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Rediffusion MK10 / MK11 Wired

 
mfd70
(@mfd70)
Trusted V-Ratter Registered

I also hauled the other Rediffusion set onto the bench, I don't know if this is a MK10 or 11, the MK11 manual I have looks correct, certainly layout and boards, though component values might be different. For those  who are not familiar with these sets, they are extremely easy to service, or at least remove boards. The LOPT, stab board (line output) and SF (signals) panel can all be removed in seconds, Steve had already warned me the overwind may be faulty but I started with the tube, the original Mullard I assume. My BK tester showed no emission at all ! I spent several minutes of sanity checking, base, tester, tube type, wiring, but no emission ? Clean/Balance however got a slight flicker, and after a few goes I was at least in the lower part of the bad range..Its off to the re-gunners when I get the time machine working.

Getting signals from a HF translator (also kindly supplied by Steve-Colourstar) the set produced a reasonable picture (both are 16:9 the raster is full height), it looks like the EHT regulation is poor since the picture is OK at low brightness but balloons at higher beam currents after a while this gets worse and I can hear the line output (which I can't normally on 625) so it may be the overwind, but would a low emission DY802 cause this ? I'm sure Ive got one somewhere.

I'm really pleased to get this set as it really is a reminder of childhood, during the seventies most of my extended family and neighbors had these in various guises, terrestrial TV reception was still problematical in some parts of town and the wired service was ubiquitous. We had the larger "Hereford" version of this TV when I was young, it developed a severe hum bar and a very low tube just before we upgraded to colour. Other relatives also upgraded with most gone by the early eighties, my grandmother held off colour until about 1987 by when her "Porchester" was barely able to produce a picture at all due to a dead CRT. I don't think Granada who had bought Rediffusion were bothered with renting out monochrome TVs by that stage, they must have abandoned them soon after.

The other memory of these sets was the schools 23" version on a large stand with external speaker, by the time I started work for the education authority any faults with these were dreaded and most were scrapped ASAP.

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Topic starter Posted : 23/05/2019 9:38 pm
malcscott liked
Tazman1966
(@tazman1966)
Reputable V-Ratter Registered

I'd try a new DY802 first although there maybe some residual damp in the overwind.
It's always nice to get hold of "childhood memory" pieces of technology. The older I get, the more I feel like this!

Tas

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Posted : 24/05/2019 7:07 am
malcscott
(@malcscott)
Noble V-Ratter Registered

Hi, the set is a Rediffusion 2T2010(Durham) EHT regulation should be very good with the valve eht rec type loptx. The faulty loptx were returned to the Rochdale plant to be triplerised. Diss one end of the focus pot should increase brill, also the 220k/0.01 boost feed on the top of the stab board is worth a check. Very reliable sets, Malc.

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Posted : 24/05/2019 7:49 am
neil1974
(@neil1974)
Honorable V-Ratter Registered

Its nice to see a picture on this set at last as I would never had got it going ? .

Cheers

Neil.

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Posted : 09/06/2019 7:16 pm
mfd70
(@mfd70)
Trusted V-Ratter Registered

I had this set back on the bench today, the set is a lot happier on 625 than it is on 405, the line output sounds very distressed and there is occasional line collapse, yet on 625 it seems ok, I've fitted new line output and boost diode valves this improves warm-up time, also as suggested lifting the earth end of the focus pot brightened up the picture. I think the next step to to take a look at the stab board as the picture width to big and the boost volts high at 900V and not adjusting (measured with an AVO) and also the system switch.

Meanwhile I've just won the guts of another HF converter on ebay and have made up a mockery of a wall switch so hopefully I can get a couple of TV and a couple of radio stations on there for the full retro effect !

wall switch
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Topic starter Posted : 09/06/2019 9:29 pm
malcscott
(@malcscott)
Noble V-Ratter Registered

A modification was to fit a 10k resistor in series with the vdr on the stab board. Very early stab boards had close mounted valve bases. These were replaced on sight with stand off types. Malc.

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Posted : 10/06/2019 9:09 am
mfd70
(@mfd70)
Trusted V-Ratter Registered

Despite the poor tube, I've been using this set as a workshop TV and radio, however the old trouble has now returned, the EHT has dropped to about 6kV and as what is visible of the raster is the correct size, I guess the overwind has given up.  I know these LOPTs were repaired with triplers, but does anyone have any ideas on a suitable unit ?

I've got some 30AX universals and a radar unit but doubt either of these would be suitable.

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Topic starter Posted : 12/08/2019 10:13 pm
malcscott
(@malcscott)
Noble V-Ratter Registered

I would try a BRC 950/1400/1500 3 stick tripler first. The eht tuning cap may need a bit of change in value, Malc.

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Posted : 13/08/2019 7:40 am
crustytv
(@crustytv)
Vrat Founder Admin
Posted by: @mfd70

I know these LOPTs were repaired with triplers, but does anyone have any ideas on a suitable unit ?

The info you required has always been readily available and still is, up top via the "blue menu bar".  Look under the "Service dept" menu. I think a lot of folk tend to forget all the useful "free-to-view" technical & service info I provide via the blog, which is a shame as a lot of work went into it.

Service Dept | Colour TV | BRC Thorn Info | Thorn ‘Jelly-Pot’ LOPT & EHT Tray

Crusty's Collection: Read the repair blogs
Crustys Youtube Channel: If you want to follow me on Youtube, please consider subscribing
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Posted : 13/08/2019 9:55 am
Anonymous
(@anonymous)
Illustrious V-Ratter Deactivated Account

RDF was a great company to work for and the guys were so friendly, my favourite TV was the MK3, preferred it to the Last Mk4.

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Posted : 14/08/2019 9:21 am
mfd70
(@mfd70)
Trusted V-Ratter Registered

Having a bit of time spare on my day off, I thought I'd take another look at my MK11 set with the EHT overwind issue. As I've only got colour triplers I tried an ITT unit which I think came from a CVC5. Two white wires and one black, I tried connecting one of the white wires to the point where the overwind went and measured the EHT, which was a bit low at 12.5kV so I tried connecting the black (earth ?) to chassis this brought the EHT up to 18kV but resulted in a very narrow picture, but quite good considering tube. There didn't seem to be any distress in the line output, but I didn't leave it on too long or take any voltage readings just in case. The picture was also quite narrow with the overwind fitted, but EHT was very low, so maybe an underling line output fault ? I've already replaced the PL504 and PY81, any thoughts ?

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Topic starter Posted : 15/04/2020 8:43 pm
crustytv liked