Thorn TX10 - did they ever fit RCA S4 CRTs in it?

[dazzlevision]

Hello,

In the Thorn TX10 service manual, it states the chassis was designed to drive either Mullard/Philips 30AX or RCA/Videcolor S4 CRT types, but I have never come across a TX10 set with an S4 CRT fitted.

Has anyone come across a TX10 with an S4 CRT fitted?

I ask, as I have a 26" Rediffusion Mk4A and they only fitted the S4 CRT in this chassis (22" & 26" versions). The CRT is a bit tired and I recall that S4 CRTs were not long lived.

I am toying with the idea of fitting a 30AX CRT into my Mk4A set but wonder if the chassis will drive it. The CRT base is probably going to have to change, but will the focus potential or the scan drives need to be modified?

Your thoughts, please.

Many thanks,


Dazzlevision

[Welsh Anorak]

Hi there
I have certainly come across TX100s with odd tubes (not sure if they were S4s as they were 'white label' types) made for Currys and branded Logik. Can't recall a TX10 with one though.
Regarding your conversion the TX10 manual might be of use if it details the differences they implemented for this CRT - if they ever did - and you can look for similarities.
The EHT, focus and A1s will be broadly similar, and heater current can be worked out.
Scan coils will be completely different so some - a lot - of experimentation might be needed here, but again resistors and capacitors (and an EHT meter) will usually get that going. The part of the circuit that may pose more of a probem is the primitive auto greyscale. Mk4s used an unusual decoder IC and you can see the autogreyscale trying its best with the (usually) hopeless CRT until it reaches a compromise.
Still, it shouldn't be impossible - the Mk4 is capable of excellent results and it would be nice to see it get a CRT it deserves - the 30AX can give oustanding pictures.
Glyn.

[bobbyball]

I had a batch of ex-rental TX10's some years ago (think they were ex-DER) from one of the disposal outlets. They were a "basic remote" with ultrasonic two button affair. Looking inside one of them I was surprised to see a CRT with a thin neck, nothing like the 30AX tube I was used to. I don't remember the type number but I guess it must have been the "S4" type mentioned above. Gave a rather "dull" picture if I remember but then these were ex-rental sets...

I am guessing but if the TX10 chassis was designed to drive both types of CRT, then, in theory, it shouldn't be "too" hard to modify the Rediffusion chassis, providing a suitable tube base could me made up. Rather a labour of love however I suspect!!

[MALC SCOTT]

The 22 inch Logik TX100 did use 30AX and Videocolour S4 tubes. These MK4 sets produce wonderfull pictures when a decent crt is fitted. I have a 22 inch mk4 which needs a crt, Malc.

[Red to black]

Yes some early TX 10s did use an RCA crt, as did some TX100s

The early TX10 PC1500 chassis (MK1) used the PC1503 crt PCB for the 30 AX, the S4 used the PC1507 crt PCB
I am not sure about the MK2 or PC 1550 chassis and I don't recall seeing an S4 fitted to the MK3 or PC1560 (plastic chassis) version, that's not to say they weren't of course.

[dazzlevision]

Hello,

Thank you for your responses.

I agree that the Mk4A chassis can deliver very good pictures and the 26" one that I have has full feature remote control and Teletext. It is in immaculate condition and came with the trolley stand, all paperwork and the original "Ruwido" made remote gun. This was bought after the Rediffusion chain of shops was sold to Granada TV Rental and has some self adhesive "Granada" badges in an envelope in the back of the set!

At my recommendation, it was bought from new by a relative. I repaired it after its guarantee ran out; mainly triplers. I wisely obtained the full service manual from the Rediffusion spares department in Rochdale before that was all run down by BET, Rediffusion's parent company.

I fitted a replacement CRT (a "Chromavac" regun) after several years and it was finally retired about five years ago and offered to me. The Chromavac CRT still gives a reasonable picture (after a few minutes of warm up), but I think a good 30AX CRT (which I have) could do even better.

I have a vague memory that I saw a TX10 manual supplement detailing the differences between the S4 and 30AX chassis. I think it was a Thorn Television Rentals manual supplement, rather than the usual Ferguson manual. I must try to recall where I saw it!

