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Forum 141

B&W TV Rediffusion MK7

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crustytv
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Posted : 24/10/2021 8:59 am
Till Eulenspiegel
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In the 17" Mark 7 aerial receiver the the press-button tuner was situated on the front panel.  Whatever type of tuner you wish to employ in the 19" model it could be attached to the front panel along with the volume and possibly the brightness control.   The best tuner to use is either the fireball or the Philips AT7650. A scrap Style 70 could be the source for the latter.   Rediffusion did use the Philips tuner in their mid-sixties models.

Till Eulenspiegel.

 
Posted : 24/10/2021 9:40 am
PYE625
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Posted by: @till

 Rediffusion did use the Philips tuner in their mid-sixties models.

Till Eulenspiegel.

That alone would be a good enough reason to use one here, should one become available of course.

To understand the black art of electronics is to understand witchcraft. Andrew.

 
Posted : 24/10/2021 9:57 am
AncientEngineer
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I used to modify a good number of these models, when the grotty Cyldon PB tuner had failed. 

Even smaller than a Fireball, I fitted the very small NSF rotary tuner, as fitted to many Pye sets of the same era. They went straight in with not even a tweak of alignment required..

I used to block off the slot in the side panel, & then use a piece of perspex  as a faceplate, and fit to the front-panel of the TV.  Some of the larger models already had the PB the tuner on the front panel. It should be relatively easy to sort out the connections for the tuner;  using a mult-imeter & physically tracing them: heaters, I.F. input, HT, AGC and ground.

David.

 
Posted : 24/10/2021 12:12 pm
19Seventie
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It really is surprising how small the fireball tuner is, definitely a leap forward in design. Also surprised it wasn't done before, it seems almost too obvious a design. Unless there's something inside which prevented them from being made before?

Having a look at the thread crustytv posted, they're more interesting than I thought a TV tuner could be! Though I have to say they don't look to easy to do component changes on! 

Till Eulenspiegel may have sourced me a Philips AT7650 which will be a massive help and will get it fitted as soon as I can, if it's available. 

I think I'm going to find a way to insert it through the slot, just so it's reversible should i find a tuner closer to the original sometime in the future. I'm not too worried about looks on the side, as that's not where you're usually looking, and it'll be somewhat hidden where it's going to be used anyway. 

I'm looking forward to getting this set working!

Thanks
'70

 
Posted : 24/10/2021 6:41 pm
Nuvistor
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The first Fireball tuners I can find were made by Standard Coil Tuners from the USA circa 1957. Interestingly they used the neutralised triode for the RF amplifier instead of the Cascode type in the early AB Metals type made in the UK. Presume AB metals licensed the design, it too similar not to be the same.

However the Standard Coil version with a neutralised triode possibly gave less gain than the cascode, it would be cheaper to make and may have been used to help cross mod problems in the dense signal areas. That is supposition on my part though.

The 2BN4 triode used had much less gain than the later Frame Grid type PC97 triode used in many UK VHF tuners in the early 60’s.

6D7CCDA1 4F68 4DA7 AC57 AA62815119ED
4BE70B95 0765 4130 A4FB 1A05FD255CA9

Frank

 
Posted : 25/10/2021 1:35 pm
19Seventie
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I wonder if the differences were due to the US standard vs our own? I have no knowledge on tuners, as they've never really been something I've had to deal with, other than changing 2 caps in my GEC. 

Seems that the UK got the better end of the stick with this design! Other than their portables, I'm surprised they were really designed as American sets had plenty of space for an ordinary tuner

'70

 
Posted : 25/10/2021 10:15 pm
Nuvistor
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@19seventie 
USA sets had the 110 degree CRT about 18 months before the UK and also had “Portable” sets so space was at a premium in some cabinet designs. Has for being a USA design I can only go off the timings were they were in use well before UK sets had them,  appreciate still conjecture.
Worth noting that 13 channel tuners for 50 to approx 200Mhz  had been used in the USA since the late 1940’s a good 7 years or so before they were introduced in the UK in circa 1954 for the advent of ITA in 1955. It gave the USA an edge on tuner production. 

The main problem I had with them was like most tuners was dirty contacts, the Fireball was one of the easiest to clean.

 

Frank

 
Posted : 25/10/2021 11:12 pm
Till Eulenspiegel
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In the USA the 110degree CRT was introduced in 1957. Nevertheless, in the UK Pye was quick of the mark late 1958 with a 17" portable TV set, the PV110.

The developer of the 110degree CRT is unknown to me but what is certain whoever was the developer was, the standard of construction was confirmed such as the 28.5mm neck diameter, the B8H base and the faceplate shape.

The 19" 110 degree CRT was announced late 1960. The Ultra V1980 appeared in January 1961.

Till Eulenspiegel.

 
Posted : 26/10/2021 10:12 am
19Seventie
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I had forgotten about their 110 degree sets and portables, that'd make much more sense. I was thinking more of their larger console/table sets. Without going OT too much, what are some symptoms of dirty tuner contacts? My GEC BT318 has a very washed out picture, even after changing the caps. I never cleaned the contacts, didn't know that needed to be done at the time. 

On the topic of tuners, why did we have so many channels, I thought it was well known that we'd never get that many channels on analogue on both 625 UHF and 405 VHF? 

Had a look at the Pye and I quite like that, i think that's another on the wanted list! Never realised the 110 degree sets were standardised either, but that makes sense really. 

