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Old 31st Aug 2018, 7:59 pm   #1
Heatercathodeshort
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Default Ferguson 989T 16" console Metal Cone CRT. 1951.

Ferguson 989T 16" console 1951

The Ferguson 989T is a 16" console model fitted with a Mullard MW41-1 metal cone picture tube. It follows closely the slightly earlier 12" model 988T with differences mainly in the timebases necessary to scan the 16" 'wide angle' tube. Wide angle in 1951 was just 70 degrees but this development resulted in a much reduced depth of cabinet.

The chassis also sports a push pull audio amplifier employing two ECL80 triode pentodes, an early 'World Series' B9A based Mullard valve.

The model sold in very large numbers costing around £100 in 1951. Different cabinet styles were available, one a very attractive design in oak, very suitable for the mock Tudor inter war houses of the time.

Picture quality was and still should be fantastic. The EHT supply to the flat faced metal cone CRT is 13.5kv and the screen phosphor produces a true black and white picture.

The 16" metal cone CRT originated in the United States in 1949. A monster 30" circular metal tube appeared a couple of years later. [30BP4] It must have been huge!

'English Electric' produced the first receiver to employ their version, the narrow angle T900. This was quickly followed by the T901 directly equivalent to the Mullard MW41-1 and the grey glass screen T901A.

During 1951 several British manufacturers produced models to utilize the new metal cone 'wonder' tube. Bush model TUG26, Ferguson 989T and 990T, Ekco TC178, PYE FV2/C and a few others. These were all 16" models incorporating the circular Mullard MW41-1 but a little later a rectangular 17" version was produced, the MW43-43 but it was only employed in the UK in very early versions of the Ferranti 17T4 and the Ferguson 996T.

English Electric, Kings of the Metal Cone CRT produced a MASSIVE 21" circular MC tube for their consolette C42, the T909. HMV also used a version of this in their huge 1820 series receiver.

So why did the MC tube have such a short life in receiver designs?

By late 1952 they had all but vanished.

The major problem was retaining the vacuum. The glass screen and neck were joined to the spun steel [? MuMetal?] cone but how they did this I have never been able to discover. To be honest when it worked, it worked well and I have seen a couple of examples in recent years with very good pictures and that is after 60 odd years.

Another problem was unequal expansion of the glass and metal. When I was a very young kid I remember seeing them at jumble sales with a crack right across the screen. They were expensive to produce and needed special care when fitted to the receiver chassis due to the metal cone being at EHT potential. A large thick plastic bag did little to prevent a zap if you were a little too adventurous while making internal adjustments.

A very thick plastic 'tyre' was fitted around the point where the screen joined the cone and can be seen in one of the pictures.

EHT leakage was very common especially when the assembly became coated with coal fire soot.
Another added expense for the manufacturer was the lack of the 'dag' outer coating as employed in all glass CRTs. This was earthed and used in conjuction with the glass envelope as the EHT smoothing capacitor.
This of course could not be done with a solid steel anode and this required the addition of a couple of ceramic high voltage capacitors and an added resistor to carry out this function. Again they can be seen on top of the LOPT. I would add that this type of capacitor is completely reliable unlike the early oil filled Bakelite tube types.

It must be remembered that the rectangular all glass tubes began to make an appearance in 1952 thus rendering the circular metal tube obsolete.
So what if any were the advantages?
1 Large flat screen area, The largest direct view CRT for domestic tv in 1951.
2 Safe to handle [when switched off!] and no risk of implosion.
3 Very light to handle.

So what is the history of this 989T?
The receiver was passed to me by an elderly customer more than 25 years ago. The cabinet is in excellent condition being cared for all it's service life and beyond. It was situated in a large house at New Malden Surrey sitting in the customers living room covered with a thick table cloth, undisturbed since around 1960.

Of course I showed interest in the partly hidden console and she was more than willing to let me have it. Apparently her husband had passed away some years earlier and it had been his prize possession and just wished it to go to a good home.

Back at the shop I carried out a few temporary repairs in order to assess the goodnes of the CRT. The mains dropper was O/C on all sections. This happens with all cement covered droppers. They obsorb dampness and over time this rots the resistance wire causing total failure. With it up and running the CRT was blank. The heater was fully glowing so no partial short circuit problem and the EHT was around 10kv. Tube base voltages were about right and the ion trap was locked solid so probably in position.

Well to cut a long story short the CRT had no emission. Applying 9volts to the heater with all the lights out, the faintest illumination could be seen and I mean faint!

There was no hope in obtaining the MW41-1 required and I did not want to convert it to a 17" all glass tube such as the MW43-69 a conversion that was carried out when these tubes failed back in their day.

The 989T was set aside and great care has been taken of it over the past 25 years plus.

