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Old 24th July 2013, 07:57 PM   #101
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Quote:
Originally Posted by tinitus View Post
Maybe, but current gain only promises 25+...
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Old 24th July 2013, 08:02 PM   #102
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Same concern. Minimum HFE=25+, might be a little low...
And they say nothing about capacitance, we need <25pF.

-----

They all give a current gain*bandwidth product = FT
that makes it seem like all these parts are really fast.
But this is pure current, operating like in a cascode.
Once you see 1 + 1 = 2 Voltage gain of a Concertina,
then Miller probably gets your way before FT does...

We could put an augmented cascode in the middle,
rather than a single lump of sand. Maybe that works
better?

Last edited by kenpeter; 24th July 2013 at 08:14 PM.
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Old 24th July 2013, 08:44 PM   #103
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MJE3439 is an ancient, slow, relatively low gain device, that was at one time offered as a TO-39 in its 2N3439 incarnation. I used to use them and their rough complement the 2N5416 30 years ago as VAS drivers out of desperation, as they were the only things I could readily find that would hold off voltage.

The transistors you want to use these days are the ones that were tailored for high voltage video drive duty. The Fairchild device may be one of them. I think Fairchild cloned them as KS from the original Sanyo 2S devices. I'll have more to say when I go home and look at my stock, as I bought some of these with VAS/hybrid tube circuits in mind. Mouser has them for the time being. I would advise buying quickly, as the need for HV video drivers is disappearing quickly as jug monitors/TV sets go away.
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Old 24th July 2013, 08:52 PM   #104
tinitus is offline tinitus  Europe
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well, I will be busy with other things for a while, so I'm in no hurry
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Old 24th July 2013, 09:29 PM   #105
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At the same time, though, the devices you'd most want to use may be going bye-bye - just a thought. Having said that, there might be a lot of NOS invenory floating around for a while, though finding it and getting it may be an issue.
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Old 24th July 2013, 09:47 PM   #106
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Quote:
Originally Posted by wrenchone View Post
MJE3439 is an ancient, slow.......... I used to use them and their rough complement the 2N5416 30 years ago as VAS drivers out of desperation......
you say it antiquated and slow

but wouldn't the 'concertina splitter' be much less demanding than a VAS driver stage ?

and since its 'slow', I guess it would be reliable ?
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Old 24th July 2013, 11:43 PM   #107
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None of these are too slow FT(current gain bandwidth) for concertina
purposes. Current gain of last two mentioned is rather low, not slow.
If you need less than 25x current gain, they might be just fine.

Several are too slow in the Miller dept, but a few mentioned were <25pF.
At least half of them you can't tell cause the spec sheet doesn't say.
You have to download a spice .model to find the CJC specification...

Slow=Reliable?, Tell that to my lawnmower...

Last edited by kenpeter; 24th July 2013 at 11:48 PM.
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Old 24th July 2013, 11:54 PM   #108
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how about if we darlington connect two devices to address current gain issue?
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Old 25th July 2013, 12:07 AM   #109
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Since KSA1381 is suitable in every category including availability and price,
I'm not sure why I would need to lean on Darlington, Sziklai, or Cadcode?
Its worth my 49 cents not to screw with a complicated pairing.

Sure, pairs could work "better", but its a Concertina. It either works right,
or it doesn't. There's not much grey area to say one or other is better.

I think Fairchild numbers them both ways, 2SA1381 is same part.
http://www.alldatasheet.com/datashee...O/2SA1381.html
Yeah, looks like Sanyo might have been the original maker...

Last edited by kenpeter; 25th July 2013 at 12:22 AM.
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Old 25th July 2013, 12:32 AM   #110
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One more P-Advantage just occurred to me:

Heatsink voltage is the low side of the splitter.
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