mentioned, this set has received some 'previous attention'.
Here's an example of the standard of work... the central
resistor has been tacked on to an extension wire with a
dry joint. The right hand radial capacitor, which looks
to be under some physical stress, does not appear on the
original circuit. This has been hitched between the anode
and cathode of the line output valve, maybe for picture
linearity reasons? It is only rated at 200v...Yuk! The anode
resistor at bottom left is 22k not 23 ohms. I have only
just started. What else will I find?
I shall have
to go through the entire circuit, component by component,
checking for mistakes, and sort everything out.
thing is to make up a selection of original looking capacitors.
Here they are, all concealing new capacitors within. Their
appearance has been based as closely as possible as those
fitted originally in the 1930s. How it used to look has
been gleaned from some photos kindly sent me by Mike Barker,
who is currently re-winding the EHT transformer.
It is possible
the large brown re-constructed 'Hunts' unit shown, situated
at the rear top of the chassis, should in fact have a silver
finish. I am awaiting some more photos from another collector
to resolve this, and if necessary the colour will then be
more days, I've finished replacing all the capacitors under
the main deck with the more authentic looking versions.
The picture shows just one area of the under-chassis. The
large block condenser is now also mounted above chassis
and connected up.
The very early
Emiscope 3/3 cathode ray tube uses its own special plug-in
base. The set arrived with the rather nicely made substitute
that had been specially made, shown on the left. However,
this was not only non-original but also tended to slip off!
the help of Cobaltblue on the Vintage
Radio Restoration discussion board I was able to find
the correct, original base - seen to the right and now wired
in. This rare part was donated for free and is a typical
example of the unstinting generosity and help to be found
on that board. Without this kind of support, it would be
much, much harder to do my job.
Note the diagram
between the two items. This shows the base connections to
the tube. Interestingly, this shows only one 'blank' connection
at the top, whereas there are actually two, on both the
tube and the base. This means it is 7-pin, not a 6-pin connector...
the main work on the main chassis finished, it's time to
look at the finishing touches. Here are the valve screening
cans. They need re-plating...
So after preparation,
into the plating bath they go. Nickel will be carried from
the positive anode plates to the negative screening cans,
connected as cathodes. The process is slow and will take
The valves - only some of them shown here - are all physically
spruced up and then go on the valve tester. The customer also
provided some spare valves. All were tested, and the
best examples have been added to the set.
Going in now
is the rather special ceramic-based X41C frequency changer
valve for the television section. Note the socket too is
of ceramic construction. At the outlandishly high frequency
of 45 MHz (in 1938), special measures like this were needed
to ensure good performance.
are all plugged in. The line output valve inside the black
perforated screening can on the right is a KT44 with an
anode cap; not the KT41 (without cap) as specified in the
manual. Since the KT44 provides considerably beefed up performance,
we might surmise this set is a later model - from 1939...
This is how
the backing card of the radio dial looks like while it's
being "re-flocked". The task is to create a new
work is coated with a special adhesive that binds the flock
powder to it. With new flock, it is sometimes possible to
squirt it through the nozzle of the flock container straight
onto the work. However once the stock of flock gets old,
it tends to stick to itself in clumps (as is the case here)
and the only realistic option is to pour it on and tap it
down lightly with the fingers. Several hours after this
picture was taken the surplus flock was shaken and blown
off, leaving a tidy-looking flocked surface.
flock I have in stock is of a tan colour so the card was
later sprayed in matt black, using several light coats to
avoid clogging the flocked surface.
original identifying label found attached to the tube neck.
It's very important to preserve little historical details
like this. A needle and magnifier was used to tease apart
the tiny knot on the other side...
paper labels are grubby, they can often be cleaned up using
the 'cheesy' type of rubber. This is a dry - and therefore
about the condition of this tube and whether it can be improved...
Previously it had been reported as giving a very dim picture.
So it goes
on the tester.
expected, to start with the emission reads almost zero.
However, after a little judicious "rejuvenation"
I was able to improve it to a steady reading at the level
shown. Tubes with this amount of emission can, in my experience,
display quite good pictures.
therefore will be to first try this tube, as it is now,
in the restored set. Then the customer can decide whether
it's worthwhile to send it off to France for a rebuild.
Another factor to consider will be the condition of the
screen, which undoubtedly will have an ion burn.
just possible I may have saved the customer around £700
as a result of this little exercise...
Back to the
radio dial now. In the end I wasn't satisfied with the result
of flocking it... it lacked a little "je ne sais quoi"...
so I decided on another approach. I bonded a piece of black
felt to the original card and added masking tape over all
the edges to ensure the felt would then cut cleanly around
This is the
result. For this shot it's not been lined up perfectly with
the dial (that goes on top) but you get the general idea.
I'm now happy with this.
It's now time
to take a look at the power supply chassis. Here it is,
cleaned up, but still looking a bit messy...
One of the
transformers - the EHT transformer - is missing. It's currently
with Mike Barker for rewinding. He reports good progress.
between the mains transformer input winding and chassis
has been megger-tested and proves to be excellent.
The unit is
now tidied up under-chassis as well.
added EHT smoothing capacitors are replaced with something
more in keeping with period of the originals, although there
was in fact one combined unit fitted when this set
capacitors actually were supplied by the customer. They
megger okay and measure correct for capacitance, though
the only real test will be try them for real. Just in case...
I shall protect the new EHT transformer, when it arrives,
with additional fusing.
that will later be found on the tops of these capacitors
will be absolutely lethal. I've added rubber caps, but these
represent only token protection.