Line output transformer

A line output transformer for a television receiver has a plurality of windings which surround a ferromagnetic core and are wound around an insulating support. The support has a plurality of grooves for receiving the respective windings, the defining wall of at least one of the grooves being provided with a slot intended to guide the starting end of a winding to the bottom of the groove and to inhibit contact between the starting end and subsequent turns wound in the groove.

BACKGROUND OF THE INVENTION 
The present invention relates to a line output transformer for a television 
set, including a number of windings, for connecting the line output stage 
to the horizontal deflection coil(s) and for supplying voltage to other 
auxiliary circuits, the transformer having at least a ferromagnetic core 
and an insulating support for the said windings, the said support being 
designed to accommodate a number of metal terminals for connecting the 
said windings to the remaining circuitry of the set. 
The current design practice in modern television sets is to use the line 
output stage as a voltage source for supplying or controlling many if not 
all the circuits of the set. A consequence of this practice is that the 
line output transformer (or extra-high tension (EHT) transformer as it is 
also called, as it also generates the acceleration voltage for the C.R.T. 
anode) has a number of different windings, some isolated and others 
connected in series. 
The current practice is to wind the windings onto two separate supports to 
form two coils of which one, termed the primary coil, contains all the 
windings with the exception of the EHT winding and the other is called the 
EHT coil, or tertiary coil, as the primary coil contains the primary 
winding connected to the line output stage and various secondary windings. 
The two coils, at least in Europe, are usually arranged parallel to one 
another on two opposite parallel branches of the ferromagnetic core. 
The primary coil, which has many output terminals (usually more than ten), 
is wound in one of the following two ways, namely: 
1. Ten or fifteen coils at a time are wound on a multispindle winding 
machine and sheets of plastics (polyester or polycarbonate) material are 
inserted between one layer and the next. The multiple windings are then 
cut to obtain the individual windings of the primary coil; and 
2. A SINGLE PRIMARY COIL IS WOUND AT A TIME. 
The first method is quick and there are programmable, semi-automatic 
machines which stop automatically after each winding or part winding has 
been wound to insert the insulating material between one layer and the 
next. The start and end of each winding must be held in place by the 
operator with adhesive tape. 
Once the primary coils are wound and separated from one another: 
THE START AND END OF EACH WINDING OF EACH COIL MUST BE PULLED OUT USING A 
CROCHET HOOK WHICH IS A DELICATE, TEDIOUS OPERATION, AND 
THE PRIMARY COIL MUST BE MOUNTED ON THE COIL SUPPORT CARRYING THE TERMINALS 
AND THE ENDS OF THE WINDING MUST BE WRAPPED AROUND AND SOLDERED TO THE 
TERMINALS. 
In the second method, each coil is wound directly on the support but the 
method is much slower. At each stop, the operator must tape down the wire 
and wind the ends around the appropriate terminals to which they are 
subsequently soldered. 
It is more difficult, using the second method, to insert the insulating 
sheets between layers automatically. 
It is also known (see for instance U.S. Pat. Nos. 2,982,888 and 3,644,986) 
to wind transformers and more particularly television transformers on 
grooved coil supports so that the individual windings are insulated one 
from the other; but with such a method there is a problem as to how to 
insulate inside a groove the starting end of a winding from subsequent 
turns and how to make in a simple and inexpensive way the connections of 
the ends of the windings and the remainder of the circuit. 
BRIEF DESCRIPTION OF THE INVENTION 
The present invention seeks to mitigate the problems encountered in the 
above prior art winding methods. 
According to the present invention, there is provided a line output 
transformer for a television receiver having a plurality of windings for 
connection to the line output stage and the deflection coil(s) of the 
receiver and for supplying voltage to auxiliary circuits of the receiver, 
the transformer further comprising a ferromagnetic core and an insulating 
support for at least some of the windings, the said support having a 
plurality of terminals connected to the ends of the windings and having a 
plurality of grooves, defined by insulating walls, for receiving the 
windings and insulating the windings for one another, a wall of at least 
one of the said grooves having a slot operative during winding to guide 
the starting end of a winding to the bottom of the groove and serving to 
inhibit contact between the said starting end and subsequent turns wound 
in the groove.

