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Old 24th Feb 2022, 10:52 am   #41
Heatercathodeshort
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Default Re: My time at Rank Bush Murphy

Those Unitra tubes were truly awful. The screen appearance was similar to blotting paper giving a very poor reproduction. Mazda had the best screens, My regun mate said the best composition was a Mullard gun and a Mazda bulb.

My experience of the A774 was a very bad one. Brand new receivers would fail within minutes due to the CRT flashing over. No problem with that as most new tubes do it a couple of times, hence the ring traps that helped dissipate the charge.

When the tube flashed over in the A774 it destroyed the line sync diodes. The first mod was to fit 1k resistors in series with them.

LOPT failure was spectacular. I fitted 4 or 5 LOPTS to a number of the early ones. It was extensively modified ending up with a stick rectifier but it was too late to save it's. reputation.

When first unpacked and tested the picture was washed out rather like a PYE 11U operating on UHF. Increasing the videos drive pot to a point just below sync crushing gave a 'better' picture but it was still well below par.

A telephone call to RBM came up with nothing and they did not like my idea of increasing the video drive suggesting I stick to the procedure in the service data.
As you can guess I did it my way..

I only encountered one A816. At first I thought it was a colour receiver with it's large solid state chassis. Fantastic picture but as mentioned it was far too late when colour was rolling in. John.
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Old 24th Feb 2022, 12:35 pm   #42
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Default Re: My time at Rank Bush Murphy

It seems that most engineers had the same experience with RBM sets. I liked the early A823 as they gave pretty good pictures and were as relaiable as anything else at the time. Then the "British Disease" set in where every subsequent model was worse than the previous one. The later two chip decoder sets, especially the ones with the AFC switch on the front suffered from patterning, purple reds, Hanover bars etc, again some sets being better than others.
RBM never did cure the interaction problem properly with the line stage and osc / frame panel they just mounted it upside down on later sets which meant the adjustments for height and frame faced into the cabinet. Then the panels became lower quality causing the print around the thermistor to burn up the resulting 'splat' hit the back of the decoder panel, which usually meant that when the power panel was replaced or repaired there was no picture or no colour. DR developments made a replacement panel which did away with the thermistor but by that time most sets were a few years old and the decoder problems combined with a tube past it's best meant that a lot of sets weren't really viable.
Then we come to the T20. Oh dear! Early models were so bad that my mate who worked at a Bush dealer said they would test sets before delivery as a proportion either didn't work or didn't last long.
This caused problems on more than one occasion when a customer expected to see their nice new telly come out of a sealed box. They suspected they had been sold an ex-demo model.
Once you got a working set I don't suppose they were too bad. For a while. The T22 was a bit better, the T26 was fine only let down by the early failure of the 30AX tube.
The T24 of course was trouble free! It was almost as if Rank decided we can't get it right ourselves let's give up , Now... Japanese sets are good... Hmmm.. I know!
Unfortunately by then the damage was done and the end was nigh...
My mate's employer stopped dealing with Bush and after a bit of a struggle started dealing with PYE. They had K35s onwards and had no further problems. In fact once the rentals had been replaced with PYE he was able to not replace one engineer when someone retired. He flogged the ex-rental T26s off fairly prematurely. I think most of the T20s were scrapped around the same time.
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Old 24th Feb 2022, 2:22 pm   #43
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Default Re: My time at Rank Bush Murphy

Almost an exact experience. The Toshiba chassis [T24E?] was incredibly reliable and many are still working today 40 odd years later.

To be fair I found the T20 and T22 reasonably reliable once you discovered it's weak points. The power supply was very reliable but it needed to sing in tune.. I had a list of must change components that were cheap and if changed increased the reliability factor.
I serviced huge numbers of these sold by the discount sheds and found their faults to be very predictable and in many cases could be fixed while the customer waited. [My Sat morning repair bar]. The tubes lasted well and gave a good picture.

Very few Z718s graced my bench. It's odd how certain models appeared in certain areas. I believe it was fairly reliable but suspect with it's precision Toshiba tube together with it's dedicated timebase components, was an expensive receiver to produce. There was also a Z179 but I can't remember it's history. John.
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Old 24th Feb 2022, 4:17 pm   #44
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Default Re: My time at Rank Bush Murphy

