Stella ST239U

[maninashed]

Hi everyone, I havent seen many of these although I dont think they are particularly rare. This one though was in a reasonable condition and well worth a 'coat of looking at'. Its a 7 valve mw/vhf superhet compact, not too easy to work on due to the lack of space. Electrically it was a different story though. Initial inspection revealed a sorry looking filter capacitor across the mains, it was split and partly melted as the attached pictures show. The set contained quite a few of those black tar covered caps which are horrible sticky things and prone to failure. I decided to replace them all especially THAT cap. The cathode resistor of the UL84 output valve was two 560ohm 1w resistors as per the circuit diagram, they had gone high and measured 330ohms so I replaced them with a 270ohm 3 watt, the 25uf bypass cap was also replaced. The mains smoothing capacitor, a 50uf/100uf double was the original was found to be o/c on the 50uf side so I decided to leave it in place for cosmetic reasons and replace under chassis with a 100uf 400v and 47uf 400v modern component, space was a bit tight but they went in ok. I also replaced the 10uf electrolytic in the discriminator circuit even though it tested ok. All the valves tested ok on my valve tester, so I powered it up on the lamp limiter, the valves lit up but no results. This prompted further inspection, and I found that the 30ohm rectifier anode reisistor (30ohms) had gone very high, looked distressed and measured 9.5k ohms! This was replaced and the set powered up again, this time stations came in loud and clear both on mw and vhf. The volume control pot 2Mohm log with mains switch seems a bit intermittent probably due to DC on the track due to leaky caps in the past and will be replaced as soon as I can get one (if anyone has a spare!) The speaker cloth has sagged just a bit from the top of the speaker area but thats soon sorted.
The cabinet is in a dark maroon bakelite type material with no cracks or major defects, it did have some slight scratches but a bit of Tcut and wax polish soon had it looking good. Now, I know these sets aren't everyones cup of tea, but I have to say the reception and quality of sound from this modest size set (its about as big as a small toaster) is very good, and you could sneak this one into the house almost without 'her indoors' noticing its there! (slim chance here!) Its certainly got character and I quite like it.

[maninashed]

Pictures as mentioned in main text

[space_charged]

I was given one of these sets when I was about fifteen. It didn't work and had a large pink resistor rolling arround inside loose - as it were.

At the time I was at school in Edinburgh and my best wireless was a Wartime Civilian Wireless that I listened to a lot.

The maroon bakalite and the styling was unusual, and I saw at once that it was a medium wave and, more excitingly, VHF set.

Now Philips (Stella) circuits are not the easiest to understand and I didn't want to dmaage the set. So, it was off to Edinburgh Central Library, the refernece section to get the Radio and Television Servicing manuals to get the circuits for my set. These had to be copied by hand, or photopied. The manuals were strictly "reference only", couldn't be taken out of the library. I went for the exensive option, photopies.

The result was that I had the set working and on the spectacular quality (for the day) of VHF FM sound! This would have been in about 1968/9.

When I went to University, then left home I had to part with all my wirelesses, a long time ago now. BUT, ebay to the rescue, and I have been able to re-acquire both my Wartime Civilian wireless AND my maroon bakalite Stella VHF wireless.

I listen to my Stella VHF wireless every night and sometimes drift off to sleep to the warm glow from the front of it.

I did have to do a wee bit of restoration of the one I got from ebay. When it arrived, I found the UL84 had shot out of its base and smashed to pieces inside the set. It takes quite an acceleration to do that, so "thanks guys" in the Post Office. (Actually I like the Post Office, they are my prefered service for all my parcels). A quick visit to my loft, where I keep my stocks of valves, provided a replacement UL84.

After fitting that, the set came up and both VHF and AM worked just fine. The only remaining problem was - silly isn't it - the lamp that illuminates the tunning scale wasn't working. Now, to a wireless addict, that iluminated dial is all important.

The circuits showed the lamp for the front pannel was supplied from the heater chain, but I think, across the heater chain NTC thermistor. Its a 19V lamp, and I couldn't find an easy supply of lamps with the right voltage/current. I did consider an LED relacement, but in the end I fitted a miniature mains transformer with a 6V seconary.

After a few weeks of blissfull listening, suddenly a hum develped on the set. That either meant a heater/cathode leak in a valve had deveoped or the smoothing capacitor(s) had given up the ghost.