DETAILED DESCRIPTION OF THE INVENTION AND THE PREFERRED EMBODIMENTS THEREOF 
As shown in FIG. 1 a line output transformer for a 24 inches television 
set, taken as an example, consists of a set of ten windings, some isolated 
and others connected in series. 
Fifteen terminals are therefore required which are marked 1 to 15 in FIG. 
1. As can be seen, the windings connected to terminals 1-2, 3-4 and 14-15 
are isolated while those connected to terminals 5-6-7-8-9 are connected in 
series, as are the windings connected to terminals 10-11-12-13. Table I 
found hereinbelow sets out the circuit connection of these fifteen 
terminals. 
The windings connected to terminals 1 to 13 are all wound on a single 
support having nine grooves which is herein termed the primary coil form 
and is shown in FIGS. 2 and 3. The support is made of suitable plastics 
material, such as polycarbonate, and may, if necessary, be reinforced with 
glass fibre. FIG. 2 shows the primary coil form complete with the 
terminals and windings as seen from the side carrying the terminals. FIGS. 
3a to 3c show three sections of the coil form before assembling the 
terminals and windings. 
As shown in FIG. 5, the complete EHT transformer comprises a primary coil 
100 and also an EHT coil, 204, which consists of the winding connected to 
terminals 14 and 15 wound using known methods on a second support or coil 
form. One of the terminals of the EHT winding is connected to a terminal 
of the primary coil whilst the other is connected to the EHT lead 
designated 206 in FIG. 5. The ferromagnetic core comprises of two U-shaped 
cores 200 and 202 of a type currently used and available (Siemens 
catalogue U 56/28/16). 
FIG. 4a shows a terminal 101 before it is inserted into the primary coil 
form. The terminal is made of plate (tin-plated) with a stamped out tab 
101a to which the winding wire is connected and having a forked end with 
arms 101b, 101c, which are forced into a slot 102 (FIG. 3B) in the primary 
coil form. The terminal 101 and the tab 101a have oppositely curved 
notches which together define a channel 101d for receiving the wire, the 
channel being best seen in FIG. 4b. The entrance to the channel is 
narrower than the wire diameter so that once inserted into the channel 
between the tab and the rest of the terminal the wire is gripped against 
unintentional release. When the tab 101a is clamped or folded down towards 
the main portion of terminal 101 the wire is prevented from escape. 
With reference to FIG. 2, the windings are wound as follows. First the wire 
106 is passed over terminal 1 (this terminal and terminal 8 are both shown 
partly cut away to show the wire route clearly) between the terminal and 
tab (in FIG. 2 the tabs are drawn closed as they are clamped after winding 
to keep the wire in place); the wire is then inserted into the first of 
the nine grooves on the primary coil form. Each groove has a slot, the 
slot of the first groove being seen clearly in FIG. 2 and a slot being 
shown in cross section in FIG. 3A and designated 105. The wire is threaded 
into the slot and wound round the groove the required number of turns (six 
in the case of the first winding: see Table II). Subsequent turns wound in 
the groove do not come into contact with the wire from terminal 1 which is 
protected inside the aforementioned slot against chafing. After six turns 
have been wound, the wire is passed over terminal 2, then terminal3 
(FIG.2) and is inserted into the second groove (103) where, this time, it 
is wound 31 turns (Table II). The second groove (103) also has a 
protective slot for the start of the winding. The latter slot can also be 
seen in FIG. 3A whre the dotted line 107 shows the bottom of the slot 
which slopes to guide the wire on its way down). The wire is then pulled 
up, passed over terminal 4 and so on up to terminal 13 which marks the end 
of the winding operation. 
The tabs on the terminals are now clamped to keep the wire in position. 
The wires between terminals 2-3, 4-5 and 9-10 are subsequently cut to 
isolate the various winding parts from one another. 
FIG. 3C shows part of the seventh groove (104) and the sloping plane for 
guiding the wire up to terminal 11. 
If necessary, the wires are now soldered to the terminals to ensure perfect 
contact after which the two coil forms (primary and EHT) are assembled on 
the core. A terminal (14) of the EHT winding is connected to a suitable 
terminal (e.g. terminal 4) on the primary form and the transformer is 
ready for inserting on to the television printed circuit where the 13 
primary terminals are inserted into the same number of holes and wave- or 
dip-soldered, as known per se. 
The advantages of the transformer according to the present invention will 
be clearly seen from the description given. The main ones can be summed up 
as follows: 
fully-automatic winding of the primary coil in a single winding operation; 
safe insulation of windings; 
safe insulation between the start of each single windings and the following 
turns. 
TABLE I 
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Terminal Connected to 
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1 Line output transistor bias circuit 
2 Line output transistor bias circuit 
3 Sound amplifier supply 
4 Ground 
5 Frame output stage supply 
6 Miscellaneous services 
7 Ground 
8 CRT heater filament 
9 Video amplifier supply 
10 Half horizontal deflection coil 
11 Tuning compensation winding 
12 Half horizontal deflection coil 
13 Line output transistor collector 
14 Ground 
15 EHT rectifier 
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TABLE II 
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Winding Wire .PHI. Turns 
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1-2 0.45 6 
3-4 0.45 31 
5-6 0.45 28 
6-7 0.45 6 
7-8 0.45 3 
8-9 0.45 25 
10-11 0.45 60 
11-12 0.45 60 
12-13 0.45 14 
14-15 0.10 1750 
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