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Old 17th Mar 2019, 1:18 pm   #1
FERNSEH
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Default Ferguson 705T Senator.

Follow up to a previous post about this set.
https://www.vintage-radio.net/forum/...d.php?t=147455

The set has worked quite well since I acquired it last year. Last week it broke down, no sound and vision although the motorised tuner continued to work. An easy fault to find, R159 (172 ohms) in the heater chain had gone open circuit. When the set is converted to 625 lines by fitting the new IF amplifier unit and valve UHF tuner R159 is shorted out by connecting a link between tags A1 and A5. In use as a 405 line only receiver the resistor dissipates 15.5 watts! I'm surprised the manufacturer has opted to use a wire ended resistor. Watts = current squared X resistance. To fix the set I found two high wattage resistors, one is 400 ohms and the other is 350 ohms. Connected in parallel the measured resistance is 178 ohms, that's near enough. In use the wire ended heater resistor sure does get hot.

The 705T Senator is working again but it really needs the alignment attending to. Picture quality could be a lot better.

DFWB.
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Old 17th Mar 2019, 8:51 pm   #2
1100 man
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Default Re: Ferguson 705T Senator.

Quote:
Originally Posted by FERNSEH View Post
I'm surprised the manufacturer has opted to use a wire ended resistor.
Hi David,
Maybe the sales rep (on commission) had just convinced the production department to buy these new improved resistors: "they are far superior and cheaper than the ones from your usual supplier" He probably forgot to tell them that the end caps would split and fall off....!

The very high UK mains voltage must have been a constant headache for set manufacturers- there's just so much heat to get rid of. 200-220V mains would have been about right!

Is that a PCB lurking down at the bottom of the picture?

Cheers
Nick
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Old Yesterday, 2:34 am   #3
FERNSEH
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Default Re: Ferguson 705T Senator.

Hi Nick,
the set under discussion is the phase 2 production version of the model 705T. Earlier sets were made for 405 lines only and employed a PY33 for the HT rectifier, that valve has a 29 volt heater which helps to reduce the value of the heater supply dropper resistor.
The convertible to dual standard operation phase 2 sets use a BY100 silicon diode for the HT supply. The 625 converter unit requires 51 volts for it's series heater chain and when the unit is not fitted that voltage has to be dissipated as heat in the heater chain resistor R159, 15.5watts!
The 600 and 700 models have two printed circuit boards, the lower one as seen in the attachments is the timbase and the upper one is the signals board. It's a similar arrangement in the 1962/63 fully dual standard models using the 800 and 850 chassis.
The 405 only 600 series models are much nicer than the 625 convertible sets.

DFWB.
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Old Yesterday, 6:36 pm   #4
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Default Re: Ferguson 705T Senator.

I very much like the Thorn 600 series. Very reliable and they give a brilliant picture.

It is unusual David to discover the alignment has been twiddled in the very stable 600. This was a common problem in the late 50's and early 60's often carried out by the old school 'Radio Men' that did not understand the principles of vision AGC, still thinking that the contrast control adjusted the gain of the RF amplifier.

A simple 6DB attenuator would have cured the sound on vision but oh no, they just had to twiddle those I.F. cores often smashing them and jamming them in the coil formers.

Every Philco 1000 and 1019 models were twiddled beyond belief followed only by the Sobell series with the useless FM radio. The Sobell models were great receivers but suffered from the phantom twiddler more than other models.

A few spot frequencies and the service manual should soon sort that out David. We now have the use of frequency counters so no excuses for not making a first class job of it.

Don't be cruel to the poor little wire wound resistor, it is 60 years old..
Regards, John.
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Old Yesterday, 7:03 pm   #5
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Default Re: Ferguson 705T Senator.

I was lucky, didn’t have to deal with sets got by the phantom twiddler, made life much easier, my customers left the sets alone.
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Old Today, 9:43 am   #6
Heatercathodeshort
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Default Re: Ferguson 705T Senator.

Hello Frank.
It wasn't the customers that twiddled them. It was the old time radio guys that were supposed to fix them!
The 850 series developed from the 600 was another candidate for Mr twiddlefix but nothing like as bad as the Philco 1019 a company that Thorn took over about the time of the 705T. John.
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Old Today, 10:05 am   #7
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Default Re: Ferguson 705T Senator.

Hello John
Just trying to remember what the late great Les Lawry Johns said about the twiddlers.
Something like "its been twiddled from breakfast time to tea time"
I'm sure you'll remember exactly what he used to say.
Regards Alan
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Old Today, 10:29 am   #8
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Default Re: Ferguson 705T Senator.

Hi John,

The shop I worked at generally only fixed what we sold, the boss who at one time used to do the repairs knew what he was doing and so did the other chap I worked with. So perhaps thatís why I didnít see them.

I was a young teenager when I started there and he said to me, ď see those things that have a screwdriver slot or a hex hole, touch them without good reason and I will kick your .

With the technical college and what I learned in the workshop I was shown how and when they may require adjustment and how to perform it.

Happy days, a grand man and a good boss.
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