This is my second R1475 as received
An abandoned project?
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A rather nice undamaged plastic dial cover was
included. The condition of the chassis is about the same as mine
but with less corrosion present. I'll finish off derusting it
before reassembly. The guard receiver (out of focus) is all there
but the main dial assembly has been worn at the LF end and will
benefit from some signwriting or re-labelling. Touch wood.. everything
looks present... and having got an assembled receiver putting
the second back together should be straightforward.
Last night I finished off the main chassis which was
going rusty (again?). I then sorted out the guard receiver chassis
on my earlier R1475 by copying
the dimensions and layout of the one in the box of bits.
At this point I realised that the last owner had disassembled
everything and had painted the front panels but had probably
intended to clean up the chassis components, and no doubt go
through all the components and replace any that had gone bad.
I went through the larger bits and wire brushed the ones that
needed rust etc removing. During this process I noticed that
some parts seemed to be missing and other mechanical assemblies
were seized so the task now is to work out exactly what's included
in the box of bits and if nothing vital is missing maybe begin
refurbishing and reassembly.
Next ... ASSEMBLY of the receiver commencing with
the fitting of the tuning condenser. |
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As it appears possible to swap the components
fixed to the tuning condenser assembly I left the originals in
place after a quick check on their values. Above... various views
with the one immediately above showing the tuning condenser assembly
screwed to the main chassis.
Below shows the drive shaft in position. This was
slightly awkward because the ball bearings for the left hand
bearing were loose in a packet together with a larger ball bearing
which locates in a socket made up from the end of the shaft and
a centre screw with a locknut (picure below right).
In this example the shaft was an interference fit
needing some pressure to align it with the end ball.
One important point is to wind the inner gear wheel
on the tuning condenser a couple of teeth clockwise to activate
the anti-backlash mechanism. If this isn't done some backlash
will be felt. Fitting the balls in the left bearing needed patience
and grease to keep them in place. Fitting the single end ball
was also tricky. I used long nosed tweezers and the ball covered
in grease to place it in the shaft aperture via the hole immediately
above the adjuster. Once fitted the ball is kept in place by
pressure against the end plate. Some force was needed to push
the ball into the mating aperture in the adjusting screw (fully
out). Finally the screw is turned to just eliminate end play. |
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During the fitting of the geared assembly (above)
I'd noticed that the centre gear of the three had a small peg
sticking out and wondered what it was used for. I decided to
check this before proceeding otherwise a lot of rework may be
necessary. I've come across this potential trouble before. In particular in the case of
getting my HP8640B working (click to see). In fact that little
peg is the key to the R1475's designers solution to preventing
damage when spinning the tuning too close to the tuning condensers
limit. Fortunately I have my assembled R1475 for reference and,
although not easy to see, should enable me to set the geared
assembly to the correct position. If I hadn't noticed, the tuning
range would have been limited because a small mechanical assembly
triggered by the peg would have prevented the dial from reaching
its limit.
So back to the fitting of that geared shaft. I must
disengage the tuning condenser gears and set things up as best
I can. |
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This is the key part of the revolution counter
mechanism that prevents mechanical damage. It's mounted on the
chassis between the two rightmost gears and triggered by a tiny
peg on the centre gear against a spring. The end of the arm (left)
prevents the cylindrical dial from rotating further than its
end markings. Goodness knows how the set was designed... there
are so many strange levers. One looks as if it's been twisted
and bent out of shape.
The pictures below show my attempt to permit adjustments
of the gears so that the peg correctly engages to stop the dial. |
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Looking at my assembled receiver the peg is
in-line with the chassis edges so a long screwdriver is positioned
to indicate the peg position in relation to the chassis. The
red marks on the shaft indicate its correct position.
Above, the tuning condenser gear position at its end
position, noting that the twin gears have been set for anti-backlash
operation.
In my case the end shaft screw is loosened to allow
the ball bearing race (once its securing screws have been removed)
to be pushed upwards to disengage teeth (but only just enough
to prevent the balls dropping out).
A final?? check revealed I may have aligned the gears
for the wrong end of tuning so I may need to repeat the exercise!
In fact neither fully min or fully max of the tuning condenser
be achieved so I balanced the two.
Next... fitting the dial to check everything is aligned. |
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Was this an accident or is it a factory instruction
to "bend and twist" to fit?
Do I straighten it now or wait until I get to fitting
it?
Anyway it turns out to be the part I need to do a
trial fit mounting the drum dial.
The dial has a ball bearing race at each end with
the two tuning knobs at one end and the wavechange at the other.
