineering business (a Villiers Service Agent) there in 1948.. presumably he'd rented the rooms over his shop to Moreton Chayney Limited? I can find no record of insolvency or in fact any record of the company in either the newspaper archive or the London Gazette so they must have just packed up and gone back to a non-radio venture or a normal employment.

 

 

 

 

Above the forthcoming birth announcement October 1945

then possibly a little late, March 1946

 

 Above it had reached the ears of the Wireless World editor November 1946

 
 

 

 Here's a statement from June 1947 and an ad from Wireless World, August 1947 which gives a little more information about their Dragon receiver. As mine does not have bandspread.. does this mean it's a Silver Knight rather than a Dragon? Or is mine an earlier version without bandspread?

Note also the alternative address in Bilston.

Without better details I can't exactly identify their premises but here are three possibilities... take your pick..

Top left: next to the Baptist Church grounds (my preference)

Top right: opposite the Baptist Church.

Bottom: further up the road from the building at top left.

Click picture for 1939/1945 map.

 

 
 

 

 

 

 

 

From the timings I'd hazard a guess that they moved into large premises but soon downsized to 52a Gaol Road which may just have been a store for parts and unsold receivers and amplifiers?

 Not a lot to see on the Net other than classified ads , but I did find them in the 1947 edition of Radio Who's Who  

 

 
Looking at the earlier mention of the firms address the letters "BCM/REME" are quoted. I understand that this code was like a box number from which post would be forwarded by British Monomarks (the BCM bit) The REME part might have been chosen by the proprietor of Moreton Cheyney who may have been in R.E.M.E. during WW2? Perhaps, by 1949, the company was in dire straits and was saving money by dropping their box number?

 

 An advertisement in a 1949 Wireless World... maybe no-one had noticed their previous publicity drive in November 1946?

Pretty pricey when you consider such things as a N.O.S. AR88 at half the sum.

 

 

 All is revealed in the excerpts from the London Gazette below:

A creditors meeting 3rd November 1948, insolvency recorded 3rd November 1948, claims requested 19th October 1948, and notice of the Liquidators Report 5th November 1950.

 
   
   

 

 So.. who started the company? Other than the company name there isn't a clue in any of the records and at first I thought.. maybe a Mr Moreton and a Mr Cheyney but then I searched around and came across Albert Edward Moreton born in 1880. He married Annie Cheyney and they lived in Stafford. I then came across a family marriage.. Muriel Moreton married a chap called Albert Tarry.. so the three names Moreton, Cheyney and Tarry (see above) are linked in Stafford. Albert Moreton had several children including two boys James, born 5th August 1902 and Albert born 25th February 1914 (who I think died aged 4). Their father was a tin smith and later a shopkeeper who lived at 1a Rowley Street only 400m from Gaol Road. Another snippet is that Muriel Moreton, who married a Tarry in 1936 later changed her name by Deed Poll to something quite different.. was this a case of "blaming the messenger" (P.A.Tarry called the creditors meeting)?.

Albert's son James Henry might have been the owner of Moreton Cheyney but he is a tricky individual. First he has no birth record under the name James Moreton because he was born 6 months before the marriage of Albert and Annie and in 1911 he was living with his uncle and aunt at Ruyton on their farm. He was however listed on his father's Army record as his first child born 5th August 1902 in Stafford.

1a Rowley Street looks like an ordinary terraced house so Albert must have rented a shop somewhere else, in fact it was just round the corner at 24 Stone Road in a fairly imposing building, now a bed shop.

Looking back to 1901 I found Albert living with his parents at 24 Gaolgate Street (now Gaol Road) and that address since demolished, but it did give his father's occupation as a general dealer shopkeeper and noted that Albert was a general dealer. The address is only a stones throw from 52a Gaol Road....research continues...

 

 As you can read above this old receiver was designed just after WW2 and no doubt was inspired by the huge amount of dirt cheap government surplus radio components. My example has some condensers dated 1947 so post dates the earliest radios. I haven't yet found any record of the manufacturer after 1949, other than the snippets above. The reason may have been the glut of high performance government surplus communications receivers released around that date at knock down prices and the collapse of the business.

At first the old chassis looked to be in dire state with that white crumbly aluminium oxide, but inspecting underneath revealed all was well, apart from a bent alumium screen or two, and looking much like it did in 1947. Mechanically, it mostly looks OK. One of the first considerations is the tuning arrangement of a receiver and, as this cleaned up easily, the set is a good candidate for light restoration. This example was presumably sold for amateur radio use when a suitable power supply can be knocked up by the purchaser; or a commercial one such as the Type 123 can be used. Below a view as received here.. then a larger view from the rear and then with the valves removed. Lots of surface corrosion on the aluminium chassis due to storage in a damp garage for over 50 years.

