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From: Boris Mohar
Subject: Re: Low leakage parts
References: <8npR9.16063$jM5.firstname.lastname@example.org> <email@example.com> <3E17D633.378A@sneakemail.com> <3E184B38.588B@sneakemail.com>
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Date: Sun, 05 Jan 2003 12:13:29 -0500
NNTP-Posting-Date: Sun, 05 Jan 2003 12:16:54 EST
Organization: Bell Sympatico
On Sun, 05 Jan 2003 10:11:52 -0500, Mike Monett
>Boris Mohar wrote:
>> On Sat, 04 Jan 2003 22:52:35 -0800, Mike Monett
>> >Boris, can you tell how you cleaned the chambers to achieve low enough
>> >leakage to measure 1fA?
>> There was only one part to clean was large glass feed through that
>> supported the collection electrode. The chambers were polished nickel and
>> were cleaned with deionized water and alcohol.
>Anything special about the alcohol? Some have mentioned that plain
>store-bought isoprop is unsuitable, but I've cleaned keyboard switches
>with it and they measured over 1 gigohm, which is the top range on the
Use as close as you can get to100% isopropyl. Rubbing alcohol may have
oils added to it.
>>We actually had very
>> little problems with leakage once the electormeter was encapsulated in
>You mentioned this before. Where do you get it, and how do you ensure it
>is not contaminated? Any there special precautions in applying it, like
>disposable rubber gloves?
Product Dilwax#35 tel 514 272-5714 It has been a while. I do not know
if the number or the company are still valid.
I do not think that minor contamination is a problem as wax encapsulates
the contaminants. I used to solder right through it when doing tests.
You might want to try some soft cross country ski wax. Paraffin is to
>>The only insulating part exposed to humidity was the outer surface
>> of the glass feed through. The feed through support ring was grounded.
>> Do you know of any good subs for 3N155A?
>That was my next question - what input device do you use. I can't even
>find a datasheet on it, but perhaps the 2N7000 that Win and John are
>playing with might be suitable.
Low leakage, low threshold matched pair fets are the holy grail for
this kind of stuff. 3N155A is obsolete and the reason that you cannot find
it is that Motorola or whatever thy call themselves these days is that
they have a policy of obliterating information on any component that they
obsolete. I have not even been able to fine their obsolete list.
The data is in their Small Signa Transistors, Fets and Diodes book.
It is a P channel enhancement mode FET with Rgs of 1x10E16 ohms and
Vgs(th) of about -2.5V
Viatrack Printed Circuit Designs
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