This long twisted/bent lever connects the wavechange knob to
the yaxley switch wafers. Looks like another high precision fit. |
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This is a view showing the mechanism at the other
end of the lever. That bend is supposed to be present.
The rear metal plate is used to engage with end stops.
After 40 minutes of squeezing in my bench vise and
twisting with pliers the bar was still slightly distorted but
then fitted perfectly between the wavechange switch (above) and
the operating knob (right) which fits at the left end of the
tuning dial (the end of which fits into that bearing). The whole
assembly needs to be very rigid and in my example (the assembled
version) the whole thing is seized up. |
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Here's the lever in position between the switch
and the ident mechanism for the yaxley switch. It passes through
a slot in the chassis and has to be threaded through this from
bottom to top as the slot is too narrow for the small bush on
the end of the lever. The thing works perfectly so the reason
for the mangled lever isn't explained.
Next I need to add the dial although this will be
a temporary fit as it's too fragile to leave in place whilst
the rest of the parts are fitted. I've copied the picture of
the dial below. From left to right are the scales for the four
wavebands. Each has a spiral slot into which locates a pointer
indicating the frequency to which the receiver is tuned. The
applicable section is illuminated by a lamp under the drum.
The ranges are a follows:-
2.00 to 3.62 MHz
3.58-6.44 MHz
6.38 to 11.38 MHz
11.24 to 20.14 MHz
Dial markings look most peculiar but are better once
the MHz numeric strip is in place. This links the double digits
to the whole MHz figure.
Once finally fitted I'll need to signwrite missing
numbers on the dial and on the MHz strip (which is blank.. having
been painted??)
Once I'm happy with the tuning arrangements I'll add
the harness carrying the module sockets. |
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I was inspecting the end stop lever and its
operating pin and noticed wear on the lever. This was because
the pin was so badly worn it had produced a groove in the lever
and itself ending up with a flat section. The flat section was
now clearly wearing the lever more as the bearing surface was
obviously shiny. I couldn't see how to replace the pin without
lots of dismantling including taking apart the centre anti-backlash
gears so considered fiting a bush.
The pin had a max diameter of 2.34mm and a length
of 5mm (which was now 0.5mm too short due to lateral movement
from wear in the lever mounting bush). I found an M4 screw having
5mm of uncut thread (diameter 3.56mm) and drilled this with a
1.86mm drill, then enlarging the hole to 2.41mm. This gave a
clearance of 0.07mm, then cut off about 6.5mm of the resulting
tube, filed the ends flat and superglued the bush over the worn
pin. See opposite. |
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I fitted the set of module sockets (above) This
is quite a messy task (ideally three handed) because the sockets
mate into chassis apertures plus a set of four brackets held
in place by a line of bent metal strips (four long plus two short)
carrying captive 6BA screws. Next I'll fit the two loose tagboards
then various pieces of metalwork. The main task is fitting the
nine modules and I found that the previous owner had detached
the valve skirts so that each circuit can be removed from its
can, so I'll first check the components to see if any should
be swapped. At this point I noticed numbers had been marked on
the modules which had all been cleaned, assemblies detached and
all the decoupling condensers had one end unsoldered. I wonder
if these had been fully tested or just checked with an ohmeter
for leakage? I checked all the resistors and none was too distant
from its correct value. Some seemed to have parallel components
because they read low. Nearly all the tubular condensers were
bad with some readings cycling (marked "unstable")
from high leakage.
Below, a list of plug-in units and the tuning indicator
followed by a listing showing marked and measured (in brackets)
resistor and condenser values (where 100n = 0.1uF). |
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UNIT A: AERIAL UNIT (145) |
10K (12.4K), 100K(113K), 100K(114K), 100K(102K), 10K(10.4K)
10n(68n), 10n(unstable), 10n(unstable) |
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Left is the old "Post Office"style relay
with its RAF code marked on the side (10F-2495). My uncle (born
in 1916) was emplyed at Strowger Works for the whole of his working
life from before the war, then a break in the Army, rejoining
the factory when demobbed until retirement in 1981. His job was
tensioning relay springs.. he always refused offers of promotion,
preferring to have a completely worry-free life.
During my graduate apprenticeship
in 1965 at Strowger Works, then Plessey, I popped over and spoke
to him (whilst he was adjusting a relay). About 12,000 people
worked in the factory.
Note the yaxley switch wavechange sections located
in the various modules need to be aligned with the main ident
mechanisms then a connecting rod inserted so that all turn together.
The main purpose of the relay is to disconnect the
aerial from the receiver in the second (calibrate) setting of
the mode switch. In that setting, test signals from the BFO crystal
oscillator should match a set of dial markings where the frequency
is indicated in a black disk. Associated with this feature is
a front-panel fine tuning control that enables the operator to
match the frequency to the dial. This allows very accurate frequency
readings to be measured.
