Ferguson 705T Phase II

[Heatercathodeshort]

Just a quick thought David. Have you checked the anode load resistor typically 22k on the frame osc section of the ECC82? J.

[FERNSEH]

Originally Posted by Heatercathodeshort

Just a quick thought David. Have you checked the anode load resistor typically 22k on the frame osc section of the ECC82? J.

Hi John,
that's a good idea, I'll do that and report back later.

DFWB.

[FERNSEH]

The 22K oscillator anode load resistor is OK. The sync feed to the timebase board has been disconnected and the syncs at the anode of the EF80 sync separator are perfect, however, there is a high amplitude pulse at frame rate present on the sync supply wire to the timebase. This might be the result of a fault in the CRT blanking circuits.


DFWB.

[FERNSEH]

Connected a 68Kohms resistor in parallel with the 180Kohms anode load resistor of the sync separator valve.
As can be seen in the lower oscilloscope trace the trailing edges of the sync pulses have been sharpened up.
The result is now reasonable interlace is possible when the frame hold control adjusted, but the setting is critical.

Like the Ferguson 705T the Philips 17TG100U employs a frame sync pulse differentiator to trigger the frame oscillator instead of the more common RC integrator circuit. The 17TG100U has the extra refinement of having a line sync shaper valve interposed between the sync separator and oscillator. The advantage of this buffer stage is that line oscillator pulses cannot be reflected back to the sync separator and impair performance.


DFWB.

[FERNSEH]

Perfect interlace at last. A number of components in the frame timebase oscillator needed replacement, see the attached circuit diagram.
Interesting thing to note about the Hunts capacitors was that when these suspect parts were tested on a capacitance meter the indicated capacitance was actually higher than the value indicated on the component.

After replacing the components and powering the set up again the height and linearity controls needed a considerable amount of adjustment.

Other components replaced are R136, R137 and R139 which are in the frame sync coupling circuit.

DFWB.

[Heatercathodeshort]

Put your hunting suit on David, mount your horse and hunt those Hunt's!

They are now 60 years old and must be retired. They were very good capacitors in their day. Those solid black type were still going well until relatively recent years.
Hunts capacitors are often criticized unfairly.

The 600 and 700 series Ferguson chassis were excellent, reliable examples of 405 line receivers. J.

[FERNSEH]

"Put your hunting suit on David, mount your horse and hunt those Hunt's!"
Hi John,
Those old Hunts capacitors will be used to restuff old waxies.
That yellow 0.1uF 630V capacitor is now fitted inside the restuffed capacitor.

DFWB.

[FERNSEH]

The interlace has gone bad again and with critical adjustment of the frame hold control the best I can get is line pairing.
Also, a strange background shading effect which resembles those striations you see when the damping resistor across the line linearity coil goes open circuit, except the 705T hasn't got such a device.
The fault is caused by funny waveforms present at the CRT grid. The line blanking circuit consists of the negative going line sync pulses supplied via a 0.005mfd capacitor and series 22Kohm resistor to the CRT grid. For the frame blanking the negative going flyback pulse present on the secondary of the output transformer is supplied via a 0.05mfd capacitor and series 22Kohm resistor to the CRT grid. A 0.01mfd capacitor is connected from one end the 0.05mfd capacitor to ground.
Just checked the Hunts capacitors, the 0.05mfd has changed value to 0.016 and the 0.01mfd one is open circuit.

Replace those components and the picture shading fault will be fixed? But the interlace problem will be still present.

DFWB.

[FERNSEH]

"Just checked the Hunts capacitors, the 0.05mfd has changed value to 0.016 and the 0.01mfd one is open circuit."

"Replace those components and the picture shading fault will be fixed?"

The faulty capacitors have been replaced and the picture background shading effect has gone.
As far as the bad interlace problem, the set seems to have fixed itself.

The Ferguson 705T has been taken off the bench so that I can get on with another set.

DFWB.

[unitaudio]

Lovely stuff!

Regards,
Paul

[FERNSEH]

"Lovely stuff!"

Hi Paul,
405 only sets like the Ferguson 705T were made in 1961/62 and are quite rare. The industry was going though a bad time because of the indecision about line standards and colour. The press didn't help either - warning readers to delay buying a new TV because it will be obsolete in a few years time.

DFWB.

[MonochromeMarc]

Hi David,

I have to say I'm well impressed with the Ferguson, darn good job young man !

Marc

[FERNSEH]

Hi Marc,
The only issue I have with the Ferguson 705T and the Decca DR101 is that I can remember these sets when they were new, more than fifty-five years ago! Of course I was very young.

DFWB.

[beery]

Hi David,
That's a great result. It is always good when all the little niggles are ironed out and you can take the set off the bench.
I often find clearing up the last few faults seems to take forever.

Anyway, that's a really nice set now. I have to admit I have a soft spot for Fergusons.

Cheers
Andy

[FERNSEH]

Hi Andy,
I've avoided the temptation to convert it to dual standard operation.
I have the converter IF amplifier unit to hand and although the fitment is simple enough, a new cabinet back is needed to accommodate the new unit.
Much better to look out for a 23" convertible version of the 705T and fit the converter in a convenient space inside the large cabinet.

405 looks good on the 19" CRT but the lines are all too apparent on the 23" sets.
Witness that on my Pye V600A.

DFWB.

[FERNSEH]

Now a replica metal stand will be made for the set. We've seen the 1961 sales brochure pictures so it should be possible to create something from those.

DFWB.