Philips X25K121 first European colour TV set.

The LOPTX including over wind, GY501/PD500 valve holder stack look identical to the Ekco/Pye dual standard CTV circa 1967.

Hi Frank,

I notice that the IF amplifier is all valve and the luminance amplifier is a PFL200. Having three PCF200 10 pin triode-pentodes as colour difference amplifiers I'd guess the colour decoder is similar to the G6.

"Met de introductie van de K6 werd de "rechtoekige" beeldbuis A63-11X geïntroduceerd. Deze beeldbuis is een directe kopie van het RCA =-=-= model."    That'll be the RCA 25AP22 first introduced in CTC17 models.

Even the back cover looks familiar. 

Till Eulenspiegel.

More pictures of the X25K121 on Marcel's site:

http://www.marcelstvmuseum.com/photoalbum31.html

(My Chrome browser automatically translates pages into English).

Philips cheekily tried to pass one off as a British prototype at the 1966 Earl's Court show!

It's a pity that the YouTube clip is widescreen, that the room is so brightly lit and no attempt has been made to cover the windows!

The programme material shown on the set is widescreen, the actual clip appears normal when I view it. Agreed, the viewing conditions of the actual set could be better, but it does give proof of a very good emission CRT.

It is a very smart set though, I really like the style.

It looks a very interesting set to have worked on, I have never seen one but the all valve CTV would have been different. Looking at the USA sets from the same age, the NTSC sets look much less complicated but there is only the PAL switching circuits that are additional.

Presume the USA set makers had had years to learn what they could trim and keep the set working. The 19inch RCA CTC19 circa 1965/66 was designed to be a cheaper set using innovative circuits, also appears to be all valve except perhaps UHF tuner. How well it worked in the field is another matter I suppose.

I know NTSC has had a bad name in some quarters but properly set up TV with a good signal and the transmission being correct, the pictures are excellent. Evidence the Mexico Olympics in 1968 when the source was NTSC and converted to PAL, the pictures were excellent. Slight HF video resolution difference but nothing that spoiled the picture.

Still the PAL system as proved itself to be excellent under many different conditions.

Sorry a bit of a ramble.

When I was young Sesame Street was one of the few video-taped American shows I watched, & the picture quality didn't seem much less in quality compared to a PAL image.

I think it was low quality news footage quickly converted, & people watching via hotel distribution systems that gave people a bad impression of NTSC.

Posted by: @nuvistor

Presume the USA set makers had had years to learn what they could trim and keep the set working. The 19inch RCA CTC19 circa 1965/66 was designed to be a cheaper set using innovative circuits, also appears to be all valve except perhaps UHF tuner. How well it worked in the field is another matter I suppose.

Hi Frank,

A picture of the 19inch CTC19A model "Bartram"  It's not a very good picture  but it does show that this must be a very compact set especially when one considers it's an valve receiver.

Till Eulenspiegel.

The transistor UHF tuner fitted in the RCA CTC19 series.  No RF amplifier  and a crystal diode is used as the mixer.   The IF output receives further amplification through the valve VHF tuner. See attachment.

With regard to the Philips X25K121 colour TV set, the subject of this topic. It will be interesting to find out what type of multiband tuner was used. I'm certain it was not the UV1 unit as was fitted in the G6. 

Part three of the Philips television tuner history website covers the introduction of transistors in 1964 and later developments.

https://www.maximus-randd.com/tv-tuner-history-pt3.html

Till Eunspiegel.

Posted by: @till

With regard to the Philips X25K121 colour TV set, the subject of this topic. It will be interesting to find out what type of multiband tuner was used. I'm certain it was not the UV1 unit as was fitted in the G6. 

That page link strongly suggests it was:

https://www.maximus-randd.com/tv-tuner-history-pt3.html#at7672

"Well behind the Krefeld tuner development, also the central organization in Eindhoven started its development of an integrated transistorized VHF-UHF tuner, the AT7672 or UV1."

I am reasonably sure some early rotary UHF tuners in Japanese sets imported into the UK had the same type of UHF circuit as the RCA one but with an outboard extra IF amp stage instead of a VHF tuner.

Posted by: @nuvistor

I am reasonably sure some early rotary UHF tuners in Japanese sets imported into the UK had the same type of UHF circuit as the RCA one but with an outboard extra IF amp stage instead of a VHF tuner.

Hi Frank,

                    the circuit diagram of the tuner in the 1970 Crown portable TV receiver model TV201.

Today, I had the opportunity to take a look at the circuit diagram of the Philips X25K121. The line output stage employs two power valves , a PL500 and a PL505.  Much of the colour decoder resembles that in the UK made G6. The all valve vision IF amplifier has four stages using an EF183 two EF184s and the pentode section of a PCF201.    Frame timebase employs one section of a PCC85 and a PL508. A very nice set to have in a collection if one can be found.

Till Eulenspiegel.

Thanks for the information David, my memory cells not quite given up yet. The  USA type of UHF tuner may be a continuation of the early valve UHF tuners of the 1950’s when there wasn’t a good RF amplifier valve for domestic sets, they used a valve LO and diode mixer very similar to the transistor one in the Crown.

From reading various articles of those valve UHF tuners the LO was driven hard and had a short life and the mixer diode gave problems, it seems some diodes worked best if turned around, the NF was much better one way, unfortunately which way was trial and error.

