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From: John Woodgate
Subject: Re: Low leakage parts
Date: Tue, 7 Jan 2003 08:41:37 +0000
Organization: JMWA Electronics Consultancy
Reply-To: John Woodgate
NNTP-Posting-Date: Tue, 7 Jan 2003 10:15:18 +0000 (UTC)
X-Newsreader: Turnpike (32) Version 4.01 <5Z8C9wtxbnpWyFnyfFzqmVF739>
I read in sci.electronics.design that Phil Allison
wrote (in ) about 'Low
leakage parts', on Tue, 7 Jan 2003:
>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 the
>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.
Were you able to measure the resistors? 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.
Regards, John Woodgate, OOO - Own Opinions Only. http://www.jmwa.demon.co.uk
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