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B&W TV Rediffusion MK7

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19Seventie
(@19seventie)
Busy V-Ratter Registered

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. 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.

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 PCBs

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, and then deciding on whether or not it's worth restoring. 

'70

front 2
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Topic starter Posted : 19/10/2021 6:33 pm
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crustytv
(@crustytv)
Vrat Founder Admin
Posted by: @19seventie

Missing still is the tuner,

I'm way out of my depth here and maybe Malc can educate me, but I was under the impression this TV did not have a 'Tuner' as such.

Is this TV a wired system TV (TDUK2/3), and thus only been able to receive BBC and ITV via the Rediffusion system via the signals panel? (similar to a standard IF, but different frequencies). The user being able to switch between the two channels via the windowsill selector box, not a tuner as such. Or is the signal's panel either a TDUK2 or TDUK3 AWOL, Is this what you mean by tuner missing? As I say, totally don't know this TV.

As for no valve heaters, assuming all valves are present, start by checking the chain continuity, valve to valve. However, looking at the heater chain there are E9, H9, E10 & H10 in series. I believe these might be edge connectors, if they are disconnected or missing, this will be why you don't have heater continuity.

Circuit added to others can pitch in, as I say out of my depth on these TVs.

MK7cct
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Posted : 19/10/2021 7:15 pm
19Seventie
(@19seventie)
Busy V-Ratter Registered

I may also be wrong, but I believe that the cable sets had the windowsill selector without a tuner as such and the aerial sets (which is what I have) had a tuner and didn't need the windowsill selector.

I'm not sure if it's a TDUK2 or 3, I can't say I've seen any form of identification on the boards other than "MK6 & MK7 Aerial" on the signals panel. I believe that there's continuity as I've got voltage readings, I'll have another check though. 

Thanks for that diagram, I have another that was sent to me that's split, that looks much easier to follow and may actually have more than the other

EDIT: Sorry, didn't see your edit, those connectors are connected but may not be making contact, will give them a wiggle and a clean and have another go

Thanks
'70

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Topic starter Posted : 19/10/2021 8:23 pm
Jayceebee
(@jayceebee)
Noble V-Ratter Registered

Not an expert on Rediffusion but we did have a couple of cable models in Thorn and that IF board seems to be much more complex than for a SF cable set, it would seem it is an aerial version. As others have said, if the tuner is missing the you WILL have to bridge out two of pins the tuner plug/socket to make up for the missing RF amp and mixer/osc valve heaters.

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Posted : 19/10/2021 8:39 pm
mfd70
(@mfd70)
Active V-Ratter Registered

This looks like an aerial set as it has a belling lee (coax) connector, the wired input would be an octal type, the diagram is for the wired set. In the other thread about the Mk7, I posted a diagram from the field technicians handbook which I think had the chassis layout. This may have had a VHF tuner as Rediffusion also had some smaller scale VHF systems in addition to the larger HF wired type.

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Posted : 20/10/2021 10:03 am
crustytv liked
19Seventie
(@19seventie)
Busy V-Ratter Registered

It is 100% an aerial set, as it's etched into the PCB on the underside. I'm not 100% sure what pins are for the tuner just yet so will need to figure that out. I'm sure tracing the wires back should reveal all. 

Do you have a link to the thread with the diagram? I've not seen that

I'm hoping to be able to bodge modify it slightly to accept a more conventional VHF tuner for the time being (If it seems worth restoring, which I hope and think it will be, it looks fairly low hours.

Thanks
'70

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Topic starter Posted : 20/10/2021 9:43 pm
19Seventie
(@19seventie)
Busy V-Ratter Registered

I can’t seem to determine the two specific wires that are for the tuners valve heaters for some odd reason. I’m at a complete loss here as I can’t refer to the circuit diagram as the tuner section doesn’t 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 I’d think the brown and white should get shorted out, but this doesn’t 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. I’ll do some testing tomorrow when I have some more space. Some valve sockets also seem like they need “tightening” too, which I’ll do too and see if that helps.

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

Thanks

’70

BF4976F8 A766 43B0 9E68 81C8B14F1CAA

 

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Topic starter Posted : 21/10/2021 9:59 pm
mfd70
(@mfd70)
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Here are the pages from the field handbook for the MK7 aerial set;

Mk7 6
Mk7 5
Mk7 4
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Posted : 21/10/2021 10:15 pm
19Seventie
(@19seventie)
Busy V-Ratter Registered

Thanks for posting those, they look pretty interesting. Judging by the A N V, does that mean my set (AT1970) can accept a wired radio input? I'm not sure if I've confused myself there! 