 

 

 

 

 

 

 Apart from a broken IF valve, and two missing valves, one below the tuning indicator, and the other in a vulnerable corner, all were present and are common types. It was a relief to see under the chassis as this could easily have been a rat's nest of rusty and corroded bits and pieces. In fact it looks nearly new. The tuning arrangement is fairly clean and after greasing works very smoothly although I have two grumbles... there isn't a quick tuning control so lots of twiddling is needed to go from one end to the other, and, what I consider to be a major failing... the knob can be turned beyond scale ends and thus offset the tuning condenser from the pointer. I found this fault recently in another receiver so made a simple modification to prevent this effect. Because this receiver probably stopped production before 1949 neither fault was likely to have been remedied and users would have quickly learned to not turn the knob too far. The fact that this example of the set probably never had a cabinet made it simple to push the pointer back in place, and while on the subject of the pointer... why is it so big? The dial is squashed in shape so you need an odd arrangement to make a suitable pointer; or what was intended.. the end would be hidden inside a case so would not look odd when vertical. The answer may be to redesign the dial and make it a semicircle but that would destroy the oddness and the originality. I do need to give the cardboard scale some TLC as dampness has made the red ink run. Probably scanning it and printing a new one is the best bet...

 

 

  Below, a view of the contents of those four aluminium cans. I can see spots of verdigris so I wouldn't be surprised to find some open circuit IF coils. Unusually, each can is held in place by only a single nut and grid leads are taken from the bottom of the can making it simple to get at the components. Many receivers do not have this facility, instead cans need to be released from under the chassis and detached only after wiring is cut. Three cans lifted off but the lock nut on one was seized resulting in the bolt turning. The top of the can was flexible enough for the bolt to be broken off by bending it back and forth and the bolt can easily be replaced. The dark coloured material appears to be either ebonite or possibly bakelite and is the same as that used to mount the tuning gears. I spy an old fashioned diode on the right. I wonder why a valve wasn't used.. maybe the designers thought the new diode being state of the art was better?

 

 

 What about the receiver specification? Well, the write up above says that it can deliver 10 watts of audio at less than 2% distortion.. but can it? It covers five wavebands which from the dial markings (in metres) are... 10m to 17.6m, 20m to 34m, 75m to 100m, 200m to 550m, and 800m to 1800m. The dial markings are essentially based on station names and the actual wavelength markings are few and far between. In fact each band has quite a large additional range which is uncalibrated so it will remain until the set is working to establish its full coverage. On the two higher HF bands there are megacycle equivalents which oddly are to 2 decimal places so, for example 34 metres is marked 8.84Mc/s. The selectivity control, clearly designed for audio reception from AM transmissions, is marked.. 5Kc, 8Kc, 11Kc, 15Kc, 18Kc and "TRF" which is stated in the write up to be 24Kc/s. So, there it is... the Moreton Chaney receiver was aimed at what have been referred to lately as Hi-Fi enthusiasts and not as a communications receiver. The latter would require a BFO and a means of reducing bandwidth suitable for CW reception. The very limited demand for such a receiver, especially in bare chassis form, must have been a marketing failure for the fledgling company. It's price in 1946 was pretty high. Over £63 and nearly £95 for the chassis and cabinet versions respectively. Around that time, just after the war, rather handsome Murphy radios cost from £30 to £35 so it must have been only real enthusiasts prepared to hand over close to £100 for a radio with zero pedigree.

Reading the advertisements for the receiver you'll note that intially the set has the "sensitivity" of a communications receiver and later the "performance" of a communications receiver. Presumably a last ditch effort to clear remaining stock and quite possibly my example was bought with the understanding that it was equivalent to a communications receiver. It was quite likely to have been purchased by a radio ham because why else would the job lot include a T1154 and a heavy duty AM modulator? My guess is that the firms liquidator probably offered unsold stock at bargain basement prices (hence attractive to a radio ham).

The first step was to tidy up the top of the chassis using a brass brush in a high speed drill. This removed most of the aluminium oxide leaving what was left of the grey paint in fair condition. then I used phosphoric acid to neutralise rusted areas, mainly screw heads and brackets.

 

 

 

 Then I looked for any damage that needed to be repaired. Most of the controls, other than the tuning which I've already sorted out as this would have been a major concern if it was damaged, are seized and a few are not yet identified. Under the chassis are several areas that need attention, no doubt some of these are due to rough handling in the past. I've shown a selection of these below. Some will be easy to fix, others will need some care to avoid further damage.

 

 

 Left, two trimmer condensers squashed at right angles to their original positions.

 

Right, bent plate

 

 

 Left, another bent plate, clearly its taken a heavy blow but fortunately none of the yaxley switch wafers are affected.

 

Right bent coil tags

 

 

 Left, a missing rear panel control or more likely a hole for mounting a Belling Lee socket, indicated by disconnected green and black wires?

 

Right, a pair of wires carried through a hole in the front panel.These are wired to the bandwidth switch.

 

 

 Left, a white wire left dangling.

 

Right, another bent panel

 

 

 Now for some general details...

 

 Control pot to the left of the coil pack.. maybe a tone control?

 

 

 Rotary switch for AVC off, Radio and Gram
 

 

 Pot, maybe the volume or second tone control, on extreme left fitted with a switch carrying a cable fitted with a 2-pin socket maybe for switching a PSU on and off ?
 

 

 One of the two valveholders that was missing its valve, probably an X61 frequency changer.
 

 

 

 Fitted to the wavechange switch are two of these epicyclic metal cams which press onto spring loaded plungers which operate through the chassis.

