VOXSON T1741 CHASSIS 3.55 CRT TUBE PHILIPS A44-510W.

CRT TUBE PHILIPS  A44-510W.

 1. INTRODUCTION
Equipment design should be based on the characteristics as stated in the data sheets. Where deviations from these general recommendations are permissible or nec- essary, sta~ements to that effect will be made. If applications are considered not referred to in the data sheets of the relevant tube type extra care should be taken with circuit design to avoid that the tube is overloaded due to unfavourable operating conditions.


2. SPREAD IN TUBE CHARACTERISTICS
The spread in tube characteristics is the difference between maximum and min- imum values. Values not qualified as maximum or minimum are nominal ones. It is evident that average or nominal values, as well as spread figures, may differ according to the number of tubes of a certain type that are being checked. No guarantee is given for values of characteristics in settings substantially dif- fering from those specified in the data sheets. .


3. SPREAD AND VARIATION IN OPERATING CONDITIONS
The operating conditions of a tube are subject to spread and/or variation. 3. 1 Spread. Spread in an operating condition is a permanent deviation from an av- eragecondition due to, e.g. ,component value deviations. The average condition is found from such a number individual cases taken at random that a;. increase of the number will have a negligible influence. 3.2 Variation. Variation in an operating condition is non-permanent (occurs as a function of time), e.g. ,due to supply voltage fluctuations. The average value is calculated over a period such that a prolongation of that period will have negli- gible influence.

4. LIMITING VALUES
4. 1 Limiting values are in accordance with the applicable rating system as defined by I.E.C. publication 134.


Reference may be made to one of the following 3 rating systems.
4. 1. 1 Absolute maximum rating system. Absolute maximum ratings are limiting values of operating and environmental conditions applicable to any electronic device of a specified type as defined by its published data, and should not be exceeded under the worst probable conditions.

4.1.24.
1.Note*.These values are chosen by the device manufacturer to provide acceptable serviceability of the device, taking no responsibility for equipment variations, environmental variations, and the effects of changes in operating conditions due to variations in the characteristics of the device under consideration and of all other electronic devices in the equipment. The equipment manufacturer should design so that, initially and throughout life, no absolute maximum value for the intended service is exceeded with any device under the worst probable operating conditions with respect to supply voltage variation, equipment components spread and variation, equip- ment control adjustment, load variations, signal variation, environmental conditions, and spread or variations in characteristics of the device under considerations and of all other electronic devices in the equipment. Design -maximum rating system. Design -maximum ratings are limiting val- ues of operating and environmental conditions applicable to a bogey electronic device* of a specified type as defined by its published data, and should not be exceeded under the worst probable conditions. These values are chosen by the device manufacturer to provide acceptable serviceability of the device, taking responsibility for the effects of changes in operating conditions due to variations in the characteristics of the elec- tronic device under consideration. The equipment manufacturer should design so that, initially and throughout life, no design -maximum value for the intended service is exceeded with a bogey device under the worst probable operating conditions with respect to supply-voltage variation, equipment component variation. variation in char- acteristics of all other devices in the equipment, equipment control adjust- ment, load variation, signal variation and environmental conditions. 3Design-centre rating system. Design -centre ratings are limiting values of operating and environmental conditions applicable to a bogey electronic de- vice* of a specified type as defined by its published data, and should not be exceeded under average conditions. These values are chosen by the device manufacturer to provide acceptable serviceability of the device in average applications, taking responsibility for normal changes in operating conditions due to rated supply -voltage variation, equipment component spread and variation, equipment control adjustment, load variation, signal variation, environmental conditions, and variations or spread in the characteristics of all electronic devices. The equipment manufacturer should design so that, initially, no design -centre value for the intended service is exceeded with a bogey electronic device* in equipment operating at the stated normal supply-voltage. A bogey tube is a tube whose characteristics have the published nominal values for the type. A bogey tube for any particular application can be ob- tained by considering only those characteristics which are directly related
to the application.

4.2 If the tube data specify limiting values according to more than one rating system the circuit has to be designed so that none of these limiting values is exceeded under the relevant conditions .

4.3 In addition to the limiting values given in the individual data sheets the direc- tives in the following paragraphs should be observed.

5. HEATER CIRCUIT
Any deviation from the nominal heater voltage (in case of parallel connection) or from the nominal heater current (in case of series connection) has a detrimental effect on tube performance and life, and should therefore be kept at a minimum.
Such deviations may be caused by:
a) Mains voltage fluctuations. b) Spread in the characteristics of components such as transformers, resistors capacitors etc. Designers of heater circuits are strongly recommended to bear this in mind when dealingwith equipment to be used in areas where the actual mains voltage is like- ly to differ from the nominal value.

5. 1 Parallel connection
The maximum deviation of the heater voltage should not exceed ± 15~ (design maximum value). This conditionwill be fulfilled when the mains voltage fluctuates by ± 10~ and a ordinary transformer (see below) is used.

