Ferguson 989T 16" console Metal Cone CRT. 1951.

[simpsons]

The metal coned MW43-43 did give a good display not only because it was almost flat faced but I am sure used a thinner face plate reducing optical distortion.

Only recently, I was lucky enough to watch both test cards and programmes on a Bush TUG26 which were very good, if not quite to the Ferguson standard though. The Bush TUG 26 I think still used an EF91 video out and despite a 10" loudspeaker, no negative feedback to tame the pentode sound.

The Head of Engineering at Ferguson must have been ahead of the time using a PL83 with DC coupling to the CRT and frequency compensated negative feedback on the audio output; almost unheard of, no pun intended, in the design of radio sets of the day let alone televisions.

As an aside, my parents had a Bush TUG26 installed for the Coronation. The neighbours came round to see the marvel of TV and sat cinema like in the back room where the set had been installed. My father, a salesman, told the audience, whilst the set was warming up, how difficult it had been for him to get hold of the set as demand outstriped supply.

We waited for the sound and the picture. Nothing. Not a squeek. Not a glimmer. The set had failed at its first outing. Red faces all round and everyone went home I guess to listen to the event on the radio. Happy Days.

[Heatercathodeshort]

It's just a thought, the inside surface of the metal cone may have been polished giving an aluminising effect. It is certainly as bright as an aluminised 17" Mullard MW43-69.

It must have been expensive to manufacture. English Electric took advertising space for the T901 on the back covers of Practical television for the whole of 1952/53/54. I have never seen an advert for the Mullard version. They probably knew rectangular tubes were literally just around the corner.

£24.6.5 inc tax! I think replacements were even more expensive hence the modification when they failed, to all glass tubes.

Interesting to note that the first MC tube the T900 [53 degree] and the more common T901 [70 degree] had .6amp heaters. For this reason alone, this would have excluded many manufacturers from employing them in their AC/DC chassis. EE were into a loosing battle.

The advert mentions that a new version was just about to be released with a .3amp heater, the T901A. I wonder if the .6amp gun assemblies were sourced from the USA? I am almost certain that these tubes were produced by EE in the UK.

[Freya]

Originally Posted by Heatercathodeshort

It's just a thought, the inside surface of the metal cone may have been polished giving an aluminising effect.

What are you planning to do with the original no emission CRT, if its to be consigned to recycling then you could see if the cone surface is indeed polished.

[Jac]

Originally Posted by Heatercathodeshort

It's just a thought, the inside surface of the metal cone may have been polished giving an aluminising effect.

I'm not sure what you mean John.

Ideally you'd want a matte black surface to minimize reflections.
In that respect, an aquadag layer is helpful in glass tubes.
Aluminising the back of the screen and omitting the ion trap would have been a major step technical forward.
On the other hand, it has a nice flat screen and the high EHT gives a very sharp picture.
I wonder how do they realize a sharp focus over the whole surface, having a non-curved shape of the screen?

Jac

[FERNSEH]

More evidence of the care in the design of the model 989T taken by Ferguson to ensure that the best possible picture can be displayed on the MW41-1 flat faceplate CRT. Extracts from the Ferguson circuit diagram. Note that the cathode of the PL83 video amplifier valve is returned direct to chassis, no bias resistor. As John mentioned earlier in this topic grid bias for the valve is derived from the HT negative return resistor R90 (35ohms). A similar arrangement was used in the View Master TV receiver.
The DC component is maintained from the detector and to the cathode of the CRT. Inductors L21 and L22 will improve the high frequency response of the amplifier.

DFWB.

[Nanozeugma]

If the inflation calculator I have used is anywhere near accurate, a 1952 price of £24 for the CRT equates to £670 today (approximations). I wonder who could have afforded to purchase one of those!

[FERNSEH]

Originally Posted by Nanozeugma

If the inflation calculator I have used is anywhere near accurate, a 1952 price of £24 for the CRT equates to £670 today (approximations). I wonder who could have afforded to purchase one of those!

Almost half of the 24 pounds asked for the CRT included a punitive purchase tax.

DFWB.

[Heatercathodeshort]

Hello Jac,
When tubes are aluminised the micro fine layer is deposited over the screen and glass bowl, internally of course. All Mazda tubes from 1950 [CRM151] were aluminised.

Aluminised tubes appeared around 1948, introduced by Cossor and EMI. Mullard did not carry out aluminising until 1955, [MW53-20 and AW36-20] I think the last tube maker to do so.

Stephen, it seems such a shame to smash up the original MW41-1. I will put it aside and store it with all the other junk, at least for the time being... John.

[Jac]

Thanks John,

You're right of course. I wasn't thinking straight.
The Al will vaporize onto everything within reach.

Jac

[Heatercathodeshort]

The art of aluminising and it's effect has always presented me with a confused state of mind..J.