I'll need to investigate these because they're seized. I think the plungers change the settings of the cores in the windings of two IF transformers.

This cam is set slightly to the right of its correct position.

The spring ensures the plunger can return to its fully out setting.

 

 These two pots are coupled together via brass gears. Maybe this is an RF gain control feeding the RF amplifiers and the IF amplifiers via two separate circuits? Alternatively it might be a pair of pots used for treble or even a volume control? I'll trace the circuit later and determine this.

 

 I'll now straighten any bent metalwork then attempt to free the various controls all of which are seized solid. When I tackled what I believe is a tone control I found it was seized because the small panel used for mounting the pot was bent.. not just leaning forward, but it had a dog's leg bend which was positioning the long fibre extension shaft at an angle and preventing it from turning without excessive force. I had to remove the panel and this meant loosening the front panel bush, detaching the coupler between the pot and the shaft, then removing a couple of almost inaccessible locknuts. The panel had been mounted before the pot had been fitted and wired up so was very tricky to detach. Once this was done I pressed the panel in a vise and checked it was square before refitting it. Attaching the coupler was also tricky as it's a fibre type and the screw holes needed to be perfectly aligned before they could be fitted. Once the work was completed the tone control worked OK, at least mechanically. Next I tackled the wavechange switch. This was also seized solid. I straightened the securing bracket which is made from thin aluminium and was then able to apply oil to the ball bearings in the click stop mechanism and then a little to the front panel bush. The switch was then serviceable although slightly heavy in operation.
 
 I then looked at the bandwidth switch which was seized. There are two plungers operated by cams secured to the centre spindle. When the switch goes from its first to second setting (5Kc/s to 11Kc/s) the cams should start to press on the plungers, but both are seized. The plungers seem to have three positions, but once unseized may have more settings.. in fact one for each bandwidth? The first setting will be at whatever frequency the IF stages are tuned, this is the 5Kc/s setting, Setting 2 for 11Kc/s and Setting 3 for 15Kc/s etc.... The design of this feature is pretty weak because the plunger is fairly long and the slightest play makes it move sideways and it tends to get jammed and end up at not quite the design position. Initially the rear plunger appeared to be seized and when trying to free it I heard something fall from the IF transformer onto the table (see later). I didn't check to see what it was but it may be part of the tuning slug as these can rust and get jammed in the coil. I'll look into this when I test the IF coils for any that are open circuit. Usually in prolonged damp conditions the copper wire ends will corrode and the verdigris consumes the copper wire although with care, if this is confined to the soldered ends, a repair can be made.

 

 

 

Above are sketches of the IF transformer innards. IFT1 first appeared to have just a perspex rod running through the coils so that the plunger will merely move the coils closer together thus increasing their coupling, whereas IFT3 has an iron dust core which changes both coil inductances and mutual inductance at the same time. In both cases one coil is glued to a piece of bakelite which is bolted to the plunger and prevents any undesirable rotation of the coil which would increase stress on the coil connections. After closer inspection I found IFT3 looked as if it had carried two dust cores but one had broken off when I'd previously been freeing up the bandwidth switch, but no, the shaft was made with a different material to that in IFT1. The other two IFTs have their coils mounted horizontally on an iron dust core. Both coils are moveable so can have their inductance and mutual coupling preset. Aligning the receiver's response in the factory must have been a nightmare.

Turning to IFT1/IFT3.. aging has unfortunately resulted in the glue failing so that the moveable coils are no longer fixed to their mounting plates and therefore their plungers. Wear has also resulted in the core in IFT3 failing to pass cleanly through the hole in the upper mounting plate (in fact this was due to the iron dust core rusting resulting in seizing). 

 
   

 This is IFT1 with its perspex plunger. Visible are the cracks indicating the coils have come unstuck. The pair of springy connections allow the lower coil to move.

 Here is IFT3 with the top detached. You can see why I first thought there were twin iron dust cores. The upper one is broken off and the upper coil has fallen from its mounting plate. The plunger material is different (grey). Maybe a design change introduced the perspex type opposite because it is smoother and less prone to jam.

 As the plungers didn't move properly and were jamming or bending instead of passing through the coils I ended up having to remove the first IF transformer from the chassis. This involved cutting three wires and detaching two solder tags secured by locknuts. Once the thing was removed I could see the plunger was only operating over part of its travel. After a lot of investigation there was a cracking noise and an iron dust core hidden in the coil broke off the end of the perspex plunger. It was only then I discovered that rust had seized the dust core inside the upper coil. I unsoldered the coiled connecting wires, removed the securing screws from the lower bakelite plate and detached the lower coil with the plunger. I found a replacement dust core and filed it down to fit the inside of the upper coil. The new core had a hex hole and I was able to make this roughly circular at one end then file the brass screw to which the broken core had been attached then superglue the new core in place, ensuring it was perfectly in line with the perspex rod. I superglued the lower coil in place and superglued the upper coil. In this case I had to use a mandrel (a screwdriver with exactly the same diameter as the hole through the coil) to centralise the coil and line it up with the hole in the upper plate through which the dust core can protrude, otherwse the new dust core would foul the edge of the hole in the plate holding the coil.

After reassembling IFT1 I shall have to repeat the operation on IFT3.

