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Old 14th Jun 2017, 7:35 pm   #1
FERNSEH
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Default Beau Decca television. Second attempt at a reconstruction.

The new chassis for my Beau Decca TV is displaying pictures. The first attempt was successful but it did involve using a sound and vision chassis from a Defiant TR1247. The chassis assemblies will be refitted in the Defiant and instead I decided to make a new chassis for the Decca.
The new design resembles the Plessey Mark 1 chassis, at least the timebases do, the signal section was removed from a scrap Cossor 916.

The attachments show the working receiver and a rear view of the internals of the set.
I will make a more in depth description of the design and construction of this receiver and why the Plessey Mark 1 circuit was chosen.

DFWB.
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Old 15th Jun 2017, 2:02 pm   #2
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Default Re: Beau Decca television. Second attempt at a reconstruction.

Hi David,

That picture looks nice and linear.

Where did you get the parts from for the Plessey timebases?

Cheers
Andy
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Old 15th Jun 2017, 3:42 pm   #3
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Default Re: Beau Decca television. Second attempt at a reconstruction.

"Where did you get the parts from for the Plessey timebases"?

Hi Andy,
The Plessey Mark 1 timebase parts were removed from an unfortunate Regentone BIG12 type of set.
The decision to adopt the Plessey Mark 1 timebase design came to me early this year after restoring a Defiant TR1250 12" table set. The circuit design is very simple and very easy to construct. The original Beau Decca line and frame timebases employ Mazda T41 thyratrons as the oscillators, very simple but not very nice. The Mark 1 employs a clever self oscillating line timebase which operates on the Miller transitron principle. The characteristics of the EL38 line output pentode are exploited in this circuit. The frame timebase employs a 6SN7GT double triode as the oscillator and a triode connected Mazda PEN45 as the output.
The RF and IF circuits were removed from a scrap Cossor 916, that's the set with the very deep chassis.
By using flyback EHT the original mains EHT transformer was removed from the power unit and will be transferred back to the Defiant TR1247.
There's still some electrical and mechanical work to do, but the results are so far very encouraging.

DFWB.

Last edited by FERNSEH; 15th Jun 2017 at 3:53 pm.
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Old 15th Jun 2017, 7:26 pm   #4
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Default Re: Beau Decca television. Second attempt at a reconstruction.

Great picture David. Is it a CRM121B or a Mullard? You have certainly made a good job reconstructing a Plessey chassis.

I wish I had bought the Beau Decca that was in that junk shop in Mitcham in the very early 70's. I managed to get the back off to find an original Plessey Mk1 chassis in dusty condition. They must have produced the final run during the production of the MK1 chassis and fitted it in the later models so yours is true to form.

Of course Plessey produced all the Decca television receivers including the projection models. The first Decca produced model was the DM1 [Decca manufacture 1] John.
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Old 15th Jun 2017, 9:25 pm   #5
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Default Re: Beau Decca television. Second attempt at a reconstruction.

Hi John,
the present CRT is a CRM121. However, because the EHT is much higher than the 5KV delivered by the mains transformer I'm considering taking the CRM123 out of the Murphy V180C and installing it in the Beau Decca.
The reason why I finally decided to construct a Plessey Mark 1 type of chassis for this set was because you mentioned that you had seen a Beau Decca with this type of chassis installed instead of the Plessey "standard" TV chassis.
So in due course the Defiant TR1247 will receive all it's original innards. In fact the receiver chassis has already been returned to it's original state and the EHT transformer fitted on the power unit.

DFWB.
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Old 6th Jul 2017, 9:55 am   #6
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Default Re: Beau Decca television. Second attempt at a reconstruction.

The frequency changer stage has been causing a few problems but it seems to be behaving itself now, the set has been on for over an hour and things seem OK in that department. However, a number of other problems had manifested in the form of picture shading at the left side and frame timbase faults. Any easy fix. The three leads that connect to the line hold and line linearity controls carry high peak voltages and by rights these wires should be kept well away from the other control panel leads. This has been done and the results prove that this should have been done in the first place. Later on I will replace the wires to the height control with screened cables and it might also be a good idea to do the same with the line timbase controls leads.
The EHT smoothing capacitor is now fitted on the TV chassis. I did consider fitting it on the CRT gantry but it is on the chassis is where the EHT capacitor is located in the Plessey Mark 1.
The octal socket is for the gram pre-amplifier and radio unit.