Would be cool if I could get a fireball tuner, I'm sure they're much more common than the Cyldon push button units.

Thanks
'70

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Topic starter Posted : 21/10/2021 10:35 pm
Till Eulenspiegel
(@till)
Famed V-Ratter Registered

The Cyldon PC60A is the not very reliable push button tuner unit that was also fitted in certain RGD and Regentone TV receivers.  Valves are 30L15 and 30C15.

Till Eulenspiegel.

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Posted : 22/10/2021 10:22 am
Till Eulenspiegel
(@till)
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The Cyldon PC80 tuner showing it's application in the 1960 Regentone Ten-17 TV receiver. 

Cyldon PC60

Till Eulenspiegel.

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Posted : 22/10/2021 11:51 am
19Seventie
(@19seventie)
Busy V-Ratter Registered

Would be nice to get one of those tuners. I may have actually sourced a turret tuner which could work. Need to double check size though as the area seems very tight. 

thanks

’70

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Topic starter Posted : 22/10/2021 8:35 pm
Till Eulenspiegel
(@till)
Famed V-Ratter Registered

It would have to be a very small turret tuner, the Philips AT7650 for example. The tuner employed in the Philips Style 70 range between 1965 to 1967.

Much better try and find a Cyldon PC60.  Worth mentioning that Plessey made a compact push-button VHF tuner which was often used to replace the unreliable Cyldon unit in certain convertible and dual-standard RGD and Regentone TV sets. Models 194 and 196 for example.

Till Eulenspiegel.

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Posted : 22/10/2021 9:32 pm
19Seventie
(@19seventie)
Busy V-Ratter Registered

I realised the tuner I was looking at was way too big, being identical to the one in my GEC, other than its mounting brackets. 

I didn’t know turret tuners could get as small as that!

Is the PC60 common? I’d have thought something like that would be fairly rare. I’ll also keep an eye out for 194’s and 196’s. Probably also quite rare but never say never

 

Thanks

’70

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Topic starter Posted : 22/10/2021 11:17 pm
19Seventie
(@19seventie)
Busy V-Ratter Registered

Oh I just realised the 194 and 196 were TV sets themselves, not tuners. Oops!

 

thanks

’70

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Topic starter Posted : 22/10/2021 11:44 pm
PYE625
(@pye625)
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Posted by: @19seventie

Would be cool if I could get a fireball tuner, I'm sure they're much more common than the Cyldon push button units.

Thanks
'70

Having a TV set with one in, and after a fiddly repair, I am quite a fan of the trendy "Fireball". It's a good tuner.

https://www.radios-tv.co.uk/community/black-white-tvs/marconiphone-vt161/

The name conjures up images of Fireball XL5 in my mind and all that great Gerry Anderson space-age stuff 😀 

MV5BNGQyMDI0M2QtYTgxZS00Y2U5LWE2ODctMjY1NWQxYzQxMzhmXkEyXkFqcGdeQXVyMDYyNzQyNA@@. V1

 

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Posted : 23/10/2021 9:49 am
Katie Bush
(@katie-bush)
Illustrious V-Ratter Moderator
Posted by: @19seventie

I didn’t know turret tuners could get as small as that!

How about the tiny little tuner in the ubiquitous Sony 9-90UB? - Now there was a small tuner!

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Posted : 23/10/2021 12:46 pm
19Seventie
(@19seventie)
Busy V-Ratter Registered

I always thought the fireball was a sliding unit for some odd reason, but relooking tells me otherwise. the inside of the fireball isn't much different to something i'd expect to see in a sci-fi programme like that!

@katie-bush I never realised the 9-90s tuner was even smaller, i never gave it much thought. I wonder what the smallest tuner was, if not the 9-90s?

'70

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Topic starter Posted : 23/10/2021 10:32 pm
PYE625
(@pye625)
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No doubt there are better images of a Fireball tuner, but here are a couple of snaps of the one in my VT161.

They are of a compact design compared with others from the same era.

IMG 6106 50
IMG 6107 50
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Posted : 24/10/2021 8:58 am
Nuvistor
(@nuvistor)
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Practical Television August 1961 has an article on the repair of the Fireball tuner, available in the Data library.

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Posted : 24/10/2021 9:43 am
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