Build your own TV

Installment Six

 

Materials you will need for this installment: Misc electronic components, per schematic diagrams.


In this installment you are given the three main schematic diagrams consisting of:

1) Video/Sync amplifier

2) Phase Comparator and Motor Driver.

3) Television Sound Amplifier

Build these up as you see fit, using PC boards, vector board, etc.


The first two schematics are included here with the permission of Peter Smith, a long time NBTVA member. These are circuits that he developed and refined over the years. The third is an amplifier that I have used successfully many times, based on an application note from the National Semiconductor Company.

1) The Video/Sync Amplifier:

video amplifier circuit

This circuit consists of an input emitter follower driving a DC restorer, sync pulse clipper and video amplifier with an FET output stage. The circuit operates from a single 15 vdc supply.

This can be built up as a PC board or on Vector Board stock. In my case, I used PC boards for the three circuits in this installment. This photo will give you an idea of the size and complexity of the Video/Sync circuitry when set up as a PC board. You might have noticed that this board, like the one following, has "fingers". These two boards plug into 15 pin, single row PC card connectors mounted in the cabinet. This allows the use of a cable extension on the connector so that testing can be done with PC board external to the cabinet. It also makes it possible to easily replace a board with a working spare, in the event of trouble, say during a demonstration.

*Printed board layouts are not available

 

 

 


2) Phase Comparator and Motor Driver:

phase camparator and motor drive

This circuit receives pulses from the video/sync circuit and from the scanning disc fork; compares the two in time and drives the output FET stage and the motor. Up to 30 Vdc can be used, depending on the type of motor used. In my case. I found that 15 Vdc to be adequate. Here again, the type of construction is up to you. I generally use PC boards, so here shown below, is a photo of the actual board.

* Printed board layouts are not available.

 

 

 

 

3) Television Sound Amplifier:

This amplifier has only one active device, yet it has a gain of 100 and can easily provide ample sound levels to a 4 or 8 ohm speaker. A small heat sink on the TDA-2002 is advised.

The amplifier is pictured in the photo on the right. It too is built on a printed circuit board that includes its own dedicated 12 Vdc supply. The 10k volume control is on the monitor front panel and connects to the amplifier with shielded wire. A switch to control the AC power to the amplifier can be added to the control for those times when there are no associated sound signals with the video signals.

End, Installment Six

On To Installment Seven

Peter Yanczer

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