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Old 1st Apr 2018, 12:04 pm   #1
Heatercathodeshort
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Default Ferguson 988T 1951. A general check over.

This 12" Ferguson table model was presented to me by a customer more than 30 years ago together with a GEC BT1748, both of which I still have safely in my collection.

This Ferguson model was fully up to date when released in 1951 employing the latest Mullard 'World Series' B9A valves in a compact and lightweight design that proved to be very reliable setting the industry standard for basic low cost television production for over 20 years. It is built for service with a removable card cabinet bottom and easy access to all the components. 90% of servicing can be carried out without actually removing the chassis, a speedy operation in itself.

At the time, around 1980, I overhauled the Ferguson replacing the wax capacitors and replacing a section of the O/C mains dropper. The familiar then current Radiospares MDC capacitors made by Dubiliar were used as replacements and are still 100%. It was not thought back then to maintain under chassis originality but I now decided to give them a dab of paint to give them a more realistic appearance and are certainly not out of place as Dubiliar capacitors were used in the original construction. Electrolytics were restuffed way back together with some of the wax capacitors resulting in me fooling myself about their goodness!

That was all that was necessary to return the receiver to full working order.
The Mullard MW31-16 CRT was still bright giving an excellent picture.

At the time I sent a picture of it working to TCE service dept and they were delighted to see the old timer. During a later phone call to the service dept they admitted that they sometimes overhauled an old model 'for old times sake'. [I will find that picture and post]

Recently I had noticed the old gal was getting a bit grumpy and it was time to see what could be done.

The frame sync had become very critical and once set would drift one way or the other. There was also heavy motor boating when the volume was advanced and a gentle crackling from the speaker that occured continuously even with the volume turned to minimum.

First to tackle was the weak frame sync. The cause was far too simple and was discovered on first test. The anode load of the sync separator, a pentode section of one of a number of ECL80 valves had risen from it's correct value of 100K to over 800K, reducing the anode voltage to 7v compared with the correct 36v. Replacing this restored strong frame sync pulses providing encouragement for solving the sound problem.[Why do sound faults prove to be so difficult to solve in television receivers?]

The table model 988T employs a single triode pentode ECL80 for sound for amplification and output. This little valve has a common cathode connection requiring good decoupling to prevent feedback between the two sections.

It was soon discovered that the common cathode by pass electrolytic a 50uf was O/C. Replacing this removed the sound of a motor launch but the constant low level crackling persisted.

Shorting the anode of the triode section to earth removed the sound of course but the bacon frying continued. The coupling capacitor had been replaced by a Mullard 'mustard' all those years ago and was eliminated on the grounds of reliability.

After some head scratching [thoughts of conducting valve holders..] the fault turned out to be one of the 180 ohm cathode bias resistors that had become 'noisy.' Both were replaced as a precaution and silence was now maintained.

The console version the 983T uses two ECL80 valves in a push pull circuit, one of the very rare television models to sport a push pull circuit in the sound stage.

I thought it advisory to replace the cathode bias capacitor of the frame output valve. It was of identical contruction to the one in the sound so was probably about to go pop a half hour after placing the receiver back on it's shelf!

A long soak test proved that everything had now returned to 1951 standards and hopefully will remain so for another 30 odd years.

Pictures show: Back view showing LOPT. [Greg's thread re lopt] Under chassis Sound circuit. [C71 bias cap] Test card. Film [Guess what film] Regards, John.
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Old 1st Apr 2018, 12:14 pm   #2
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Default Re: Ferguson 988T 1951. A general check over.

The console version with push pull sound. Several other Ferguson models around this vintage had this sound feature.
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Old 1st Apr 2018, 12:58 pm   #3
linescan87
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Default Re: Ferguson 988T 1951. A general check over.

Cracking job John, what a happy little set.

The film, What ever happened to baby Jane?

Cheers,
John Joe.
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Old 1st Apr 2018, 2:10 pm   #4
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Default Re: Ferguson 988T 1951. A general check over.

Correct Joe. That must be one of the best films ever made especially with those two cats at war! John.
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Old 2nd Apr 2018, 8:30 am   #5
mark pirate
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Default Re: Ferguson 988T 1951. A general check over.

Great work John, Fine sets these Fergusons!
I restored one of these excellent sets for a friend a few years back.
It was bought new by his grandparents and gave good service until replaced in the early 60's by a dual standard Ferguson.

It was then stored under the stairs until the 1980's when the house was cleared.
Since then it lived as a display piece among my friends radio collection.
He had never attempted to power it up, but after visiting me and seeing some of my sets working, he fetched it round for me to restore.

The set was in remarkably good condition, lovely cabinet and clean rust free chassis.
After a good check over it was powered up via my variac & series 100w bulb, after a little dust burning off the dropper, it showed great promise with sound and EHT present, but had frame collapse.

A day spent replacing capacitors, a few out of spec resistors & a new EY51, the set gave an excellent picture

I found it very easy to work on compared with other sets from the era, the set has continued to work well since restoration, only needing a replacement ECL80.

I have a 998T in my collection, one of the first sets I restored, it too is a great set and produces a smashing picture on it's "Re-View" regunned CRT.

Mark
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Old 2nd Apr 2018, 3:57 pm   #6
rogerdup
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Default Re: Ferguson 988T 1951. A general check over.

Nice set John.
The main dropper look like having hard heat time.
I can make it like new if it fails. I become a Dropper restorer specialist. So don't hesitate to contact l me.
Regards,
Roger
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Old 3rd Apr 2018, 11:28 am   #7
Heatercathodeshort
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Default Re: Ferguson 988T 1951. A general check over.

Thanks very much for you kind offer Roger.
The mains dropper is not as bad as it looks and yes, it should be at that angle!

I will leave well alone at the moment but thanks again for you offer.

Your Pye dropper is fantastic! Better than new, and Cambridge blue.

John.
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Old 3rd Apr 2018, 11:50 am   #8
rogerdup
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Default Re: Ferguson 988T 1951. A general check over.

Hi John,
I had some concern about the paint vs temperature, but it follows very well the characteristics specified! No color changes and superb aspect.
Regards,
Roger
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