[jhalphen]

Hello to all,

@HeaterCathodeShort : here are some pictures of the aluminising process taken at the late-RACS plant in France a few years ago.

Best Regards
Jhalphen

http://s281.photobucket.com/user/jha...?sort=9&page=1

[Freya]

Aluminium pellet for vaporization https://www.youtube.com/watch?v=byCeMKzPJgM at about 1 min 30
and
Aluminizing. https://www.youtube.com/watch?v=byCeMKzPJgM

both videos noisy with the vac pump running but its fascinating watch anyway if not seen before.

[Heatercathodeshort]

Thanks for the link Jhalphen. Amazing but simple.

This evening I tackled the final part of the chassis, the audio amplifier.
As mentioned earlier it is designed around a couple of ECL80 valves in a push pull circuit. The pair are tucked away in the front left corner and to gain access to the wiring the bottom chassis board has to be loosened.

First to deal with was the burnt resistor R56 2.2K. This feeds the screen grids of the two ECL80 valves. It is decoupled by an 8uf electrolytic which was dead S/C. Even Interlace would have found that one a doddle with his latest toy I gave him, a neon test screwdriver.

A quick check of all the resistors proved they were within close tolerance, amazing when you consider the age of this chassis. I was at least expecting the two triode anode loads R49/R54 [220K] to be well out including the grid leaks R57/58 [680K] but they were within 5%.

The coupling capacitors C45/46/47 [.002uf] were replaced as a matter of course together with part of the tone correction circuit, C50 [.005uf]

With this completed, a test PP O/P transformer was connected and the chassis tested.
The result is impressive. Very good sound only requiring a tweak to the local oscillator to remove a bit of vision on sound.`

The final job was a bit of a clean up. Just a chassis scrub with a toothbrush [not the one I am currently using] and a general clean up of the valves and top of the chassis coloured plastic insulated leads.

Altogether a very satisfactory job thanks to the gift of the MW41-1 CRT.

I will probably take the chassis to the Television Day at the museum on Saturday so you can have a poke at the metal cone tube. [While it is switched on of course.] Regards, John.

[FERNSEH]

Seventeen years after the introduction of the Ferguson 989T a pair of ECL80 triode-pentodes were employed in the sound output stage of the Dynatron TV95A. The push-pull sound output unit was plugged into the PCL82 valveholder of the unmodified Pye 368 chassis.
In 1968 the ECL80 must have been still considered a current equipment type.
Output power was only 3 watts, in fact it's likely the single PCL82 would deliver more audio power.

DFWB.

[Heatercathodeshort]

I have never encountered a Dynatron TV95A. As you say the sound output would not have been much more than a single PCL82 but probably of better quality.
For some reason I always thought the PCL82 never produced a 'clean' sound compared with the later PCL86.

The ECL80 is quoted as 1.4W in class A. With a pinch you may have been able to squeeze a pair to 3.5/4W. It feeds a good quality 8" speaker in the 989T suitable for a very large room or maybe a golf club lounge.

It would have been great to meet the actual designers of these excellent receivers. John.

PS The ECL80's are 'British made' together with the PY82s, PL81. The PL82, PL83, all the EF80s [early type with gray cylinder top screens] and the PY80 are 'Made in Holland'.

[Heatercathodeshort]

The 989T traveled well to the museum on Saturday. I fitted it into the cabinet on Sunday morning and it looks grand! I will post a final picture very soon. J.

[line sync]

Another really good restoration john , just what we expect from you.
A very enjoyable read.

Robin

[Heatercathodeshort]

A lot of good luck really Robin. Clean chassis, mostly dry stored and a bit of knowledge from a lifetime in the trade. Just a bit of fun you could say. Thanks, John.

[Peter.N.]

I used to service a couple of English Electric sets with that CRT, it made a very threatening crackling noise as it warmed up but did give an excellent picture.

Peter

[Heatercathodeshort]

When I was a kid I was presented with a EE 16T11D. Wish I still had it!

The last pictures of the 989T and I must say it has been the most difficult to photograph.

The Perspex implosion protection screen is tinted slightly pink similar to the PYE. This is really caught by the camera to give it a much deeper colour than it is in real life.

I have printed one in black and white to show what it is like to actually watch!

Very good picture and rock stable. The screen colour is bright white, no gray glass filter so I guess Ferguson added the tinted filter to improve daylight viewing.

The sound is a very marked improvement over standard output pentode but I doubt if it was noticed by the average viewer. You can turn the volume on full with no noticeable distortion.

It has lots of gain with a slight 'hiss' from the speaker with the aerial unplugged.

I very much like this one! Thanks for all your interest and kind comments. Regards, John.

PS We moved to Merton Park in 1956. Merton Park Studios were just a short distance from our house and we used to watch the studios making the Scotland Yard series and later, Edgar Wallace. They never ventured far from base!