Improving old TV sets.

[Geordie McBoyne]

Many mid fifties TV sets were to put it bluntly made on the cheap.  Yes, there was  a lot of cheap and nasty TV receivers about in those times, however, the set I've chosen for this topic was although reasonably priced it certainly wasn't nasty.

The 1952 Sobell T143:  This receiver always had only just sufficient picture height to fill the CRT mask, very little spare picture height to compensate valve and component aging.

In the Sobell T143 the frame blocking oscillator is supplied from the main HT supply. Later models such as the T144 and T145 employ a modified frame oscillator circuit. In the later sets the frame oscillator is supplied from the 320 volt boost HT supply. This modification has been carried out in my T143. As can be seen from the attachments there is now plenty spare picture height along with an improvement to frame linearity.

So to date the set has been fitted with Mullard AW43-20  electrostatic focus CRT and now it has an improved frame timebase.
Lets find out if any other modifications can be done to this set to improve it's performance.
Many major TV rental firms carried out modifications to TV receivers during the time the sets were in service.

Geordie McBoyne.

[ppppenguin]

[Dons asbestos safety suit]

I'm sure there are some sets that would best be improved by a short journey to a long drop

As GMcB says, many sets were made on the cheap and it shows. Some sets, like the notorious HMV1807, suffered badly from the relatively poor quality capacitors that were standard at the time. Even later on, component problems didn't go away. Even the mighty Mullard made the appalling PCL85, cause of so much grief until they replaced it with the PCL805.

[Geordie McBoyne]

Hi Jeffrey, the 1807 was a truly terrible set and yet in terms of cabinet construction and quality it was as good as any any other EMI product. I'd guess that EMI tried to compete with the true masters at making low cost TV receivers, Sobell.
The very first Sobell TV sets were beautifully over engineered but before long the company realised low cost reliable TV sets were the only way to survive in a very competitive market place. The first low cost Sobell TV was the T90 of 1949 which was a neat little 9"CRT table model. A year later the T121 came along. The circuit design of this set was almost certainly derived from the Mullard application notes. The T121 was housed in a Bakelite console cabinet.
Possibly the worst 405 line TV set ever made was the Spencer-West 9" portable TV, it was made in 1957.
With reference to the PCL85, in competition with Mullard Ltd. Mazda developed the reliable 30PL13 for service as a frame output valve in TV receivers equipped with the 110 degree CRT. Clever thing about the 30PL13 and 30PL14 was that it was pin for pin compatible with the PCL82. Manufactures didn't need to redesign PCB artwork in order to use the new valve. For example Regentone and Rediffusion employed the 30PL13 in lieu of the PCL82 in TV receivers that were originally designed to employ 90 degree CRTs.

Geordie McBoyne.

[ppppenguin]

It's a definite art to make a product that's both cheap and good. Cheap is easy, good is a little harder but no too bad if you have the budget but doing both at the same time is much harder.

[Murphyv310]

Hi.
With modern decent components most sets that we restore will no doubt be far more reliable than they were early in their life.
To be honest some sets really could have been endowed with better design and parts, just as today they were made for a price.
Look at the humble TV22 and the Pye V4 for example, both sets had poor line transformers, EHT regulation left a lot to be desired and often de-focussing occurred at high brightness and contrast levels.
Certainly David's mods on the Cossor are worthwhile and will improve the set. What about the HMV that had its front end modified by an unknown person many years ago, how is it performing?

[Geordie McBoyne]

Hi Trevor,
             The HMV continues to work very well indeed.   Only the sound needs attending to.   Picture interlacing could be better and the only way to achieve near perfect inlerlace is by critical adjustment of the frame hold control.  The unknown engineer must have been aware of this problem because a Pye type of interlace filter module had been introduced into the circuit.  The original HMV 1804 and Marconi VT50 employ a D63/6H6 double-diode as the interlace filter, but only one diode section is used. It's V8 in the EMI circuit diagram.  I'm certain it would be much better to employ both diode sections and reintroduce the Pye "positive interlace filter" circuit.    The attachment shows the interlace filter circuit employed in the Pilot CV34, it is very similar to the circuit which was used in the Pye FV1 series of TV receivers.                                                                                                                                                             Mike Barker rewound the original EHT transformer, now the EHT circuit is delivering a stable 4KV to the CRT anode.   The CRT is surprisingly bright considering it is the original.

