BRC 2000 CTV: ready for the Queens Speech?

[FERNSEH]

In another tread about the BRC 2000 series colour TV I mentioned I'm restoring a 19" Marconi 4701. This set was found in a bad state of repair.
Will it be ready in time for the Queens Speech this year?

Today I made a new cabinet base to replace the rotten original.

DFWB.

[ntscuser]

That looks superb

I'd be tempted to add RGB input, in part to take advantage of the BRC 2000's colour processing, but also as a hedge against decoder failure.

[FERNSEH]

Adding RGB inputs is a distinct possibility. The idea of supplying the set with baseband video was discussed on another forum. Some argue that doing this detracts from the set's originality but it well known a number of BRC 2000 receivers were converted to become studio monitors.
If one studies the circuit diagram of the 2000 it becomes all too apparent that the addition of a a CVBS input is not all easy. The luminance signal path is not the problem, it is the method of extracting the chroma signal where the difficulties arise. A separate detector stage in the IF amplifier board is employed to extract the chroma. All these obstacles can be overcome but is it really worth all the effort? The truth is the colour decoder is a fairly conventional affair and was known to be reliable.

DFWB.

[FERNSEH]

Hi John
you'll be amazed at the speed of this restoration. The cabinet will be reassembled by the weekend, that's the easy part of the job. It's the electronics that will be the hard part.

A picture of the router tool used to make those slots in the cabinet base.
Very useful tool to have.

DFWB.

[FERNSEH]

Useful progress over the weekend. The first picture shows the new mains transformer mounting blocks which are attached to the cabinet base.
The second picture shows the new cabinet base clamped into postion.
There are still a number of jobs to do the cabinet before the repair can be finally signed off.

DFWB.

[FERNSEH]

Even more progress today. The wooden battens around the rear edge of the cabinet have been refitted. The upper one was repaired, a section was missing. A completely new one was made for the bottom edge, like the cabinet base, the original part was rotten. The three vertical parts were in good condition. The chassis supports are attached to these. Later on the underside and rear edges of the cabinet will painted the usual TV industry standard colour, that is, brown.

DFWB.

[mark pirate]

The cabinet is coming along nicely David, I scrapped the same model many years ago when the red gun died in the CRT
I am looking forward to the electrical restoration.

Mark

[FERNSEH]

Hi Mark,
The cabinet repair is the easy part of the restoration. The initial stages of the chassis restoration appeared in another BRC2000 thread:
https://www.vintage-radio.net/forum/...d.php?t=114235 See post #2.
It's not often one has to cut out sections of a TV chassis because of rust.
Tomorrow I will attempt to remove the CRT in order that the metal shield can be cleaned up.

DFWB.

[HurtyAC]

Hi, Are you in need of the steel chassis for this set??

[FERNSEH]

Hi Hurty,
The bad metalwork was cut out and replaced by 20 X 20mm L shape steel stock bought from B & Q. The PCB guides were sourced from RS.

DFWB.

[FERNSEH]

This morning the CRT was removed, not an easy task as the 0BA studs are rusty. A squirt of penetrating oil helped to undo the four CRT securing nuts.
The tube is not the original, it is a Mazda A49-191X Rimband 3 type.
The original CRT fitted in 19" 2000 series receivers was the Mazda CTA1950 or A49-11X.

[mark pirate]

Is the CRT good, or will you be fitting a replacement?

Mark

[FERNSEH]

Hi Mark,
The set was taken out of service in 1978 and as this is the second CRT to be fitted in the set I've a good feeling that it is OK. What I should do is test it on the Muter CRT tester and regenerator.
While the CRT is out a strip of wood veneer can be attached to the bottom edge of the cabinet. See the third picture on post #5. That plywood looks horrible.

DFWB.

[yesnaby]

Hi,

The CRT was removed - you are braver than me.

Are there any TV engineers that also had a career in bomb disposal?

Michael

[ekcopyephilips]

Hi Michael

The implosion protection employed in tubes of this era make them quite safe, the rim band stops the implosion from happening.

Many years ago i worked at Sanyo in Lowestoft, we used a vacuum hoist to lift the tubes into the cabinets, i actually managed to mis-attach a 28" 4:3 tube onto the hoist one day and as i lifted it up it fell off onto the floor - from about shoulder height. Nothing happened, the tube was fine. My underpants on the other hand....

We also had a problem, once, with a batch of 28" 100Hz videocolour tubes cracking along the faceplate horizontally exactly half way up/down. To test the tubes we had to unbox hundreds of finished sets from the warehouse, power them up and hit the face with a rubber mallet quite hard. Just to see if we could induce the failure. The older technicians did this facing the set - i was too chicken and did it from behind the set with the set facing a mirror. Even hitting them with a rubber mallet didn't make the good ones or failed ones explode.

However that was with new glass, i suggest you do not try that at home.

Regards

Mike

[FERNSEH]

The "P" band CRTs are safe to handle. Nevertheless, it's worth remembering although the faceplate is reinforced the reverse side of the tube isn't.
Introduced in 1964 the early P band tubes like the A47-11W employed a large metal shell around the faceplate. In 1967 the thinner P band was introduced and these new tubes allowed set designers to install the CRT in the "push-through" style of presentation. The 19" Mullard tube was designated A47-26W. I still prefer the earlier presentation which has the mask around the edge of the CRT screen. Push-through is cheaper to make of course.
Mullard called the reinforced tubes "Panorama" and Mazda used the Rimband name.
The first 19" and 25" colour CRTs were produced in Rimband 1. A49-11X and A63-11X.

DFWB.

[vidjoman]

Originally Posted by yesnaby

Are there any TV engineers that also had a career in bomb disposal?

Many of us used to change tubes every day. We used a re-gunning guy who used to swing the tubes up under his arm and crack the glass near the pins with a small metal hammer. He only did this after he rolled his van and about 20 tubes imploded. He didn't really hear it as he was deaf and wore a hearing aid that hung around his neck and had a single headphone. It had 2 valves and was battery powered of course.

[FERNSEH]

I'm absolutely sure it is not allowed to be done nowadays. In the "old" days we used to replace CRTs in the customers house. In fact some rental sets such as those manufactured by Rediffusion were made in a manner so that the tube could easily be replaced by undoing webbing straps and springs.
Even in the BRC 2000 it is a simple enough job to replace the CRT. Just remove the chassis after undoing a few connectors. Remove the four brass 0BA nuts holding the tube and mag shield, and that's the tube out. Easy.

DFWB.

[FERNSEH]

Originally Posted by FERNSEH

While the CRT is out a strip of wood veneer can be attached to the bottom edge of the cabinet. See the third picture on post #5. That plywood looks horrible.

A strip of veneer has been glued on the bottom edge of the cabinet so that unsightly plywood can no longer be seen. The bottom edges of the cabinet sides have been tidied up, the whole structure is now very solid.

Today I'm going to test the mains transformer, let's find out if it is any good.

DFWB.

[FERNSEH]

The mains transformer is certainly a rusty old thing, but nevertheless it is still servicable. I connected the full mains supply to it today and so far every thing is fine. It runs cool off load and all secondary voltages are correct.

DFWB.