Recently I had a phone call from a very generous Forum member. 'Are you still looking for a MW41-1 tube'. You can imagine my surprise. I'm having a clear out and discovered a brand new one in it's box complete with guarantee card..'
It tested 100% it's yours if you want it!

It is indeed as described and being dated 1959 it must have been one of the very last produced for replacement purposes. It has a blue Mullard label similar to the style used on most of the AW43-88 types of 1960 vintage.

So this is where we start part 2 of a restoration started over 25 years ago. They say if you wait long enough the bit you want will turn up. It did.
I will start the work soon and take plenty of pictures of the dismantling. It should be interesting...

Pictures show the console, cabinet top, internal view and the CRT removed from the chassis. It is very clean as can be see protected by it's polythene frock.

The first job is to rebuild the dropper and I will post pictures as the fun continues. John
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Old 31st Aug 2018, 8:04 pm   #2
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Default Re: Ferguson 989T 16" console Metal Cone CRT. 1951.

These pictures show the original faulty MW41-1 after removal from the chassis and the Mullard box containing the replacement.

Seems such a shame the original tube was useless. As can be seen it is very clean but beauty does not prove worthiness. More to follow. John.
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Old 31st Aug 2018, 8:56 pm   #3
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Default Re: Ferguson 989T 16" console Metal Cone CRT. 1951.

Thank you John.

Very interesting!
I'll follow it with pleasure.

Jac
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Old 31st Aug 2018, 9:06 pm   #4
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Default Re: Ferguson 989T 16" console Metal Cone CRT. 1951.

Excellent stuff John, I always wondered what the picture would be like on one of these tubes. Keep up the good work!

John Joe.
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Old 31st Aug 2018, 10:55 pm   #5
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Default Re: Ferguson 989T 16" console Metal Cone CRT. 1951.

That was a challenging component to find.
It is going to be interesting to see you get it up and running again.
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Old 31st Aug 2018, 11:53 pm   #6
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Default Re: Ferguson 989T 16" console Metal Cone CRT. 1951.

Thanks for posting these pictures of this type of tube. I had read in old copies of Practical Television from the 1950s about the 'plastic bag' insulating cone but I always imagined it to be about half inch thick. I don't think I would fancy making adjustments within inches of this cone with such a thin sheet of plastic in between. Good luck with the restoration and look forward to seeing the results.

Alan.
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Old 1st Sep 2018, 5:14 pm   #7
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Default Re: Ferguson 989T 16" console Metal Cone CRT. 1951.

What luck to get a new CRT, I had an English electric set where the tube had gone to air
They are indeed incredibly light for the size, but that cone connected to EHT is somewhat scary!
Looking forward to the restoration John, Fine sets, these Fergusons.

Mark
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Old 1st Sep 2018, 5:25 pm   #8
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Default Re: Ferguson 989T 16" console Metal Cone CRT. 1951.

I carried out a bit more work today on the 989T As you can see from the under chassis view it appears to be as it left the factory other than the cap in the top right hand corner C24 the .1uf boost reservoir capacitor.

I fitted the cleaned up plastic insulating bag and the insulator ring and fitted it with great care to the new Mullard CRT.

It was only necessary to tidy up the mains dropper, no easy task. Whatever you do with it makes no difference to it's nasty appearance. The original dropper was held in place by two spear ended clamps into holes in the ceramic tube.

I gave Interlace a huge box of droppers to sort through but he only selected the stupidly large examples that would never have fitted physically. I think like me he got bored with all the differing types that looked correct but never would be..

In the end I employed a 160 ohm and 40 ohm power section plus a 350 ohm resistor to bridge the old style thermistor. It ain't pretty but is technically correct until I summon up the courage to do another dropper hunt.
The tube assembly was fitted to the chassis baseboard. Great care was taken with nothing under strain.

I didn't even bother to snip the very large mains filter cap. It was only first test with mains applied so I thought I would be brave and just 'Plug It In'.
After a while the EY51 lit but the screen was blank. I turned the brilliance control three quarters on then stepped back to allow Interlace to do what he likes doing best, adjusting ion traps.
For some reason he was very suspicious of the whole business and sat on the floor gently tapping the metal cone of the old tube. It clanged and that put him on guard.

After a few moments he climbed up on the wood box provided and very gingerly turned the trap 180 degrees. With his usual grunt of delight the screen flooded with light. He had done his job and could now go outside and bask in the afternoon sun.

It took but minutes to arrive at the picture below. It's very bright with high contrast so it looks like it may be an easy one, yes again!
The capacitors are my favorite Dubiliar make and despite 67 years old are still capable of just about working.

Pictures show the new CRT waiting to be fitted with it's plastic cloak and the picture obtained by Interlace after he fiddled with the ion trap.
It's interesting to see that the original 41-1 was made in Holland and the new replacement was made in the UK. These late MC's may have been sourced from English Electric, just a thought. The gun does not look like a Mullard and the Bakelite base is slightly fatter.

