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Beau Decca mirror lid TV set.
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July 15, 2017
6:05 pm
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Till Eulenspiegel
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Have measured the HT voltage supplied to the line timebase in the Defiant TR1250 and it is indeed 260volts. This might be higher than other sets of this type because the old metal rectifier was replaced with a silicon diode.

According to the voltage tables for the Philco BT1410, that's the strange looking "upside down" 9" set the maximum HT voltage measured on the reservoir capacitor C52B is 250V and on the HT smoothing capacitor C52A is 230volts. Early versions of the Plessey Mark 1 chassis employed an energised loudspeaker which functioned as the smoothing choke. Later Mark 2 sets employ a conventional smoothing choke which might result in the HT voltage being slightly higher. 

In the Beau Decca the timebases draw a current of 180mA when supplied with an HT voltage of 280V. This is too high so I have a special high wattage vitreous enameled 150 ohm resistor to do the job of reducing the HT to the timebases.

Till Eulenspiegel.

July 15, 2017
6:37 pm
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nuvistor
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Till Eulenspiegel said
This is too high so I have a special high wattage vitreous enameled 150 ohm resistor to do the job of reducing the HT to the timebases.

Till Eulenspiegel.  

Keep the set warm and dry wink

Frank

July 16, 2017
11:28 am
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Till Eulenspiegel
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Hi Frank,

               Here's the 150ohm resistor that will be used to reduce the HT supply to the timebases.  100mm long

Till Eulenspiegel.

BeauDecca220310.jpgImage Enlarger

July 16, 2017
11:54 am
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nuvistor
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Those vitreous enameled resistors are excellent, very reliable.

Frank

July 19, 2017
9:01 pm
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Till Eulenspiegel
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The 150 ohm resistor has been inserted in series with the HT supply to the line and frame timebases.

The HT line voltage is now 260V, only slightly above the figure in Mark 1 Plessey receivers.  The picture shift is achieved by altering the position of the scan coils about the CRT neck. The method employed in this set is not entirely satisfactory, made worse because of the difficulties of carrying out adjustments in a mirror view set.

Till Eulenspiegel.BeauDecca_220102.jpgImage Enlarger

BeauDecca_220103.jpgImage Enlarger

July 20, 2017
8:29 pm
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nuvistor
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It's a nice bright picture.

The picture shift, are the scan coils a " loose" fit and need wedges to centre the picture, similar to some inline colour CRT's?

Frank

July 20, 2017
9:25 pm
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Till Eulenspiegel
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Hi Frank,

             In fact my statement that the scan coils were adjustable to effect picture shift is incorrect.   It is the focus coil assembly that is adjustable on the neck of the CRT.  The focus assembly is mounted about the neck of the tube by three springs on a metal plate which has  three long screws to set the picture position. 

I'll post up a close up picture of the CRT neck components.   

Till Eulenspiegel.

July 20, 2017
11:15 pm
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Till Eulenspiegel
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Pictures of the CRT assembly.   The tube is a Mazda CRM121.

 

BeauDecca182854.jpgImage Enlarger

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