Yes I suppose the T20 once you got one out of the box that worked wasn't too bad. I remember the 910R ? Being a common fault. Triplers failing and taking out the LOPT? lots of dry joints! The front end and decoder were good though!
Compare that to a Pye 731 where the tuner was intermittent, the IF panel was intermittent, the A1 cap failed and took out the tripler, LOPT and line output transistor which the bolts were soldered into the heatsink....
Yes maybe the T20 wasn't so bad!
I didn't see that many Z718 sets. I didn't like the overwind idea on the LOPT it was a flashover waiting to happen but again compared to the early Pye "Chelsea" not a bad set!
It is strange how some engineers don't get on with certain chassis . I was brought up on BRC 3000 3500 and 9000 and never had a problem with them and yet some engineers hated them and couldn't understand why Thorn didn't just use BU208s and a thyristor like the G8. I suppose it is what you get used to? With the Colour Boon years we didn't have a lot of choice of course - dealers sold whatever they could get and there were far worse sets than RBM!
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Old 25th Feb 2022, 12:38 pm   #45
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Default Re: My time at Rank Bush Murphy

We also saw a lot of T22s. Usually a 910 ohm resistor (1k paralled with 10k if you were stuck) - the 1k as some repairers used resulted in an unstable 12v line. Along with that a 1 ohm wirewound (in the base of the BU208), a tripler, a mains switch/volume control and a reel of solder would deal with most faults. Reasonable prictures too, easily as good as a G11 which was a relief after the A823A series. Most faults cleared (except the Pressac connector on the line panel) on the T26, but the early 30AX put an end to that.

The 18" Z718 was really good and showed the Pye CT200 and Thorn 8000 the door. The bigger ones with the EHT rectifier were a bit troublesome. Saw a teletext one of those full of TTL. The A816 was very similar to the Z718 in design as I'm sure the OP will tell us.

The Z179 was an oddball which had a continental feel to it with touch tuning and a 26" 110 degree tube. But what's this - an SL901 and SL918? Worked well which shows how good a performer the A823A could have been.
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Old 26th Feb 2022, 10:40 am   #46
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Default Re: My time at Rank Bush Murphy

I took these two pictures with different lighting conditions from the screen of a Bush T24E yesterday. The Toshiba chassis was the first produced at Plymouth in 1980. I sold many of the Toshiba model C2290B/C2295B and never had a service call on any of them.

This Bush example was donated to the museum. It worked perfectly when tested and an internal check just showed a thin layer of dust. I think it was the first time the back had been removed since assembly at Plymouth.

An interesting note. My Toshiba rep informed me that papers found at the factory during the refit by Toshiba showed that only 23% of receivers worked at first switch on after assembly, the rest having to be returned on the line for repair work. I think that would have been the T22 series.

When Toshiba was up and running the switch on rate was over 98% and this increased to over 99% better than Japan! John.
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Old 26th Feb 2022, 10:52 am   #47
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Default Re: My time at Rank Bush Murphy

Was the C2290B a UK design and was it built from components or assembled from imported ready made PCB’s etc?
I remember the Toshiba/Rank collaboration and may have seen these sets but it was just before I left the trade.
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Old 26th Feb 2022, 11:51 am   #48
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Default Re: My time at Rank Bush Murphy

The CRT was a Toshiba 22" 560ETB22 imported from Japan together with most of the components, transformers etc. I'm not sure of the exact make up but early versions used the RBM tuner that was a bit dodgy, soon replaced in production by the Toshiba unit.
I think they must have been one of the most reliable colour designs ever. John.
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Old 26th Feb 2022, 10:17 pm   #49
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Default Re: My time at Rank Bush Murphy

Fully agree John, the T24 was a great chassis and had excellent reliability. I recall seeing a few on my travels that never gave any trouble from new. It would have been an ideal rental set.

I generally liked most RBM sets. The A823 early version wasn't bad but not the easiest for access.

The Z718 was quite a decent chassis with a great CRT. I thought the 18" versions were the best. Appearance wise, the Z718 had some similarities to the T20 though was quite different circuit wise.

The T20 was a bit of a disappointment but could give a decent picture if set up correctly. Reliability was the biggest problem. A lot of the breakdowns could have been avoided with better component specs at the design stage. Agreed the tuner/IF/Decoder was pretty reliable and gave good results. Rank tuners were generally a cut above the average and probably more reliable than say the Mullard ELC1043 used in other makes of TVs, though the latter could often be repaired with care.
Thinking back, I remember having a number of problems with the CRT base socket, a Pressac made 20AX socket including spark gap ring. Focus faults became a problem due to corrosion and tracking in the socket assembly. It was sometimes possible to pull the socket apart and effect a repair. Replacement was the best option especially if the set was used in a damp atmosphere. The T20 was easy to repair in most cases and I didn't mind having one on the bench.

The T22 was a little better and the 30AX T26 was quite decent too, though I didn't see many of the latter.