More to follow next week, all being well. Regards, John.
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Old 1st Sep 2018, 5:25 pm   #9
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Default Re: Ferguson 989T 16" console Metal Cone CRT. 1951.

Quote:
Originally Posted by AJSmith625 View Post
Thanks for posting these pictures of this type of tube. I had read in old copies of Practical Television from the 1950s about the 'plastic bag' insulating cone but I always imagined it to be about half inch thick. I don't think I would fancy making adjustments within inches of this cone with such a thin sheet of plastic in between. Good luck with the restoration and look forward to seeing the results.

Alan.
I'm following this thread with a great deal of interest as metal cone CRT's were commonplace in the US. Practically every manufacturer used them at one time or other. RCA seemed to use them the most from the 16" rounds to the 27" rectangulars . Also, the first RCA color CRT's, the 15GP22 and the 21AXP22 were also metal cone CRT's.
The Poly sheeting used around the cone was a bit of help, as all that happened was the hairs on your arm stood up, but not a real nasty shock.
The RCA's never used the cone insulation except on the color CRT's.
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Old 1st Sep 2018, 10:20 pm   #10
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Default Re: Ferguson 989T 16" console Metal Cone CRT. 1951.

That is one very rare good tube.
It will be done in a day or so now you have got a locked picture the screen.
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Old 1st Sep 2018, 10:32 pm   #11
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Default Re: Ferguson 989T 16" console Metal Cone CRT. 1951.

There's an RCA 21AXP22A metal cone colour CRT upstairs. It was removed from the Pye 405 line CTV. It's most likely it's now down to air, the getters have that milky look.
Link to a Ferguson 989T I serviced over eleven years ago. The MW41-1 CRT was found to be in excellent condition.
https://www.vintage-radio.net/forum/...ad.php?t=17527

DFWB.
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Old 1st Sep 2018, 10:48 pm   #12
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Default Re: Ferguson 989T 16" console Metal Cone CRT. 1951.

Wow, what a great set. I had read and seen pictures of metal cone CRT's, but I have never actually seen one in the flesh.

It is good that you found a NOS tube, that always makes a huge difference with a vintage TV restoration. You can get the best out of the image and see the way it performed when the set was new. Probably the image on a set like this would be fantastic when the tube was in good focus and the vision IF set up correctly.

Interesting to see that two stage filter with the doorknob capacitors on the EHT and the rounded edge clips to prevent corona discharges, it is all very cool. Sometimes early doorknob caps can be unreliable, the one in the RCA621TS 1946 set for example, is nearly always faulty. But at least they are fairly easy to get if you need some replacements.
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Old 2nd Sep 2018, 10:26 am   #13
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Default Re: Ferguson 989T 16" console Metal Cone CRT. 1951.

Yesterday evening, after obtaining such promising results, I found it impossible to abandon the 989T and I crept back into the workshop.

The sync and frame timebase circuit is shown. It has a three stage sync separator that guarantees excellent interlace on the 16" screen and it is certainly one of the best in it's class.

I tacked in just three capacitors C62 .1uf frame coupler to PL82 output valve, C63 .05uf and C64 .05uf frame linearity feedback loop and with just adjustment to the height and linearity pots was rewarded with the test card you see.

It really is quite amazing, even the picture centering was reasonably good. Just as well because it is seized solid and will have to be dismantled and cleaned.

The local oscillator fine tuner was spot on and the alignment is as good as the day it left the Ferguson factory in Edmonton London N18, 67 years ago. A real tribute to the 'New Boys on the Block' as they were named by so many snooty dealers of the time.

We now have an odd puzzle that is difficult to explain. The LOPT is in very good condition with bright windings and no signs of stress.

The service manual quotes an overwind resistance of 250 ohms. Mine reads 9.1K! The EHT is exactly 13.5kv as quoted and does not fade with time. The only answer must be that later LOPT overwinds were wound with resistance wire and after careful examination it is possible that the transformer was replaced during it's service life.

Beside the resistance value given in the manual there is an asterisk but no answer as to why on the page! We will never know.

I did say that most of the capacitors are Dubiliar. My mistake, they are HUNTS and have survived very well. There are a few Dubiliar and I must have looked at those first and made a hasty mistake that they were all from the same stable.

No nasty stick mess from the Hunts waxies as can be seen from the pictures. Some are of an early hard cased construction and have held up better than most 70 year old capacitors!

An unusual feature in the power supply is a fixed bias supply for the video output stage and line output valve. It is obtained in exactly the same way as portable battery radio receivers, returning the HT negative to chassis via a resistance and decoupling capacitors, C68 C69 and R90 35ohms.