 
 

 A view of IFT1. Someone has looked at a problem previously because the pin securing the spring was badly bent and I suspect a washer was originally fitted.. now missing. I suspect they gave up once the complexities of repair became apparent.
 

 A view from the opposite side of IFT1. Before refitting I'll need to check and probably replace thse two waxed decoupling condensers.

 Below the broken dust core and once repaired with the coil glued in place. Both IFTs needed this repair.

 

 

 

 

 This picture shows the hole above the upper coil through which the dust core should protrude as the cam operates the plunger. The upper coil was detached and the upper dust core rusted. As the cam turned against the plunger it pressed the dust core which was partially seized up against the edge of the hole (the coil was off-centre). Eventually the pressure caused to dust core to break off. Refitting the coil has to be done so that the hole through the coil lines up precisely with the hole in the upper plate. The designers should have allowed for tolerances and drilled the hole shown oversize.

Not only that, but the two bakelite plates, one holding the upper coil and the second guiding the perspex rod are held in place by a single 6BA screw either side. That means the plates can be inadvertently fitted at a slight angle causing either the dust core or the rod to jam slightly. Final assembly has to be done so that the two plates are perfectly level and the rod can slide in and out with a minimum of friction. In fact, once I'd adjusted the plates perfectly level I applied superglue around them to lock them in place. IFT1 has two decoupling condensers which I'll swap for new ones.

Both IFT1 and IFT3 had the same problem so I'll tackle the other next... see below.

 

 

 

 
 

 Oddly, this transformer uses an ebonite plunger rather than perspex as in the IFT1, but the fault was identical with the rusted and jammed dust core broken off.

 I usually supply hints and tips for anyone carrying out a similar restoration, but in this instance, I don't think there are any other Moreton Cheyney receivers in existence so all I can do perhaps is describe one or two of the many reasons these sets were scrapped by their users.

These variable bandwidth IF transformers are fine if perfectly assembled and in good condition, but given some aging the things will fail and may make the receiver unusable.

They're made by fitting two coils within a bakelite or ebonite structure. One coil is glued to a fixed bakelite (upper) plate that is held in position by a single screw each side. Why single screws? So the upper plate holding the coil can be rotated through a minute amount which is necessary to allow a dust core to pass through unhindered. The lower plate carries a quarter inch clearance bush through which the rod holding the dust core is fitted and is also secured by a single screw to either side. The rod is quarter of an inch diameter. This means that the lower plate bush and the upper plate coil need to be absolutely and precisely aligned otherwise the rod will jam. Alignment needs to be made by twisting either plate to align with the rod. I noted that the fixing holes for the plates are drilled to suit the assembly and the plates are marked with scratches to tell the assembler which way to fit them. Once in use, if the thing gets knocked or a screw is inadvertently tightened (rotating the plate) the dust core will jam.

 Looking at the socket under the magic eye in which there should have been a valve, I see it's wired for something like an ECH35 or an X61/X65 so that will be the frequency changer.

The coilpack has three sections and it's clear that the rearmost is for the RF amplifier coils because the aerial socket is wired to this circuitry. The centre will be the input coils for the frequency changer and the front section carries the oscillator coils where some condensers looking like padders are fitted. The centre section carries a feed to a top cap of a valve on the opposite side of the chassis, undoubtedly the first IF amplifier.
 

 The coilpack seems a little strange because not all the coils are fitted with adjustable cores. As some cores are fairly loose it's likely that some have fallen out although the medium and long wave coils do not appear to have ever been fitted with cores. This would be acceptable if the coils are accurately made proprietary items having very accurate inductance values and are being used with the correct tuning condenser in line with the coil specifications. Again, not all the coils appear to have associated trimmers. Again, if the coils are tuned with the correct tuning condenser, meeting the coil specification, they will probably track reasonably well. The absence of trimmers will explain the rather vague tuning dial and overall these clues will explain the use of twin tuning condensers. Whilst checking the coilpack I found several bad solder joints which will need fixing when I attempt to fix the bent trimmers.
 

 I took a break from repairs and started to trace the circuit. I immediately realised that some fairly extensive changes have been made by a previous owner and in doing this there were a few bad solder joints that may have resulted in the set being stood down from service. I initially began in the rear corner of the receiver which is occupied by an L63G (equivalent to the 6J5) and two metal 6J5 valves. I had overlooked the fact that there is no trace of an output transformer and no evidence of one having been fitted so I must assume that the output transformer was supplied with the loudspeaker which, from the 1946 Wireless World advert above, indicates it was supplied only with those sets fitted in cabinets. The transformer must have been fairly special because I cannot recall ever seeing a pair of 6J5s being asked to supply 10 watts. The next thing I spotted was that there are no direct connections between either rear socket and the 6J5 anodes. There clearly should be something and indeed I found a small condenser which I measured as about 4.7nF connecting one 6J5 anode to a pin on a rear socket. The wiring to this particular 6J5 is a little odd in that both its heater pins are wired, not to the sets LT line and ground, but to the rear connector to which that condenser is wired. Below, I've shown the area occupied by the output valves.

In the picture below the resistors are marked as follows: Individual anode feed 51Kohm, joint anode feed 10Kohm, cathode 3.3Kohm (see notes below for what this means).

