Philips TX500U Fixing

[Mikey405]

Hi everyone.

Several weeks ago my pal Tone and I went over in my trusty Renault to The Netherlands to collect a monster Philips 21KX100A colour TV that I’d bought from a retired Dutch TV engineer. As part of the deal came a 12 inch 625-line Philips TX500U TV from the early 1950s. I’m not really sure of the exact year because apparently the TX500 and its smaller brother the 9 inch TX400U started production in 1949 and carried on until 1952.

The set itself, the first 625 line set made (well, the second if you count its smaller brother the TX400U) is a bit of a monster for the relatively small size of the tube and a little bit on the ungainly side; the sets being known as the “dog kennel” in The Netherlands. The valve count is quite something – 22 valves not including the tube, and all valves except one “Rimlock” valve have B9A bases.

Anyway, to business… The first thing we did was to re-form the 10(!) main HT smoothing caps – this didn’t actually take long as we connected my Heath-Robinson death-trap capacitor reformer to all the caps at the same time in typical bodge-worthy fashion. It turned out that they were all in remarkably good condition though and in no time at all were all holding a good charge. (Well, they would have done but for all the other leaky caps decoupling the supplies all over the rest of the set discharging them.)

After an hour or so on the reformer we decided to apply mains to the set (not the full macho 240 volts brute force of the British mains, but a slightly more genteel 220 volts of that special European variety piped in specially all the way from France to my dining room). After a minute-or-so we had a bit of crackle through the speaker but not a lot else.

First of all we checked to see whether there was any action going on in the line output section but alas there was none. There was HT on the Anode of B20 (the PL81 line output valve), some voltage on the screen grid, but not a thing on the control grid. Working back to the line oscillator revealed that there was no HT on the anode of B19 (the ECL80 line oscillator); this was traced to an open circuit 3.3K resistor (R6 from the power supply) feeding both anodes of the valve. On replacing that and powering up again (and this time with my ancient Telequipment scope wired up to the grid of the line output valve) we had an output from the line oscillator – sort of, but still no line output or EHT. When I say “sort of” what I mean is that the frequency was rather too low. Through the speaker we could hear a “click, click, click…” noise – about 2 or 3 clicks per second – and on the scope we had a nice healthy negative pulse from the line oscillator but just at 3Hz instead of 15,625Hz. After a bit of cold component checking, this was traced back to the 680K grid resistor in the pentode section of the line oscillator valve having gone open circuit. Replacing this resistor and turning on again revealed a picture – Hooray – although it wasn’t really much of a picture, just a horizontal line really. Twiddling with the height control brought up a little bit of frame scan but not really very much.

I could witter on now about how we changed each capacitor in the frame stage one or two at a time and how the frame slowly improved after each cap change, but it would be deadly dull so, to cut a long story short I’ll just say “we changed each capacitor in the frame stage one or two at a time and the frame slowly improved after each cap change” and leave it at that.

Once we’d got the frame into some sort of order, we decided to feed in a signal. This was bodged in by wiring an unbalanced coaxial feed from my European VHF modulator to the balanced input on the back of the set, and supplying the modulator with a 625-line test card signal and a bit of jolly test card music from a nearby laptop. The tuner was very touchy and twitchy but eventually we did manage to resolve some kind of low-contrast over-bright rolling test-cardy-type image and some very distorted sound on channel 3. We managed to stabilise the rolling picture by changing a couple more of the normal Philips black pitch caps in the frame stage. (As an aside, most of the horrible leaky pitch capacitors in the set were replaced with old-stock Philips “Mustard” or the bright-yellow Vishay “Custard” caps, but not a single electrolytic needed to be changed.)

After we’d sorted out the rolling picture, attention was turned to the uncontrollable brightness and poor contrast. This turned out to be R102 open circuit, a 3.9K resistor feeding the screen grid of B16, the PL83 video output valve. Unfortunately, after replacing R102, the brightness was then way too low and no amount of fiddling with the ion-trap magnet could improve matters. On measuring the A1 voltage though, we only read about 75V – This turned out to be another very leaky capacitor – C22 – which was then replaced with another bright-yellow Vishay MKT “Custard”.

Another few caps were replaced to sort out slightly poor sync and to centre the line-hold control until (after every single black pitch cap had been changed) we were left with a lovely picture.

The 5.5MHz intercarrier sound, however, was (and is) another story. The tuning is exceptionally critical to get any sound at all and even then it is quite distorted. The set uses an EQ80 nonode valve as an FM limiter and intercarrier sound demodulator but the circuit looks quite complicated to a simpleton like me and I’m not entirely sure how it works. I will put another thread up about this issue though.

