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Old 31st Jul 2019, 10:53 am   #1
FERNSEH
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Default Stella ST1007U

Introduced late 1959 the Stella ST1007 is a development of the earlier models ST8617U and Philips 1768U. Both models were introduced late 1957. Cabinet apart, the main difference from the 1957/8 models is the tuner unit. The original tuner uses PCC84 and PCF80 valves. In the Stella the RF amplifier is a PCC89.
Noteworthy in the Stella is the position of the front controls, on the left of the CRT. I think it is an attractive set, got a continental look about it.

Before any serious work can commence on this set the line output transformer windings must be warmed up in order to drive out any moisture. Usual procedure, connect the bench power supply unit to the overwind and the top cap connection of the PL36. Supply between 20 to 30 volts.

Information for the Stella ST1007U and the 21" ST1001 can be found in the 1960/61 Radio and Television servicing book. Pages 613 through to 621.

DFWB.
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Old 31st Jul 2019, 11:50 am   #2
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Default Re: Stella ST1007U

Quote:
Before any serious work can commence on this set the line output transformer windings must be warmed up in order to drive out any moisture. Usual procedure, connect the bench power supply unit to the overwind and the top cap connection of the PL36. Supply between 20 to 30 volts.
Do you advise this on any vintage set, even those that have been kept in a dry warm house? I guess it does no harm.
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Old 31st Jul 2019, 12:18 pm   #3
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Default Re: Stella ST1007U

Hi Martin,
I wouldn't do any harm warming up any unknown transformer using this method. I applied the same procedure on the recent Bush TV22 restoration. It, like this Stella had been stored in a damp environment.

DFWB.
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Old 31st Jul 2019, 12:54 pm   #4
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Default Re: Stella ST1007U

Yes.....it just looks wrong! Maybe they were designed for left-handed people! Maybe the design for the cabinet got reversed but they had made too many before it got noticed....!
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Old 31st Jul 2019, 1:47 pm   #5
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Default Re: Stella ST1007U

The same tuner / valves is used in the 1708U, another version of 1768U.
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Old 31st Jul 2019, 5:48 pm   #6
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Default Re: Stella ST1007U

Initial observation of the underside of the chassis reveals loads of Philips black tar capacitors and the few I've checked so far have really bad leaks. Might get away with reforming the HT smoothing capacitor. Resistance reading between HT and chassis is 50 ohms! No doubt there is a black tar capacitor across the HT supply. Back in the sixties these sets were considered an easy fix. Used to replace quite few line output transformers in them though. That was an easy job because it is a plug-in unit.
Philips TV sets were the favourite make for renting out anywhere far from base.

DFWB.
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Old 31st Jul 2019, 8:00 pm   #7
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Default Re: Stella ST1007U

I got mine working a couple of years ago and have to say cracking picture with excellent linearity.

TTFN,
Jon
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Old 1st Aug 2019, 9:28 am   #8
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Default Re: Stella ST1007U

Hello David,
These were quite rare in my part of London. As you mention the tuner is the later 17TG100U series with PCC89 and printed circuit coils.

Certainly an odd cabinet layout and I feel they may have sold more if produced in the conventional style.

1768U chassis noted for it's reliability and very long life. The LOPT is a complicated expensive affair with a rubber pot of rod magnets that you add to or take away to obtain line linearity. Only Philips but a great chassis evolved from a large range of reliable chassis from 1951. John.
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Old 1st Aug 2019, 10:58 am   #9
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Default Re: Stella ST1007U

Hi John,
That certainly looks a lot better but the reason for siting the extra push-button control panel on left side of the screen was because the cabinet was slimmer than the earlier ST8617. The Philips 1768 and Stella ST8617 had deep cabinets so it was possible to fit the large tuner and controls assembly on the cabinet side well away from the CRT bulb. In 1959 the big sales theme was the new "slimline models" and obviously Philips wanted to be on the act so came up with the ST1007. But there was no space for the side mounted tuner so the quick fix was to make the cabinet wider to accommodate the tuner unit.

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Old 1st Aug 2019, 7:34 pm   #10
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Default Re: Stella ST1007U

I quite like the look of it. It is always nice to see something different.

It looks odd from the inside too I think.
That lopty can is quite a beast, but then it looks like the only valve in it is the rectifier (DY86?), so it is probably quite cool in there as opposed to a housing the contains the line output valve and boost diode as well.

