Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!samsung!uunet!portal!cup.portal.com!ISW
From: ISW@cup.portal.com (Isaac S Wingfield)
Newsgroups: sci.electronics
Subject: Re: Crystal radios - wasn't it a 'galena' crystal?
Message-ID: <24473@cup.portal.com>
Date: 25 Nov 89 23:10:38 GMT
References: <5386@internal.Apple.COM> <24441@cup.portal.com>
  <1989Nov25.080724.19517@utzoo.uucp>
Distribution: na
Organization: The Portal System (TM)
Lines: 32

Henry Spencer writes:

>Um, possibly this is a reflection of my ignorance, but I always figured
>that if it walks like a duck and quacks like a duck, you might as well
>treat it as a duck -- isn't there an agreed-on standard for the forward
>drop of a 1N34?  (I don't have a spec sheet handy.)  If so, do I really
>care whether it's germanium, silicon, or praseodymium in there?

Good question: I suspect the real "don't really care" for almost all
applications is the FCD, but many people want to replace a 1N34 with
another "1N34", so that's what manufacturers print on the outside of it.

I was trying to interface a Honeywell minicomputer to standard TTL;
the Honeybucket (for obscure reasons) used standard DTL running on
6(!) volts, and I really wanted that 0.3V FCD. TI listed a 1N34, so I
ordered up a bunch, but they all had 0.6V FCD. (This was for a military
application, so everything had to be "worst case" designed.) I brought
things to my boss's attention, and he observed that TI hadn't processed
any germanium for years! After much looking around, and some *very
careful* data sheet reading, we concluded that germanium diode specs
were all kind of loose, and it was possible to duplicate (or even better)
all specs *except* FCD using silicon, and that's what nearly everybody
was doing! The ITT devices came in at 0.3V, and everything was fine.

With respect to the second part of your question, "do you really care
what's in there": it has been my impression that the FCD is pretty much
defined by the material used in the junction (discounting peculiar dopings,
or metal-semiconductor junctions, for example). So, if it's a certain
FCD you need, then you most certainly do care.

Isaac
isw@cup.portal.com


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