Thanks
'70

 
Posted : 26/10/2021 11:52 pm
Nuvistor
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@19seventie 
Depends how dirty the contacts are, from crackly intermittent reception if the channel knob is moved to no reception, although a fault would be reported before that occurred.

Important that no abrasive cleaner is used, most contacts are silver coated and abrasive cleaners will remove it. Very often a rub over with a soft lint free cloth and a slight smear of MS4 grease or Electrolube. Servisol can be used if very dirty but don’t spray it inside the tuner but onto the cloth.

The number of channels were required to stop interference, VHF Band 1 signals can travel a long way so it’s possible to receive  Sutton Coldfield on Channel 4 in South Lancashire. Not a perfect picture but still enough signal to cause interference if the same channel was used for Holme Moss which used channel 2.

It’s the same for Band 3,4 and 5 even though they don’t tend to travel as far. Interestingly the original layout of the 4 UHF channels could cause image interference  to  the highest channel in the group from the lowest, this required a tuned RF input to give the required image rejection, this also I understand would increase the noise factor slightly. Many Continental sets didn’t have this requirement. Thorn usually left it out, not that it mattered a great deal as it was 20 years after the start of UHF transmissions that Channel 4 was put on air.

We were never in the same position as USA for tuner performance, with only usually only one channel in Band 1 and 3 being designated for each area, performance tended to be about gain and low noise. The USA had a number of local high power stations using channels in each Band. They had to balance strong signal performance to reduce cross mod with the ability to receive weak stations for those using the TV set in the rural areas. Not easy as the two tend to require different characteristics.

Corrections etc greatly appreciated, it’s a long time since this was day to day stuff for me.

Frank

 
Posted : 27/10/2021 7:40 am
19Seventie
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Ah so it sounds like my tuner is okay. There's no intermittent-ness to it. Will keep how to clean them in mind as no doubt I'll be getting more VHF sets in the future. 

Interference never crossed my mind, I'd always assumed that say BBC was on channel 3 and ITV was on channel 8 (for example) for both transmitters. I don't know why as I know that isn't the case for 625 line UHF. Never really put thought into it before, though it all makes sense.

I have a couple friends who live in the USA/Canada and when talking about their systems, my god does it get confusing. Still haven't been able to wrap my head round it. It's no wonder they were ahead of us! 

Getting back on topic: Till Eulenspiegel may have sourced me a Philips AT7650 so I've not done much more until I can get a tuner in, I still havent been able to fully distinguish two pins for the heaters and don't want to cause damage. I thought may be best to fit a tuner before going on further, that way I'll get an even better idea, too.

Thanks for explaining all of that though, it cleared a lot up!

Thanks
'70

 
Posted : 28/10/2021 8:49 am
19Seventie
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A couple weeks ago Ancient Engineer dropped by for a visit to have a look at the set. We (I say we, I mean David!) had the set in bits, cleaning all the contacts, testing all sorts. We got to the point of switch on, flick the switch and up goes a resistor. Switch off and call it a day. May not have had the outcome we wanted but it was a good learning exercise for me. We decided it was best to replace the caps around the resistor and to retry, so that takes us to now.

I replaced all six 0.1uFs and the singular 0.25uF wax caps on the IF board, along with the resistor and give it a run up through my lamp limiter. Nothing. I gave the set a check over to find an edge connector wasn't fully connected. Run up again. Nothing. I took the lamp limiter out of circuit and gave her full mains. The heaters slowly come up, then sound rustles up, then a nice healthy sounding line whistle. No picture though. I think the brightness is up full but I go to make sure, I put my hand on the brightness control and a flash on screen, I hold the control in place and get a nice and bright, although collapsed, raster! Brilliant. It's a great feeling to see a CRT light up for the first time in how ever many years

I still have all of the wax caps to change on the other PCB and a tuner to source and fit, but I'm really pleased with the progress made.

Apologies for the poor photo, it was the best I could get

First Light

 

 
Posted : 04/12/2021 11:26 pm
crustytv
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As you've no doubt found when David @ancientengineer paid you a visit, being in the company of an ex trade engineer is a priceless opportunity to learn. Well done on the progress thus far. This should spur you on further and hopefully soon sort out something with the missing tuner.

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Posted : 05/12/2021 10:27 am
19Seventie
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It really was a great opportunity to learn some more, and I'm sure it'll prove invaluable in the future. Thank you, though I have to say a lot of it was down to David! It has definitely spurred me on, I'll be ordering the replacements for the wax caps in due time and fitting them. 

I've had a couple of potential offers for tuners and a couple ideas raised on how to adapt some, so that shall be pretty interesting, when the time comes.

Thanks
'70

 
Posted : 05/12/2021 11:30 am
19Seventie
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Sieve head here completely forgot to do an update

I recapped the timebase panel and the CRT socket, but I'll most likely go over these as some replacements aren't great, using caps in parallel or others tacked in using old leads to reach, a much nicer job could easily be done. 

AncientEngineer has very kindly sourced a VHF tuner and switch bank, and will construct a tuner for me out of the two to fit into the set. 

On powering up the set I still don't get a raster which is a shame, but shorting cathode to chassis I get a very, very bright raster, which is painful to look at, and now with full height too. I'm guessing the lack of a raster is probably down to the lack of a tuner, thus a lack of a signal.  

There are still some odd problems to be sorted, like hearing frame hold pulses through the speaker, but will probably look into this further when I can get a signal into the set as a bit of a guide. 

The picture doesn't show how bright it is as the scan had just gone off screen, so the photo is the persistence showing

Second light

Thanks
'70

 
Posted : 03/01/2022 5:17 pm
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