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Old 13th Sep 2005, 7:34 pm   #21
Heatercathodeshort
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Default Re: Ferguson 951T - Where to start......

Hello again Sean,
I have checked the voltage readings given on the original 941T circuit issued by FERGUSON in 1949. The control grid is not quoted but the cathode voltage is qouted as 2.23V. The manual states: 'V16 bias volts calculated. Cathode volts depend upon setting of width control.'
The value of R61 is quoted at 3.9K. Suggest you check C48 grid coupling cap. The stage cannot work if you short the grid pin 5 to earth. Suggest you recheck your pin connections..Its easy to make a mistake when they are bent over. The PY31 should read: With 240v mains input, - [minus] 25volts [approx] Regards. JOHN.
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Old 14th Sep 2005, 11:54 am   #22
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Default Re: Ferguson 951T - Where to start......

Hi all,

More faults have been found!

I had a look around V8 (line oscillator?) and found that a resistor (r27) was open circuit - with this replaced the familiar ear splitting whistle was back! - Checking the anode voltage before this was done revealed a voltage of over 200v as opposed to 44v!

I then fitted the missing C26, and am now rewarded with a near full screen "picture", and what I guess to be flyback lines.

So, my next question would have to be "what do I expect to see - do I see snow, or a blank screen?"

I have also found that the "picture" cannot be centred - any ideas?

Cheers
Sean
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Old 14th Sep 2005, 6:59 pm   #23
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Default Re: Ferguson 951T - Where to start......

Well, A picture tells much more doesnt it!

Piccy shows screen with 400c/s modulation applied via signal generator

Any comments?
Sean
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Old 14th Sep 2005, 7:35 pm   #24
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Default Re: Ferguson 951T - Where to start......

Hello again Sean,
You will not see 'snow' on a receiver of this type. The first sets to show 'snow' were the fringe models with flywheel sync and high gain I.F. stages. Its time to apply a signal and from what you have said I think you will get some sort of picture maybe a lot better than you would imagine.

Without a signal you should be able to get a full size 'raster' or screen illumination. The scanning lines should be visible if the focus is good and the 'flyback lines' should show on high brightness setting. These are about 1" apart and will flick across the screen when viewing an 'unlocked' raster. [No signal]

You will need a channel 4 signal source. For Gawds sake don't be tempted to 'fiddle' the tuning cores in the RF transformers. It is highly unlikely that these will require adjustment. You will mess the old set up good and proper and probably damage the transformers themselves. You CANNOT retune this receiver to channel 1.
Good luck with it. John.
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Old 14th Sep 2005, 11:50 pm   #25
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Default Re: Ferguson 951T - Where to start......

Hi John,

OK on all the info, as for the tuning slugs, I fear an alignment will be needed, as the vision appears at 69megs......with sound around 70megs....,

Still, I have a reasonable RF source, and a spectrum analyser, as well as some of the more mundane test gear, so realignment should be impossible

I was thinking about building the modulator designed by David Looser, and using a VHS source - any input on this would be good

Cheers
Sean
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Old 15th Sep 2005, 7:43 am   #26
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Default Re: Ferguson 951T - Where to start......

David Looser's modulator is fine. So is my design using the Rediffusion HF modulator cans. David Robinson's design is inherently multichannel tunable. I have not seen his modulator but I've known David for many years and I have no doubt that he will have done a good job. Darius's design looks good too.

You have a lot more RF experience than me so you should be able to get excellent results whichever route you choose.

It really is worth treating yourself to a standards converter. You are welcome to borrow my Aurora to try it out.
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Old 15th Sep 2005, 8:56 am   #27
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Default Re: Ferguson 951T - Where to start......

Hi Sean,
this looks good! Your tube has the same ion burn in the center like
the one in my LV20.

BTW you are the first ham who makes first the receiver and than the
transmitter. hi hi

73 Darius DD3ET
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Old 27th Sep 2005, 4:02 pm   #28
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Default Re: Ferguson 951T - Where to start......

Ok, I am now playing with alignment - The phantom has been having a good time with the slugs....

I am trying to follow the trader instructions, but I am unsure that I should be getting a negative voltage at the required measurement points (cathode of CRT, and wiper of vert hold control)

The cores appear to be fully unwound to get any form of result at the correct frequencies - I wonder if the set has been modded for Manchester??

Anyway, the alignment is a country mile out, so any pointers would be well recieved.

Cheers
Sean
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Old 28th Sep 2005, 6:05 pm   #29
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Default Re: Ferguson 951T - Where to start......

Hmm, well at some time in its life it was converted to channel 3!!, however this has not been done too well, as I feel the sensitivity is not as good as possible, still, this does explain why I could not peak the rf stages at 61.75 megs.....

I might look into putting it back to original, but for now a new oscillator coil in the modulators..........

Cheers
Sean
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Old 28th Sep 2005, 6:51 pm   #30
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Default Re: Ferguson 951T - Where to start......

Hi Sean,
did you test the coils with a griddipmeter?

Darius
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Old 28th Sep 2005, 10:24 pm   #31
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Default Re: Ferguson 951T - Where to start......

Hi Darius,

No, I did not use a dip meter (I dont own one), but I did couple my spectrum analyser to the rf stages, and just swept the signal generator up and down...

There have been a lot of capacitor changes in the RF stages, so this appears to make sense.

I modded the alexandra palace oscillators in your modulator, and so far the sound is perfect! broadcast quality!

However, I need to look at the video side of things, as I appear to have a problem there - video is getting through, but I am getting nothing sensible on the screen.......

I do have a serious problem with sound on vision as well, but I am sure a spot of alignment work will deal with that. I have noticed that if the contrast control is backed off this problem is reduced

Cheers
Sean
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Old 28th Sep 2005, 10:35 pm   #32
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Default Re: Ferguson 951T - Where to start......

Quote:
Originally Posted by m1ecy
Ok, some preliminary info.

I have found the original HT smoother to be completely shorted (no suprises there then), so first question would have to be can I still get a replacement 100+200uf@275v?
Hi Sean. I have a NOS 200+150uF@325v. I would guess that it is about 30 years old but it IS new and would probably reform very well. It is made by CCL and is approx 5" long by 1/4 dia. If it's any good to you, I'll just pop it in the post.


Rich
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Old 29th Sep 2005, 10:52 am   #33
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Default Re: Ferguson 951T - Where to start......

Quote:
Originally Posted by Richard_Newman
5" long by 1/4 dia.

Sorry that should be 1 1/4 (one and a quarter) inches diameter! It was late!!
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Old 29th Sep 2005, 7:59 pm   #34
Sean Williams
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Default Re: Ferguson 951T - Where to start......

Well, success of sorts, I have work to do on the video modulator I think.
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