Re: Replacing CC resistors


Miroslav Pokorni
 

And low inductance should not be forgotten. Those dastardly carbon
compositions are quite irreplaceable as (50 Ohm) terminating resistors.

In these days, ceramic composition is offered as replacement for carbon,
with low inductance, high surge etc., but no one is talking about long term
stability. Examples are Ohmite's 'OX', 'OY' and 'Little Demon' series.

Construction of those ceramic composition resistors appears to be same as
that for carbon composition, so the same problems might crop up past 1000
hours standard test for resistors. A true hermetic seal would certainly
improve long term stability, but that is a difficult proposition. It appears
that only thing that would do that trick is a layer of glass or glassified
ceramic around resistive element and phenolyc encapsulant to provide
mechanical protection for that fragile sealing material, but that would
drive price of resistor sky high.

Regards

Miroslav Pokorni

----- Original Message -----
From: "Michael Dunn" <mdunn@cantares.on.ca>
To: <TekScopes@yahoogroups.com>
Sent: Friday, January 16, 2004 2:26 PM
Subject: [TekScopes] Replacing CC resistors


Yes, old carbon comp resistors *can* drift. Just a thought: if
you're replacing CCs with film resistors, keep in mind one of CC's
attributes - their high surge capacity. Analyze or measure the
circuit (most likely during turn-on), and overrate the replacement's
power if necessary.

Michael


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