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From: max@zion.berkeley.edu (Max Hauser)
Newsgroups: rec.audio,sci.electronics
Subject: Re: I really ***HATE*** electrolytic capacitors
Message-ID: <20069@ucbvax.BERKELEY.EDU>
Date: Tue, 11-Aug-87 19:14:22 EDT
Article-I.D.: ucbvax.20069
Posted: Tue Aug 11 19:14:22 1987
Date-Received: Thu, 13-Aug-87 06:37:56 EDT
References: <3646@sdcsvax.UCSD.EDU> <3650@sdcsvax.UCSD.EDU>
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Reply-To: max@eros.berkeley.edu (Max Hauser)
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Organization: U.C. Berkeley
Lines: 39
Keywords: capacitor flame wars
Summary: Transistor hfe's are still flaky
Xref: mnetor rec.audio:2774 sci.electronics:1150

This is a nit-picking response; I must make clear that I completely
agree with Brian Kantor's recent articles and I think his indictment
of electrolytic capacitors was eloquent and sound. I only want to
address a peripheral remark.

In article <3650@sdcsvax.UCSD.EDU> brian@sdcsvax.UCSD.EDU (Brian Kantor) writes:
>
>... a solidly-biased transistor stage can easily
>withstand the few microamps of leakage that a new tantalum electrolytic
>provides.  Remember, we're talking about old equipment here, when it
>wasn't unusual for transistors to have hfe spreads of 10:1 in a single
>lot.  It's Dynaco, circa 1973.  Right out of the back of the RCA
>transistor manual.

First, it is still usual for transistors to have hfe spreads of 10:1 in
a single lot, depending on the part number you buy. Indeed most 
modern (i.e., planar) transistors inherently have wide hfe
(common-emitter current-gain) spread when manufactured, since the hfe
depends more or less exponentially on the Gummel number (which they
teach in school) and the emitter-region lattice integrity (which
they do not), and both of these are difficult to control in 
ordinary bipolar fabrication processes. Often if you get a
discrete bipolar with a tighter spread it is a selected version with
its own part number. This is a feisty point with me only because I
have designed some bipolars and seen what happens.

Second, this doesn't matter. Well-designed circuits employing
bipolars will be insensitive enough to the infamous hfe that they
can tolerate wide spreads without much change in overall specs.
So in the end, I agree completely that transistor stages can
tolerate electrolytic leakage (and also that the old Dynacos,
bless them, are right out of the venerable RCA transistor manual
-- old farts unite!). I just disagree about why.

   M. Hauser, curmudgeon-in-training

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