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Old 17th Aug 2019, 3:56 pm   #21
Heatercathodeshort
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Default Re: Stella ST1007U

It looks good David but what a shame that AW43-80 is a bit flat. That 90 degree tube is usually faultless other than the odd partially short circuited heater. That is probably why it was retired originally.

I probably have a couple up in the garage loft dungeon. It frightens me going up there with all the spooky sounds. I sometimes hear test card music emanating from the roof space but when I pop my head through the hatch...It stops!

I'll sort you out a good one when I've been reformed. If all else fails I have a backless Ferguson 406T with the same tube you can have.
Aghh, I've just thought. You will probably end up repairing the 406T thus ending up back at square one...I've done that.

Seriously it's yours if you want it. Regards, John.
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Old 17th Aug 2019, 8:39 pm   #22
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Default Re: Stella ST1007U

Hi John,
the Stella is still showing reasonable pictures but the CRT isn't too good, but it isn't too bad either. The picture is bright but if the brightness control is advanced too far that "going negative" effect is apparent. The cabinet is clamped up in an attempt to stiffen it up. See attachment. The CRT securing band is a bit rusty and it's possible a friend can make a new one if the Kurust treatment doesn't work. There is no sound, the speaker reads 4 ohms but there is no connection to the output transformer secondary, that's something else to sort out. The line output transformer is holding up well, delivering 13KV to the CRT anode.
Did attempt to fit an on-off switch but have abandoned that project because there are too many complications fitting a later production switch. The rear controls are bit twitchy especially the frame and line hold controls. Might be able to do something about this. I remember these sets well and both the Stella and Philips versions were noted for reliability, did replace a few line output transformer though. Picture definition was always excellent. It's nice to work on one again after almost fifty years or so. These sets were still about when I opened the shop in 1972.

I might have to take up your offer of the CRT.

DFWB.
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Old 19th Aug 2019, 8:39 am   #23
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Left-handers? This Rediffusion set was noted - reclining in the Malta classic car museum ........
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Old 19th Aug 2019, 9:39 am   #24
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Default Re: Stella ST1007U

Now that does look weird! John.
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Old 19th Aug 2019, 10:14 am   #25
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Default Re: Stella ST1007U

The Rediffusion Mark 7 used to look like this:

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Old 19th Aug 2019, 11:56 am   #26
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Quote:
Originally Posted by Heatercathodeshort View Post
Now that does look weird! John.
Ho! And for those who like their 'money's worth' ......
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Old 19th Aug 2019, 12:25 pm   #27
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Default Re: Stella ST1007U

Wouldn't look forward to a service call to that one. At least it has a symmetrical cabinet design.

DFWB.
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Old 19th Aug 2019, 12:40 pm   #28
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Default Re: Stella ST1007U

That has some class! I rather like that but of course you need a large room. It is free from embellishment and I bet it sounds and performs very well.I might be able to fit it in...John.
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Old 19th Aug 2019, 2:46 pm   #29
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Default Re: Stella ST1007U

The only obvious 'omissions' as far as I could tell were - the fax machine/telex and a telephone! Oh - and the tea/coffee maker !!!!
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Old 19th Aug 2019, 5:31 pm   #30
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Default Re: Stella ST1007U

The secondary of the sound output transformer is OK. The fault was caused by a bad solder joint on Tag Strip 1. In fact it looks as if it had never been soldered in the first place.

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Old 19th Aug 2019, 7:23 pm   #31
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It's quite amazing how many times I've found that type of fault - and equally amazing that the relevant device functioned in that state for as long as it did! So much for U.K. QA/QC in those days eh?
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Old 19th Aug 2019, 9:56 pm   #32
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Default Re: Stella ST1007U

hello David in the photo is that a yellow capacitor i can see which looks like one of its leads is loose
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Old 19th Aug 2019, 10:11 pm   #33
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Default Re: Stella ST1007U

Hi Tractionist,
Resoldering the wire to the tag didn't solve the no sound fault.
Sure there is some activity from the loudspeaker when the tuner is rotated and the valves wiggled about in the sockets, but there's still sound.
First, the PCL83 audio amplifier and output valve will be replaced , it's valve that was well known for going faulty. Also, R26 the 2.7megohm anode load resistor of the triode section should be checked, it has the unusually high value because the HT comes from the boosted HT line.

DFWB.
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Old 19th Aug 2019, 10:26 pm   #34
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Default Re: Stella ST1007U

Pity - but is still sounds as tho' the circuit was O/C at that point. The PCL83 sounds like a plan ... any blue glow/checked the emissions?

Keep us all informed .... its a handsome set.
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Old 19th Aug 2019, 11:31 pm   #35
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"Keep us all informed .... its a handsome set."

It is indeed a handsome set and the news is it's now got sound! The fault was the high value anode load resistor R26. It had gone completely open circuit.
R26 along with C28 form the interference limiter. C29 is the coupling capacitor between the triode and pentode sections of V5 (PCL83)

DFWB.
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Old 20th Aug 2019, 12:09 pm   #36
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Great news - a cheap fix ..... once you've isolated it! "Completely OC" .... was it burnt [and if so why]? Anyway .... what's the sound quality like?
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Old 20th Aug 2019, 1:35 pm   #37
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"Great news - a cheap fix ..... once you've isolated it! "Completely OC" .... was it burnt [and if so why]? Anyway .... what's the sound quality like?"
Hi Tractionist,
The resistor wasn't burnt out. As it was rated at 1 watt it should have been OK in it's application as an anode load resistor even if it has 400 volts across it. 0.06watts is dissipated in R26. Many of the original high value resistors in the set needed replacement.
Sound quality is nothing special. During the warm up period all sorts of weird sounds come out of the loudspeaker.

DFWB.
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Old 20th Aug 2019, 8:16 pm   #38
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Default Re: Stella ST1007U

The attachment shows the excellent definition this set is capable of displaying.
The line structure is noticeable because the camera has captured only one picture field. Only one adjustment of the vision circuits was required, coil S17 the 38.15Mc/s sound trap.
Interlace is good despite having no interlace filter. The frame sync pulse from the sync separator is supplied to the frame oscillator via a differentiation capacitor rather than the usual practise of using an integrating circuit.

DFWB.
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Old 20th Aug 2019, 8:26 pm   #39
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Default Re: Stella ST1007U

Nice to see one fixed rather than being used for parts! Don't forget a nice pic of it working when you've boxed it all back up and Mr Sheen'd the cabinet.
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Old 20th Aug 2019, 8:42 pm   #40
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Default Re: Stella ST1007U

Hi Kevin,
The cabinet is presented in a high gloss polyester finish. The surfaces have a few scratches which I should be able to polish out.
That rusty CRT band will be replaced with a new one.
Back in the old days these sets were considered easy to fix, this one hasn't been so easy.

DFWB.
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