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Old 19th Oct 2021, 5:27 pm   #1
19Seventy7
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Default Rediffusion MK 7

Hi all

I was given a Rediffusion MK7 some time ago, but unfortunately it was missing some parts, with no info online it took a bit of a backseat until I was told of a Rediffusion expert, Malc Scott, who has helped me massively, along with Vintage Engr.

I was going to wait to make this thread as I already have several other projects on the go (I like to rotate them around, and spend more time on them, more fun that way!) As both Malc and Vintage Engr have said they were interested in following the progress I thought I'd create the thread and give progress as I'm going along.

So far I've only replaced three capacitors, two 0.1uFs and a 0.068 Wima on the tag strip next to the LOPT, and 3 valves. Two were missing and one had gone down to air. EY86, ECC82 and a 30PL13.

Missing still is the tuner, there's a couple on that site which should work, although it wont be pretty as the original tuner was a sliding unit, so it has a long vertical slot, it'll get the set going which is the most important thing. It'd be nice to find a matching tuner but the chances of that are probably close to impossible.

That does lead me onto a question though. Running the set up on a lamp limiter has yielded no results with no valve heaters. There is voltage getting through as I have measured about 200v on one of the PCB joints.

Does this set require the tuner valves to be in circuit for the rest to light up?

I know a lot of sets do but I thought as these aren't used just for aerial sets, but their cable system, that they may have been produced to work without the tuner valves?

I mainly want to get a raster on screen to see whether the CRT and/or LOPT are okay before throwing any more money into the set, if I can help it

'77
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Old 19th Oct 2021, 6:36 pm   #2
toshiba tony
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Default Re: Rediffusion MK 7

This set will require a tuner to enable the heaters, thats assuming the tuner has valves, looking at the set I would say that's likely. You can bridge the heater pins (temporarily) to enable you to check the rest of the set. I would imagine you are going to have a lot of faults. Indeed pumping mains into it is not recommended, it will want waking up carefully. Methods of doing this will no doubt, will be on this site.
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Old 19th Oct 2021, 7:33 pm   #3
19Seventy7
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Default Re: Rediffusion MK 7

Thought that would be the case, would make sense to be.

I'll try bridge the heater pins and see what happens, if I can work out which pins would be for the heaters. I'd imagine a lot of faults too, it's more just an exercise to see if the CRT and LOPT seem happy enough to continue further. It's only been run up using a lamp limiter, it hasn't seen 'raw' mains power, and won't until at least all the paper caps have been changed.

Thanks
'77
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Old 19th Oct 2021, 9:09 pm   #4
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Default Re: Rediffusion MK 7

Wish I knew the set, Ill have a look and see if I can ID the plug that it uses, there will be two heater wires, HT + and - and possibly an AGC lead.
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Old 19th Oct 2021, 11:43 pm   #5
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Default Re: Rediffusion MK 7

There's "two" spare wires that would go onto the tuner

1 is an edge connector with 4 "teeth" that bite onto the PCB, and the other is singular, possibly the AGC lead?

I'm sure ill be able to trace the wiring back tomorrow and figure out which two i need to short out

Thanks
'77
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Old 21st Oct 2021, 8:55 pm   #6
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Default Re: Rediffusion MK 7

I canít seem to determine the two specific wires that are for the tuners valve heaters for some odd reason. Iím at a complete loss here as I canít refer to the circuit diagram as the tuner section doesnít appear on either one I have which is a shame.

The separate brown and white wires lead to the signals panel; The other three lead to the user control panel, so Iíd think the brown and white should get shorted out, but this doesnít result in anything.

On further testing on the signals panel there is a lack of continuity between the valves on the top and the valves on the bottom of the board so I think a component or two may have gone O/C. Iíll do some testing tomorrow when I have some more space. Some valve sockets also seem like they need ďtighteningĒ too, which Iíll do too and see if that helps.

If anyone has an idea on which pins need shorting out I would appreciate the help as Iím a little stuck otherwise.

Thanks
Ď77
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Old 21st Oct 2021, 9:47 pm   #7
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Default Re: Rediffusion MK 7

The chances are they will be the same colour. The valves will be a PC86 and a PC88. The heaters are on pins 4 and 5 on each valve and they are series connected. I'm assuming you have electronic knowledge, I was an engineer for over fifty years and dementia has hit but my years in the trade have stayed with me. Its simply a matter of identifying which two wires are the heater ones. But be careful, you dont want to be injecting HT into the heater line. There will be two connections coming from the tuner specifically for heaters. These two connections want bridging to re-establish heater continuity, but you still need to wake the set up slowly, can you post a picture of the tuner, or did I read the tuner is absent?
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Old 21st Oct 2021, 10:27 pm   #8
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Default Re: Rediffusion MK 7

Ah that would make sense, there are 2 white wires, no others are doubled. I have some electronic knowledge, enough to work with it safely and all, still learning some of the more in depth stuff though. I've already switched the set on with a lamp limiter, not a variac. I was told the lamp limiter should be okay, and I haven't had any problems with using it on a lamp limiter yet.

