PYE TT1 - First Transistor Portable UK TV

[FERNSEH]

The frame oscillator is of the blocking oscillator type. Transformer feedback is between the emitter and base of V25, an OC72 transistor.
The collector of V25 is supplied from -60volts which originates from the collector of the line output transistor.
Obviously without the -60 volt supply the frame oscillator will not work, but by momentarily short circuiting the frame hold control to ground the oscillator can be kicked into action. About 0.5V P - P sawtooth waveform is present across the ramp forming capacitors C74 and C75. Ref to post #7 for the circuit.
The frame output stage is working OK.

DFWB.

[Heatercathodeshort]

I have only repaired one Pye TT1 and that was around 1968. The receiver was around 10 years old even then.
This is my Ferguson 743T. It is missing it's sun shade but other than that, very clean and complete. I must sort it out.
The 743T dates from 1961 and was manufactured in very small numbers. The TT1 was very advanced and I think was manufactured 3 years earlier.
I hope you get it working David. Regards, John.

[FERNSEH]

Hi John,
The Ferguson 743T is the rarest of the early UK made all transistor TV sets. Information for the set can be found in the 1961/62 Radio and Television servicing book. Pages 325 to 331. The 743T seems to be a considerably more developed set compared with the Pye. The latter is somewhat crude in it's construction. The Ferguson has five stages of vision IF amplification using five AF114 transistors. The Pye uses the earlier OC171 in the four stage vision IF amplifier.

More progress with the Pye. The no sound fault was traced to one of the output transistors gone base to emitter short. The original push-pull output stage employed OC72 transistors, these must have failed a long time ago and were replaced with two AC128s. It was one of those AC128s which had failed.
Work is going well with this set. The sound stages are working and so are the vision circuits up to the base of the video output transistor.
The video amplifier does not work because the -60volt supply from the line output stage is absent.
Interesting to note that in the Ferguson and Pye the CRT is grid modulated, supplied with a positive going video waveform.
The reason for this is because the sync separator transistor is a pnp type.
The transistor conducts only on the negative going sync pulse tips.
In normal valve practise the valve conducts on the positive going sync.

The next stage of the restoration is line output stage. The 2G221 is unobtainable but there is a limited number AU101/3 transistors available from on-line traders.

DFWB.

[Studio263]

AU113 from an early BRC 1590 should work if you get really stuck.

[FERNSEH]

As two line output transistors are employed in the TT1 the AU113 ratings will be more than necessary for the job. The -70 volt flyback pulse at the collector of the "upper" line output transistor V35 is distributed across both transistors.
The flyback tuning capacitor C97 has the remarkably high value of 0.17microfarads.

DFWB.

[FERNSEH]

Late production BRC 1590 sets employed a silicon transistor as the replacement for the AU113. In fact the later PCBs were fitted with links to allow this.
The NPN silicon transistor was wired "upside down", that is,with the collector to ground. A type BD160 comes to mind.
The BRC 1612 mono TV of 1974 employed modern silicon transistors so the power supply line was positive. According to the circuit diagram a PNP line output transistor was employed. The transistor VT8 was wired into the circuit with the collector to ground, again, upside down.

The attachment shows the circuit arrangement in the 1612 chassis when a PNP line output transistor is employed. I'd consider something like this for the TT1.

DFWB.

[FERNSEH]

Simplified circuit of the line output stage. Note the capacitor C95, connected between the junction of the two line output transistors and a tapping on the line output transformer primary. The efficiency diode V38 is an OC28 transistor. The collector is connected to ground and the base serves as the diode anode.

DFWB.

[The teleman]

Ah the pye TT1 would love to get one of those , never seen one for sale . Oh well I'll keep looking
Nice to see someone managed to get one , can't wait to see it working .
Interesting article , I'll be following this with great interest .

Chris

[FERNSEH]

I think it is agreed that employing the 10 volt battery as the supply regulator is not all that good really.
The attachment shows the circuit of the supply regulator of the Ekco T544 portable TV of 1972. If the mains transformer can supply sufficient headroom voltage I'd consider using this power regulator in the TT1.
The Ekco T544 draws much less current than the Pye, 1.25amp as against at least 2amps in the Pye so the OC26 or AD149 series regulator will have to be shunted with a 10 ohm resistor. The series regulator transistor in the BRC 1590 uses similar an arrangement in order not to exceed the current limits of the AD149 transistor.

Two AU113 line output transistors have been ordered from an online supplier in Holland.

DFWB.

[Studio263]

The 1612 was a lovely set, the best of the BRC portables. Neat and pretty too, shame that most of them went for export (note the German markings on the PCB silkscreen). The way that the line driver transformer has been wired makes it easy to fit an NPN line output transistor if you want to, the only difficulties are mechanical (e.g. dealing with the transistor body which is no longer grounded). From memory, these used an AU113 as well.

