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Old 20th May 2024, 4:40 pm   #1
beamcurrent
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Default Unidentfied Valve TV PCB

Does anyone recognise the valve IF unit in the photos? or know the date?

It is part of a dual standard tv receiver tuner unit made by Thorn in the early 1960s?

Tuners bottom left and transistor PCB sound/vision output.
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Old 20th May 2024, 5:33 pm   #2
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Default Re: Unidentfied Valve TV PCB

The top board is a Thorn 850 series. Just a guess but I think the bottom board is some form of relay decoder. No visible CRT or timebase chassis. J.
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Old 20th May 2024, 6:50 pm   #3
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Default Re: Unidentfied Valve TV PCB

Wow!! some time since I've seen cable lacing on a consumer product if ever!!.

Whilst it may well be a Thorn designed IF chassis, the cans point to this, the metal work and sleeved connections to a control, just in view, together with the above suggests perhaps a school receiver. The turret tuner suggests non cable.

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Old 20th May 2024, 7:17 pm   #4
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Default Re: Unidentfied Valve TV PCB

Thanks for the replies, I have googles a picture of the Thorn 850 and that is indeed the set, jolly good!

The unit that it is in is a "check" receiver installed in BBC MCR21. This is a special purpose item and is best thought of as a "tuner" in the sense that a radio tuner used in a hifi system has no speakers the Thorn WJ11 set has no tube and only a small speaker.

The handbook for it can be downloaded from the MCR21 site https://mcr21.org.uk/wp-content/uplo...1-Receiver.pdf
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Old 20th May 2024, 8:43 pm   #5
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Default Re: Unidentfied Valve TV PCB

It's not exactly an 850 IF panel, as there's no video amp, sync sep or sound output stages.

Maybe the PCB has been "cut down" as was done on a standard 950 chassis board, to put into the 16" 960 chassis....?
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Old 21st May 2024, 8:46 am   #6
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Default Re: Unidentfied Valve TV PCB

This was quite a common practice for both Broadcast TV & also Relay companies such as Rediffusion, Top Rank, British Relay etc.

These types of unit were generally referred to as 'OAR'' - 'Off-air-receivers, and it was common to utilise a current IF /tuner combination followed by some fairly decent base-band video & audio processing. Thus the video output would be the standard 1v p-pk, and the audio a 600 ohm balanced output. Power supplies were also normally stabilised.
The extra electronics for processing was often of high quality, compared to the 'consumer' I.F/tuner etc.

Some manufacturers used fixed-frequency tuners, supplied to order, & even used a crystal oven, for better tuning stability. Many were rack-mounted construction.
As well as Thorn, there were various other manufacturers including Rediffusion, Top Rank, (a huge heavy valve-base unit), Decca, (such as the RU4011) Rank-Bush-Murphy etc.


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Old 21st May 2024, 3:37 pm   #7
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Default Re: Unidentfied Valve TV PCB

Although the RBM A 640 black-level design is so good, anyone looking to use gated AGC on their Thorn dual standard need look no further.

Chris
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Old 22nd May 2024, 10:03 am   #8
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Default Re: Unidentfied Valve TV PCB

Quote:
Originally Posted by dazzlevision View Post
It's not exactly an 850 IF panel, as there's no video amp, sync sep or sound output stages.

Maybe the PCB has been "cut down" as was done on a standard 950 chassis board, to put into the 16" 960 chassis....?
Correction. The PCL86 audio output stage is present and used on the "cut down" Thorn 850 dual standard IF panel.

The PCL84 video amplifier valve holder is present but not used.
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Old 23rd May 2024, 10:38 am   #9
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Default Re: Unidentfied Valve TV PCB

Progress has been made on this check receiver and it is now installed and working in MCR21. We found a Humax freeview box that produces a correct 4:3 output remodulated on to the RF output socket so this connects nicely to the AE input of the Thorn receiver, just a rather big "lump in the wire".

Thanks for the help in identifying the TV the IF PCB is from and yes it has been shortened and one valve is not fitted.

The hand book for the Thorn WJ11 receiver can be downloaded from https://mcr21.org.uk/technical-handbooks-slug/ scroll down to the foot of the page.
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