TV 1936-39
When 405 line TV transmissions started by the BBC at Alexandra
Palace London in 1936. Marconi EMI provided most of the transmitting
equipment. This company produced a series of televisions under the brand names of HMV and
Marconiphone. In this page we can have a look at some technical aspects of their pre-war
models
HMV 900
This set was introduced in
1936 It is mirror lid TV with a 12 inch round screen. This TV had a SW.MW.LW radio
incorporated in the design . The chassis layout consisted the
radio unit upper left , a power supply and EHT transformer unit bottom left The RF
sound and vision with the scanning timebase was mounted vertically at the right. The
main TV controls of the TV receiver were placed on the right looking from the front of the
set. As can be seen from the image the HMV company provided a card to familiarise the
viewer with the functions of the controls. This was intended to be a temporary card but in
this example it has survived
The Emiscope
tube was the heart of the TV this 12 inch round
version was the first of its type to be introduced into a domestic receiver. It's length
was was reason that the tube had to be mounted vertically. it is usually shielded in a
metal housing but has been removed to photograph.
The views of the tube mounting of the Emiscope
shows the green EHT rectifier capacitor on the left. The central detail highlights the tube base connector and the scanning coils at the top of
the tube neck Below them is a coil for centering the picture.
HMV Sales Brochure
(Courtesy APTS* see note)
MARCONIPHONE 702
This set was also introduced in 1936. A Marconiphone 702 was one of four
models exhibited by the EMI company at the 1936 Radiolypmia exhibition two months
prior to the start of the television service by the BBC in November 1936 This set
shared certain of the electronics with the HMV models the main differences being in the
cabinet designs This set uses a 12 inch Emiscope
tube type 6/4 this tube has a hexode gun with electrostatic focusing. The chassis
layout consists of the RF stages on the left with the timebase chassis on the right. The power pack was situated in the bottom of the cabinet.The image
of the power pack shows it after restoration. The transformer seen is the one which
generated the 5,000 volts for the Emiscope tube. The original was faulty and has had to be
rewound. Another image shows the cabinet rear with
the tube and power pack removed for cleaning and restoration.The sound IF and output stage
was a separate unit fitted behind the emiscope tube.
Marconiphone Sales Brochure
( Courtesy APTS* see note)
HMV 905
This television was a smaller 7 inch TV
introduced in 1938. It was a 16 valve set with a 3 band radio. The chassis layout was a compact single unit which provided all TV and
Radio circuitry. the tube
mounting of the 7 inch round Emiscope 3/2 tube
consisted of a bracket at one end which held the scan coils and this was fitted to the
cabinet top at the front of the tube fitted into the screen surround and was held securely
this view clearly shows the clear view through he tube to the white screen phosphor
coating. the tube could not be viewed this way in later pictures tubes as they had a
aluminised internal coating to reflect light from the screen forward to the viewer
rather than to the back of the TV.
This restored example had to have the mains/EHT transformer replaced together with a
number of defective capacitors and resistors to restore it to working order.
HMV Sales Brochure
(Courtesy APTS* see note )
Murphy A58V
This set was built in 1938 is a
particularly modern looking design for this period. The TV
chassis swung down to help in valve replacement the overall design was very
compact. This model was TV and Radio unit which was based around the A56V TV
chassis. The radio chassis was adapted with a few modifications from a standard Murphy A46 radio of
the time.
The traces of brown paper which once covered the rear of the cabinet was
a condition of continued guarantee by Murphy when TV transmission was halted for the war
in September 1939.
The A58V had a production run of more than 300 in 1938, and may have had more
unfinished units that were then completed and sold in early 1939.
The A56V being which was the TV only version was the most popular and sold at
£30 and was still being sold into 1946, as those stored in the war were brought out and
checked and then sold when broadcasting was restarted. Various other Murphy pre-war sets
were either modified or just checked and sold at the same time before production started
on new sets.
This set required an EHT transformer to be rewound to supply the 5KV for
the tube. Several capacitors and resistors also needed replacement together with a
considerable time and effort to restore the 1938 A58V to working order
Cossor 1210
Cossor
Sales Brochure
(Courtesy APTS* see note )
This TV and Radio console model was introduced in 1939.
The receiver is divided into three separate decks one forming a radio receiver covering three wavebands and television sound,
the vision deck which included the vision frequency amplifier, the line and frame time
bases and the cathode ray tube and lastly the power pack
which supplies the high and low voltage current for both decks. The radio controls are fitted on a sloping front at the top
of the cabinet
Note;
*APTS (Alexandra Palace Television Society) see links page
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HMV Sales Brochure
(Courtesy APTS* see note)