The Philips set looks very interesting, I would have liked to have worked on those.

Hi Frank,

                   The K6 is certainly one set we all would like to work on, at least nowadays because we don't have any  irate customers pressurising us to get the set going for some program they'd want watch later on that day. Over the weekend I had the opportunity to work on a derivitive of the K6, a Philips G6, and a rare one at that, the  26" version made in 1971.  I'll introduce a topic on how the set was restored to full working order in the matter of only two days.  Although saying that there was three of us working on the set, Gary who is Colourstar in this forum, Mikey405 and myself. 

Getting back to early UHF tuners, the circuit diagram of the UHF tuner in the Alba T10.  It's obvious that this unit has had an RF amplifier stage added on because otherwise it is similar in design to the tuners shown in previous posts. A diode mixer is employed just like all the other early UHF tuners.

Till Eulenspiegel.

Posted by: @richardfrommarple

When I was young Sesame Street was one of the few video-taped American shows I watched, & the picture quality didn't seem much less in quality compared to a PAL image.

I think it was low quality news footage quickly converted, & people watching via hotel distribution systems that gave people a bad impression of NTSC.

When I was at college we two 21" RCA NTSC sets and I can assure you that NTSC, as broadcast by the BBC, was excellent! The main reason NTSC got such a bad reputation in the US was that they tried to run before they could walk.

As soon as the National Television Systems Committee gave the go-ahead for the colour system that bears their initials, they couldn't wait to get on air fast enough. Apart from the reliability of early sets - another bad name! - the transmitters and distribution circuits had only been designed for monochrome and, bearing how long many of those circuits were, it is not surprising that they suffered badly from differential phase distortion.

Differences in phase between programmes from different sources and stations weren't a problem - you just adjusted the hue control for natural flesh colour and everything fell into place. But when the phase changed at different video/modulation depths, you couldn't do anything about it!

Our lecturer once told us of an important difference between UK and US, which applies equally to monochrome. In the UK the broadcasters leased their camera tubes from Marconi et al - it seems it was common practice back in the day - London Transport leased all their bus tyres! - but, in the States they bought them and, all being commercial operators, they demanded value for money and so long as they produced some sort of picture, they stayed in service! Of course, here the ITV companies had no choice but to follow the BBC's attitude to quality.

Certainly, the terrible smearing apparent on some optically converted monochrome material couldn't be put down to the conversion method although, of course, that was far from perfect, anyway!

I recall being in a customer's house repairing a Dynatron colour set in 1968 when the trade test transmissions had been replaced by live satellite coverage of Bobby Kennedy's funeral. Fortunately the customer left us alone to carry on her housework and didn't see some of the appalling pictures we saw.

One shot in particular was behind and slightly above the motorcade as it progressed along a country road. All the vehicles had their lights on and there was a line of red lights along one side of the motorcade and a second one on the other side of the hedge slowly moving up the field beside the road!

Hi Terry,

                I'm glad you have come to the defence of NTSC colour, in fact if you think about it the vertical definition of NTSC should be better than PAL because there is no line delay element in the decoder.  The delay line error cancelling works on the principle the content of the delayed line will not be all that different from the direct line. In most cases this is so, however, if the lines do differ in any way then there will be incorrect colours. In practise PAL does works extremely well and all phase errors are corrected and the only trade off is a reduction of output signal amplitude when errors are present.  

In the US didn't they introduce some method of phase error correction into the NTSC transmission specification?

Those that seen it say that 405 NTSC colour was pretty good as well.

Till Eulenspiegel.

Posted by: @till

In the US didn't they introduce some method of phase error correction into the NTSC transmission specification?

Those that seen it say that 405 NTSC colour was pretty good as well.

I can't see how it would be possible to introduce phase error correction to NTSC in a way that would be compatible with existing sets. You could always convert it to PAL of course, and make every existing set obsolete overnight, I suppose! ? 

Improvements were possible, though - as I alluded to in my previous post. Simples! Pay attention to the quality of transmission and distribution systems and equipment. Derive suitable test signals to enable these parameters to be adjusted and checked. Don't forget that the BBC and a Rank unit visited Russia and showed that it was possible to send NTSC down a 1,000km line and back again without loss of quality and the Russian engineers couldn't tell the two pictures, before and after, apart. (They must have used slides for this A-B test as the time delay would have let the cat out of the bag with moving images!)

Of course, this was before de Gaulle got in on the act and brought politics into it.

As for 405 NTSC, when I saw a demonstration at the Earls Court Radio Show about 1959/60, where all the manufacturers* demonstrated their experimental prototypes in one long gallery, it was very good indeed.

* Bear in mind that this was before  the groupings that we saw later in the 60s took effect, so there were quite a few!

I have read but more importantly not completely  understood the following article on colour correction with NTSC colour TV but as you say Terry it would only be available in later TV sets. This is from the 1970’s. I will have another read. ? 

americanradiohistory.com/Archive-PF-Reporter/70s/Electronic-Servicing-1976-07.pdf

Page 30.

Hi Frank,

                    that's the article I've been looking for:   "Automatic Color at Last!"  There's little information this side of the pond about the improvements to the NTSC transmission technique but the magazine article helps us to understand how the error correction works.  

Till Eulenspiegel.