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Old 14th Feb 2016, 6:02 am   #1
rbm1973
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Default Can anyone identify this transistor?

Not having much luck finding a tuner for my Rank A823, I decided to open the tuner up and check for poor connections, which were OK.
However, I did find a transistor in the final RF stage of the tuner to have broken up, with one leg detached. I carefully removed it and it fell apart. There are no markings on the transistor whatsoever, but it is a different colour to the other 2 transistors in the tuner. It has just 3 tags and looking in tuner from top it is blue and the underside is green. Does anyone know what the type of transistor fitted, It's about the size of an aspirin tablet with 3 tags on it, although in the pic there are no tags as it disintegrated !

See attached pic, It's from a Z776 tuner unit in an A823B Bush BC6318.
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Old 14th Feb 2016, 9:53 am   #2
Malcolm G6ANZ
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Default Re: can anyone identify this transistor??

Bfr90 ?
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Old 14th Feb 2016, 12:39 pm   #3
rbm1973
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Default Re: Can anyone identify this transistor?

just looked at the z718 manual and there is a schematic of the tuner and it lists the transistor as a bf263 well i have ordered a bf263 from cricklewood electronics for less than a £1 well we can but try
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Old 14th Feb 2016, 1:06 pm   #4
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Default Re: Can anyone identify this transistor?

If it's just a bipolar transistor then lots of types are likely to work. It's worth trying anything you have to hand.
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Old 14th Feb 2016, 1:18 pm   #5
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Default Re: Can anyone identify this transistor?

The types mentioned are for use at UHF frequencies.
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Old 14th Feb 2016, 1:20 pm   #6
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Default Re: Can anyone identify this transistor?

The BF263 is one of those 'acorn' like transistors (legs sticking out sideways) with an ft* of 500+ MHz. Paul is right that any (modern) NPN would work. But as you have one on order it is a moot point.

*transition frequency, where gain is one.
 
Old 14th Feb 2016, 2:55 pm   #7
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Default Re: Can anyone identify this transistor?

Quote:
Originally Posted by vidjoman View Post
The types mentioned are for use at UHF frequencies.
Yes, I didn't appreciate that this was a UHF tuner when I posted. That said, it's amazing what you can get away with even at these frequencies. The manufacturers have to select components conservatively because they have to work first time every time, but if you can experiment then a much wider choice is available.

It's all academic though, as the correct replacement is on its way.
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Old 14th Feb 2016, 2:59 pm   #8
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Default Re: Can anyone identify this transistor?

Sounds like someone failed their test, or it was deliberately sabotaged?
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Old 14th Feb 2016, 5:54 pm   #9
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Default Re: Can anyone identify this transistor?

Could it have had a minor lightning twinge? It's sometimes takes a funny path through things. It might be worth checking the state of the other semiconductors in the tuner. Or, less excitingly, perhaps that lead-out style could be prone to corrosion and splitting the plastic pill if the metal-plastic bonding was less than good.
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