Decca Bradford - the beginning

[Sean Williams]

What's this - Colour - far too modern to be here...

Well, Thanks to Mikey405, my reprogramming and general corruption is nearing completion

Anyway, the Bradford.

It is a Granada badged set, it basically works, the convergence needs a bit of fiddling with, and the brilliance control is somewhat wierd in operation

So, questions.

As the brightness control is wound down to nil we get a full colour picture when on max, a yellow picture, at about 60%, and a green picture at around 30%.

Now, obviously this is relevant to the individual guns backing off, first blue, then red, leaving the green gun working.

Is this effect just down to the age of the tube, or do I have a tangible fault to play with? The voltage driving the guns is constant at around 150v WRG.

Convergence? - I am OK with the theory - to get the three guns aiming at exactly the same place on the phosphor, in order to produce a nice clean white. However, is this a black art, or is it just practice that makes perfect?

I did have a focus problem, the picture was slightly blurry, adjusting the focus control worked for a while, but it all went to rats shortly after - fault fixed now though - one of the 4.7M resistors had gone o/c (a modern replacement metal film one I hasten to mention - a nice 1960s carbon lump has gone back, nicely matching the original one at the other end).

Was a little suprised at the hot end of the focus unit though, the tripler does hold a good charge

So oh mighty TV experts, where to start?

Cheers
Sean

[Danny]

Hi
It sounds like the guns are not tracking, and yes, this could be the tube, but check the A1 voltages are constant for all three guns.
If the cathodes are constant with adjustment of the brightness, then it's tube tester time.
If you can run the heaters at 10% higher voltage this should prove the fault.
Danny

[Steve_P]

What's the model no? Then I can look for a manual.

Look here: www.oldtellys.co.uk

Convergence is not a black art, but it needs practice. A mirror is handy - not for you, but for the TV. So you can see the tube from behind the set.

Static Convergence first (Back of tube) then dynamic. Don't just fiddle! It gets like a rubik cube if you do!

Remember - get it right on B+W first, then turn the colour up and hope. Colour Decoders can be hard to do, but not impossible. Again, don't just fiddle with pots.

Cheers,

Steve P

[Sean Williams]

Does CS1917 help?

Ok on convergence - no fiddling, OK, following info from 1971/72 red book

Cheers
Sean

[Tazman1966]

Ah-ha Sean....colour reaches Hitchin. Funny we've had colour here in St Albans for years.

From the model number it sounds like a Decca 10 series, that is, the early "Bradford" type.

I does sound a little as if the tubes a little low. I have a very under used B&K tube analyser/rejuvenator here if you want me to bring it over and test it out.

Good luck with the convergence.

[Steve_P]

Fine! I've got it here now in case you need any advice. It's the first Decca Bradford, and nice sets they are too when set up right. Run it a while to bring the tube back up.

I shant tell you to go over the whole set for dry joints, etc. I think you already know that sort of thing.

Now, being nasty sometimes the way some teachers are, I'm going to shut up and let you do as much as possible yourself. I had to...

Cheers,

Steve P.

[Mikey405]

Although it was only the other day when Sean collected the set, my memory is kinda hazy as to what the problem with it was. However, I seem to recall that it wasn't a "normal-looking" problem when the brightness was turned down. From what I remember, I think the colour-difference signals disappeared one by one as the brightness was turned down (although the grey-scale changed also), and you were left with a monochrome picture at minimum brightness. The tube wasn't actually that bad, and the set produced a pretty good picture for a Decca-hybrid, although I think the blue could've done with a little bit of something. (Part of what looked like a convergence problem was actually the width of the blue beam compared with the red and green.)

[Sean Williams]

Ok, have had a prod around the set with a meter, the cathodes are around the 130-150v mark, and the A1 voltage appears to be around 650v

Mike's comment about the blue being a bit wide certainly seems to make sense, there seems to be a blue shadow around white objects.

Well out of my depth here - any pointers for where to start would be useful

Cheers
Sean

[Steve_P]

Have you done all the setting up first of all.

The blue channel has R338, then 15K across L210. Then try D205, C215 and C216. Also C214.

Cheers,

Steve P.

[MALC SCOTT]

Hi Sean, check R476 390k. I have had this cause similar problems. The A1 settings may be a bit too high, try backing them off a little. The best of luck Cheers, Malc.

[Tazman1966]

Hello Sean.

Also check the 100k resistors on the tube base. They sometimes go high as well.

[Sean Williams]

Thanks all - will look into the above suggestions