Many years ago, I did obtain data sheets for the RCA/Videcolor S4 CRT types. The UK office of Videcolor (an Italian CRT manufacturer that produced S4 CRTs under licence from RCA) was based in Witney (Oxfordshire) then, which is where I lived. So, I popped in and asked for data sheets! I must fish them out from my loft and compare and contrast with the Mullard 30AX data.

Regards,

Dazzlevision

[Philips210]

Hi

I never came across a TX10 with an S4 tube but ITT certainly used a lot of them during the 1980's. The sets which used the CVC825, CVC1204, CVC1215 chassis etc had either the 22" A56 701X or the 26" A67 701X tubes. They seemed to suffer from an odd focus related problem with a pulsating picture effect on highish beam current.
ITT also used the 30AX tube with the CVC830 chassis. This is almost identical to the CVC825 so there is a comparison there for interchanging the S4 for the 30AX.

Regards
Symon

[Red to black]

Here is a scan taken from the TX10 PC1500 sheet, it has the Mullard components shown.
Sadly I now have very few bits of the TX10 manual left, this is one of the few bits I do have, so no component differences or later versions/supplements.

IIRC the TX100 crt PCB had an extra daughter pcb fitted to it for the S4 tube, this had the adjustments on it, but I cannot recall if the TX10 had this fitted (I don't think it did), it may have just been to accommodate the different base on the early TX100 PCB layout, I don't think it was for any additional components, just the Physical layout.

[Leon Crampin]

The Rediffusion Mk 4 (and 4A) were designed around an S4 Videocolor (sic) tube in all versions - including the 20" which used a lower rail voltage and required less geometry correction to achieve convergence.

I was working for Rediffusion when this set was designed, and the choice of tube was dictated by scanning power (the S4 has a narrow neck, hence requiring a lower scanning field strength for a given deflection) and the results of reliability testing at that time on the 30AX....

The 4A chassis is capable of the very best results of any contemporary chassis if it has the later SAW filter (red paint spot on can) and if the baseband video is fed into a Sony monitor. The problem with the "consumer" grade tubes used in the set was largely the Videocolor second source - which was ITT. These tubes had a very poor life. The Videocolor tubes were not bad - certainly better than the 30AX at the time and would age gracefully due to the stalwart efforts of the monster Motorola single chip decoder which had auto black level correction. This was achieved by sampling the beam current in a few redundant lines.

I think you would have problems driving a 30AX with a 4A chassis,. The power supply although reliable, has little overhead and the field timebase would need beefing up.

I would search for a Videocolor tube and keep the set original - I have a 20" CITAC set with Text, which I'm keeping for old times' sake.... (=more junk).

Leon.

[dazzlevision]

Originally Posted by Leon Crampin

I would search for a Videocolor tube and keep the set original

Hello Leon,

That's very interesting information.

I would prefer to keep my Mk4A original but I have never seen any S4 CRTs advertised on Ebay or elsewhere for years and finding a good one in an old TV that uses them is rather unlikely, given they don't age very well.

However, if modifying a Mk4A to take a 30AX CRT is that involved......I must locate that TX10 supplement that details the alterations required; for the TX10 anyway!

Regards,

Dazzlevision

[FERNSEH]

I've never seen a TX10 fitted with the RCA S4 CRT but the basic TX10 was designed to accept a variety of 22 and 26" CRTs including the S4, but not smaller tubes, that was left to the equally excellent TX9 chassis.
The first Ferguson TX10 TV set appeared June 1980 as the model 3765.
Thorn consumer Electronics was Mullard's biggest customer, all part of an initiative to keeps TV set and CRT manufacturing in the UK.
The first TX100 set was delivered to me in late 1984 and like the TX10 Fergusons it was fitted with the 30AX CRT.
In 1987 Ferguson Limited as TCE became after the Thomson takeover had to act on the demands from dealers demanding a budget price set to compete with that 22" Logic TV marketed by the Dixons Currys group. I can tell you that many Ferguson dealers were very angry over that affair. The Dealers' reaction was, "do something or you're out of here" Don't forget the Japanese manufactures were knocking at their doors.
So Ferguson limited came up with the Ultra U2201, a TX100 set fitted with a S4 type of CRT. The dealers kept up the pressure and Ferguson did in due course supply a stand for the set.
I had loads of them on rental. All the U2201 sets were in time converted to remote control. The sets in their final form lasted well into the mid nineties.

DFWB.