Unfortunately the tuner is absent which is a shame, and I've not got a circuit diagram of the tuner section, only the diagram for the wired, tuner-less, version

Thanks
'77
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Old 22nd Oct 2021, 7:58 am   #9
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Default Re: Rediffusion MK 7

The tuner in the MK 7 would not have had a PC88 and PC86 they only came along when 625 lines started. The original tuner may have had a PCC84 and a PCF80.
I never found these set to be very reliable at least not the aerial version. Always had lots coming into the workshop. I had just started at Rediffusion in 1964 and was 19 years of age. Sorry no circuit diagram just faint memories.

John
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Old 22nd Oct 2021, 11:05 am   #10
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Default Re: Rediffusion MK 7

It's most likely the Mark 7 aerial set was equipped with the Cyldon PC60 push button tuner.
The attachment shows it's application in the 1960 Regentone Ten-17 TV receiver. For the Mk 7 the on-off switch will not be attached to the tuner.

DFWB.
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Old 22nd Oct 2021, 4:04 pm   #11
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Default Re: Rediffusion MK 7

This was posted by Jayceebee on one of my threads as it looks like I am using the same LOPT as this in my project.
Quote:
Originally Posted by jayceebee View Post
https://www.radios-tv.co.uk/communit...2/#post-108145 Circuit of the cable version in this thread over on Vrat.

John.
Thought it may as well be here as well for information. I know the two threads are for the same set.

Adrian
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Old 22nd Oct 2021, 4:55 pm   #12
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Default Re: Rediffusion MK 7

Quote:
Originally Posted by toshiba tony View Post
The chances are they will be the same colour. The valves will be a PC86 and a PC88. The heaters are on pins 4 and 5 on each valve and they are series connected. I'm assuming you have electronic knowledge, I was an engineer for over fifty years and dementia has hit but my years in the trade have stayed with me. Its simply a matter of identifying which two wires are the heater ones. But be careful, you dont want to be injecting HT into the heater line. There will be two connections coming from the tuner specifically for heaters. These two connections want bridging to re-establish heater continuity, but you still need to wake the set up slowly, can you post a picture of the tuner, or did I read the tuner is absent?
Sorry, but the valves are not PC86/88.
This set is a405-line only, ands had a Bird push-button tuner . I seem to remember that it was a PCF80 & PCC84; the usual standard for that time. I will see if I have any info in my archives.

I would not be tempted to just s/c the heater connections, - unless you have the set connected to a lamp limiter, as you'll be overloading the heater chain by around 16v.
I've just had a look at the circuit that I sent, and the tuner would probably
have been connected at point E10. This is where the SF board would have been connected on the wired receiver; on your model it goes to the I.F. board.

I would suggest that you systematically trace the heater chain back from the 'cold' end with a meter on ohms. (Disconnect the mains first!!) Then you should be able to trace it from the I.F. board to where your o/c point is, i.e where the tuner should be.

Hope that helps.

Addenda: The tuner that Fernseh has given the picture for is the correct one. (Dreadful things, plastic sliders used to break with great regularity).

David.

Last edited by Vintage Engr; 22nd Oct 2021 at 4:58 pm. Reason: Added info.
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Old 22nd Oct 2021, 6:25 pm   #13
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Default Re: Rediffusion MK 7

Quote:
Originally Posted by raditechman View Post
I never found these set to be very reliable at least not the aerial version. Always had lots coming into the workshop
I have read that they were unreliable and that a lot of engineers hated them, which made me more pleased to have it, don't know why that would though!

Quote:
It's most likely the Mark 7 aerial set was equipped with the Cyldon PC60 push button tuner.
The attachment shows it's application in the 1960 Regentone Ten-17 TV receiver. For the Mk 7 the on-off switch will not be attached to the tuner.
That looks like it'd fit well, so would imagine that'd be a suitable replacement too, but as you have probably seen in the other thread it says PC60/A. The only thing is my set has the markings for 4 channels, not 5 (A, B, C and D) so not sure if it'd have fit through the opening? That photo helps though as now got an idea on what I need to look out for.

Quote:
This was posted by Jayceebee on one of my threads as it looks like I am using the same LOPT as this in my project.
Quote:
Originally Posted by jayceebee View Post
https://www.radios-tv.co.uk/communit...2/#post-108145 Circuit of the cable version in this thread over on Vrat.

John.
Thought it may as well be here as well for information. I know the two threads are for the same set.
I have just had a look at your thread and the LOPTs are physically identical. Thanks for linking the other thread with the diagram, I thought a diagram had been posted here but I was wrong.

