Ferguson 14" portable TV set model 454T

[FERNSEH]

I know another Forum member has one of these sets, the Ferguson 454T also known as thw "The 45". Information for the set can be found in the 1958/9 Red Radio and Television servicing book.
I've tried to search the forum for a thread on this set but with no luck.

The cabinet had been damaged some time in the distant past and there was a problem dismantling the set, the bottom part was stuck to the CRT mask.
At last I've managed to remove the cabinet without doing any further damage so it's now possible to take a look at the chassis. A can type electrolytic had blown up apart, see second picture. It turns out that it is the boost capacitor, it's designated as C50 (24mfd) in the circuit diagram. Very unusual to see such a high value in this part of the circuit, a typical value would be 0.1microfarads. In the 454T the 24 microfarad electrolytic is rated at 500 volts. I've got plenty elcos but they are rated at 450 volts, a bit too close to the max boost volts which in this set is 450 volts. Also unusual is that the capacitor is returned to chassis instead of to the HT line. There must be a reason why the Ferguson designers have chosen such a high value boost capacitor. Perhaps the answer to the problem will be to connect two capacitors in series and fit balancing resistors across each one. Suggested value 470K each?
The last time I worked on one of these receivers was in the early 60s.

DFWB.

[Focus Diode]

I remember the bottom of the cabinet had broken and repaired with glue in the past, probably through being dropped, only for the implosion screen to be glued in as well, hence the difficulty in taking the set apart.

The high uF boost capacitor is unusual to say the least. As David says values usually range from 0.1uF to 0.47uF. I would've thought much of the circuit would be much the same as employed on table models, eg: the 306T, so why such a high value for this portable is a mystery. It certainly causes problems in finding one with a suitable working voltage.

Looking forward to hearing more about the set and of course seeing it again.
Cheers,
Brian

[Nuvistor]

I wonder if they had a problem with the design and found they required the large value. The only type would have been a can electrolytic and it may have been easier to take it to ground than insulate the can from the chassis.

[mark pirate]

I bet that cap made someone jump when it exploded!
I nearly bought one of these last year, but the knobs were missing and the cabinet was very tatty, certainly not worth the £40 asking price!

Mark

[Heatercathodeshort]

These are nice receivers David, probably the best 14" transportable of the 1950's. My next door neighbour owned one when I lived in Merton Park back in the 60's.
The 'beached whale' HMV version, the 1864 is very 'lumpy' when compared with the slick Ferguson.
Being a full range design with flywheel sync, it was considered by Ferguson to be a truly nationwide model. The mains voltage selector was a customer control clustered with the hold controls etc. Not a good idea as owners tended to set this for 200v to 'brighten up' the response in very weak signal areas. I did have one of these a good while back but it has vanished. I probably gave it to a visitor who fell in love with it...Regards, John.

[Barry Lloyd]

Why not just use the 450V one and return the negative to the HT line? OK, it's not as per original, and the can, if not isolated, will need to be well insulated,but that's also true for the series option. I suppose it may increase he amount of 10khz ripple on the HT line, which may or may not be objectionable. Might be interesting to try.
It might also be interesting to see what the effect is of using a much smaller value, e.g. 0.47 - just out of curiosity to find out why Ferguson went for such a high value.

Barry

[FERNSEH]

Before plugging the set into the mains I carried out the usual inspections. The mains filter capacitor and also the capacitor connected to the top of the heater chain have been clipped out. I don't want the mains dropper resistor destroyed. Both caps are TCC waxies so you can be sure they will fail before long. The heater chain checked as OC, no valves were faulty just simply corroded valve pins. The boost capacitor has been replaced with a hi-viz 1 microfarad 630 volt component.
Time to switch on the set. The line timebase came to life with lots of EHT, a ticking noise could be heard from the frame output transformer, but no raster.
Voltage tests at the CRT base revealed there was 375 volts for the first anode, 100 volts at the cathode but just a few volts at the grid. Perhaps R51 has gone high or OC? It checked OK. C51 and C52 are OK so what's dargging down the brightness control voltage? It turned out to be the control itself.
Fortunately I had a spare NOS dual 500Kohm + DP switch control, only problem was the shaft is too long, but reverting to 1960s practises the shaft was cut down to the correct length. The replacement was fitted and the set switched on again, this time real results, a very bright but distorted raster.
The CRT is excellent. No flashes when the turret tuner is operated so there is a signal stages fault to find.
Standby for more news on this resto job.

