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Vintage Radio (domestic) Domestic vintage radio (wireless) receivers only.

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Old 15th Aug 2019, 9:14 pm   #1
morrig47
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Default Sobell 305BT

Many years ago I inherited a Sobell S305BT from an aunt. It spent many years in the loft I regret to say, but recently I re-discovered it when undertaking a clear-out. At this point I decided to try to revive it. Unsurprisingly it was as dead as a dodo, but I managed to purchase the correct battery and power was restored. The main problem is that I can access very few stations on the AM/LW frequencies and the volume is very low. I can get BBC Radio Five Live, but I have to turn the volume full on. There is no aerial with the radio and I wondered if this is the root cause of my problem. If it is the aerial is there any chance I could source the aerial given its age which I take to be late 1950s or 1960s? At this point I should confess to very little technical know-how when it comes to these old trannies. Any advice would be appreciated.
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Old 15th Aug 2019, 10:14 pm   #2
Nuvistor
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Default Re: Sobell 305BT

The aerial is built into the radio and are usually very efficient. The radio does use a type of transistor that are known to fail.
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Old 16th Aug 2019, 8:08 am   #3
Cobaltblue
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Default Re: Sobell 305BT

Nice little set worth a bit of effort but as Nuvistor says its full of Tin Whiskered AF117's /OC170's

https://www.radiomuseum.org/r/sobell_transistor.html

Do a search on Tin Whiskers or AF117's

The service Data is available here:
https://www.service-data.com/product...62/4884/m15862

Cheers

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Old 16th Aug 2019, 9:07 am   #4
morrig47
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Default Re: Sobell 305BT

Many thanks both. A real education for me - Tin Whiskers has now entered my vocabulary. To my surprise the inside was really clean despite the years in the loft. I did give it a good clean, but not much difference sadly. My listening seems limited to Radio Five Live and Radio Wales with volume full on. I will download the service data to see if I can make sense of it. Loved the Radio Museum link with the price in Guineas. Thanks for that. Again my thanks for your help.

Gareth
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Old 16th Aug 2019, 10:11 am   #5
paulsherwin
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Default Re: Sobell 305BT

Tin whiskers are unfortunately a problem that most of us here are familiar with. It's usually reasonably easy to replace the bad transistors with alternatives, but you do need some basic electronics skills to do this. There are many threads on the issue if you search the forum.

However, the first thing to do whenever an old transistor radio is performing badly is to clean the wavechange switch contacts. Ideally you would use contact cleaner like Servisol 10 to do this, but I suspect you won't have any and won't want to buy a can just for this job. You can use white spirit, turps substitute or WD40 at a pinch, but be sparing with it. You only need a small amount on a cotton bud - don't spray WD40 everywhere as it makes an oily mess which attracts dirt.
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Old 16th Aug 2019, 12:35 pm   #6
morrig47
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Default Re: Sobell 305BT

Thanks Paul. That sounds like a good first action for me. Well within my technical ability as well! Really appreciate everyone's help here. I fear the bad transistors option will be beyond me as I really have no technical expertise in this area. I would rather have it in its current state, working to a limited extent, rather than ruin it completely through my incompetence.

Gareth
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Old 16th Aug 2019, 5:06 pm   #7
TrevorG3VLF
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Default Re: Sobell 305BT

My inclination would be to measure the voltages on all the transistors and see if any are unusual. Germanium transistors are prone to leakage.
Radio frequency signals can often get through a faulty transistor but will be strongly attenuated.
Depending on how the circuit is configured, it may be possible to deduce any whiskered wonders.

I have tried to look up the diagram but do not see the Sobell 305BT. Perhaps it is the same as another set.

Last edited by TrevorG3VLF; 16th Aug 2019 at 5:11 pm. Reason: Diagram not found
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