Quote:
I would not be tempted to just s/c the heater connections, - unless you have the set connected to a lamp limiter, as you'll be overloading the heater chain by around 16v.
I've just had a look at the circuit that I sent, and the tuner would probably
have been connected at point E10. This is where the SF board would have been connected on the wired receiver; on your model it goes to the I.F. board.

I would suggest that you systematically trace the heater chain back from the 'cold' end with a meter on ohms. (Disconnect the mains first!!) Then you should be able to trace it from the I.F. board to where your o/c point is, i.e where the tuner should be.
The set has only been run up with the lamp limiter and will continue to be so until at least all the waxies have been replaced. I’d imagine the same connectors were utilised so the others could go to the same places. Will have a look at that.

What is the “cold end”? I’ve not heard that term before. I’ve not really worked a great deal with valves before. I’ll have a look at E10 when I get the chance.

I wonder how many of those tuners still exist if they were heavily flawed.

Thanks
‘77
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Old 22nd Oct 2021, 6:53 pm   #14
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Default Re: Rediffusion MK 7

Right, having never seen one of these sets I wasn't sure. I assumed it was a UHF\VHF set. Even so the current taken by the VHF tuner's heaters shouldn't harm anything (short term)
The only worrying thing is not to include HT into the heater chain.
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Old 22nd Oct 2021, 7:18 pm   #15
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Default Re: Rediffusion MK 7

I think they were convertible to 625 lines too. I’ve only powered the set on for seconds at a time to see if the heaters light or not. I think I’ve avoided HT in the heater chain. What happens if it does get into the heater chain? I assume the heaters go OC or something?

Update: Sourced a VHF tuner from a scrapped GEC set so that should be arriving soon

Thanks
‘77
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Old 22nd Oct 2021, 8:23 pm   #16
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Default Re: Rediffusion MK 7

The "Cyldon" tuner was manufactured by Sidney S. Bird Ltd.
From Grace's Guide: https://www.gracesguide.co.uk/Sydney_S._Bird_and_Sons

Yes, it was truly was a terrible tuner. Don't know how Rediffusion dealt with the servicing of the unit, but I remember in the 1962 Regentone model 194 replacing the Cyldon PC60 with a much better Plessey push-button tuner.

Wired versions of the Mark 7 were converted to dual-standard operation.
Complex conversion.

DFWB.
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Old 22nd Oct 2021, 10:43 pm   #17
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Default Re: Rediffusion MK 7

I wonder if the tuner was a major part in the reputation of unreliability, and the set itself was okay? Or was the set itself just as bad?

I’m surprised this didn’t use a plessey tuner, as I believe the chassis is Plessey?

Thanks
‘77
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Old 4th Nov 2021, 4:12 pm   #18
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Default Re: Rediffusion MK 7

Quote:
Originally Posted by 19Seventy7 View Post
I wonder if the tuner was a major part in the reputation of unreliability, and the set itself was okay? Or was the set itself just as bad?

Iím surprised this didnít use a plessey tuner, as I believe the chassis is Plessey?

Thanks
Ď77
This was a Rediffusion own-make chassis. Manufactured at Chessington. The later mark 8 was a Plessey chassis, which was also branded as Defiant & quite a few others.

Rediffusion had previously used Plessey chassis in a number of their early 70 deg. aerial models, such as the CA/17/4B & TA/17/4B. I actually converted a CA model to 625 line only, (and back again) but that's another story!

The MK 7 was never destined to be a 625 line model.

Incidentally the one you have was marketed under the model name of 'Sheerline', on account of it being very slim (at the time) front-to back. Nice polyester finish, if it hasn't cracked...

I wonder how you are getting on with it? Once it's up & running you will need a standards converter, if you don't already have one.


David.
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Old 5th Nov 2021, 10:03 am   #19
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Default Re: Rediffusion MK 7

Oh that's interesting, I'm sure i read 'plessey' on a PCB within the set but I may have imagined that, or got it mixed up with a MK8 as I had read about one of them not long before.

The set is lovely and slim, I think it is one of my slimmest sets. The finish on it is in great condition too, just a little 'dull' but thats okay. It should be easy to work with.

As for progress I've not got any further unfortunately, I was messaged with a prospect of a Philips AT7650 tuner so decided to hold off until I had the tuner or if I was told I wouldn't be getting the tuner I'd carry on without so far.. I've not heard anything yet so I'll send a message to see how it's going. I've got a Hedghog which I use for my GEC so getting a signal to the set should be okay.

Thanks
'77
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Old 6th Nov 2021, 9:07 am   #20
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Default Re: Rediffusion MK 7

Quote:
Originally Posted by 19Seventy7 View Post
Oh that's interesting, I'm sure i read 'plessey' on a PCB within the set but I may have imagined that......
Thanks
'77
Itís possible you saw ĎPressací on the PCB, as that company manufactured PCB panels and other parts for the Radio & TV industry.

Iím sure if Dazzlevision sees this post, then heíll be able to provide some information.

Cheers.

SimonT.
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