DFWB.
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Old 6th Jul 2017, 8:22 pm   #7
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Default Re: Beau Decca television. Second attempt at a reconstruction.

I think we should have a celebration and invite the Foden Motor Works Band.

Looks good to me David. That Plessey design is probably the best chassis of it's period.
Your rebirth of it employing the Cossor 916 signal section looks very original. John.
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Old 6th Jul 2017, 9:00 pm   #8
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Default Re: Beau Decca television. Second attempt at a reconstruction.

Hi John,
Seems the Foden band is still going strong. Pity the motor works is no more. http://www.fodensband.co.uk/

This has been one my fastest construction projects, it has taken only seven months to get this far. The Plessey Mark 1 timebases are very stable, so much so the that the user control panel could omit many of the controls and these could be simply be fitted on the chassis. However, for the sake of originality and because this is a large mirror view receiver it's probably better the controls remain as they are now. It's just the need of having such long leads from the TV chassis to the control panel. In the original Beau Decca TV chassis all the controls and the supply leads were at near chassis potential and didn't carry any timebase waveforms.
The HT voltage is still too high and some means will have to be found to reduce HT supply down to 260 volts.
Reverting back to the UU8 valve rectifier might help matters.

DFWB.

Last edited by FERNSEH; 6th Jul 2017 at 9:06 pm.
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Old 14th Jul 2017, 1:30 pm   #9
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Default Re: Beau Decca television. Second attempt at a reconstruction.

As a temporary measure the Mazda UU8 HT rectifier was replaced with two BY127 silicon diodes each having a series 47ohm resistor to compensate for the low forward voltage drop across these devices.
Even so with the additional resistors at >300 volts the HT was far too high for the Plessey Mark 1 timebases.
To reduce the HT voltage a UU8 rectifier valve has been found and refitted. The 47ohm 7watt resistors have been inserted in series with the anodes of the UU8. At 280 volts the HT supplied to the timebases is still too high and the picture is overscanned horizontally even when the width control is set to minimum. A further reduction of 20 volts would improve matters.
Interesting to note that after reducing the HT voltage the EHT regulation has improved. Also, when the HT voltage was too high the picture width would reduce when the brightness control was turned up to a high setting.
The frame timebase still delivers more than enough scan amplitude. Another benefit from reducing the HT voltage is that the performance of the RF unit has improved, there's more than enough gain and the definition is excellent.

The leads to the control panel height control have been replaced with screen cables to reduce hum pickup and unwanted line pulses from the cables to the line timebase controls.

DFWB.
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Old 20th Jul 2017, 6:48 pm   #10
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Default Re: Beau Decca television. Second attempt at a reconstruction.

A 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.

DFWB.
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Old 13th Aug 2017, 7:00 pm   #11
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Default Re: Beau Decca television. Second attempt at a reconstruction.

A new chassis adaptor plate has been made to replace the one that was made for ex-Defiant chassis. The pictures show the new chassis installed in the cabinet. Except for the TV-radio-gram switch the set has all the correct knobs, thanks Andy.

DFWB.
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Old 14th Aug 2017, 1:08 pm   #12
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Default Re: Beau Decca television. Second attempt at a reconstruction.

Hi David,

It looks like your new chassis was always in this set!

No worries about the knobs. I spotted them at Harpenden a few years back and as I recognised them as the ones you needed, I snapped them up.
It is amazing what turns up sometimes. That's one of many good reasons for attending BVWS events and collectors fairs.

Cheers
Andy
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Old 13th Dec 2020, 10:54 pm   #13
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Default Beau Decca TV revisited.

