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Vintage Television and Video Vintage television and video equipment, programmes, VCRs etc.

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Old 10th Nov 2018, 11:24 pm   #1
FERNSEH
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Default Cossor 54.

Follow up to previous threads about the Cossor 54 TV receiver. Picture focus has been improved by replacing the 3.3megohm resistors R44 and R46 in the focus control bleeder chain, see attached circuit diagram. Both resistors had risen in value to 11 megohms. The original 2megohm focus control was replaced some time in the forties or fifties with a 5megohm radio volume control, it even has the on-off switch attached to it. The replacement focus control has a log law track but seems to work OK.
The correct value for R45 is according to the parts list is 2megohms.

DFWB.
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Old 11th Nov 2018, 1:59 am   #2
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Default Re: Cossor 54.

Replacing those resistors in the focus bleeder chain has effected a slight improvement to the picture quality.
25 volts P - P video supplied to the CRT grid.

DFWB.
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Old 11th Nov 2018, 3:10 am   #3
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Post Re: Cossor 54.

Hi David,

What a difference from your first picture a rather large pat on the back from me! Superb work!

Terry.
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Old 11th Nov 2018, 9:25 am   #4
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Default Re: Cossor 54.

I would leave it at that David and be pleased that there is any emission left at all. Looks good to me. John.
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Old 11th Nov 2018, 9:39 am   #5
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Default Re: Cossor 54.

It looks better than mine. The CRT in my set is very poor indeed.

Cheers
Andy
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Old 13th Nov 2018, 1:30 am   #6
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Default Re: Cossor 54.

In the Cossor 54 the sawtooth waveform on the anode of the line oscillator valve is supplied via C30 to the Y1 defector plate of the type 3244 CRT. Normal convention is to supply the horizontal deflection waveform to the X plates.
Because I can't find the X100 'scope probe there has been no attempt to measure the waveform present on the anode cap of the MS/PEN oscillator valve, I'd guess that it is >500 volts P - P. The Y2 deflector plate is at near full EHT voltage, 3000V.
Likewise, no attempt to measure the waveform on the anode of the pentode section of the 4TP frame oscillator valve although it is possible to estimate what the waveform amplitude will be. The sawtooth voltage is developed across series capacitors C33 and C50. The grid of the triode section is connected to the junction of the two series capacitors. The 'scope indicates 30 volts P - P. across the 0.15microfarad capacitor C50. The capacitance ratio is 16.66:1 so it possible to guess that the waveform voltage on the pentode anode will be about 500 P - P. Refer to the attached circuit diagram in post No.1
It will be noted that there is no electronic picture shift circuits. Instead, adjustable magnets are fitted to the cabinet sides, a rather crude arrangement but it works.

A 7" CRT console version of the Cossor 54 was manufactured,.It was designated as the model 65. Six by five inch picture.

DFWB.

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Old 13th Nov 2018, 8:59 am   #7
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Default Re: Cossor 54.

I have never seen a model 65 David but I do have a very large factory blueprint of the circuit.
I found it many years ago in a pile of rubbish at a derelict radio shop in Hanworth Middlesex. J.
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Old 13th Nov 2018, 1:47 pm   #8
FERNSEH
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Default Re: Cossor 54.

Such is the simplicity of the Cossor 54 that here is a TV receiver that could be considered as an alternative construction project to the Argus or any of the other TV sets that used electrostatic CRTs of the VCR97 type.

6.3 volt valves in lieu of the older 4 volt types.

DFWB.
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Old 13th Nov 2018, 4:12 pm   #9
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Default Re: Cossor 54.

Quote:
Originally Posted by Heatercathodeshort View Post
I have never seen a model 65 David but I do have a very large factory blueprint of the circuit.
I found it many years ago in a pile of rubbish at a derelict radio shop in Hanworth Middlesex. J.
Hi John,
1938 sales brochure shows the model 65 along other models including the well known model 1210.

DFWB.
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Old 16th Nov 2018, 11:18 am   #10
FERNSEH
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Default Re: Cossor 54.

A short circuit between the HT line to chassis was traced to perished wiring in the vision IF amplifier, to be precise in the IF transformer box which is mounted above the 4TSP and 4TPB IF amplifier valves.
These pre-war Cossor TV receivers employ a clever arrangement in the coupling between the vision IF amplifier stages. The first valve is a Cossor 4TSP which has a top cap anode connection. The second valve is a Cossor 4TPB which has a top cap grid connection. By employing these specially made for television valves coupling between the IF amplifier stages is simplified, see the attached pictures.
By using modern silicon rubber insulation wire the original appearance is maintained.
The set is now working again and with use the picture is getting better, although it is still lights out to view the picture.

DFWB.
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Last edited by FERNSEH; 16th Nov 2018 at 11:26 am.
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