DFWB.

[FERNSEH]

More progress. The blank raster was caused by instability in the second vision IF amplifier. This turned out not to be OC decoupling capacitors but to be the PCF80 triode-pentode V4. Evidence of instability was discovered by the 10 volts present at the video detector. When the control grid was grounded the voltage dissappeared. There's still lots to do to this set, a full recapping of the frame timebase to cure the frame linearity fault and also the line sync is weak. This set has a flywheel sync system employing two selenium diodes W3 and W4 which are a STC type V3/1/17.
The line frequency was too low and this was caused by R117 (330Kohm) which had gone high to 420Kohm. R117 is connected between the slider of the line hold control and pin 9 of V14B, another PCF80. The pentode section V14A functions as the sync separator.
This is truly a high performance receiver, very good sensitivity considering no special valves are employed in the signal stages. PCC84 and PCF80 in the tuner. An EF80 and a PCF80 in the vision IF amplifier. Nothing really special just first class circuit design.

DFWB.

[FERNSEH]

It is all too clear why such a high value boost capacitor is employed. The anode of the frame output valve is supplied with all of 450 volts from the boost HT line. Refer to the circuit diagram in my first post. I was wondering to what point "P" is connected. It is common practice to supply the ramp forming capacitor via the height control from the boost supply but finding that the anode of the pentode section of the PCL82 frame output valve was fed from the boost HT came as a surprise. Surely the valve is not designed for such high voltages?

[Nuvistor]

Typical anode voltage is 170v according to the booklet. The cathode resistor, is that 1200 ohms? if so that is much higher than normally used, presume to keep the Ik down. The Ik is about 16ma if I am reading the cathode voltage/resistance correctly, that is much lower than typical, again I presume to keep the valve within it Po rating.
The Frame output transformer appears to have two primaries in series, this could be standard for FOTX and not usually shown be it could be something in the design.
Is the frame fault you have due to you using the 1 microfarad instead of the 24?

The other item I found interesting is the charging capacitor C80 is taken to the cathode of the output valve, decoupled to chassis by C84.

[FERNSEH]

Originally Posted by Nuvistor

Is the frame fault you have due to you using the 1 microfarad instead of the 24?

It is. I've taken a chance with a 450 volt electrolytic of the correct value and the frame linearity has improved considerably, but it is still not perfect. I reckon that only by replacing those Hunts capacitors C60 and C61 will the linearity will become what one expect from this receiver.

The other item I found interesting is the charging capacitor C80 is taken to the cathode of the output valve, decoupled to chassis by C84.

Another common practice. The cathode bypass electrolytic would have smallish value of 50 microfarads. The idea is that a parabolic waveform is developed across the cathode capacitor. By connecting the bottom end of the charging capacitor to cathode non linearity of the ramp waveform is cancelled out.

The cathode resistor of V13B is 1.2Kohms. The circuit diagram indicates that the cathode voltage is 19.2. Simple Ohm's law tell us that the cathode current is only 16mA.

DFWB.

[Focus Diode]

One wonders if the Thorn/BRC group were experimental with their portable models, the unusual heater chain and dropper capacitor in the 16" 950/960 model I recently restored also coming to mind?

I too wondered if the lower value replacement boost capacitor contributed to the height problems, then yet again could be co-incidental. Most sets that are woken from a long sleep are found with this problem due to aged capacitors and the likes.

Excellent work so far. I'm looking forward to seeing the set again.
Cheers,
Brian

[Heatercathodeshort]

I can't think of any other receiver that feeds the frame output stage from the boost line.
They probably went a bit OTT with the introduction of the wider angle 14" CRT It may have been Ferguson's first 90 degree model. I think the 406T was not introduced until a few months later in 1958.
I don't want to see another Masteradio saga here David. Finished and back on by Sunday and no excuses..John.

[FERNSEH]

Originally Posted by Heatercathodeshort

I can't think of any other receiver that feeds the frame output stage from the boost line.