I should imagine this set must be quite rare these days. I must smash up more of those common TV22s

Cheers
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Old 1st Aug 2019, 8:24 pm   #11
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Default Re: Stella ST1007U

I'll help you..John.
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Old 1st Aug 2019, 8:43 pm   #12
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Default Re: Stella ST1007U

The short circuit across the HT line has mysteriously disappeared, the reading between the HT line and chassis is 50Kohms, that's OK.
The HT supply electrolytic capacitors C69,C70 and C71 are useless, will not reform so a replacement will have to be found. The capacitor is the type which has the twist tags to secure it to the chassis. A conventional can type capacitor will be used along with a mounting clip.
Clipped out a few black tar capacitors. All found to be leaky. C54, (10,000pF) the line drive capacitor. C57 (56,000pF) and C63 (29,000pF) the boost capacitor and CRT A1 supply smoothing. The frame oscillator, the audio amplifier and focus control are also connected to the A1 supply.
The reason for the unusually high voltage to the audio amplifier is because the anode resistor R26 is 2.7Megohms. R26 along with C28 (560pF) together function as the audio noise limiter. Work that out?

Beery wrote: "I should imagine this set must be quite rare these days. I must smash up more of those common TV22s"
And use the parts to repair those unloved TV24s.

DFWB.
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Old 9th Aug 2019, 8:18 pm   #13
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Default Re: Stella ST1007U

That's all seventeen black tar capacitors removed and replaced with Philips "mustard" ones. The special value capacitors arrived today from Holland. Many thanks to Jac for sending the 0.33mfd and 0.056mfd capacitors.
These are the capacitors that would have been fitted as replacements by a Philips service depot in the late sixties after supplies of the tar capacitors ran out.
So now the HT smoothing capacitor is to be replaced. I've found a 100 + 200 + 16microfarad electrolytic capacitor to replace the original part which can't be reformed. It's useless! The chassis must come out and the CRT removed to perform the HT capacitor substitution.

Meanwhile the line output transformer is still receiving the warm up treatment.

DFWB.
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Old 13th Aug 2019, 1:10 pm   #14
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Default Re: Stella ST1007U

Summary of work done so far: The chassis has been removed from the cabinet and the CRT taken out and stored in a safe place.
The old HT smoothing capacitor removed and the replacement test fitted on the chassis. It's going to be a difficult task drilling the holes for the condenser clip and it might be much easier simply to solder it in place.

The replacement smoothing capacitor was fitted on Saturday evening along with the 10mfd electrolytic capacitor (C76) connected between the screen grid and cathode of the EF80 video amplifier

The smoothing capacitor has been reformed and there is now a steady 230volts across the HT rail. That's slightly higher than the working voltage. It's time to refit the CRT and test the set.
A new CRT securing band will be made, the attachment shows the condition of the original part, it's rusty and liable to break anytime.

DFWB.
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Old 14th Aug 2019, 4:21 pm   #15
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Default Re: Stella ST1007U

Powered up the Stella today without the CRT. After a bit of fiddling about with the line timebase we have a very healthy spark at the EHT connector. I reckon there's 15KV there. The line output valve was a Mazda PL36 but somehow the set didn't work properly with this valve so a Mullard PL36 is now being used, the correct make for a Philips TV of course. For the next stage of the restoration I'll turn my attention to the frame timebase.

Attachments show that the Mazda PL36 is a late production type and has the electrode structure of the cavitrap PL504.
13KV spark at the CRT anode connector.

DFWB.
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Old 14th Aug 2019, 4:41 pm   #16
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Default Re: Stella ST1007U

The frame timebase was an easy fix. Oscilloscope connected to the control grid of the PCL82 frame OP valve. A Sawtooth waveform present but it is apparent that the timebase is running too slow. Check the value of R87 (3.3megohms) and it is >5megohms. After replacing the faulty resistor the frame hold control can be adjusted for 20mS repetition rate. Sawtooth waveform at the anode of the PCL82 is 50volts P - P + flyback pulse.

DFWB.
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Old 14th Aug 2019, 8:25 pm   #17
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Default Re: Stella ST1007U

Testing the video circuits. The oscilloscope shows that 50 volts P - P video is present at the anode of the video amplifier. The sync pulses have excellent rise and fall times.
It's about time to refit the CRT and see what the picture really looks like.

DFWB.
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Old 15th Aug 2019, 9:36 am   #18
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Default Re: Stella ST1007U

AW43-80 CRT refitted on the chassis. As the attachment shows the tube doesn't display a very bright picture. It's possible the tube might become brighter if the set is left working over a longer period of time. It's a low emission condition but it's not caused by the common problem of having a partially shorted heater.
Lack of height is likely caused by the frame output valve cathode bias capacitor gone low capacitance.

DFWB.
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Old 15th Aug 2019, 8:21 pm   #19
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Default Re: Stella ST1007U

A much brighter picture now. Gave the tube a tickle with the Muter BMR90 CRT reactivator. Heater voltage between pins 1 and 12 is 6.25V.

DFWB.
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Old 17th Aug 2019, 10:02 am   #20
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Default Re: Stella ST1007U

A 0.68megohm resistor is connected between the height control and the anode of the frame oscillator valve. The resistor had risen in value to 4.5Megohms.
After replacing the faulty resistor full picture height was restored.

The CRT is holding up but for how long?

DFWB.
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