And so, that was it – a reasonably straightforward restoration (sound aside) completed in a day. The set now produces an outstandingly good picture – I really have never seen a set of this age display a picture like it. It is of course 625 lines so you do get almost 200 lines more than an equivalent British set, but the picture really is stunning and has to be seen to be believed.

Thanks everyone for reading.

Kind regards.

From Mike.

PS. Better resolution versions of these pictures can be downloaded here: http://www.oldtechnology.net/misc/TX500U.zip

[Colourstar]

Hi Mike- wow, what a lovely set! I see that some liquid refreshment was required to see you through the ordeal. Tone can really put 'em away can't he? I don't know how you keep him in check. I trust this was some time after the ultra-safe cap reformer was deployed... Fascinating to see a 625 line set of such an early vintage. Great write-up too as per usual. Steve

[mark pirate]

I have always been impressed with the picture quality on these Mullard 9" tubes, I can only imagine how sharp the picture must be on 625 lines!
Philips sets always seem to have been good performers, I am sure you will sort the sound/tuner issues.

Mark

[Heatercathodeshort]

Oooooo! What a cracker! A PL83 used as video output with a 12" tube. That is what you call a full spec receiver. I can't follow the EQ80 FM sound circuit either! Looks a bit like the EH90 locked oscillator circuit used on the Pye 11U series and many GEC receivers.
Tuning was critical but once set up performed well.
A great repair/restoration Mikey. Those pitch capacitors held up very well over the years but are found to be all shot these days. You took rather a long time me thinks.... Regards, John.

[Tazman1966]

I love the idea of "a buy one get the cheapest one free"
A cracking write up and a great result too.

[Maarten]

Nice find, especially the K4.

I think production of the TX400/TX500 would have started around 1951, but I can be mistaken. The production date can be determined as close as possible by collecting all date codes from IF cans, transformers and the deflection yoke. The set will have been built not too long after the most recent date, except in case of repairs which will be obvious from the other date codes.

[bobbyball]

I had wondered when the big Philips would arrive but nice to see the little'un working. Look forward to seeing them both (in action!)... I have a 625 line set from about '58 - that Swedish "Dux" contraption that I had from Steve. Your set predates mine of course!

[Mikey405]

Thanks Steve, John, Mark, Tas, Maarten and Bobby for the kind and interesting comments. I have to admit that I did add a few cans and bottles just to make the picture more interesting, although I think most of the Stella cans were genuine. I wonder if anyone noticed my deliberate mistake about "almost 200 extra lines" between 405 and 625 lines. Ha ha.

Thanks again all.

Kind regards.

From Mike.

[Nickthedentist]

Originally Posted by Mikey405

I have to admit that I did add a few cans and bottles just to make the picture more interesting...

Ha ha, I didn't even notice them until you pointed them out. Must have really been concentrating on your lovely telly

[Jac]

Originally Posted by Mikey405

I wonder if anyone noticed my deliberate mistake about "almost 200 extra lines" between 405 and 625 lines.

Still, it is about true, if you only count the number of active lines (that contribute to the visible picture content)!

Jac

[PE9ZZ_JO22KI]

Sound is finicky because it's not intercarrier but instead demodulated at 16.5 MHz. The EQ80 is a self-limiting quadrature detector. The TX400/500 manual contains a lengthy explanation of it. It never gained traction and was quickly replaced by the ratio detector (and intercarrier sound at 5.5 MHz).

I really have to finish my own TX500 soon now! Speaker cloth I now have.

Tjerk, 9ZZ

[Maarten]

Regarding the comment on your site: Knowing Philips, they probably used the speaker cloth cutouts for radio sets. Or initially they didn't but then some employee earned a 2,50 guilders bonus by suggesting that they should do that.

[FERNSEH]

Hi Mike,
The TX400 and TX500 are an important part of European television history. The first production 625 line receiver.
I look forward to seeing the set when I'm down your way sometime in the near future. Enjoyed your write up about the restoration. It would be interesting to see a 625 line picture and a roundie CRT.

Is it true that Russia made the first 625 line TV receiver? The KBH49

DFWB.

[PE9ZZ_JO22KI]

Finally done my speaker cloth. Not really to my liking but it's my first attempt to fix something like this and in any case a huge improvement over the torn and faded original cloth.

Now I have to fix the sound and contrast/AGC circuitry.

Tjerk, 9ZZ

[Mikey405]

Originally Posted by FERNSEH

I look forward to seeing the set when I'm down your way sometime in the near future. It would be interesting to see a 625 line picture and a roundie CRT.