The set continues to work but there still a few issues to attend to.
First the gram pre-amplifier cannot be fitted in it's position on the cabinet shelf because the Plessey Mark 1 line output transformer is much larger than the transformer fitted on the original chassis.
The pre-amp can be repositioned but a better solution would be to replace the EF37 valve with a miniature type, the most obvious type is the EF40.
The 6AM6 mixer-oscillator continues to stop working after half hours use. The valveholder is suspect.
The HT voltage was reduced to 260 volts by adding a 150ohm resistor in series with the HT supply to the TV chassis. I'm considering replacing the resistor with a choke between the cathode of the UU8 rectifier and the reservoir capacitor. The power supply and audio amplifier chassis was made by Plessey. Uses two PX4 triodes.

Fit two new springs for the mirror lid.

DFWB.
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Last edited by Station X; 14th Dec 2020 at 11:32 am. Reason: Threads merged.
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Old 14th Dec 2020, 10:01 am   #14
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Default Re: Beau Decca TV revisited.

I think I missed the earlier thread but it certainly is looking good. I take it the case is not the the charity shop "up-cycled" one?

Peter
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Old 14th Dec 2020, 11:24 am   #15
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Default Re: Beau Decca TV revisited.

Hi Peter
The Beau Decca was donated in to me in 1994 by the late Chas E Miller.
The TV receiver parts had been removed and substituted with a BSR record deck. Fortunately the radio receiver and audio chassis was still in place.
The top panel had been carved up so a new one was made, two attempts to get that one right. A local engineering firm made the parts for the CRT mounting arrangements. There was a great deal of measurement and adjustments in order that the tube neck is positioned centrally in the focus coil.
The TV chassis was taken from a Defiant TR1247 and modified for installation in the Decca.
In mid 2017 it was realised that there is still a good number Beau Decca TVs in existence and it is the Defiant is the rare set.
The same engineering firm had made a box type chassis and the plan was to make an ersatz chassis for the Defiant. Now the Defiant has it's original chassis and the Beau Decca has the special chassis.

As for the green "up-cycle" Decca, the only thing holding up the completion of the cabinet assembly is those eighteen vertical slats that fit in the loudspeaker aperture.

DFWB.
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Old 14th Dec 2020, 8:39 pm   #16
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Default Beau Decca Television.

Follow up to yesterdays work on the Beau Decca TV set.
https://www.vintage-radio.net/forum/...d.php?t=137423
In order that a B8A valveholder can be fitted in lieu of the octal socket an adaptor plate must be used.
That part has been fitted along with a salvaged B8A valveholder.
The pre-amplifier employed an EF37 pentode. Very simple circuit consisting of a 3.3Kohm bias resistor, the anode load is 270K and the screen feed resistor is 1Mohm. Pin 6 on the octal valveholder was used to anchor the anode and screen grid resistors, now a tag strip will have to be used for the resistors.
The second picture shows I've just got away with sufficient clearance between the valve and the line output transformer box.

DFWB.
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Old 16th Dec 2020, 5:53 pm   #17
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Default Re: Beau Decca Television.

What a horrible little unit! It took far longer than anticipated to replace the valveholder. Anyway, the job's done. Considering the time it takes to assemble these things it amazes me how they ever put these sets into mass production.

DFWB.
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Old 16th Dec 2020, 9:42 pm   #18
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Default Re: Beau Decca television. Second attempt at a reconstruction.

The Beau Decca has a push-pull audio amplifier which employs a pair of triodes.
At 5watts the output is much less than the record reproducer of the same name.
When switched to radio the CRT heater was still energised. Because the set under discussion now has flyback EHT the 5KV transformer was removed and replaced with a 2volt transformer to supply the tube heater. So now the tube heater is switched off on the radio and gram positions.

DFWB.
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Old 17th Dec 2020, 10:14 am   #19
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Default Re: Beau Decca television. Second attempt at a reconstruction.

David, I think the mods should remove your first sentence just in case Google searches reveal it in the wrong quarters.

Peter
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Old 17th Dec 2020, 10:50 am   #20
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Default Re: Beau Decca television. Second attempt at a reconstruction.

Done.
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