In science in general, radio/tv servicing is about making guesses about what the problem MIGHT be, then finding a witty and, hopefully, easy way of testing if I'm right!

My guess was the main smoothing capacitor, which is the usual two in one can. SO, easy peasy lemon squeezy, stick a couple of modern caacitors across each. Bye, bye hum. SO I also took the risk of leaving the original can in place. No sudden BANGs in the night - so far.

Chas

[jim_jobe]

I restored one of these some years ago and also had some trouble with the dial lamp. Like yours the one that came with it was shot but I managed to find a replacement. Fitting this gave me light but, after a few minutes it suddenly started to increase in brightness until it finally blew. I eventually came to the conclusion (after messing about and blowing two more!) that the trouble lay with the thermistor but, as I couldn't get a replacement for that, I did without light for a while until I snagged the flex one day which brought the set crashing onto the concrete garage floor completely demolishing the case. It did still work however but has been relegated to a corner in case another case ever turns up for it.
Jim
M0JBJ

[space_charged]

Yes I think the lamp is across the thermistor. The thermistor is probably in series not only with the heater chain but the HT as well. SO, when the valves heat up and start to conduct, more current flows and the voltage on the lamp also goes up. Maybe somebody fitted a 6V bulb. The holder is a standard torch bulb size. The service sheet shows the lamp as being a 19V type at, I think, 100Ma. I couldn't get one with that voltage hence using a miniature 6V transformer. Mine is bolted to the metal chassis behind the glass scale. I did think of making a power supply for an LED working from the voltage across the thermistor. Its a hot environment for power LED though. I did buy a few 3Watt warm white LEDs and they have a very similar look to a torch bulb. Not the same all round illumination though.

Just recently I replaced the UL84 (sound output) and the UABC80 (detector/FM ratio detector). The set comes on much more quickly and there is a bit more volume available now. The UL84 was an old one I had in my loft. It looked really mucky inside. I'm always surprised that valves go on working when they look like that. Some line output valves go that way too, but seem to work just fine. The replacement UL84 was bought on ebay as (Philips) new old stock.

Chas

[Leon Crampin]

The so called 19V 100mA MES lamps are in fact 24V 2.8W commercial vehicle instrument panel lamps. These are still cheaply available if you look around, although some have a larger envelope size than is ideal for radios (but will usually fit).

Restrictive practices were thriving in the days of valve radios (BVA price fixing etc.), so makers would do everything possible to maximise spares revenue. Identifying a standard automotive lamp as being rated at 19V is a perfect example. Another was the 0.545 uF (as I remember) capacitor used as a motor phase splitter in the Morphy Richards hairdriers.

The give-away was the tolerance - +/- 20%...

Leon.

[space_charged]

Yes, in fact I ended up buying 100 24Volt lamps for another project, the restoration of a set of vintage Christmas/party lights. I realized that these would probably have worked in my Stella wireless. Its a good idea anyway to under-run the lamps so they last longer.

Are you saying the 24Volt lamp blows when the set warms up? That suggests the thermistor is faulty, or an excess current is flowing. If it were the latter I'd expect some other symptoms such as smoke or a bang. The excess current woud have to be going somewhere.

Thermistors like the one in the Stalla could be difficult to source. The voltage on mine is about right. Some sort of triac based solid state device could be designed to emulate the soft start the thermistor used to provide.

Chas

[jim_jobe]

What surprised me about the UL84 was how long it took to warm up compared to say the EL84.

[space_charged]

Well the replacement UL84, a Philips new old stock, seems to get going much faster. When the UL84 warms up, you can hear a hum. A fair bit later, the sound used to come in, so I thought the UABC80 (FM discriminator ratio detector) might be the problem. I replaced that too and the set now starts up much more quickly and there is more "volume" available. The IF mixer/osc and RF stages are very low power valves (UF80 UCH81 UF89) and don't normaly give any trouble.

I always switch it on when I go to bed and listen to the shipping forecast, then I listen to whatever is on the World Service. quite often I drift off to sleep with it on, waking up hours later... Its on again to listen to the news in the morning at weekends. Weekdays I use my digital Pure Evoke III digital wireless.

Chas

[jim_jobe]

I must have another look at mine Charlie; I always liked that set.

[AC/HL]

Two posts referring to an eBay item deleted