 

 

 
 Above is what I traced for the two 6J5 valves that were originally used for audio output which I suspect have been modified in some way, as yet undetermined. At first it looks like the left valve provides a sngle phase output to a external amplifier via a pin on one of the two rear 5-way sockets. The change was either done by the manufacturer or the user. I guess the external amplifier has a phase splitter so that this one is redundant but further work is needed before this is certain. To see the amplifier click the above circuit. Read on for some thoughts...

Initially I assumed that this chassis carried the complete receiver circuitry; although a couple of important things are clearly missing ie. an audio output transformer and a power supply. I assumed however that the statement about the audio output being 10 watts push-pull with a maximum of 2% distortion meant that two of the 6J5 valves were responsible for this, but later, having found that none of the 6J5s were wired for this I realised that either some later modifications had been carried out, or more likely the audio output was carried on a separate chassis and that this chassis also housed the mains PSU.

Firstly, working at some theoretical figures based on published information we can say that if the push pull audio output is given as 10 watts and assuming this is actually 10 watts RMS, then each 6J5 valve would need to deliver 5 watts of audio at max output. Assuming an efficiency of say 70%, each valve (because the max anode dissipation is 2.5 watts) would draw about 7 watts. Given an HT rail of 300 volts each valve would draw 23mA or from an HT rail of 250 volts, 28mA.

Taking an average an HT rail of 275 volts each valve would draw 25mA.The valves have an auto-bias cathode resistor of 3.3Kohm so the grid of each would be negatively biased at 82 volts which seems rather odd. I would expect the negative bias to be circa 4 to 6 volts so the cathode resistor should be 160 to 240 ohms. I'm unsure about the anode resistors. If they are original then they must have been fitted to protect the valves when operated without their transformer. Looking at the 3.3Kohm cathode resistors I can only assume that these were fitted by the last owner so that the valves would be acting as a driver for an external power amplifier. In that role an anode current of between 1 and 2mA would be typical. Assuming an anode current of 1.5mA the common 10Kohm would drop 30 volts (both valves total 3mA) and each 51Kohm would drop 77 volts leaving an anode voltage of about 170 volts which seems sensible.

Now the circuitry around the ganged pots... I'm still not entirely clear about the purpose of these two pots. Given a slight complexity in producing a decent treble control these pots may be used for that function?

 

I've yet to trace these circuits, but I did notice the left hand pot is wired to a large grounded electrolytic.  

 

 Next steps: identify all the components and trace the circuit diagram. This will help to work out the purpose of the four mystery valves. There are a few possible functions.. the TRF receiver, maybe an anode bend detector, and a "loudness" amplifier. V12 and V13 look like they are a pair of audio drivers for the PA fitted on the amp/PSU chassis. A brief check of the wiring tells me only a single audio feed is now wired to the output connectors and a new phase splitter circuit fitted to the modified external amplifier.

See the components listings which relate to the numbers shown on the following four pictures

Note X1 and X2 noted in IFT4 can are copper oxide "Westector" diodes whose "6" marking refers to the number of elements.

 

 

 

Condensers

Resistors

 

 

 
   This area is hidden under wiring and parts and carries some of the AVC components connected with white sleeved wires.

 

 

 

 Now that I've identified 99% of the components I can start to trace the circuit. Once I started I soon found modifications made by the previous owner plus a number of poor solder joints. I decided to find out the actions of the bandwidth switch as this should lead me to the TRF section of the receiver. The switch has four wafers spaced widely apart and I discovered it needs switch cleaner treatment as I found continuity tests didn't make sense. Each wafer has a pair of single pole 5-way contacts. Starting at the wafer nearest the front panel, one switch is not used and the other strangely has all 5 contacts wired together.. so why bother with a switch? The wiper goes to the HT line via R32 and the output contacts to IFT1 where it is routed via the primary coil to the anode of the mixer valve, V1.

The second wafer is where the TRF receiver is switched in (this, I imagine is an anode bend detector). 4 output contacts are wired together and route via IFT2 primary coil to R30 to HT and the TRF contact wired to R13 which is the anode load resistor for V4. Therefore, this switch removes HT from V6, the second IF amplifier and connects instead to V4, presumably the TRF receiver valve. Again the other 5-way switch is unused.

The third wafer has both 5-way switches in use. One switch has its first position unused then selects either R39, R40 or R41 which are wired together and connect to the fifth switch position. Here we find a modification. One of a pair of gold coloured wires connects to position 5 and the second to the output contacts (which are all wired together) of the other 5-way switch then are routed through a hole in the front of the chassis. The wiper connections of both switches are as yet untraced, however that combination of all 5 outputs connects to pin 3 of V9. This valve was broken, but I believe it to be a KTZ63, making pin 3 its anode. I've marked this as a "Loudness" valve which is a modern term recently given to enhancing speech.

The fourth wafer has both 5-way switches used.One handles the normal bandwidth settings plus an output for TRF and is associated with the Radio/Gram switch. The wiper of the other 5-way switch connects to a condenser. This is C27 wired to the anode of V9. Two other resistors are wired to V9 anode viz. R51 and R48 (the anode load resistor for V9). The normal bandwidth outputs for the 5-way switch connect sequentially from R68 (to ground) to R33, R34 & R35. The TRF position is not used.