5.2 Series connection
The maximum deviation of the heater current should not exceed ± 8~ (design maximum value). When a small number of tubes with large differences in the heater voltage is used in series connection combined with a series resistor or a series capacitor, the maximum permitted deviation of the heater current may be exceeded. To avoid this, certain restrictions must be imposed on the composition of the heater chain; the maximum part of the supply voltage that can be eliminated, and the tolerances of the voltage dropper in series with the heaters. A number of circu.'.ts for If = 300 mA will be described in detail below.

CATHODE TO HEATER VOLTAGE
The voltage between cathode and heater should be as low as possible and never exceed the limiting value given on the data sheets of the individual tubes. The values given under "Limiting values" relate to that side of the heater where the voltage between cathode and heater is greatest. The voltage between cathode and heater may be D.C. , A. C. , or a combination of both voltages. Unless other- wise stated, the maximum values quoted for the voltage between cathode and heater indicate the maximum permissible value (D. C. component). If an A.C. voltage, or an combination of D. C, and A.C. voltages. is applied the peak value may be twice the rated Vk{; however. unless otherwise stated, the peak value shall never exceed 31~ V. The D.C. component is not allowed to exceed the pub- lished value. Unless otherwise stated, the V~ max. holds for both polarities of the voltage; however, a positive cathode is usually the most favourable in view of insulation during life. In order to avoid excessive hum the A.C. component of the heater to cathode voltage should be as low as possible and never exceed 20 Vrms (mains frequency).

7. INTERMEDIATE ELECTRODES (between cathode and final accelerator) In no circumstances should the tube be operated without a D.C. connection be- tween each electrode and the cathode. The total effective impedance between each electrode and the cathode should never exceed the published maximum value. However, no electrode should be connected directly to a high energy source such as the hot line. When such a connection is required, it should be made via a se- ries resistor of not less then 1 kohm

.8. ELECTRODE VOLTAGES
All electrode voltages are given with respect to cathode.
For cathode drive service the reference point is grid No.l

8. 1 Grid No.l cut-off voltage
Generally curves showing the limits of grid No. 1 cut-off voltage for specific values of the first accelerator voltage are included in the data. The brightness control should be so dimensioned that it can handle any tube within the limits shown, at the appropriate first accelerator voltage. The published limits are determined at an ambient illumination level of 10 lux with the aid of a focused raster. Because the brightness of a focused spot is in general greater than that of a raster, the visual cut-off voltage determined with the aid of a spot will be more negative by about 5 V.

8.2 Grid No.2 voltage
For each individual tube the grid No.2 voltage can be adjusted so that the beam current is cut off at a fixed value within the published range of the grid No.l voltage . In the data, graphs are included giving the relationship between. the grid No.2 voltage and the grid No. 1 cut-off voltage. ~8.3 Focusing electrode voltage Individual tubes will have satisfactory focus over the entire screen at some value within the published range of the focusing voltage. If centre -focusing is desired this range will shift in the negative direction.

9. LUMINESCENT SCREEN
To prevent permanent damage to the screen material care should be taken
a. not to operate the tube with a stationary picture at high beam currents for ex- tended periods
b. not to operate the tube with a stationary or slowly moving spot except at ex- tremely low beam currents
c. to choose the time constants of the grid No. 1 the grid No.2 and the time bases supply line circuits such that sufficient beam current is maintained to dis- charge the e. h. t. capacitance before deflection has ceased after equipment has been switched off.

10. EXTERNAL CONDUCTIVE COATING
The external conductive coating must be connected to the chassis. The capac- itance of this coating to the final accelerating electrode may be used to provide smoothing for the e.h.t. supply. The coating is not a perfect conductor and in order to reduce radiation caused by the line time base it may be necessary to make multiple connections to the coating. See also 12.

To centre the raster on the screen it is recommended that either a magnetic field just behind the deflection coils (viewed from the screen) be used or a direct current be passed through the deflection coils. The centring device should provide a shift to allow for non-centrality of the spot with respect to the geometric centre of the screen, in addition the centring device should provide the shift needed to allow for non -centrality of the visible raster (i. e. to compensate for line blanking and also time base non-linearity, if any) andtheearth magnetic field. The use of a too strong centring magnetic field should be avoided; this may result in raster distortion and even corner cutting.

PRO-ELECTRON TYPE DESIGNATION CODE
Single letter, group of figures, hyphen, group of figures, letter or letter group. The first letter indicates the prime application of the tube:

A -Television display tube for domestic application.
M -Television display tube for professional application-direct view.

First group of figures: Diameter or diagonal of the face in cm. Second group of figures: Development or design number. Final letter or letter group: Properties of the phosphor screen. The first letter denotes the colour of the fluorescence, the second letter, if any,other specific differences in screen properties.

W -White screen for T '~ display tubes.
X - Three-colour screen for T.V. display tubes.