Geordie McBoyne.

[beamcurrent]

I'm not at all sure I agree with improving sets beyond their original specification, careful repair is OK with new components, if no suitable old ones are to hand.

If you have a 1950's set it is a 1950's set and you need to accept it for what it is. It is a point in the development of radio and TV and it's performance reflects the age it was made in. Future historians and collectors will curse your improvements.

In a parallel collecting world if you have a vintage car you try your best to restore it to as it was made. At a car show there are no points to be had for upgrading the engine.

A similar scene is the vintage military radio collecting world, many being spoiled by improvements. recently a clean and unmodified WS No. 19 sold for £1500, possibly 3 times the going rate!  


I am now sat in my nuclear bunker hiding under the table with a brown paper bag to hand.

[Murphyv310]

Hi Brian.
I'm not sure I fully agree..... although I do see your reasoning.
The way I see it is if you do a modification and design it well all in the context of the era it can do no harm. if it is documented it of course can be reversed. I see no real difference in doing a well thought out modification or fitting modern polypropylene capacitors rather than the wax types or even hiding a modern component inside a wax cap outer covering.
We constantly talk of up coming collectors, I'd actually like to meet some of these people, collectors now rarely have sufficient technical know how to repair and restore these sets, we are a dying breed and there is very little new blood (young people) even interested.
Think back to the 40's right through to the 70's, we were awash with businesses selling parts, valves, kits, second hand military gear etc. This has gone, even the weekly Military Auctions at Lanark market have stopped. In the main prices have tumbled other than a few items its gone.
Think of the number of 50's cars that have been fitted with Ford Sierra 5 speed gearboxes or with electronic ignition and modern solid state fuel pumps rather than unreliable SU contact type pumps.
I got terrible abuse on VRAT when I fitted a Jellypot to a TV22....... Why? its my set and mine to do as I wish, I could chop it up for bits if I wished. I think we need to be realistic and to draw young ones into the hobby we have to realise that this stuff is old and to keep it running we may need to introduce parts that are more modern (which we do with caps, resistors, PVC wiring etc) and if that means LOPT substitution then fair enough. We either have a TV working or one languishing on the shelf doing nothing.
To my mind a mod like fitting an electrostatic focussed tube replacing a magnetic duff one is sensible to do especially when its a 14 inch that are like rocking horse poo, same with LOPT's.
This has to be the individuals choice don't you agree?

[ppppenguin]

The restoration vs conservation question is a never ending discussion in museum circles. if we wish to restore to working order then some changes are inevitable. For example using modern capacitors. My view here, partly born of laziness but also of honesty, is to use modern parts visibly except where doing so would be a real eyesore, such as some smoothing cans above chassis.

In the case of one of David Boynes' sets it had already been extensively modified when it was relatively new. In this case he's working out what a previous highly skilled engineer did and why. For common sets there is no harm in experimenting. For rare or unique ones you need to think more carefully.

As for cars, one of my neighbours has a 1904 Wolseley. Beautifully restored and regularly run, both locally and in rallies such as the London to Brighton. One mod he's made is to fit an electric headlamp, powered from a battery concealed in a box. The whole arrangement looks authentic unless you observe very closely. It makes the car much more usable and arguably safer at events such as the London to Brighton. It's a reversible mod as he has kept the original parts. I would find it hard to quibble with what he's done.

[Murphyv310]

Hi.
I was also thinking of museums bar say the Museum in Dulwich. Any one I have been into that has old Radio's & TV's on show are display only none are working.

Back to vehicles. I have contact with many that have restored cars over the years and I regularly visit car shows up here. The modifications to old cars are countless. Many are done to improve braking, safety, lights, and suspensions mods. Heads have hardened valve seats fitted for unleaded petrol, this is a modification, alternators fitted, again a modification. Radial ply tyres instead of crossply's, Halogen bulbs, as previously mentioned the use of Ford Sierra gearboxes in MGB's and many other types, these are all mods and they are not frowned on by the car enthusiasts in fact they are a plus. Many cars that go through a full rebuild get galvanised, surely that is a mod as originally it didn't even have a proper coat of paint let alone any form of rust protection.
So why all this protectionism about old electronics? I'd rather see or hear a set working and if that means a mod so be it.