 

 Above is a first pass at the receiver block diagram

I've called the area concerned with volume, bass, treble and loudness, "Audio Proc = Audio Processing"

AVC or Automatic Volume Control is the feature which uses the detected carrier level to feed back a negative bias voltage to earlier stages in the receiver to maintain the carrier at a preset level. The carrier of any broadcast station will produce an AC voltage at the last IF amplifier which will be rectified by a diode whose anode produces a negative voltage representing the signal strength of the station. A negative voltage is used because this can readily be used to reduce the gain of input amplifiers. In order for this to work certain of the amplifier valves are variable mu types whose bias determines their gain. Strictly speaking the feature should be termed AGC or Automatic Gain Control because, in a receiver aimed at high fidelity reception the audio output will not be fixed but should be linearly passed through the receiver to produce exactly the same audio output as exists in the broadcasted audio. I would expect this receiver to have fast AGC so that gain is increased instantaneously to combat any fading in the signal, hence I've postulated an AVC amplifier (its old term).

 

 I've traced the front end circuitry. It's fairly standard except that the wavechange switch selects a smaller tuning condenser than that used on the lowest three bands.

The coils are normal with the oscillator having a tapped winding and the RF amlifier coils a tuned primary with an untuned coupling coil.

From inductance measurements the IF seems to be 465KHz.

Resistor R7 looks distressed and lost its banding and measures high in value, possibly due to failure of condenser C49.

I suspect it should be 100 ohms?

 

 This started off as a real puzzle. Some connections were hidden but having sketched out the wiring I realised that Pin 6 was a tie-off point and not a weird valve electrode. The valve in this position was either a KTW63 or KTZ63 and is wired as a very interesting cathode-follower triode.

The anode current is set to a very low value giving the valve a large reverse grid bias. For example with an anode current of 1/4mA the grid bias would be minus 25 volts.

The RF input from the tuned mixer input is rectified by anode-bend characteristics and filtered by R12/C7/C10 and passed to the receiver audio amplifier via DC blocking condenser C8. The anode circuit is grounded to RF by C37 and C74.

This receive mode is selected on the front wafer of the bandwidth switch where IF stages 2 & 3 (V6 & V7) are deselected at the same time as HT is applied to V4.

 

 Putting the two together, here's a schematic of the front-end. There's a fair bit of switching involved in coil and bandwidth selection which is omitted for simplicity.

At this point I haven't spotted a provision for AFC. If it's there it may be located within the coil switching circuitry?

 

 Next I'll re-install the repaired variable bandwidth IFTs, rewire them, sort out the various broken solder joints and the bent trimmers mentioned earlier.

IFT1 and IFT3 had two and one 0.05uF wax condensers respectively; in my listing C59/C60 & C64. Testing these with a 200Kohm series resistor put about 30 volts across each condenser with an HT set at 300 volts. I noticed that this voltage, in all three cases, rose continuously at a very slow rate (about 0.1 volt per 5 seconds). This may mean that the inside of the condenser has some dampness which is slowly evaporating from heating due to the leakage current. Whatever is happening the basic leakage through the old condensers is way to high at around 1mA (making the the condenser the equivalent of a 22Kohm resistor).The final test was to measure the capacitance of the three condensers which was 0.15uF to 0.2uF instead of the marked 0.05uF. I fitted three new capacitors marked 0.047uF x 250VAC, rewired the IFTs where the old 18SWG wires connecting to external circuitry had perished insulation, then screwed them back on the chassis. I'll delay resetting the cams which currently are pushed out of the way until I'm ready to align the IF strip.

One problem I met in fitting IFT1 and IFT3 was probably also encountered when the receiver was in production. IFT1 was OK but IFT3 had a jammed plunger once fitted. The adjusting screws for the upper coil mounting plate are inaccesible so I'll need to adjust this with fine-nosed pliers to set the dust core perfectly parallel to the hole in the coil.

Now the various broken solder joints and those bent trimmers...

 
 

 I looked at the circuitry around the socket in the corner of the chassis which didn't have a valve in place. Iinitially thought that the socket was wired for a double diode triode, so based on the other valves will be a DH63 but later I spotted that Pin 6 was not a tie-off point but a feed for g2 so revised my idea and nominated a 6B8 which is about the only double-diode pentode with an IO base. The circuit is not what you'd expect and is probably an AVC amplifier rather than a signal detector and LF amplifier. As voltage gain is not really needed the valve is wired as a cathode follower which essentially provides a lot more current than the usual AVC diode. The cathode feed of the 6B8 includes a preset potentiometer (located in the rear corner of the chassis) which also sets the grid bias of the second IF amplifier valve. I guess this control is used to preset the maximum overall gain to minimise distortion on very strong signals. In other words arrange for AVC action to be linear and not result in saturation from high level signals thus preventing insufficient negative feedback.

There are a few errors in the circuit shown. but a revised version is to be found further down this page within the IF amplifier circuit diagram.