I've never seen a 1590 without the links; I had an Ultra one with red resist that was pretty early, that certainly had them. They used a Ge AD149 for the regulator as well, in the late 1951s (14") I think that that was changed to Si too. A PNP Ge line output transistor could have been considered out of date by 1970, there would have been better choices by then (unless you were Rigonda!). Even the Sony TV9-306UB (late 1965) has a Si NPN transistor here.

[FERNSEH]

The 1612 portable TV. Sold in the UK as Ferguson, Marconi and Ultra.

DFWB.

[FERNSEH]

Update on the progress of the restoration of the Pye TT1.
Today the two line output transistors were replaced. Not a very easy job, in fact it's an even more difficult task than the replacement of the two line output transistors that are employed in the Rank A823 chassis. The original Texas 2G221 transistors are impossible to find and for that that reason two of the more common germanium PNP AU113 transistors have been fitted.
I've every reason to believe the new transistors will work satisfactorily because even without the line scan coils connected a -30 volt pulse is present at the collector of the "upper" line OP transistor.
With the line scan coils connected the flyback pulse at the collector of the upper transistor is -60volts, the service manual indicates it should be -75V.
The EY51 EHT rectifier heater is lit and there is an audible ticking noise from the frame output transformer.
Things are looking good for this set.

DFWB.

[FERNSEH]

The EHT voltage is down a bit, it's about 7KV. The service manual states it should be 9 to 9.5KV. Even that is a low figure for a 14" CRT.
The auxiliary supply voltages are present and are close to the correct figures. The video amplifier HT is -63V, this is supplied through an OA81 diode which is connected directly to the collector of the line output transistor.
The negative CRT brightness control voltage is 43V, should be 53V. Again supplied from the collector of the line OP transistor.
The first anode supply for the CRT is +285V, it comes from a tapping on the EHT winding. An early silicon diode is used, type FST1/A.
The CRT is grid modulated which means the video waveform is positive going. The brightness is controlled by varying the tube's cathode voltage.
There is no modulation present at the grid of the CRT. It's possible the video output transistor has failed. It's a Newmarket PNP type V15/20R.

DFWB.

[FERNSEH]

C97 is the line flyback tuning capacitor. It is almost certain that it has developed a leak, it is now rather hot and there is wax oozing out at the ends. The set continues to work except the flyback pulse at the collector of the "upper" line output transistor now down to 55volts.
C97 is 0.17microfarads. The replacement will have to be made from capacitors of various values to get something near the correct figure.

DFWB.

[FERNSEH]

That's more like it. The EHT is now almost 9KV and the video amplifier HT is -75volts. The faulty capacitor had the less critical value of 0.15microfarads.
Now there is the video circuits to sort out and then hopefully the set will be displaying pictures again.

DFWB.

[FERNSEH]

Everything was just about ready to reinstall the chassis into the cabinet, then disaster! Two OC171 transistors in the vision IF strip have gone down with the dreaded whisker problem. Fortunately I found an AF114 which is a near equivalent to replace one that would not respond to cutting off the screening can lead. As for the other OC171 I just got with simply disconnecting the metal can lead.
Now 25volts P - P video is present at the CRT grid connector.

DFWB.

[FERNSEH]

Well, after all that effort the results are to say the least disappointing. Apart from the lack of height and the picture the wrong way, those faults are the least of my problems, it's that strange picture definition that is the real concern.
There is a fault in the vision IF amplifier or possibly the alignment has been got at.
I've always been led to believe the Cathodeon C36-23 CRT is a special tube made for the TT1. Well it turns out to be nothing special at all. For starters the heater is the standard 6.3 volt 0.3amp type, not a low current consumption type made for battery powered TVs. Also it was always thought tube was special high sensitivity type designed to operate on low level video drive. In fact the tube is similar to the Mullard AW36-20.
The attachment shows the peculiar picture.

DFWB.

[Hybrid tellies]

Looks promising. I think the line scan coils are connected in reverse. Someone once played a trick on me at Mastercare. In my absence the TX9 I was working on was got at by a colleague. He reversed the connections to the scanning coils, luckily I noticed before I sent the set out.

[FERNSEH]

Originally Posted by Hybrid tellies

Looks promising. .

Hi Simon, it sure is. The line scan coils have been reversed so at least the test card is the right way around. A little probing around the IFs revealed that the final IF amplifier was a bit "peaky". A tweek of the core of the last IF transformer has cleaned up the picture.
The AGC system in this set is a bit primitive. It's a mean level system operating on the first IF amplifier transistor only. An increase of signal strength reduces the negative bias voltage to the PNP OC171 transistor.
A base bias potentiometer controls the gain of the RF amplifier transistor, an AF102
Six years later with the introduction of silicon transistors the forward AGC control system became the norm.

The frame linearity controls will have to be replaced.

DFWB.

[FERNSEH]

Getting there. Even with the CRT heater drawing 0.3amp the total current consumption of this set is under 1.6amps from a 10.8volt supply. 17watts!
Compare that with a 14" all valve TV which can be as high as 160 watts.

DFWB.