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

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Old 23rd Nov 2014, 4:03 pm   #1
FERNSEH
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Default BRC 680 series.

Looking though my newly acquired 1970/71 Radio and Television servicing book, (after over forty years I've finally bought one) I found a BRC/Thorn TV chassis I never knew existed. The 680 series, what's that all about?
Well it turns out that the 680 is not a BRC design at all and is in fact a special version of the Radio Rentals Baird 680 chassis. The chassis was modified to operate on the Rediffusion or Top Rank wired TV systems.
The circuit diagram and other drawings are presented in the usual BRC style.
We know that Radio Rentals became part of the Thorn Group in 1968 and that the Bradford factory switched over to making BRC/Thorn products until it closed in the eighties.
The BRC 680 monochrome chassis must be the only example to employ the PL802 as the video amplifier.

DFWB.

Last edited by FERNSEH; 23rd Nov 2014 at 4:05 pm. Reason: BRC680 chassis.
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Old 23rd Nov 2014, 4:09 pm   #2
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Default Re: BRC 980 series.

Moderators. The title should read: BRC 680 series.

DFWB.
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Old 23rd Nov 2014, 4:23 pm   #3
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Default Re: BRC 980 series.

Yes, a very interesting set. I have the BRC service manual for it. Never seen one though.

Regards,

Dazzlevision
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Old 23rd Nov 2014, 5:25 pm   #4
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Default Re: BRC 980 series.

I was surprised to discover how many cable TV sets BRC made.
The 979 series, a Modified 950. A cable version of the dual-standard 850 series.
The 680 series, originally a Baird chassis.
Later on a single standard cable TV chassis was made, the 1579, a modified 1500. Unlike the earlier sets which were supplied the loudspeaker directly from the cable network, this chassis employed an audio output transistor. A high voltage type, probably a MJE340.
So it follows, did BRC make wired TV versions of the 3000 series CTV?
We do know that a VHF tuner was available for the 3000 and possibly the 3500 series colour sets to enable them to operate on VHF distribution systems.

DFWB.
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Old 23rd Nov 2014, 5:48 pm   #5
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Default Re: BRC 980 series.

Quote:
Originally Posted by FERNSEH View Post
So it follows, did BRC make wired TV versions of the 3000 series CTV?
We do know that a VHF tuner was available for the 3000 and possibly the 3500 series colour sets to enable them to operate on VHF distribution systems
Hello,

I'm not sure about the cable version of the 3000/3500, but I think it probable that one was produced.

I have a BRC VHF tuner conversion kit for those 3000 sets that had a removable section of the cabinet front, to allow the standard Thorn valved VHF turret tuner to be fitted. It uses EC97 & ECF805 valves and wideband cable frequencies turret coils (for the 625 bandwidth) and there is a small power supply PCB and an IF filter PCB in series with the tuner's IF out coax to the standard 3000 IF panel.

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Dazzlevision
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Old 23rd Nov 2014, 6:19 pm   #6
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Default Re: BRC 680 series.

Thread title changed to "BRC 680 Series" as requested
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Old 23rd Nov 2014, 6:31 pm   #7
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Default Re: BRC 680 series.

Hi Robert, many thanks for that.

So when the VHF tuner is fitted to a 3000 series receiver, does that mean the set operates on VHF only. Or, the output from the UHF tuner is routed through VHF tuner so that it is still possible use the set on UHF?
A "UHF" position on the tuner knob?

DFWB.
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Old 23rd Nov 2014, 6:53 pm   #8
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Default Re: BRC 680 series.

Hello,

The pushbutton UHF tuner is removed and replaced by a set of dummy buttons (just like the old days, when UHF tuner dummy knobs were fitted in dual standard sets without a factory fitted UHF tuner - but in reverse!).

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Dazzlevision
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Old 23rd Nov 2014, 9:08 pm   #9
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Default Re: BRC 680 series.