Hi John,
The were other sets that sourced the HT for the frame output stage from the boost line. For example, your favourite make, Masteradio. The models were the TF7T and TF21T. In these receivers the Frame output valve was a 12BH7 double-triode.
Advanced Masteradio technology.

DFWB.

[FERNSEH]

The Ferguson 454T has a simple but effective line flywheel sync system.
A description on how the flywheel circuit works can be found in pages 425 and 426 of the 1958/8 Newnes R & T servicing book. The info relates to the HMV version of the 454T, the model 1864.
Reference to the attached circuit diagram. I secured an improvement in line sync performance by replacing capacitors C91, 92 and 93 in the filter circuit that feeds pin 9 of V5B. C93 (1mfd) was particularly leaky at 300Kohms. All were Hunts make. The discriminator diodes were replaced with two BA148s. Remember them? The BA148 which was used in many early colour TVs was later replaced by the BY206. Green coloured diodes.
The oscilloscope trace shows the sawtooth waveform developed across C89, this is the reference for the discriminator. When the line sync correctly locked the rapid changing part of the sawtooth waveform is coincident with the negative going line sync pulses. No correction voltage is produced on locked picture. Any variation in line frequency will result in a correction voltage being supplied to the grid line oscillator V5B. a positive voltage to speed up the oscillator if the frequency tends to go low and vice-versa.
On account of the excellent signal handling characteristics of this set on strong and very signals as well the flywheel sync to remove ragged pictures this receiver is as HKS says and truly go anywhere portable TV set.

DFWB.

[Andy Green]

Hi Dave, I bought one of these back in 2007. I'm sure I posted photos of it (half) working back then but just did a quick search of my posts and nothing came up. Still have the set but haven't done much with it since then! I had one as a child donated by the local TV repairman. Back then not many kids had their own TV in their bedroom!
(If anyone knows of any scrappers working or not pm me. )

[FERNSEH]

Real progress today. A number of capacitors in the frame timebase needed replacing. The easiest method to access these components is to remove the CRT. This can be done simply by removing six screws that secure the CRT assembly to the main chassis. Three Hunts capacitor C80, 81 and 82 all checked OK but somehow I had suspicions about these capacitor so they were replaced by new hi-viz components. The cathode bypass capacitors of the frame output valve and audio amplifier V12 have also been replaced. V12 is an ECL80 and as this valve has a common cathode for both sections and it is usual practice to use a very high value bypass capacitor. In this set it is only 50mfd. I think the low value coupling capacitor permits a low value cathode cathode capacitor. The coupling capacitor C73 is only 0.003mfd.
The pictures show the chassis and the CRT which is the type that has bumps around the cone. You see a lot of Continental CRTs like this.
The picture linearity is nearly perfect. Not much more to do now.

DFWB.

[Ed_Dinning]

Hi David, its looking good. A tip with ECL80 and high valve cathode bypass caps is to add a 1uF or so paper cap in parallel. This often overcomes instability problems even when a new e cap has not totally cured it.
Some paper caps from old sets will test out OK on a DVM, but are usually found by an Avo on the high ohms range. Best of all is a small power supply that takes them up to their working voltage to reveal all. Probably quicker just to change!

Ed

[FERNSEH]

Hi Ed,
Thanks for the tip. A 1mfd 30 volt non electrolytic capacitor would take up little space and will improve the stability of the audio amplifier.
Ferguson made good use of the ECL80 as a push-pull amplifier in many of their earlier TV sets.

Reference to the timebase circuit diagram on post #9 of this topic. The Hunts capacitor C83 (0.005mfd) in the frame linearity feedback was tested and found to be low value, down to 0.0015mfd. No apparent leak. Replaced by a 0.0047mfd mustard. Same goes for C111 (0.01mfd) in the frame oscillator, this one had risen in value to 0.02mfd! Again no apparent leak.
After replacing C83 the frame linearity improved dramatically, it's now perfect after readjustment. The result of replacing the oscillator capacitor C111 is now the frame sync locks in the middle of the range of the hold control.

The picture quality is superb. Perhaps the recent circuit changes in in the line stores in my standards converter might also be reason for the excellent pictures.

DFWB.

[Heatercathodeshort]

Looks great to me David. Those 90 degree Mullard tubes really are superb, the equivalent quality to the later colour 30AX series and just 12 years later... John.