B&W TV Rediffusion MK7
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.
Rediffusion did use the Philips tuner in their mid-sixties models.
That alone would be a good enough reason to use one here, should one become available of course.
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.
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!
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.
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
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.
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.
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.
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.
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!