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From: "Phil Allison"
References: <email@example.com> <8npR9.16063$jM5.firstname.lastname@example.org> <email@example.com> <firstname.lastname@example.org>
Subject: Re: Low leakage parts
X-Newsreader: Microsoft Outlook Express 5.50.4522.1200
Date: Tue, 7 Jan 2003 22:59:42 +1100
NNTP-Posting-Date: Tue, 07 Jan 2003 22:49:18 EST
Organization: Telstra BigPond Internet Services (http://www.bigpond.com)
"John Woodgate" wrote in message
Phil wrote :
> >I *did* attempt to make pre-amps for condenser mics once ( 25 years
> >ago) and could not source the essential 1000 Mohm resistors in small
> >quantities so I resorted to drawing the component, zig zag and all, on
> >PCB with a fountain pen filled with resistive ink.
> > I got my 1G resistors OK but the PCB leakage was in the same order
> >order of magnitude if the weather was even slighly damp.
> > Any clear coating I applied over the area to solve this ate the
> >resistor. Very frustrating.
> Did you try a soft pencil? Very soft pencils were used to make 1 to 2
> Mohm grid leaks for valves/tubes in the 1920s. The solvent in the
> lacquer wouldn't affect the graphite.
** The drawing ink I used ( Penguin ...) was suggested for coating plastic
to make one's own ESLs.
> Were you able to measure the resistors?
** Using a 30 volt supply and a DVM's 10 Mohm input Z as nanoamp meter -
> I still have a 'Twenty Million Megohmmeter' from the 1960s. It has a huge
mirror-scale meter, far too> impressive to throw away, but it doesn't get
enough use to keep it
> working. Lots of EF37/6J7G.
** I used to own a Sanwa 501 - 2 uA FSD ( 500 kohm/volt) taut band
It fell off the bench - very sad.
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