The video stage employs the Mullard PL83 valve not often seen in British designs other than a few projection models and oddly the frame output valve in the PYE V14. It was widely used on the Continent due to it's high gm [10Ma/V] more suited to the wider bandwidth of 625 transmissions.

The audio amplifier sports a pair of ECL80 valves in Push pull, one of the very rare UK models to go to the expense of what would have been considered an unnecessary luxury in 1951.

R56 the common screen feed resistor to the ECL80's is burnt O/C probably due to it's decoupling capacitor, C48 8uf being shorted. It could be a short in one of the pentode sections but I doubt it.

Some more work to do and would you believe that mains filter is still holding up. To my horror Interlace gave it poke this morning in a hope that I would snip it. Maybe.

The pictures show progress to last evening. Screen shots show main lighting switched off and lit by bench lamp. This gives a better overall exposure. John.
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Old 2nd Sep 2018, 6:01 pm   #14
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Default Re: Ferguson 989T 16" console Metal Cone CRT. 1951.

Be ready for Last Night of the Proms I reckon
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Old 2nd Sep 2018, 6:43 pm   #15
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Default Re: Ferguson 989T 16" console Metal Cone CRT. 1951.

Most interesting post John- I'd heard mention of metal cone CRTs in the past but never with information or pictures, so this is very enlightening! I wonder if there was any military impetus in the development of metal cone tubes for bigger and bigger radar displays, egged on by WW2- it wouldn't be the first or last time that military requirement led to profitable consumer spin-off. Or maybe it was simply the post-war desire to put a big smile on the US consumer's face with more and bigger domestic gizmos. It must have taken quite a bit of development to get a good glass-steel bond over such a long seam, I can imagine that cone thickness must have been something of a compromise between being strong enough to resist collapsing like a beer-tin, yet having a bit of give to save stressing the glass over the expected temperature range. Good cleaning and thorough de-gassing of the inner surface must also have been needed. I wonder if the cone could also cause scanning field distortion if the yoke was close? So many questions.... I do hope that nothing like these ever found its way into something with a PSU like Ekco's TSC113! i like the statement that, in the US, only colour tubes seemed to get the plastic collar treatment, maybe they felt that anyone digging around in tellies should be on their wits anyway. Perhaps something like those polythene cones used on dogs' necks to stop them scratching facial wounds would be handy.

Good luck with it, an absorbing thread,

Colin
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Old 2nd Sep 2018, 9:06 pm   #16
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Default Re: Ferguson 989T 16" console Metal Cone CRT. 1951.

Very interesting that high resistance Lopty overwind.

Recently I came across some unexpectedly high fine resistance wire as the central conductor in some coax cable as a single strand. The resistance wasn't helpful but a total of about 1k for a 10 foot cable didn't matter as the cable fed a 1Meg termination and a frequency compensation box. Looking at it realized why they had used thin nichrome wire, they wanted low capacitance with a thin wire, and if it was that thin as copper it would have been far too weak and broken.

So I think sometimes enameled nichrome gets used on long windings with very fine wire just for its physical strength because copper is more fragile, that is if the added resistance has no negative effects on the circuit.

Many wire specialist companies in the USA made fine enameled nichrome wire, but it was rare as a UK/European product because Constantan wire was preferred.

Nichrome is hellishly difficult to solder to and for the recent coaxial cable I repaired it had to be crimped, but Constantan wire is a dream to solder.
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Old 4th Sep 2018, 12:45 am   #17
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Default Re: Ferguson 989T 16" console Metal Cone CRT. 1951.

John sent me a picture of the gun assembly in the replacement MW41-1 CRT.
Although it was sold as a Mullard tube it is evident that the gun assembly was not made by Mullard or Philips.
My opinion is that the tube was made by English Electric Ltd and was bought in by Mullard from a third party source. Back in the sixties Mullard marketed a range of valves which were made by Mazda, these valves had a special symbol to indicate that the valves were from a 3rd party and not direct from Mazda.

DFWB.
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Old 4th Sep 2018, 7:55 am   #18
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Default Re: Ferguson 989T 16" console Metal Cone CRT. 1951.

Does 250 ohms sound right for an overwind? They contain a lot of fine wire.
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Old 4th Sep 2018, 8:30 am   #19
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Default Re: Ferguson 989T 16" console Metal Cone CRT. 1951.

Hi David and John,

Very interesting!
The "Radiant Screen" really does what it says!
It is the same with my little Perdio (thanks David!).
Can you see if the AW21-11 was made by Mullard/Philips?
Please find attached a photo of the gun assy.

Jac
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Old 4th Sep 2018, 9:19 am   #20
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Default Re: Ferguson 989T 16" console Metal Cone CRT. 1951.

That looks very Mullard/Philips to me Jac. John.
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