PYE CT72

Members Set: Andrew Saunders

Manufacturer: PYE
Chassis: 691
Model: CT72 (Hybrid)
Year: 1969
System: UHF 625 line PAL single standard
CRT: Mullard A56 120X
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Here is one of PYE’s early single standard ( 625-line only) hybrid colour television. This set is a unique example that was found by Andrew. He spotted it  on e-bay and it came from Southend. Thankfully rescued from a house clearance and not taking a trip to the local tip like so many sets fate. 

Photos Of How It Arrived

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Then in Andrew’s own words:

I know the seller of the set had powered it up and had used a video to try it out. So, I briefly did the same with a DVD player and modulator. When  tuned in and was astonished at what I saw. ( see below)

Is it really true? How can this be?

No doubt there are capacitors that are past their best, Callins for example, but look at the initial result… I have made no adjustments other than tuning, brightness, colour and contrast.

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Indeed I think we can all agree that the resultant picture after initial switch-on is incredible. As most TV repairer/restores know, this just does not happen. What’s more from Andrews initial inspection, this set was still running on all its original components. This was starting to suggest the set might be been New Old Stock or bought and never used.

Andrew then picks up the story:

I changed a small electrolytic on the frame board as it was swelling at the rubber end and leaking, all others seem fine.

The pic below is the side flap removed and the convergence panel in the set-up position. Further inspection shows the date FEB 69 on two CCL caps. One on the CDA, the other in the line stage .

Time for a good inspection of the components in that stage….a resistor across the linearity coil looks over-heated.pyect72-8

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This I’m sure you agree, is an interesting set and one that is shaping up to be a very nice example for Andrew’s collection. Now for a brief interlude and some technical information

I.F. Panel

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Transistor
Function
Type
VT1 1st I.F. Amplifier BF196
VT2 2nd I.F. Amplifier BF197
VT3 2nd I.F. Amplifier BF194
VT4 3rd I.F. Amplifier BF197
VT5 1st Phase Splitter BF194
VT6 2nd Phase Splitter BF194
VT7 Sync Separator BC147
VT8 A.G.C. Amplifier BC148
VT8a A.G.C. Crossover BC158
VT9 A.G.C. Rectifier BC148
VT10 A.F.C. Amplifier BF194
Decoder

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Transistor
Function
Type
VT12 A.C.C. Amplifier BF194
VT13 Burst Amplifier BF194
VT14 Burst Gate Amplifier BF194
VT15 D.C. Amplifier BC148
VT16 Reference Oscillator BF194
VT17 Limiter Follower BC148
VT18 Line Phase Identity BC148
VT19 Colour Killer BC148
VT20 Chroma Amplifier BF194
VT21 Delay Line Driver BF195
VT22 PAL Bistable Switch BC148
VT23 PAL Bistable Switch BC148
Colour Difference Panel

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Transistor
Function
Type
VT28 Blanking BC107
VT29 R-Y Pre-Amplifier BF184
VT30 G-Y Pre-Amplifier BF184
VT31 B-Y Pre-Amplifier BF184
Valve
Function
Type
V6  Luminance Output PL802
V7 R-Y Amp and Clamp PCL84
V8 G-Y Amp and Clamp PCL84
V9 B-Y Amp and Clamp PCL84
Frame Timebase

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Transistor
Function
Type
VT24 Frame Oscillator AC127
VT25 Frame Driver AC128
VT26 Frame Output Pair BD124
VT27 Frame Output Pair BD124
Line Timebase

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Valve
Function
Type
 V1  Line Oscillator  PCF802
V2 Line Output PL509
V3 Boost Diode PY500
Transistor
Function
Type
VT35 Beam Limiter BC108
Convergence Panel

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Transistor
Function
Type
VT32 Blue Line Clamp AC128
VT33 Frame Clamp AC128
VT34 Red/Green Line Clamp  AC128
The CRT PCB

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Back to the story of the set

we shall let Andrew pick up the events:

well it was too good to last…. ( see below)

Line hold had become weak and twitchy with slight bending at the top plus the hold control has to altered on channel change with a hard to lock picture. I tried a new PCF802 with no difference.

It looks like some proper fault-finding is now required and I will start to check the oscillator circuitry around the discriminator diodes and PCF802 voltages etc.

Let the fun commence….

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A 100k in series with line hold control was completely O/C.

Replacing it cured the fault. All other components checked out ok.

I have carefully replaced all of the smaller black Callins type and have not found any of them to be electrically useable.

Upon measurement, their values are way high and it has been mentioned that this is due to excessive leakage.
When using a bench PSU to apply some volts, just below the rated value on the cap, I found that most of them draw current of say a mA or so and in some cases, it started to rise. The same can be said for some of the smaller blue caps that I have replaced too.

The danger is of course that they will explode with some force as the electrolyte heats up :aacI don’t want that happening in this set !
So, in this case, prevention is better than cure.

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And some final words from Andrew

I think this is an important piece of history, not just because of its near perfect cosmetic and operational condition, but mainly because it is an example of one of the first single standard UHF colour televisions to be released in the UK.

In my humble opinion, it gives an excellent picture and is easy to service and adjust. A good uncomplicated design.  I Hope this is of interest to the readers at Radios-TV,  please feel free to leave comments below and I will respond if any more info is needed.

Kind regards, Andrew.

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8 thoughts on “PYE CT72

  1. We sold these and I installed and fixed them, I liked them, easy to repair and as reliable as any other sets perhaps better.
    Good picture, I think the CDA helped that rather than the early RGB drive sets, i.e RBM A823. The mechanical tuner gave me less trouble than the later varicap push buttons and Mullard 1043 tuners used I think it was the 693 variant.

    Frank

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  2. Thanks for all the feedback everyone.
    It goes to show just how capable these early sets were at producing good pictures and how time and usage was their biggest enemy.
    Needless to say, I don’t use this set very often, just an hour or so every few months.

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  3. Hi,
    Great to see pictures and images of the very first family colour television, purchased around 1970. I used to get into trouble from my dad for fiddling with the hidden controls to adjust convergence and colours within the left-hand side, screwed side panel. In the day, the TV was prone to become unaligned, so I experimented realignment using the famous ‘Test Card’ etc. I had seen the TV engineer when on occasions he was called upon using the panel…

    The TV rarely had any problems, other than my mucking about with the ‘hidden panel. I always put it right, and became a dab-hand at electronics and the like at the tender age of 12.
    Best Regards
    David

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  4. Excellent set! I didn’t see too many of these when I started Philips but the ones that did come in were easy to fix and gave excellent results. It’s full of Mullard ‘Mustards’ so probably not even worthy checking them. Great job….it should go on for many more years.

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