Hello all, this set caught my attention last week on ebay. It looked in fairly good shape, and as it was only five minutes drive down the road, I thought I would place a bid. It was mine for not too silly money at 40 quid.
It has been stored in a dry barn, and there is very little corrosion that I can see. However I will take the precaution of running a small current through the LOPT overwind for a few days to ensure it is dry.
To understand the black art of electronics is to understand witchcraft. Andrew.
I tested the CRT and was pleased to see that it should be in a serviceable condition, with emission slowly increasing after a few minutes of being gently run up to full heater volts of 6.3 on the B&K. I always like to start off low with the heater voltage and slowly increase instead of just switching straight on at full rating.
To understand the black art of electronics is to understand witchcraft. Andrew.
I have just removed the chassis from the cabinet for some examination and it was very simple to do. Firstly, the side control panel was withdrawn by loosening two screws and rotating the clips. The main chassis was withdrawn by removing the base cover and then four screws that hold the chassis and CRT on a wooden plinth in place. The LOPT was also easily unplugged and withdrawn from it's can. It would seem to be in very good visual condition. (last pic).
There are of course a number of Philips black tar capacitors that may well need replacing, as can be seen in the second picture. Oh I wish I had a supply of the Philips mustard colour caps, but fear I may need to use modern types.
To understand the black art of electronics is to understand witchcraft. Andrew.
Here are a few general snaps of the underchassis. A resistor and a potentiometer (second pic) plus five Pinnacle valves seem to show the only work done on the set in the past. The remainder of the valves seem to be the original Mullard and Philips Miniwatt types.
To understand the black art of electronics is to understand witchcraft. Andrew.
Service data uploaded to the library for those who wish to follow along. Trader sheet 1318/T135 covering Philips 1768U/2168U & Stella ST8617U/ST8621U ?
p.s.
I think I've got the Philips/Stella manufacturers data for this, will check over the weekend
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Thanks Chris, I will use that data for any circuit references.
To understand the black art of electronics is to understand witchcraft. Andrew.
Ah, 'Pinnacle' valves - The mainstay of many a repair shop! I wonder how well they've stood the test of time. In their time, they seemed to be very good, and we bought quite a few from CandL's service depot, and Charles Hyde (If I remember right).
I guess the valves 'upstairs' are indicative of the component failures 'downstairs' - All in the timebase section, by any chance?
All in the timebase section, by any chance?
They sure are, and one half of the HT rectifier, a single PY82. The other PY82 is a Philips Miniwatt.
To understand the black art of electronics is to understand witchcraft. Andrew.
I have placed the LOPT overwind on a gentle bake with 25v flowing through it. It is slightly warm and hopefully this will, over time, drive off any moisture ingress. The transformer looks in perfect condition as I mentioned, so it would be good to make every effort to prepare it for the high voltages it hopefully will encounter in due course.
To understand the black art of electronics is to understand witchcraft. Andrew.
Hi Marion,
Pinnacle valves supplied dealers with a display cabinet to keep the smaller valves in. The company slogan was: "Pick of the World's valves"
I remember the Stella ST8617U. Fixed loads of them in the sixties. This was the set which along with Philips 1768U was used for rental when high reliability was demanded. Presentation and type of tuner apart, the Stella ST1007U is electrically similar.
The set I serviced last year: https://www.radios-tv.co.uk/community/black-white-tvs/stella-st1007/
Weakest component in these sets is the line output transformer.
Till Eulenspiegel.
We changed over to Pinnacle valves in the early 1970’s. Good valves and 12 months guarantee instead of Mullard, Mazda etc 3 months. Never any quibble on replacements, Pinnacle provided the valves we both decided we would use. We had a full stock of valves on the shelf and only paid for those we used on a monthly account, rep came to visit every month.
The 3 digit number on the valve was a date code, I.e 430 on one of those in the photo, can’t remember the code but think it was month and year it was delivered to the workshop. Even if it was on the shelf sometime there were so few returns they would just swop whatever the date.