 

 

 After another session of peering into the wiring I came up with this circuit. The switch marked QAVC off/Radio/Gram is a four pole 3-way affair with a long extension made of tufnol which is not entirely suitable (like the ones used for tone controls) because it flexes giving a wobbly feeling to switching. Also, because the switch is fairly stiff the knob has twisted over use and its securing screws have made a deep gauge in the tufnol (below).

Of interest is V9 which must operate with a very low anode current (circa 1 or 2mA). Oddly its heater connections (x, y) are not wired to the remainder of the valves, instead being brought out to the 5-way chassis connector. From the circuit V9 appears to be an audio pre-amp (maybe fitted to work with a gramophone deck using a very low output) and it's possible its heater is provided from a 6 volt DC supply to minimise hum.

 

 Just a passing thought.. what is "QAVC off" (engraved on the knob)?

Looking this up it stands for a rarely used term "Quiet Automatic Volume Control". Ordinary AVC must be noisy. Then again, delayed AVC is common so could the Q stand for "Quick"? AVC is used to maintain the same audio level from the speaker for different broadcasts which is what a cultured listener wants.

Fast AVC would indeed be noisy when tuning across the band and when a strong station fades out and background noise pops up so I guess this receiver uses another form of AVC which can be switched to normal AVC for night time listening or searching for weak stations. One common AVC feature is its amount of "hang". Tuning to a strong station puts a large negative bias on the RF and IF amplifier valves and adding capacitance to the line carrying the voltage will result in a time delay for this to discharge. Tuning away from the strong station will result, not in an instantaneous rise in audio from the signal skirts and background noise, but will make the transition more gentle which is probably what is meant by "quiet".

Once I've understood the whole of the receiver circuit and dry joints and squashed connections tidied up, plus maybe changing some of the wiring to plastic where the original insulation is in poor condition, I could fit a set of valves and apply 6.3 volts for the heaters then carefully apply an increasing HT voltage and monitor any leakage. It may even be possible to work out the function of the various controls before starting on component changes?

I replaced a few wire links that had cracked or missing insulation with plastic covered wire. I use the stuff from old computer power supplies as it has a decent voltage rating. Then straightened the bent RF trimmers. Without any valves plugged in I applied 105 volts to the HT line. Initially the current was 30 to 40mA but this soon dropped to around 15mA after there was a faint pop from somewhere down in the audio section.. but no smoke. I measured the voltages at the valve anode pins after the current had settled down with the following results. I've noted the likely leaky component where I've already traced a circuit. V6 appears to have a s/c condenser or an open circuit IF coil (I found later that I had missed soldering new HT and AVC control wires). V4 has very high value anode resistor which will accentuate the effect of any leaky condenser. V5 has a new capacitor at C24.

 

 

 VALVE

 V1a

V2

V3

V4

V5

V6

V7

V8

V9

V10

V11

V12

V13

 Anode volts

 42

 100

 97

 1.5

 105

 0.3

 100

 46

 87

82

68

98

98

 Theory

 105

105

105

105

105

105

105

105

105

105

105

105

105

 Leaky

 C21

 C49

 C37/C74

 C24

 C14

 C29

C29

 
 

 I scanned the old dial which is printed on plastic which has buckled with age. Wherever this buckling touched the glass cover damp has resulted in the printing ink running. I managed to clean most of this using PhotoShop (above) but as you can see the original size is nearer foolscap and my scanner is A4. The outer scale shows that the receiver tunes below 10 meters and this may answer the question Silver Knight or Silver Dragon because the Wireless World write up quotes 10.5 meters for the Silver Dragon as well as stating its number of valves is 16 which doesn't seem right for this example which clearly tunes down to 9.5 meters and has 14 valves and a separate chassis for the power amplifier. The argument isn't clear cut because a further advert then quotes 9.8 meters, however I can find no feedback to the local oscillator which would be necessary for the quoted "automatic frequency control".

At this point I decided to look for a treatise on AFC and found exactly what I was looking for. In fact I wouldn't be at all surprised if the Moreton Chayney designers hadn't themselves used this very book in their design of the Silver Dragon. It was written in 1937 and explores circuits used in contemporary receivers. Click the dial above to read this very informative book.

Once I'd looked at established AFC circuits a couple of puzzling facts suddenly became resolved. The previous day I was tracing the circuitry of the IF strip and thinking it was straightforward sketched a general circuit from which to identify the components. When I looked at IFT4 I found something odd and also in IFT2 I found something else that was puzzling. IFT2 has grid connections to not one, but two valves, V6 and V7. One connection looks normal, feeding V6 from the IF transformer secondary coil, but the other to V7 has a small condenser feeding from the anode of the IF amplifier V5.

