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Old 27th Feb 2021, 12:12 am   #1
efchase
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Default Bush VTR103C repair

Have been given a 1964 VTR103C. It powered up and gave some stations on MW, LW and FM for an hour. A bit faint maybe but I am no expert on what volume it is supposed to deliver. But next time I turned it on it gave a one second burst of sound and then went dead, as if a component failed on switch-on. The amp side after the volume control is OK. Have added contact cleaner to the switches but no joy. Any ideas please on something simple I can try? I am not expert on radio repairs, though I do a lot of general electronic repairs.

As both FM and AM side has failed does that not point to a small part of the circuit common to both that may be the culprit? E.g. the power supply to these (4.5V is the most I can find in any RF/IF section) or the common audio out?

Is the circuit diagram available? Can anyone post one please?

Unless it is really simple to fix I’d be inclined not to bother and just offer it here for spare parts. Anyone want it? I have a few transistors of that generation too.
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Old 27th Feb 2021, 2:44 am   #2
Graham G3ZVT
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Default Re: Bush VTR103C repair

Hi and welcome to the forum.
With those symptoms, it will almost certainly be one or more of the AF11x transistors with internal shorts.

In the first instance you could try tapping the ones that you can see with the handle of a screwdriver and see if it bursts into life, there are also a pair of these troublesome transistors in the VHF module that are a bit more difficult to access.

Search this forum (and Google) for the key words "Tin whiskers" and you will see what a common problem this is, and that there are several options to deal with them.

The circuit is available from this forum.
https://www.service-data.com/product...73/1118/m10673
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Old 27th Feb 2021, 11:29 am   #3
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Default Re: Bush VTR103C repair

The most important parts of this set are probably the case and the telescopic aerial. If both are in decent condition and the aerial in partricular still has its little red finial present then anything else can be fixed relatively easily.

A good working one can fetch anywhere between about £25 - £100 depending on how many bidders get excited about it!
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Old 27th Feb 2021, 7:47 pm   #4
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Default Re: Bush VTR103C repair

Many thanks for inputs. Tapping the 3 AF116s did bring it to life again louder and for a few minutes with more FM stations than before but it failed again. Sniping off the screens does not fix it.

https://www.markhennessy.co.uk/artic...ransistors.htm says the AF12x is the best replacement for a AF11x. Turns out I have 3 unused AF124s. But all with HFEs at 45ish so probably much lower than the original AF116s. Also have 3 quite rusty looking AF116s with HFEs 80 to 120. How important is it to match the HFE to the one removed? The spare AF126s show up with a “body” diode from C to E on my tester. Why?

None of the 3 AF126s in the set and the 3 spares show any leakage from screen the B/C/E but as Mark Hennessey says that does not prove it’s not got or had whiskers.

The circuit website offers 3 different version of the circuit/manual. Which would you recommend please? https://www.service-data.com/section.php/1118/1/vtr103
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Old 1st Mar 2021, 6:45 pm   #5
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Default Re: Bush VTR103C repair

Found I have a 4 legged AF124 with HFE of 110 so I used that for the middle AF116 that was showing with zero B to E voltage. Now the sound is “as good as new” which I am a little surprised at considering the age of the caps. MW and LW volume is good. FM a bit fainter. Is that normal or has my transistor substitution affected the alignment?

Anyone got 2 of the mounting clips for the chassis to case joint that they can spare? Plus self-tappers, although I could find something similar. That is all that is missing to make it a sellable set, apart from the aerial tip. Where is the best place to sell these? eBay?
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Old 5th Mar 2021, 5:47 pm   #6
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Default Re: Bush VTR103C repair

What is the recommendation for cleaning up the cabinet? Mine is fairly yellowed on the front and less so on the bottom and back, as compared with the colour on the inside (which strikes me as a rather odd colour, being neither cream, white or anything recognisable. It’s off white with a slight sickly blue or green tinge to it. Was that the original colour?) The handle is cream though. A light polish with say a fine abrasive similar to jeweller’s rouge (not not red) might work to remove some of the yellowing but might just be a disaster.

I joined Plessey 10 years after this radio was built. By then I don’t think they were still making capacitors but rather more high end components like RF transistors and ICs. Mullard did the capacitors then. Have some new Plessy resistors with a 1973 date code on them though. Interesting that this radio's nearly 60 year old electrolytics are still OKish. Maybe they made them too well and so could not make money out of them. My son is currently doing some work for just about the only bit that is left of the Plessey organisation https://plesseysemiconductors.com/ (if you ignore all the many bits sold off to other companies and still going strong).
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Old 5th Mar 2021, 8:28 pm   #7
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Default Re: Bush VTR103C repair

Quote:
Originally Posted by efchase View Post
Found I have a 4 legged AF124 with HFE of 110 so I used that for the middle AF116 that was showing with zero B to E voltage. Now the sound is “as good as new” which I am a little surprised at considering the age of the caps. MW and LW volume is good. FM a bit fainter. Is that normal or has my transistor substitution affected the alignment?
Replacing the transistors with a different type could have changed the effective capacitance the IF-amplifier-transformers 'see' - so a realignment could be called-for.

Don't just go randomly twiddling though or you may make things worse!

They're not spectacular performers on FM though, even at the best of times.
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Old 6th Mar 2021, 10:19 am   #8
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Default Re: Bush VTR103C repair

Its worth noting that AF124 = AF114, AF125 = AF115, AF126 = AF116....and so on. In practice they are all the same but specially selected for gain and noise. I doubt that replacing an AF116 with an AF124 will change things much since the 124 has a higher HF range but going the other way (a 126 for a 114) might. I've never noticed any real difference between them.
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Old 6th Mar 2021, 12:43 pm   #9
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Default Re: Bush VTR103C repair

Quote:
Originally Posted by Sideband View Post
Its worth noting that AF124 = AF114, AF125 = AF115, AF126 = AF116....and so on. In practice they are all the same but specially selected for gain and noise. I doubt that replacing an AF116 with an AF124 will change things much since the 124 has a higher HF range but going the other way (a 126 for a 114) might. I've never noticed any real difference between them.
It is interesting that in my case the 3 brand new AF124s I have are only have hfe of 40-45 which i think is lower than the old AF116s but the 4 legged AF124 was 110.

It did not notice much difference in term of position of the stations on the dial but I guess that is not affected by this transistor. (My RF theory is hazy here. Learnt it on a 1960s Radionic construction set, which I still have, but don't think that extended to superhet designs. I need to check it out to see if it's got any transistors in it useful here.).
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Old 6th Mar 2021, 8:47 pm   #10
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Default Re: Bush VTR103C repair

Hi, in my experience FM is always slightly quieter than MW and LW . Not stellar performers on FM but adequate . The cases on these yellow with age , I have been experimenting with the Retrobright Method , see my post , Bush TR82 Retrobright Test in the Chassis and Cabinet refinishing section . It involves a fair amount of Parts stripping and unless you intend to keep it I wouldn`t bother . The front and rear cases on a rare Bush ETR82 Export model have ,after a bit of effort come up like new , they look fantastic , the pictures of it alongside my next project an untouched Bush ETR92 don`t do it justice. Regards, Tim.
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Old 16th Mar 2021, 4:36 pm   #11
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Default Re: Bush VTR103C repair

Very impressive although looks like a lot of hard work and would ruin the silver Bush lettering. I was wondering what would happen to the slots if i used polish.
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