I'd almost forgotten about that chassis, Baird M640 (?) was the only model I ever saw, cabinet presentation was classic Radio Rentals from the mid to late 60's but without tuners of course. Thankfully we didn't have many out on rental as we had no Rediffusion cable signal in the workshop.

There was some home brew Heath Robinson lash up that someone had made which consisted of a standard 950/1400 VHF tuner and two 850 IF panels, it produced a very weak and crude picture of sorts but no audio. How it was done I have no idea, any cable experts care to speculate?

John

Last edited by jayceebee; 23rd Nov 2014 at 9:37 pm. Reason: more info
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Old 23rd Nov 2014, 10:17 pm   #10
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Default Re: BRC 680 series.

Quote:
Originally Posted by jayceebee View Post
I'd almost forgotten about that chassis, Baird M640 (?) was the only model I ever saw, cabinet presentation was classic Radio Rentals from the mid to late 60's but without tuners of course. Thankfully we didn't have many out on rental as we had no Rediffusion cable signal in the workshop.
That must have been the cable 680 chassis which is the subject of this discussion.
I have never seen one of these sets. I can only speculate that the cable version of the Baird 640/650/660/670 and 680 series would have only four front controls: On-off, contrast and brightness grouped together and the volume control in the position where the tuner would be in the aerial sets.

As for the 850 with two signals panels. Perhaps that was the converted to dual standard version. The 625 conversion chassis was attached to the upper section of the chassis. A real lash-up it was for sure. I had quite few of these horrors out on rental. 625 UHF performance was hopeless until an additional transistor IF amplifier was fitted. The IF booster plugged into PL304 which is the UHF tuner socket.

DFWB.
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Old 23rd Nov 2014, 10:48 pm   #11
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Default Re: BRC 680 series.

Sorry Fernseh, I didn't quite explain my self properly but the home brew contraption built by one of the bench engineers which was a tuner and two 850 series signal panels took a normal off air 405 signal and converted it to a very crude output to feed in to the octal socket on the 680 chassis sets. How this was done I have no idea, these sets and the converter were on their last legs when I joined Thorn.

John.
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Old 24th Nov 2014, 12:35 am   #12
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Default Re: BRC 680 series.

Hi John,
Got it! He actually made an unit on the similar lines as the Rediffusion "Telebox" adaptor which enabled RVS cable sets to receive off air signals.
There was a discussion about the unit here:
https://www.vintage-radio.net/forum/...ad.php?t=71088

DFWB.
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Old 25th Nov 2014, 7:35 pm   #13
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Default Re: BRC 680 series.

A similar thing (but in reverse) was the "Baird 720" series which apparently used the Thorn 2000 dual-standard colour chassis. I have a little bit of Baird documentation which mentions the 720 series and how to modify the Thorn multiband tuner for VHF 625 operation etc. but I have never seen one myself. (I've never even seen a picture of a Baird-badged 2000 set.)

Kind regards.

From Mike.
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Old 26th Nov 2014, 11:38 am   #14
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Default Re: BRC 680 series.

Quote:
Originally Posted by FERNSEH View Post
the 680 is not a BRC design at all and is in fact a special version of the Radio Rentals Baird 680 chassis.
Interesting! I wondered about this interesting model for years, thinking an older chassis lacking the Jellypot LOPT which couldn't be right as it uses a PL802 video output valve.

Have any survived I wonder?

A most interesting thread.
Cheers,
Brian
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Old 17th May 2015, 8:45 pm   #15
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Default Re: BRC 680 series.

I'm fortunate to have found a comprehensive Baird 620 series service manual. It covers almost all Baird dual-standard models including the 620, 640, 670 and 680 series.
Two cable receivers were made about 1963/64, models M634 and M636. 19" and 23" model respectively. The fact these sets have the "M" prefix indicates that the sets were distributed to independent retailers.
Also found in the service manual is a special schools receiver, the model 636.
This could be the subject of a separate topic about schools receivers.

DFWB.
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