[Red to black]

Come on David you must have seen a TX10 at some point with the S4 tube, we used to just lovingly call it the Yank tube.

It did look much older fashioned than the 30AX, with the big square yoke with the windings visible.

They were comparatively rare compared to the Mullard version though, the TX100 with the S4 rarer still.

I wonder why Thorn used it at all, unless there were shortages of the 30AX at the time ?, as I say I can only really remember the MK1 version of the TX10 using it.

Edit: I noticed on the diagram I uploaded earlier there was a 1 ohm resistor added in the heater circuit marked S4 only

[FERNSEH]

Hi Baz,
Honest, I know we are talking about twenty-five years ago but none of my Ferguson TX10 sets were fitted with the S4 CRT. How about asking the DER guys. Although after 1980 were they still branding sets as DER?

DFWB.

[Red to black]

Hi David,
We got most of our stock de-badged from the Thorn warehouse, that might be why I saw them and you never, we also never (or very rarely) bought new sets, the shops I worked for mainly sold ex-rentals

I did see the odd one in for repair (both TX10s and 100s) that we never supplied, but these were more than likely ex-rental as well.

I thought it more than likely you would have had at least one in for repair though.

Ah well.

Edit: The cabinet type on these sets (TX10) usually was the earlier style with the sweep tuning and flashing yellow led reminiscent of the earlier 9K sets.
Although some were manual with the sliders again with the earlier styling.

[FERNSEH]

Hi Baz,
you've jogged my memory now. From time to time the odd black fablon covered TX10 set would come in for repair. Obviously these were ex-rental sets. Yes, some of these sets did indeed have the S4 tube. The origins of these sets would have been DER or Radio Rentals.
Almost all these sets were remote control and many had teletext. Never saw any eight button non remote models.
I actually came across an black fablon ex-rental TX9 RC teletext set last year. The digital changeover killed it off. The owner took it to the Council dump.

All the new Ferguson TX10 sets supplied to my business from TCE had Mullard tubes.


DFWB.

[1955APREN]

Hi All
My memory as also been jogged about TX100 Tubes , R622 was changed from 3R3 to 3 ohm I think this one is heater circuit this was on 30ax tubes pc1173. Another Mod was for increased line drive when using 59cm tubes was to change the resistor R143 from 15 ohm to 6R8 , this resistor was in the supply to the line driver stage. I think also that a 12 ohm was fitted in some 22inch sets.
Regards Derrick (one of the Logic guys)

[Welsh Anorak]

Hi
You've jogged my menory too - the earliest metal chassis ex-rentals with the fablon cabinet and the yellow LEDs had those CRTs. They always seemed to have worked far harder than the nicer looking Fergusons. I don't think I ever saw a non-rental that had the S4 tube, though.
Glyn

[dazzlevision]

Hello,

I've managed to find a Thorn TX10 Technical Information Sheet that covers replacing a 22" Mullard 30AX CRT with an RCA S4 type; scans attached.

The main TX10 chassis requires no changes whatsoever The only change, apart from the CRT and eflection yoke, is the change of CRT base PCB and that is largely due to the different CRT base connector required for the S4 tube.

Clearly the TX10 caneasily cope with either CRT type. Whether the Rediffusion Mk4A can is, of course, another matter.

I am going to continue to investigate this possibility and the next step is to fish out the data sheets for the 30AX and S4 CRTs, to see what the similarities/differences are. They are buried somewhere in my (very full) loft.

Regards,

Dazzlevision

[FERNSEH]

One gets the impression that Thorn preferred the RCA CRT. Was it for technical reasons or more likely the company got a better deal from RCA?
As the TTR sets were not sold directly to public, only rented, it probably didn't matter what CRT was fitted in the rental sets.
All the Ferguson TX10 TVs were issued with Mullard CRTs which would seem to be have been for marketing reasons rather than for technical or supply.
In 1980 there was still a buy British ethic so the buyer would expect the most important component in the set should be British as well.

DFWB.

[Welsh Anorak]

Hi
I'm sure the 30AX CRT was a big selling point in the advertising of the time. They also claimed a large video bandwidth, partly from mounting the RGB transistors on the CRT base - maybe this was a first? They did have an unusual circuit with the green LED that looked at you through the back of the set.
I was never too impressed with the S4, but probably that's from seeing far too many tired examples quite early in their lives.
Glyn