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Old 27th Feb 2022, 11:24 am   #50
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Default Re: My time at Rank Bush Murphy

Quote:
Originally Posted by Heatercathodeshort View Post
The CRT was a Toshiba 22" 560ETB22 imported from Japan together with most of the components, transformers etc......
I think they must have been one of the most reliable colour designs ever. John.
I can only remember servicing one T24 chassis set, it was the model with the electronic memory tuning unit that either could not be tuned to a station or would not memorise the station to a button - I can’t remember specifically.

The fault turned out to be a very leaky tantalum capacitor, only discovered after a bit of head scratching! A very reliable chassis indeed.

I didn’t dislike the A823, serviced lots of ex rental models of these for second hand sale, rarely gave me any problems. Likewise the Z718, my favourite RBM colour chassis.


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Old 27th Feb 2022, 2:40 pm   #51
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Default Re: My time at Rank Bush Murphy

The only faults I recall on the T24 were the tuner, mains swith/volume pot and, frequently, the 36k pulse feed to the decoder IC going high giving no colour. Only the last fault could be blamed on an under-specified component - the other two parts mentioned were standard Rank parts as fitted to te T20/22 and so on.
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Old 27th Feb 2022, 8:52 pm   #52
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Default Re: My time at Rank Bush Murphy

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strange flashovers across the on off switch when you switched the set off
Philips used to have a resistor of several megaohms across one of the contacts of the mains switch on several models in the 1970's. I wonder if that was to get rid of some built up charge.
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Old 27th Feb 2022, 10:05 pm   #53
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Default Re: My time at Rank Bush Murphy

Many Thorn receivers had a similar resistors across the poles of the on/off switch. providing the receiver was left connected to the mains supply socket the resistors would leak away charges that formed on the aerial due to static clouds. John.
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Old 14th Mar 2022, 12:57 pm   #54
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Default Re: My time at Rank Bush Murphy

Part three
First, ‘That’s Life’ and their ‘heap of the week’ has been mentioned. That program caused quite a stir among the engineers in the TV lab and it was suggested to management that RBM should replace the ‘heap’ with a new set. However, knowing RBM management, I doubt if that happened.

After spending time in various other departments I returned to the TV lab to work the final year of my apprenticeship. There had been some staff changes while I had been away. Two young men, fresh from university and a new project leader had joined the team. Unfortunately, the new project leader was one of those people who managed to upset just about everybody and as a result, the project was running late and engineering moral was low. The design specification for the A816 called for a fully transistorised line output stage, a stabilised thyristor power supply and a plug-in IF strip with a synchronous video demodulator and a small number of ‘A’ model sets had been made for lab development use. Quite suddenly, after some activity from senior management, the project leader left the company and the A816 design spec was re-evaluated to cut costs by removing the thyristor power supply and use a dropper resistor instead. This delayed things a little while the power supply was being sorted out, but the mechanics of the chassis wasn’t affected so the overall delay was only a few months. There were slight changes made to improve the overall picture stability with an un-stabilized power supply, and I recall some on-going problems getting a reliable interlace, but in general the A816 caused us little trouble. The only thing I didn’t like about it was the synchronous demodulator chip which was quite noisy.
There is no denying the A816 was ‘late to market’ probably by the best part of a year. I do wonder if it had been on time, would it have sold more or had the market moved on?
After the A816 was handed over to production we were told our next project would be a small screen COLOUR set – the Z718.

The Z718 was based on an 110 degree, 18inch Toshiba tube and scanning assembles collectively known as the ‘Toshiba RIS system’, with RIS standing for ‘Rectangular In line System’. The tube was a departure from the normal delta gun arrangement, instead, the electron guns were in-line with the green gun in the centre. This arrangement simplified the convergence requirements because the red and blue guns were ‘converged’ to the green gun, which, being in the centre of the tube neck became the reference.
The design aim specification for the new set called for the Mullard four chip colour decoder. I was pleased about this as I was never a fan of the SL901/918 decoder. In fact, Mullard had just released evaluation samples of a chip that replaced the TBA990 and TBA530, this chip was to become known as the TCA800 and was adopted for our design. To reduce electromagnetic interference (EMI), the line output stage consisted of two BU208 transistors and a split primary line output transformer resulting in a positive going pulse on the collector of one transistor and a corresponding negative going pulse on the emitter of the other. This arrangement may well have led to reduction in EMI, but we still had a few problems in this area.
The full wave power supply meant the chassis was sitting at half mains potential – which is fine, with the rear cover in place. However, it was noted that an accidental earthing of the chassis resulted in the 2.5 amp anti-surge fuse exploding with some force and showering glass fragments around. The solution to this was to add a fast acting 5 amp fuse in series which quietly went open circuit in the event of an accidental short, leaving the 2.5 amp fuse to protect against electronic failure.
The development of the Z718 went well taking just over a year to production.
Unfortunately, senior management had decided to re-locate the television development departments to Plymouth to be next to production. If I recall correctly very few engineers elected to move to Plymouth, so the Z718 and the Z179 were the last sets designed at the Chiswick factory. All later sets were designed by a new team of engineers based in Plymouth.
I very much enjoyed working at RBM but looking back on it now, I see a large rambling company in desperate need of streamlining. It was also top heavy with ‘managers’, for example, in the TV labs there were four office bound managers. Even the two girls who looked after the TV lab’s paperwork had a male manager.
I wonder if some of you know ‘Bill Forbes’. Bill was a technical support man who, I believe, visited trade customers and installed televisions for the company’s VIP’s
After I left RBM I joined EMI working on industrial test equipment and later joined EMI’s special project division where I designed a high spec video monitor for military use. The big difference between domestic products and industrial/military was one of cost. At RBM, we were under pressure to save every penny we could.
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Old 14th Mar 2022, 1:21 pm   #55
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Default Re: My time at Rank Bush Murphy

