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
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
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
Bottom: further up the road
from the building at top left.
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
An advertisement in a 1949 Wireless World...
maybe no-one had noticed their previous publicity drive in November
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
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
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
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
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
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
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
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
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
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
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.
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.
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
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
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
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
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
At this point I haven't spotted a provision
for AFC. If it's there it may be located within the coil switching
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
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
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
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.
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
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.
It will be a(nother) real challenge... continues