IFT4 includes the two miniature Westectors (X1 and X2) which I'd initially assumed were for AVC and AM detection but I now realise that these might form part of a discriminator. V5 and V6 are standard IF amplifiers but V7 could be a discriminator used for AFC. Time to re-check the circuit of the mixer valve and look for a connection to the oscillator grid. Another puzzle is also resolved. I found at V7, a KTZ63 which I thought strange as it is not a variable mu pentode and would be unsuited in a standard IF strip because it would not be controlled by the AVC line. I've now amended the block diagram but I'm still unsure of its accuracy. Back to circuit tracing... In the corner of the chassis is a valve socket whose valve was missing no doubt because it's in a vulnerable position and was smashed. I initially thought it might have been a DH63, double diode triode but the socket has pin 6 used. Clearly not an anchor point as is customary with the likes of the 6K7 etc because only a 1K resistor plus a decoupling condenser are present. The only valve type that fits is the 6B8 which has identical connections to the DH63 plus g2. Pins 4 and 5 are wired together and the anode at pin 3 and g2 at pin 6 are fed by 1K resistors. The anode is decoupled to ground by a 4uF condenser meaning that the valve function is that of a cathode follower. This, in practical terms, means that the normal AVC voltage is produced across a low impedance and therefore able to supply much more current than a standard AVC diode rectifier.

Given a combined anode and screen current of say 13mA the cathode voltage will be 4.68 volts. As the diode anodes rectify an AM carrier the current will increase say by 5mA resulting in a new cathode voltage of 6.48 volts.

 

 Above is the revised circuit diagram for the IF amplifiers, but not yet checked for condensers. The area around IFT4 is tricky to trace because the underside of the transformer is masked by a resistor tagboard. Westectors X1 and X2 are the diodes connected to V7 anode and the transformer secondary. At first sight the earthy side of IFT3 secondary might carry either demodulated audio or the AVC voltage (rectified by V8 diodes), although the 0.047uF condenser (replacing a leaky 0.05uF wax condenser) looks too high in value for audio decoupling.

If this is the version of the receiver that has AFC then this may be associated with V7 and its two Westectors. This area is still being checked but the tangle of components and partly concealed wiring is making things difficult. There are six connections plus ground originating from within the IFT4 can and I had to buzz them out to determine where they went. I now realise that the designer has been quite (slightly) kind... white sleeving is AVC and the like, red is HT+, maroon is 150v, green is usually audio, blue is local oscillator and oddments, and black is ground. Yellow screened wire is used for critical anode connections and valve heaters (slightly confusing!).

Whilst I was tracing the AVC connections I spotted a concealed wire carrying the 150 volt stabilised supply, so it isn't confined to circuits at the rear of the chassis, but also to the mixer and the screen of the RF amplifier. I'll add this to the appropriate circuit diagams later.

Now that the circuit is becoming more complete, you can see that the two Westectors are for AVC plus QAVC and the 6B8 diodes for audio. No AFC seems to be provided, unless I've missed the method by which the local oscillator is adjusted. Looking at the key passive components: R49 and R50 set the amount of AVC delay and VR5 is used to preset the action of QAVC. Audio is extracted from the AM carrier by V8s diodes and filtered via a low pass filter C68-R83-C69 . The job of V7 is to amplify the IF signal purely for providing AVC and QAVC and you'll note that the gain of this valve is not governed by feedback; being a KTZ63 which does not have variable mu characteristics. So how does V8 work? You'll notice that there's a link between V8 and V6 via their shared cathode resistor R23, so V8 bias will be partly governed by V6 and vice versa. V8 is a QAVC amplifier designed for interstation muting and it's linked to volume control because its two integral diodes will be controlled by its cathode voltage. V8 grid is driven by the RF voltage produced by the AVC-controlled RF and mixer plus the first two IF stages V5 and V6. Setting aside QAVC (or switching it off) will result in Westector X2 controlling the gain of the receiver. X2 is reverse biased by R49/R50 which places about 7.5 volts (assuming an HT of 250 volts and zero diode leakage) on the diode cathode and will only conduct if its anode voltage is greater then about 8 volts so any AVC action will be delayed until a strong signal is tuned in. This means that the receiver gain is pretty high when no signals are tuned so inter-station noise level will be pretty loud so the designers introduced QAVC. Once QAVC is turned on the audio level will now be dependent on the biasing of the V8 diodes. "QAVC off" places a ground at V8 cathode but when that ground is removed, when "QAVC off" is deselected, V8 cathode rises to a voltage governed by its anode and screen currents and somewhat modified by the cathode current of V6 (controlled by normal AVC). With QAVC in operation V8 cathode voltage is always positive with respect to ground and Westector X1 will be turned off unless the RF voltage across IFT4 secondary exceeds a certain level. V8s diodes will also be turned off until the voltage across IFT3 secondary reaches a certain level. With V8 diodes turned off the receiver will be muted. It will only be un-muted if the set is tuned to a strong signal and the QAVC stage V8 is drawing low enough current to allow its bias to turn its diodes on. Because of component variations and variations in HT voltage, the designers fitted VR5 which sets the quiescent current for V8 and hence the quieting level. That level dictates the strength of the weakest station for which the receiver will produce audio output with QAVC active. Note the common earth return resistor mentioned above which couples together V6 and V8. Because we are looking at decoupled voltages the AVC and QAVC lines are interdependent because the currents drawn by V6 and V8 will add together arithmetically if QAVC is active. If QAVC is turned off you'll note that the ground return for V6 is provided by R23 and R24 but V8 plays no part in V6 biasing because its cathode is grounded. In this state V8 diodes are no longer reverse biased and provide audio through R83 controlled only by normal AVC.
 

 Now.. is this the matching amplifier/power supply??

 It will be a(nother) real challenge... continues

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