The fine tuning control also serves to accurately
resolve SSB especially when tuning wear or failure of anti-backlash
makes this virtually impossible with the main slow motion control. |
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UNIT B: BAND PASS UNIT (146) |
3.3K(4K), 3.3K(3.8K)
10n(72n), 100n(134n) |
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UNIT C: RF OSCILLATOR (171) |
1K(1.2K)
100n(199n), 10n(13n) |
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UNIT D: SIGNAL MIXER & GUARD MIXER (11) |
1.5K(1.9K), 3.3K(3.8K), 33K(32K). 330(375), 3.3K(3.7K), 10K(11.9K),
3.3K(3.5K)
56K(65K), 56K(67K), 120K(133K), 3.3K(3.3K), 10K(10.4K), 100K(110K)
100n(198n), 100n(unstable), 100n(66n), 10n(12n), 100n(unstable),
100n(151n) |
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UNIT F: BAND PASS FILTER |
No resistors/condensers |
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UNIT E: FIRST IF (37) |
3.3K(3.8K), 100K(10K), 3.3K(3.4k), 1M(1M), 1M(1.1M), 560K(622K)
10n((unstable), 10n(213n), 100n(170n), 10n(64n), 100n(unstable) |
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UNIT G: SECOND IF (38) |
3.3K(3.4K), 1M(1.2M), 560K(673K), 560K(665K), 56K(67k), 3.3K(3.6K),
68K(78K0, 1M(1.5M)
10n(12n), 100n(48n), 500n(113n), 100n(100n), 100n(55n) |
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UNIT J: SIG DET & BFO (170) |
560K( ), 1K(1.2K), 47K(53K), 10K(11.2K), 270K(320K), 2.2M(1.5M),
2.2M(1.5M)
1M(414K), 120K(148K)
10n(12n), 100n(282n), 100n(210n), 100n(137n) |
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UNIT K: AF AMP & AGC DELAY (45) |
22K(22K), 1M(1.3M), 270K(326K), 120K(140K), 330K(360K), 150(165),
560(630)
500n(800n), 20n(86n) |
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I totted up the condenser requirement and arrived
at the total in the modules to be 20 x 0.1uF, 8 x 0.01uF, 1 x
0.02uF and 2 x 0.5uF.
I decided to use 500 volt surface mount capacitors
for the 0.01uF, 0.02uF, 0.1uF and the 0.5uF as I have around
700 of 100nF chips. For the 0.5uF I'm using 4 x 0.1uF in parallel.Opposite
in a saucer are 21 x 0.1uF replacements fitted with wire ends.
These tested at 122nF with a few slightly higher 124nF or lower
117nF. The new 0.5uF both tested as 498nF.
Below, the modules ready for their new stuffed capacitors.
The fact that all tubulars have been disconnected
suggests drilling and stuffing to keep
originality, With 31 of the things I made a simple jig to assist
with the drilling. This used two blocks of wood as a clamp. I
drilled a block of wood with a 17mm hole for a typical condenser
and two holes for bolts then halved the block and used M8 bolts
to hold it together. Using a pillar drill and a tool made from
a sharpened tube, I cut around the wire-anchor solder pads then
pressed them into the body. This worked fine on most condensers
but some were difficult because the size of the pad was too large
for the tube-tool. Pressure on the tool pressed the pad into
the body but larger detached pads proved difficult to remove
without help from a drill and tweezers in some cases. |
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I eventually finished the new capacitors including
one on a chassis-mounted tagboard. After unsuccessfully trying
to seal the ends with a couple of things I chose candle wax with
my soldering iron set to 200C which was the perfect solution
as at that temperature the wax didn't burn. Now comes the long-winded
task of refitting the stuffed condensers using the pictures I'd
taken earlier as a guide. To simplify matters I'd used my SM
100nF chips throughout. Finally all the modules were reassembled
ready for fitting.
Next I went through the remaining bits. I can't find
the magic eye brackets or an output transformer (driven by a
6J5 with various outputs), neither are SK1 or SK2, the 4-pin
Jones connectors present, and I've yet to see what valves are
in the box. Nothing vital is missing in terms of the contents
of my junk box.
Below is a simplified circuit of the receiver. Click
for PDF version (which is enlargable).
Because of the design of the receiver the wiring is
in two parts.. viz. the set of plug-in modules and then what
can be termed "chassis wiring". The simplified circuit
diagram below isn't at all useful for my task of rewiring. Instead
I'll be using the chassis wiring diagram on the following webpage.
This can also be selected as an enlargeable PDF.
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