Thank you for the insight, we had the RBM dealership for many years.

Has for the half chassis mains, never did like that idea but it perhaps saved money in the design.
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Old 14th Mar 2022, 1:40 pm   #56
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Default Re: My time at Rank Bush Murphy

The 'half-mains' chassis was a result of using a full wave bridge rectifier. There were two reasons behind tellies going to full-wave rectification. Firstly it needs only a smaller reservoir capacitor, and the stress placed on that capacitor (ripple current) is appreciably less.

Secondly, a half wave rectifier still needs DC continuity in the rectifier circuit, and that has to be through the substation transformer. Effectively half-wave rectifiers export their DC current back down the mains connection. The power distribution bodies were starting to get stroppy about the amount of DC current being forced on them and the size increase in their plant needed to avoid DC saturation of cores. They were agitating to get half-wave rectifiers banned.

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Old 14th Mar 2022, 1:54 pm   #57
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The power distribution bodies were starting to get stroppy about the amount of DC current being forced on them and the size increase in their plant needed to avoid DC saturation of cores. They were agitating to get half-wave rectifiers banned.
The early response from some was -ve heaters.

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Old 14th Mar 2022, 6:33 pm   #58
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My first encounter with a Z718 was after servicing T20s, and my first impression was 'where's the power supply?' I soon realised the regulation took place south of the line transistor. It comes as no surprise the Z718 was designed by the same department as the A816 as there are several circuit similarities. As I said previously, the picture quality of the Z718 was well up to Japanese standards and the 18" set was good looking and an excellent performer.

I wonder if the change to a less efficient dropper in the A816 was at the behest of the electricity boards who understandably disliked thyristor power supplies. I suspect that's why the Philips G11 used a full wave rectifier and two thyristors.

As a matter of interest, could you date the development of the various chassis? The T20 used a very similar IF/decoder to the Z718 and I wondered if they were developed in tandem or whether the T20 borrowed the Z718's development.
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Old 14th Mar 2022, 11:41 pm   #59
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Appreciate the need to stop using half wave rectifiers but a better solution was a shielded mains transformer has used in some imported Japanese sets.
Then accountants wouldn’t have been very happy, on the other hand keeping costs down didn’t save the UK manufacturing industry.
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Old 15th Mar 2022, 5:41 pm   #60
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Glyn wrote -
Quote:
I wonder if the change to a less efficient dropper in the A816 was at the behest of the electricity boards who understandably disliked thyristor power supplies. I suspect that's why the Philips G11 used a full wave rectifier and two thyristors.

As a matter of interest, could you date the development of the various chassis? The T20 used a very similar IF/decoder to the Z718 and I wondered if they were developed in tandem or whether the T20 borrowed the Z718's development.
No, the change to a dropper was internal and purely financial. There was a saying in the TV labs that the monochrome lab was priced to a penny while the colour lab was sixpence.
As for dating the dating the chassis - difficult, it was a long time ago. Put it this way, I first went into the TV lab in August 1968. The A774 was well in development and IIRC, it went to production late 1969 That means the A816 project would have started early 1970. I think it must have been mid 1971 before the A816 went to production. Then the Z718 would have started late 1971. It took about 2 Years to 'sign off' a project, and there would have been some overlap. Looking back on it now it seems a long time but the electronics is the easy bit. I know one engineer went to Fidelity, and I was later told by him that they took only four months to design a television.
I believe the basic layout of the Z718 was carried forward into later models, but the T20/22 electronics was designed by a totally different team based in Plymouth.
Sorry, it's all a bit vague now Glyn, too long ago.
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