Hi David.

That sounds excellent.

It never occurred to me that I'd never seen a 625 line picture on a round tube before (Not a mono tube anyway). It is amazingly sharp and clear and you'll be impressed, I think.

Thanks David.

Kind regards.

From Mike.

[Mikey405]

Hi all again.

Well, the sound and the tuner are now working okay again. The sound turned out to be a couple of things. Someone had replaced the first sound IF valve with an EF183 (which has now been replaced with the original type EF80) and also it looks like the phantom twiddler had been in there too. Setting up the sound wasn't too hard although trying to work out the Dutch service manual took a little longer. Using various Internet translation sites I think I have it correctly, although perhaps Maarten or Tjerk or Jac might be able to advise (I wasn't sure what that last paragraph was about and the translation sites seemed to have a bit of trouble with it too. I assume it's about the damping but I'm not sure.):

Dutch Version:

M.F. GELUIDSKANAAL

1. Sluit H.F. generator aan tussen g1 B4 en chassis.
2. Schakel diode voltmeter over R25 (meetbereik -3 V =).
3. Voer ongemod signaal toe van 18 MHz.
4. Regel S7, S8, S9 en S10 ruw af op maximum uitslag.
5. Verstem S7. Regel S8 af op maximum.
6. Verstem S8. Regel S7 af op maximum.
7. Regel S9 en S10 af op maximum.

N.B. Verstemmen door 1500 pF + 470 ohm tussen top kring en chassis te verbinden.

English Translation:

M. F. SOUND CHANNEL

1. Connect H. F. generator between B4 g1 and chassis.
2. Connect diode voltmeter across R25 (range = 3 V).
3. Inject 18MHz unmodulated signal.
4. Tune S7, S8, S9 and S10 roughly for maximum results.
5. Damp S7. Tune S8 for maximum.
6. Damp S8. Tune S7 for maximum.
7. Tune S9 and S10 for maximum.

N.B. Farthest Emmen by 1500 pF + 470 ohms between top circuit and chassis to connect.

Anyway, following those instructions, it was clear that the sound was off tune an awful lot. Setting both coils for maximum voltage on the meter sorted it right out without too much hassle. (Thank you Tjerk for your Intercarrier / Quadrature sound explanation BTW.)

The tuner however was a swine. The band 1 / band 3 switch was causing all the scratchy tuning (along with the earthing brushes). Cleaning and lubricating the earthing spring "tags" was relatively easy but trying to reach the switch (or even to see it) was a swine. In the end I just had to make a few educated guesses as to where the contacts were and give them a squirt of switch cleaner / lubricant without filling the whole tuner with the stuff. Eventually the tuner was put back together and it was successful.

Finally the implosion screen was removed and given a good clean and that was that. The unit was boxed up and is now working a treat downstairs. One modification I think I may do is to subtly mount a dropper resistor somewhere so that the set can be used on 240V mains.

As an aside, I was doing a bit of poking about on the web regarding the date of the TX400U / TX500U and I have found some Philips TX400U documentation which is dated November 1949, although this particular set is very likely 1951 (as Maarten said it probably would be) judging by the codes on various components.

Thanks all.

Kind regards.

From Mike.

[Mikey405]

Originally Posted by PE9ZZ_JO22KI

Finally done my speaker cloth. Not really to my liking but it's my first attempt to fix something like this and in any case a huge improvement over the torn and faded original cloth

Hi Tjerk.

That does look like a lovely job. I think my cloth is a little faded but apart from that (and some paint splatters) I think it has survived fairly well.

Thanks Tjerk.

Kind regards.

From Mike.

[line sync]

Well done with the restoration of that Philips TX500U.
Your lucky to have a very healthy crt and what a sharp focused picture.
I restored a Philips 385U a few years ago and every black tar capacitor in that was leaky.
I didn't realise these were the first production 625 line receivers .

Robin

[FERNSEH]

Hi Robin,
Your Philips 385U was designed in Holland, it is very similar to my Eiffel Tower model TF394. Most likely the TX500U was designed by the same team. However, I believe that the 1101U along with all the later UK sets were designed in Mitcham.

DFWB.

[PE9ZZ_JO22KI]

The cloth on my TV was really torn, guess due to a cat... In any case, I inherited this TV from someone who is no more among us and it was pretty much taken care of. All dodgy parts had been replaced, not only the "teerknollen" but also most of the power resistors. My contrast problem is prolly due to a duff EF80 but I'll have to investigate.

Tjerk, 9ZZ