They supplied styii and cartridges as well.
Frank
Hi Andrew,
I have the Philips 1708U, which looks to have the same chassis as your Stella, just looked up the thread from UKVRRR from when I restored it, and it was 10 years ago, almost to the day! It's probably second in line to my Ekco TMB272 for picture quality, and it's also been very reliable too, it was on display for 8 hours solid at the Festival of Vintage at York racecourse in 2011, and it ran flawlessly. Here's the link to my thread!
Good luck with the restoration, I'm sure it'll be an excellent set when up and running!
Regards,
Lloyd
Cheers Lloyd, your set looks really good !
To understand the black art of electronics is to understand witchcraft. Andrew.
One thing I noticed is that V7 has a PCF80 fitted instead of an ECL80. The wiring to the socket appears undisturbed so I think it is a wrong valve. I will investigate this to see if a PCF80 is really meant to be fitted.
To understand the black art of electronics is to understand witchcraft. Andrew.
Late last night I tried to re-form the multi-section electrolytic comprising of C64,82 and 80. It proved to be rather a waste of time. The leakage is very high, even on the lowest value C64 of 10uf. The can soon became warm and the current through each section remained high. I tried again this morning but there were some cracking sounds from within the capacitor and it is now dead short on the 60uf section. Here it is removed from the chassis.
There was no option but to replace it. I had to drill a couple of holes in the chassis to allow the new capacitor and it's clip to fit as I have no replacement capacitors of the twist lug variety of suitable values. Here is the new Daly capacitor mounted in place of the original faulty one.
There is just enough space for the LOPT sheild can to fit back into place.
To understand the black art of electronics is to understand witchcraft. Andrew.
One thing I noticed is that V7 has a PCF80 fitted instead of an ECL80. The wiring to the socket appears undisturbed so I think it is a wrong valve. I will investigate this to see if a PCF80 is really meant to be fitted.
According to the circuit diagram V7 is the final vision IF amplifier and is an EF80 pentode. It might be possible the sync separator valve (V13) is a PCF80 in lieu of the ECL80.
Another ECL80 (V11) is employed in this chassis and is the line sync pulse clipper (pentode) and part line oscillator (triode.
Till Eulenspiegel.
I’ll have to see f I can get to my set and see what valve is in V7’s position, I’ll have to download the manual first so I know which valve is V7! I restored mine without a manual, mostly by cheating and just blanket replacing all the tar caps, checking a few showed them to be leaky anyway. The smoother was useless in my set too, worked for a while then gave up, it also got a bit warm when in use too.
Regards,
Lloyd
Hi Till, I am refering to the Trader sheet in the library. I believe it differs in relation to the valve location numbers, certainly so from the R&TV Servicing book that looks to have a direct copy of a Philips diagram.
It looks like a PCF80 is used in this set as the circuit slightly differs from what would be a clipper-buffer amplifier of V7 (ECL80) described in the Trader sheet. V6 is still an ECL80 and is the sync seperator.
To understand the black art of electronics is to understand witchcraft. Andrew.
I have checked a selection of capacitors, namely the RF bypass C81 and another in the heater chain C79, and they are quite as expected, extremely leaky. There are a number of other critical capacitors at HT and boost potential and these are just as bad. They will need to be replaced before I apply power to the set. There are several values that I do not have, so I have ordered suitable types. 0.056uf and 0.027uf being the main ones.
To understand the black art of electronics is to understand witchcraft. Andrew.
An actual measurement on a capacitor, in this case C92 a 0.1uf 600V, showed leakage of approx. 900k at a voltage of 45vdc on my trusty old Taylor 130. As the voltage rises (as it would in use of course), the internal resistance of the capacitor will drop considerably, more so as it warms. A good capacitor (first photo) is practically infinate resistance at the full voltage of around 450vdc.
The value of the faulty capacitor measures around double it's rating of 0.1uf.
To understand the black art of electronics is to understand witchcraft. Andrew.
