Ferguson 135T

[Radio Tech]

Hello Dave

The tuner has got some biscuit coil packs in it, all there by 4 of them. I managed to get a better picture but I noticed that the tuner seemed very touchy and it looked as if two three of the trimmers on the I.F. coils had been moved by the fact the red paint on the adjusters was disturbed. I have also noticed that the frame / picture is cramped at the bottom, I think this might be a capacitor somewhere at fault. The circuit has been modified and looks like what Heatercathodeshort John was mentioning so made it a bit more difficult to work through to trace what has gone wrong.

Best wishes

Ken

[FERNSEH]

Hi Ken,
The cramping at the bottom of the picture will be the cathode bypass capacitor of the frame output valve having gone low capacity. In my 247T every capacitor in the frame timebase was replaced.
The complex line oscillator and flywheel discriminator circuit must have given many old fashioned engineers a fright when it was first encountered.
Reference back to my 247T. The problems with the line oscillator were mainly due to the two 0.01microfarad capacitors in the oscillator can having gone leaky.
It came as a surprise to discover the capacitors were nothing special, just a pair of brown Hunts make. I was expecting a pair of silvered mica capacitors.

As John states sixty years ago these sets were a mystery to many service folk and as the quick fix the line oscillator was changed to direct sync. In fact the Ferguson flywheel sync system is actually a very stable circuit. Used in high performance sets from 1952 to 1959.
The OA60 video detector diode W101 can fail. Replace with an OA70 or OA90.
In series with the cathode of the video amplifier is a metal rectifier W102, it's not above suspicion. It's there to create a constant 5volts bias for the PL83, V6.

DFWB.

[Radio Tech]

Hello Dave

I will check all of what you have said, but it may be vey difficult to put the circuit back as the manufacture had designed it, the missing transformer will be difficult to obtain now unless a donor set becomes available. I will see how I progress.

Regards

Ken

[Radio Tech]

Here a screen shot of the test card and a picture of the focus assembly, I am almost certain that there should be a loading spring at the bottom of this assembly, the reason I suspect this that the magnets are not being held in their proper position and its difficult to get the picture in focus. It looks as if I will have to remove the assembly to get a spring on where I think it should be. I changed a couple of 22k resistors and a 20pF capacitor around the fram output but not perfect yet as you can see.

Ken

[FERNSEH]

Hi Ken,
As far as the line oscillator is concerned I'd just leave the direct sync circuit in place. It's vey unlikely a line oscillator transformer will ever turn up.
The frame linearity is looking good. Have you checked cathode bias resistor of the frame output valve? If it goes low you get compression at the bottom of the picture and if it goes high the picture will be cramped at the top.

DFWB.

[Radio Tech]

Hello Dave

No not checked the bias resistor, had not give it a thought, but will check this. Yes I think its a good idea to leave in place what is there, and your right, a transformer will never turn up. Will press on, I took the focus assembly off to put a spring in place, carefully noting where the iron trap was on the tube though. will keep everyone posted.

Ken

[Heatercathodeshort]

Good advice from David and other guys. It is unlikely that the I.F. strip has been fiddled but the old 'Radio Men' loved twiddling anything that moved, probably a throw back to the old 1920's broadcast receivers with neutralized triodes.
The I.F's on this model are 16/19mc/s and without a signal generator it is virtually impossible to check the alignment.
Good examples made by Advance and AVO appear for next to nothing at swap meets [probably at WB this weekend] but you need to know how to use them. A battered TRF model such as the HMV 1807 or Bush TV12 is a good start to play with as they are easier to align than a superhet and not having any form of AGC, it is easier to observe what is actually happening on the screen. Leave alone until proved it has definitely been fiddled with. J.

[Radio Tech]

Here's a little more on the progress of the set, checked cathode bias resistor and this had gone high on the frame o/p valve, got the picture a bit more stable but still not locking fully, I am going to check the components around the controls that are for frame and replace as required. Looked at the metal rectifier, tried a silicon diode but this weakened the video o/p so put metal rectifier back.

Best wishes

Ken

[FERNSEH]

Hi Ken,
the metal rectifier W102 in the cathode circuit of the video amplifier was employed to provide a constant 5 volt bias for V6. A single silicon diode will drop only 0.7 volts. With the metal rectifier back in place, measure the volts present at the cathode of the video amplifier. If it is about 5 volts, all is well. If the rectifier is proven to be faulty the best plan is to replace it with a conventional bias resistor. In the model 247T the metal rectifier bias element has been replaced by a 330 ohm resistor. A degree of DC stabilising is effected by connecting a 47Kohm resistor between the cathode and screen grid of the video amplifier. The 330 ohm bias resistor should be bypassed with a 1000pF capacitor to improve HF response.
The video amplifier is supplied with positive going video, the syncs are negative going. So it follows if the video amplifier over biased the sync pulses will be "crushed".

DFWB.

[Radio Tech]

Hello Dave

Have solved all with set now so many thanks everyone for help and advice.

Best wishes

Ken

[FIXITNOW]

well done ken

[Heatercathodeshort]

Any chance of the final picture Ken? It's a long time since I've seen one of these performing in full glory. John.