2SC1971 for my Talkback Rig

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Wolfie G8VAT
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2SC1971 for my Talkback Rig

Post by Wolfie G8VAT » Sun Aug 30, 2020 4:05 pm

Having torn my hair (sorry, fur) out, replaced the TX RF Preamp 3 times and finally having to conclude that the ones for sale on Ebay must be El Cheapo Chinese rubbish... they won't even withstand 7V Collector-Emitter (should be 35V max).

Does anyone have or know where to buy proper Mitsubishi 2SC1971 Transistors please?

Or maybe even the ASI 2SC1971 equivalents..

Many thanks, Gra.
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Graham G8VAT

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Wolfie G8VAT
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Re: 2SC1971 for my Talkback Rig

Post by Wolfie G8VAT » Mon Aug 31, 2020 9:20 am

Or maybe just ANY equivalent transistor which would replace it?
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Graham G8VAT

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Re: 2SC1971 for my Talkback Rig

Post by g0mjw » Mon Aug 31, 2020 11:27 am

Can't you just use an RD06HVF1 and modify the circuit accordingly?

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Wolfie G8VAT
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Re: 2SC1971 for my Talkback Rig

Post by Wolfie G8VAT » Tue Sep 01, 2020 12:00 pm

Thanks for the reply.

I'd rather replace like for like, but if it comes to that then I'll need some pointers what needs modifying where, it's a device I never heard of..

I've been made to feel like I'm already going beyond the call of (Ham) duty by replacing this. When I first asked around, the first reply I received was why not just buy an xxx? And I also received links to said rigs on Ebay.. :roll:
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Graham G8VAT

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Re: 2SC1971 for my Talkback Rig

Post by M0SKM » Tue Sep 01, 2020 12:21 pm

Hi Wolfie,

See your inbox (PM) for a link to a genuine one.

Steve
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g0mjw
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Re: 2SC1971 for my Talkback Rig

Post by g0mjw » Tue Sep 01, 2020 12:54 pm

I think mostly you just need to change the bias arrangements for a MOSFET rather than Bipolar. Output matching should be the same or close enough. Input matching may need some damping to allow for the higher gain so include a 100 ohm with a DC blocking capacitor. It will need about 2-3V bias, e.g from 5V adjusted with a POT.

Mike

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Wolfie G8VAT
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Re: 2SC1971 for my Talkback Rig

Post by Wolfie G8VAT » Tue Sep 01, 2020 8:32 pm

Thanks for the pointers Mike. As I say I'll give that a thought if all else fails..

Thanks Steve. When I looked closer at these Ebay ones, they are a standard width and a short tab.. The original 2SC1971 is slightly taller and narrower.. Adding to my suspicions about what they actually might be, or more accurately, NOT be...

I'll be aiming for the real McCoy.
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Graham G8VAT

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Re: 2SC1971 for my Talkback Rig

Post by G3GJA » Wed Sep 02, 2020 10:29 am

Hi Graham

Have a look here: https://www.littlediode.com/components/2SC1971.html

They're bl**dy expensive but the guy does not sell fakes.

BTW, EY is off as it is very close to going full repeat mode.

73

Clive G3GJA

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Wolfie G8VAT
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Re: 2SC1971 for my Talkback Rig

Post by Wolfie G8VAT » Wed Sep 02, 2020 2:55 pm

Thanks Clive.. I though EY must be off air. I went out of the house last weekend to get away from the atmosphere and just chucked the Ae on the car but.. no EY found. Hope it's not too serious.

I'll have a new QTH shortly but guess what? More Trees to the East and a close brush with a cooling tower.. I'll have to see how it pans out. I stand a better chance with the Barnsley gang though.


Meantime, I've paid for some more Transistors... but while I am waiting I put in any old NPN power transistor and wound the Input voltage up with no detrimental effects.. I could read 16mV on the base.

When I had put the last chinese one in, I linked the base and emitter and it still died when the Collector reached around 6V. Just about confirming my suspicion that they are made of rarified earth or something.
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Graham G8VAT

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Re: 2SC1971 for my Talkback Rig

Post by G3GJA » Wed Sep 02, 2020 5:52 pm

Not sure about rarefied earth though Graham; I think 'Guano' would be more appropriate!

There's a full report on EY issues here: viewtopic.php?t=6870&p=24281#p24281

Sorry to hear about the move to a less helpful location. You might find the cooling tower helpful though; I know Bob G7AVU makes use of some reflections of industrial buildings to good effect.

Cheers

Clive

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