Dumont Labs 181 Schematic

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Manufacturer:Dumont Labs

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These receivers are classed as " Electrostatic and Direct Vision. " Electrostatic indicates that the entire deflection system is electrostatic and since the picture is viewed direct, without the use of a mirror, lens or other device, it is referred to as Direct Vision. The latter ensures clarity, brilliance and the widest angle of vision, Steady, clear cut, black and white pictures that are large enough for all the family to enjoy at one time are secured by the use of a fourteen inch cathode-ray tube which furnishes a picture eight by ten inches. A separate high fidelity section brings superb reproduction of the sound channel which is associated with the picture. A single control tunes both the sight and the sound channels so the receiver is no more difficult to operate than an ordinary broadcast receiver, to the above features add its compact size, minimum number of controls and simple straight forward layout and you will have an idea of the first commercial television receiver which we believe you will find easy to install and service in spite of the apparent complexity of the subject Television.

CIRCUIT ARRANGEMENT A simple straight line layout is used in these receivers that should prove extremely helpful to the serviceman. Viewed from the front the video receiver is on the left side of the chassis and the sound receiver is on the right. Fig. No. 1 shows the front controls and the sound receiver while Fig. No. 2 shows the rear adjustments and the video receiver. The top portion of the chassis contains both sweep circuits along with the modulating circuits of the cathode-ray tube. To prevent con fusion each side is considered separately, half appearing in Fig. No. 1 and the remainder in Fig. No. 2. The seven auxiliary controls shown in Fig. No. 2 are provided for the use of the installer and serviceman. These controls are necessary to make the final alignment of picture size and positioning when the receiver is installed under the operating conditions imposed by the earth's magnetic field and the power supply line voltages. Once properly set these controls do not need adjustment and since they were not provided for the owner's use we suggest that the dealer or serviceman seal the baek of the cabinet as it is not possible to tamper with the controls when the back is in place. The use of the parts and tubes shown in Fig. No. 1 and Fig. No. 2 can be checked by comparing the " V " numbers, etc., with the schematic drawings

Drawings Operating Controls of the Receiver (Front)
First, become familiar with the controls on the front of the receiver, Since the receiver has been tested before shipment, probably only A few minor adjustments will be necessary. Therefore before touching the adjustments in the rear attempt to operate the set according to the instruction sheet supplied the purchaser and make only the adjustments required. These instructions are repeated here to cover the possible loss of this sheet. Figure No. 1 shows the front of the receiver with the controls numbered and the use and the purpose of these controls is as follows.
1. Marked CONTRAST, ON and OFF
This is a power switch for starting and stopping a set. It also is the volume control of the picture signal. It should be adjusted in conjunction with the intensity control (No. 4) to produce a picture of pleasing contrast to the user. If the location is such that the signal received is very small, it may be necessary to use the full gain of this control, while in a food location it may have to be l'etarded considerably. If the picture is not satisfactory the rear controls must be adjusted as covered in a following section.
2. Marked SELECTOR
This control is a four position switch provided for covering four television channels.

3. Marked TUNING
Only one control is necessary to properly tune both the sight and sound channels. Simply adjust this control until the best reception of the sound is secured and at this point the picture signal will be correctly tuned.
The intensity or brightness of the picture is controlled by this knob. It should be adjusted in conjunction with Control No. 1 to get the best picture. Note: It is a good plan to retard (turn to the left) this control when starting the set. If about 15 seconds is allowed to elapse before advancing this control it will prevent a small bright spot from appearing on the screen which might eventually darken the screen.
5. Marked FOCUS
This control is used to sharpen the individual lines of the pattern and once set seldom requires further adjustment.
6. Marked VOLUME
This volume control adjusts the audio volume and has no effect whatever upon the picture. Rar Controls of the Receiver
As previously stated, the adjustment of these controls is necessary for the final alignment of picture size and positioning, as the earth's magnetic field and power supply line voltages vary with locations. The location of these controls is shown in Figure No. 2 and their use will be covered in numerical order. Proceed as follows: remove the wood screws holding in the back of the cabinet and pull out the back. The safety switch will open, turning the set off and since it is necessary to have the set in operation while making these adjustments the switch can be made temporarily inoperative. (A large battery clip is convenient for this purpose.) Do not reach into the set with the voltages on. (See Cautions and Warning.) There is one adjustment that cannot be made by these controls, that

Of rotating the Cathode-ray tube to cause the picture to properly line up with the viewing opening. To remedy this, turn the set oft, re move the elastic band that grips the rear sup port and rotate the tube by hand in the con rect direction.
The function of the seven rear controls are as follows:
1. Vertical Frequency Control
This controls the frequency of the vertical sweep. If the picture is not steady and slips past at intervals, vertically, this control should be adjusted until a steady picture is secured.
2. Vertical Size Control
If the picture is too narrow and out of proportion vertically. this control will remedy the trouble.
3. Vertical Positioning Control
As its name indicates, this, control will move the pattern vertically, allowing the picture to be placed directly in the center of the opening
4. Astigmatic Positioning Control
This is adjusted in conjunction with Control No. 5 to give the best possible focus on the corners of the picture.
5. Horizontal Positioning Control
This control positions the picture horizontally.
6. Horizontal Size Control
The width of the picture is adjusted by this control.
7. Horizontal Frequency Control
If no picture can be secured but modulation (dark and light spaces) can be seen on the screen, the setting of the horizontal frequency control is probably incorrect. Adjust this control until the picture forms.
With the adjustment of these controls the installation should be satisfactory. However, if the signal is weak or if ghosts or noise is present, return to the dipole antenna and make changes as previously suggested until the best position for it is secured.

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Frequency Ranges Four Television Channels provided, present alignment as follows:

Power Ratings
Power supply 110 to 120 volts, 50 to 60 cycles, 250 watts.
Audio output, maximum 4.25 watts.

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Models 180 181 182 183


Potentiometers, R200 18 ganged with R220 (a dual unit)
Figure 8 Schematic Diagram Video and Audio Receivers

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The serviceman that is engaged in installing or servicing television receivers is urged to take all precautions and run no unnecessary risks.

The high voltages that are necessary in this type of equipment are very dangerous and should not be approached in a careless manner.

It is better to shut the set completely off between adjustments than to suffer a painful or even a dangerous burn,
The set is equipped with a safety switch which automatically opens upon the removal of the back of the cabinet. This protects the operator from dangerous high voltages which would otherwise be exposed.

Figure 6 - Schematic Diagram, Voltage Divider and Socket Connection

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Large cathode-ray tubes operate at high voltages and hence are evacuated to a very high degree of vacuum. Therefore the atmospheric procure on the glass can run into tens depending on the size of the tube. A collapse therefore is as bad as an explosion and all cathode tubes should be handled with care. The Du Mont Laboratories have gone to great expense to provide a cathode-ray tube that is safe for the home and the structural results in its ability to send tests nearly twice as severe as usually employed. The serviceman, however, should observe the following rules as he will probably be the only one to hande the average tube.

1. Be careful in handling the tube.
2. Watch the use of tools near the tube.
3. Don't scratch the surface of the glass.
4. Don't stand the tube on a metal surface or in any other way cause certain parts to be quickly heated or cooled.

Figure 7 Schematic Diagram, Power Supplies

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